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AR TOF AGRICULTURE, BUREAU OF ENTOMOLOGY —PULLETIN NO. 74

L. 0. HOWARD, Entomologist and Chief of Bureau, be OM, e

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Det a ‘ OME FACTORS IN THE NATURAL _ CON TROL OF THE MEXICAN > CORTON BOLL WEEVIL. pic ai . . BY eee W., BH. AINDS, -Px,.D.. In Charge of Cotton Boll Weevil Laboratory. : Issurp DrecemBer 14, 1907. a am

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Bul. 74, Bureau of Entomology, U. S. Dept. of Agriculture. PLATE |.

STAGES OF MEXICAN COTTON BOLL WEEVIL.

¢,. 1.—Adult weevil, dorsal view. Fig. 2.—Adult weevil, side view. Fig. 3.—Full grown larva, side view. Fig. 4.—Egg. Fig. 5.—Pupa, ventral view. Fig. 6.—Adult with wings spread. All xcept fig. 3 enlarged to 4 diameters; fig. 3 enlarged to 35 diameters. (Original.)

U.S. DEPARTMENT OF AGRICULTURE,

BUREAU OF ENTOMOLOGY —BULLETIN NO. 74. L. O. HOWARD, Entomologist and Chief of Bureau.

SOME FACTORS IN THE NATURAL CONTROL OF THE MEXICAN COTTON BOLL WEEVIL.

BY

Wey HINDS; Pu. D-,

In Charge of Cotton Boll Weevil Laboratory.

IssurpD DreceMBER 14, 1907.

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WASHINGTON: GOVERNMENT PRINTING OFFICE.

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BUREAU OF ENTOMOLOG Y.

L. O. Howarp, Entomologist and Chief of Bureau. C. L. Maruatr, Entomologist and Acting Chief in absence of Chief. R. S. Cuirron, Chief Clerk.

. H. CHITTENDEN, in charge of breeding experiments.

. D. Hopxins, in charge of forest insect investigations.

. M. WesstTER, in charge of cereal and forage plant insect investigations. . L. QUAINTANCE, in charge of deciduous fruit insect investigations.

_F. Puiruies, in charge of apiculture.

. M. Rocers, in charge of gipsy moth and brown-tail moth work.

. W. Morritt, engaged in white fly investigations.

. F. Fiske, in charge of gipsy moth laboratory. . A. HooKER, engaged in cattle tick life history investigations. C. MorGan, engaged in tobacco insect investigations. S. Woc.iuM, engaged in hydrocyanic acid gas investigations. J. GILLiss, engaged in silk investigations. P. CurRIE, assistant in charge of editorial work.

MABEL Cotcorp, librarian.

Cotton Bott WEEVIL INVESTIGATIONS.

W. D. HuntTeER, in charge.

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F. C. BisHorp, R. A. CuSHMAN, SPRINGER GOoEs, W. E. Hinps, C. E. Hoop, C. R. JoNES, Witmon NeEweE ut, W. D. Pierce, F. C. Pratt, C. E. Sansorn, C. 8S. Spooner, W. W. YoruHers, special field agents.

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LETTER OF TRANSMITTAL.

U.S. DEPARTMENT OF AGRICULTURE, Burrau or ENTOMOLOGY, Washington, D. C., August 20, 1907.

Srr: I have the honor to transmit herewith the manuscript of a paper, by Dr. W. E. Hinds of this Bureau, entitled “Some Factors in the Natural Control of the Mexican Cotton Boll Weevil.” It deals especially with three important factors of natural control, concerning which our knowledge has been largely extended through the cotton boll weevil investigations of the Bureau during the season of 1906. These factors are: Temperature and moisture conditions, predaceous and parasitic enemies, and food supply.

In view of the fact that the boll weevil is not a passing pest, but rather an enemy with which the cotton grower must reckon each year, it is evident that our knowledge of every factor affecting favorably or unfavorably its development and attack must be made as complete as possible. While it may not be possible to increase the effectiveness of some of these factors, there is reason to believe that with our more exact knowledge of the nature of their effect upon the weevil and of the conditions under which they produce most beneficial results others may be utilized far more than has been done heretofore, thus lessening very materially the damage annually inflicted by the weevil at little, if any, expense.

This study of the natural control of the boll weevil is probably based upon one of the most extensive series of definite examinations and records which has ever been made in economic entomology. The paper reporting this work is therefore based upon a large amount of statistical data. This has been tabulated with a view to as much condensation as possible without. destroying the value and _ signifi- cance of the records. The illustrations accompanying the manu- script are necessary for the best understanding of the text. I recom- mend the publication of this report as Bulletin No. 74 of the Bureau of Entomology.

, Respectfully, F. H. CHITTENDEN, Acting Chief of Bureau. Hon. JAMES WILSON, Secretary of Agriculture.

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PREFACE.

In the earlier work of the cotton boll weevil investigation particular attention was given to the life history and habits of the boll weevil and the direct effect of these upon cotton production.

These phases of the investigation have been described in a number of circulars and bulletins of the Bureau of Entomology, among which the reader is referred especially to Bulletins 45 and 51, by Hunter and Hinds, and Bulletin 63, Part I, by Prof. E. D. Sanderson. The pres- ent bulletin deals especially with three factors of natural control in regard to which our knowledge has been largely extended by the work done during the season of 1906.

Those who are engaged in the cotton boll weevil investigations of the Bureau of Entomology are frequently asked if the boll weevil is not a passing pest, which may be expected in time to leave the cotton fields where it now occurs, because of a continuation of the onward movement by which it has spread through the great area which it now infests. This idea isdoubtless based upon the fact that in any locality, in a series of seasons, there is likely to occur one season in which there will be a marked decrease in the abundance of the weevils. As a con- sequence of this an unusually good crop may be made, and after such a season with little weevil injury the planter is naturally inclined to anticipate that the weevil may never again become as serious a pest as it has been in the past.

The continuation of this investigation through a number of years has made it possible to determine that local variation, such as has been referred to, may be due directly to the influence of certain natural fac- tors which, eithersingly or in combination, have exercised an unusually large degree of control upon the weevil. It has been possible to deter- mine the most important factors concerned in this control and in some measure to show their relative importance. Extensive observations, however, have but confirmed the impression, which was formed years ago by entomologists engaged in studying this question, that the boll weevil is not a passing pest, but rather an enemy which must be taken into account every year by the grower of cotton throughout the infested area. With the certainty that the fight against the weevil must be continued indefinitely, it has become increasingly evident that

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6 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

our knowledge of every factor affecting, favorably or unfavorably, the development and attack of the boll weevil must be made as complete as is possible. While it may be impossible to increase the influence or effectiveness of some of these factors, there is excellent promise that it may be possible to utilize others to a far greater degree than has been done in the past, because of our more exact knowledge of the nature of their effect upon the weevil and of the conditions under which they produce most beneficjal results. It is possible that by this greater utilization of natural forces the damage annually done by the weevil may be very materially decreased at little, if any, expense.

By ‘‘natural control” is meant the combined effect upon the weevil of all natural enemies and of all conditions or forces in nature which retard or prevent the development of the weevils and reduce the injury which they might otherwise inflict upon the crop. These are, in gen- eral, the factors which operate to produce and to preserve what is often spoken of as ‘‘the balance in nature.’’ The principal factors are tem- perature and moisture conditions in summer and in winter, the attack of predaceous enemies or parasites, and the dependence of the species upon a favorable condition of food supply.

Since the beginning of the present cotton boll weevil investigations in 1901, the work in the field has been continuously under the direc- tion of Mr. W. D. Hunter, to whom is due credit for many of the sug- gestions followed and for the breadth of scope which it has been possi- ble to give to this particular portion of the investigation. | Under his direction the work has been planned and carried out under the imme- diate supervision of the writer. Nearly all of the special field agents who have been in the investigation have had some part in the collec- tion of material or in the examinations involved in securing the data for this bulletin. Special acknowledgment is due to them for the large amount of painstaking work without which this study could not have been made sufficiently extensive to have been of practical value. It gives the writer pleasure to acknowledge this indispensable assist- ance by Messrs. W. W. Yothers, R. A. Cushman, A. C. Morgan, C. R. Jones, W. D. Pierce, F. C. Pratt, F. C. Bishopp, W. H. Gilson, and

J.C: Crawtord: W. E. H.

‘a Page at IE SO ee ll SMUReCINtIne cOMSidcration................... 2... 20-2. eee seen e eee vl ammmence of short drought in same season....................-....--2.-2----- 12 ‘Influence of a dry season upon succeeding season..................-..-.------ 14 enmewitemclimatic conditions..-............-...-- 0222-2222 eee eee eee 15 a eeterars Gt COMtrol._.- .............. 22. eee eee eee 19 Investigations showing control by heat, ants, and parasites..............-..-- 23 Saeural control in various classes of forms.........................-..-------- 26 Desirability of retention or shedding of infested forms. .................-....-- 31 Sma me WerS AGUATCS. 2... ee ee ee eee 33 Sueeivepnifol im various localities.........................2.2-.2.-222-2--e- 35 Influence of climatic conditions especially..................2---.--2-2------- 39 eI CONOIMAONS..- 22 fs 2 ns ee ee ee eee 43 9 Influence of period of infestation upon natural control..........-.-..-...----- 51 @aamciency of natural control in various sections.........................--.--- 53 ' Mortality in each class of forms for each section.................-.--.-------- 60 Seeenous proutine most by natural control.......................---..2-..+--- 62 Destruction of cotton forms by weevil attack or by natural causes...........--. 64 eee etramen. forms. in 1905... 2... .22:-22.-.2..20.....-2edene-e ee 64 Collections of fallen and of dried hanging forms in 1906..........-..--..--- 65 SIRO UUSNOUS = 2 oo ek on wins tw a ee eee ee eee 73 IME ee ee ne ee eee ete eee eee 77

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ISLUSTRATIONS.

PLATES. Page. Puate I. Stages of Mexican cotton boll weevil. Fig. 1.—Adult weevil, dorsal view. Fig. 2.—Adult weevil, side view. Fig. 3.—Full-grown larva, side view. Fig. 4.—Egg. Fig. 5.—Pupa, ventral view. Poo —Aault with wings spread ...........0...0cueee ee Frontispiece. II. Stages and characteristics of Solenopsis geminata. Fig. 1.—Adult, small worker form. Fig. 2.—Sting of worker. Fig. 3.—Right antenna of worker. Fig. 4.—Adult workers, various sizes from workers minor to workers major. Fig. 5.—Larvee and pup of small forms of worker. Fig. 6.—Larvee of workers major compared with larva and pupa of small forms. Fig. 7.—Workers dragging off adult boll weevil which they have killed.................... 24 III. Signs determining boll weevil emergence or entrance of ant Solenopsis geminata. Fig. 1.—Emergence hole of boll weevil in cotton square. Fig. 2.—Entrance holes of ants in squares. Fig. 3.—Evidences of adult activity in square from which weevil emerged. Fig. 4.— Clean interior of square entered by ants. Fig. 5.—The three evi- dences of adult weevil activity, removed from square: a, Shed pupal skin; b, refuse formed in cutting emergence hole; ¢, ex- Ee aS ed, YOUN AUN... oes oe ee ei ee ee . 26 IV. Shedding and retention of forms in cotton. Fig. 1.—a, b,c, Normal scars left by shed forms. Fig. 2.—a, b,c, Abnormal scars with forms retained. Fig. 3.—a, Longitudinal section through normal } scar; b, longitudinal section through base of retained form... ..... 26

TEXT FIGURES.

Fic. 1. Map of Louisiana, showing dispersion movements of 1903 and 1904 and reduction of infested area by winter conditions of 1904-1905. 16 EEE NIE NTU 2 mi 2 2 SOS cial oo ola ans wee om eas = = ele ee 24

SOME FACTORS IN THE NATURAL CONTROL OF THE | MEXICAN COTTON BOLL WEEVIL.

INTRODUCTION.

The natural control of the cotton boll weevil is so broad a subject, comprising the effects of so many factors, some of which are imper- fectly known and understood, that anything like a comprehensive treatment of the subject is at present impossible. Doubtless many factors of some importance have not yet been studied. Of the fact f that some factors do accomplish the destruction observed in indi- _ vidual cases we have no doubt. From extensive series of such obser-

vations we may be able to reason safely as to the general tendency

of those factors, and we may possibly be able to assign to them a

relative value in their tendency to control under the conditions then

prevailing, but we must recognize the fact that all these factors,

however many there may be, dre so interrelated and their influences _ under varying conditions may so essentially differ that a study of them becomes an exceedingly difficult problem.

CONDITIONS REQUIRING CONSIDERATION.

The magnitude of the work involved is directly increased by the extent of the area affected and by the variations in climatic, geo- logical, and cultural conditions which are encountered within the weevil-infested area. While some factors may be studied through multiplied observations as to their effect in individual cases, others must be considered from the broader standpoints of the general movement of the species, crop production, etc.

Temperature and moisture conditions are undoubtedly the princi- pal climatie factors which govern in a general way the distribution of every species. Of these two factors, temperature is unques- tionably the more important. The effect of this factor upon the continued spread of the boll weevil has been a subject of interest to entomologists ever since the weevil became a factor in the cultiva- tion of cotton in Texas. It has been supposed that the weevil, coming originally from a habitat much farther south, would finally

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2 he? NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

be checked by this temperature factor, and it was hoped that this would occur before the northern limit of profitable cotton production should be reached. Unfortunately, the insect has shown that it is capable of a considerable amount of adaptation to this change in temperature conditions, so that its northward range has been gradu- ally extended until, in the season of 1906, it crossed the Red River Valley and became established in the southern portion of Indian Territory. Humidity has proved to be an important factor, affecting more the abundance and injuriousness of the species than it does its distribution.

Considering some of the broader aspects of the effect of tempera- ture and humidity in controlling the weevil, it appears that the most marked instances of definite control have been occasioned by what may be termed the unusual variations, either above or below the usual range, in these factors. Thus it seems to be prolonged peri- ods of extreme heat in summer and the exceptional depression in temperature in winter which have produced the most clearly marked results. When these exceptional conditions occur, they affect, as a rule, rather extensive areas, so that the good results are general instead of localized, as is likely to be the case with many of the factors which will be considered in succeeding pages. The possible effect of high summer temperatures has been the prime reason for recom- | mendations designed to secure a proper spacing of the plants, which would leave weevil-infested squares most directly exposed to the sunshine. It frequently happens that this factor is sufficiently effective to so check severe weevil attack as to allow the cotton to set and to mature a reasonably good crop. It is especially effective if occurring early in the season during the period when the plant is normally setting its crop of fruit. Its value may be completely neutralized by other coincident or preceding conditions, such as a very rank growth of the plants, or a too close planting, which may cause the plants to shade a large proportion of the fallen forms.%

INFLUENCE OF SHORT DROUGHT IN SAME SEASON.

A definite illustration of the control of the weevil, largely by pro- longed and excessive heat, was found at Victoria, Tex., in 1906. ryy ; 2 The plat of cotton under observation covered only one-half acre, so that it was possible to make frequent and close observations upon

. . ’ “7. ° r the conditions prevailing on the entire plat. Table I presents a brief summary of temperature, rainfall, crop, and weevil conditions for this area during a period of four months from the planting of the seed.

2 The term “forms” is used for convenience to include all stages of the cotton fruit: The bud or square, the bloom or flower, and the boll or seed pod.

i Pity s INFLUENCE OF SHORT DROUGHT IN SAME SEASON. 13

BLE I.—Temporary control of weevil by drought in May and June, Victoria, Tex.,

It should be noted that in this field a considerable portion of the ground was exposed to sunshine through the unevenness of the stand. The rainfall during April was sufficient to give the plants a good start, and a fair growth was made through the month of May. April and May were somewhat cooler than is usual for those months. The weevils which had passed through hibernation in the vicinity of the field were so abundant early in the season that squares became infested as rapidly as they were formed. Squares began to form before May 1, but no blooms appeared, and conditions seemed to point to the inevitable failure of the crop until after the extreme heat and drought of June. During June the maximum temperature recorded was below 90° upon only one day, when it was 88° F. On three days the maximum temperature recorded was above 100° F. The mean maximum temperature for the month, 94.3°, is therefore exceptionally high. During the seventy-four days between April 20 and July 3 rains fell upon only four occasions and the total precipi- tation was less than 1} inches. This extreme heat and drought produced a very marked change in the weevil conditions found in this field. Through the gradual dying off of hibernated adult weevils and the long-continued destruction of their progeny, the number of weevils to be found in the field was very greatly reduced. Following the heavy and well distributed rains occurring in July, the plants quickly put out large numbers of squares, and before the weevils

14 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

could multiply so as to do any considerable damage the plants had set a normally good crop of fruit. While weevils became numerous later in the season, a yield of nearly one-fourth of a bale was obtained from this half-acre plat.

The beneficial effect of this drought during the squaring season in Victoria County may be shown by a comparison of the yields for the seasons 1903 to 1906, inclusive. These figures as given by the Bureau of the Census in equivalent 500-pound bales are as follows:

Yields of cotton in Victoria County, Tex., 1903-1906.

Year. Bales T9O3 ss see chsh oes ee Ce Ee a Se Se er ee D, 300 6)” eS etary ne Mene Li hyd Set ibd hg 6, 495 WOO: 2-2 Sey Eee OR a Sette 9, 016 WOOG ose oe tps Se SSP REINS SE art Fa ee en ee 16, 963

INFLUENCE OF A DRY SEASON UPON SUCCEEDING SEASON.

The duration of the dry period as related to the growing season of cotton determines primarily whether the beneficial effect shall be prolonged beyond one season. In the case cited at Victoria drought occurred only in the first third of the season, and its effect was upon the immediate crop, but the benefit would not be continued into the following year. In some of the dryer regions of cotton production it is not unusual to have an entire season covered by a period of comparative drought, and under such conditions the effect upon weevil abundance is quite different. Several illustrations of this have occurred in the region between Corpus Christi and San Antonio, Tex. One of the most definite instances is here given by way of illustration. In this case the effect was widespread, and may be judged by a comparison of rainfall, temperature, and crop conditions for Nueces County, Tex., during the years 1901-1904.

TaBLeE I1.—General illustration of drought control, Nueces County, Tex., 1901-1904.

|

Rainfall. Temperature. ' Cotton = | produc- Annual. Mar. 1-Aug. 31. Annual. | Mar.1-Aug.31.| _ tion, = — a he Year. | | County, | Depar- Depar- Anon Depar- San Depat: | equiva- Total. | 'T° | Total.| JUT® | aver- | SU7° | aver- | {U7 | lent 500- from from ees frOMs |) S55 from ound normal. normal. Be. normal. | 25° normal.| ‘bales. 2) : we 7 = Inches.| Inches. | Inches.| Inches. a ie J eae =) 18 OY Soe a 17.49 | —11.90 6.74 | — 7.42 70.7 0.0} 76.2 | 0.83 | 601 1048 se 22.22 | — 7.98 5.57 | — 7.39 71.5 + 1.4 77.3 +1.85 | 480 DOU Ser pretences ce wate ioc 36.92 | + 6.72 25.97 | +11.38 69.1; — 0.9 74.5 | — 0.9 | 4, 099 OC rere eis ree 28.54 | — 1.66 | 13.56 | + 0.83 70.5| + 0.4; 76.0/+ 0.5 | 1,556

INFLUENCE OF DRY SEASON ON SUCCEEDING SEASON. 15

In connection with this table it should be noted that the tempera-

| conditions during the six months which are of greatest signifi- -eance varied but little from the normal. In rainfall, however, a great deficiency occurred both in 1901 and in 1902. Undoubtedly the continuance of the drought throughout the season was more influential than was the boll weevil in reducing the crop for the years 1901 and 1902, which were almost complete failures. Through the season of 1903 there fell a large excess of rain and it was well distrib- uted. This would produce conditions very favorable for weevil multiplication and injury, but in spite of this the cotton crop for 1903 for this county was nearly ten times as large as during the preceding year. In 1904 both temperature and rainfall were nearly normal, but the effect of the large number of weevils passing through hiber- nation from the season of 1903 is very conspicuously shown by the reduced size of the crop of 1904. This is an illustration of the control of the boll weevil by the unfavorable climatic conditions of an entire season so effective that the weevil failed to become greatly injurious to the succeeding crop in a season when the climatic conditions were unusually favorable for its increase.

CONTROL BY WINTER CLIMATIC CONDITIONS.

Exceptionally low winter temperatures have occasionally proved sufficiently effective to exterminate the weevils from certain areas which had become recently infested and within which the weevils had not had time to become firmly established. This has been illustrated by several well established cases in northern Texas and Louisiana during the past few years.

Weevils were first found near Sherman, Tex., in the fall of 1903, when the northern limit of the dispersion reached to within a few miles of that place. No weevils could be found in that region in 1904 or until the dispersion of 1905 had taken place, thus proving that the few weevils reaching there in 1903 had failed to reproduce or that they and their progeny were completely exterminated by the winter conditions of 1903-4. Weather Bureau records show that the minimum temperature in this locality during the winter of 1903-1904 was 12° F. on January 26, 1904, and that the average monthly tem- peratures for January, February, and March at Sherman were +2.6°, +10°, and +6.9° above normal, respectively. It hardly seems prob- able, therefore, that the weevils failed to maintain themselves in this case solely on account of low winter temperatures.

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16 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

Through the dispersion movements during the fall of 1904 weevils spread over a large area in western Louisiana, as shown on the accom- panying map (fig. 1).

By a large number of very careful field examinations between May 1 and August 1, 1905, Mr. Wilmon Newell, entomologist of the Louisiana State crop pest commission, with the assistance of Messrs.

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HTH | PROBABLY DURING FALL OF 1902.

— FALL /9O3—MICRPATION OR ARTIFICIAL SPREAD.

SEPT, OCT NOV /904¢—SLOW MIGRATION. me LI STLAN LIMIT OF INFESTATION, SULY 3/ 1908

Fic. 1.—Map of Louisiana, showing dispersion movements of 1903 and 1904 and reduction of infested area by winter conditions of 1904-1905. EK. S. Hardy, J. B. Garrett, W. O. Martin, and C. W. Flynn, working in cooperation with the boll weevil investigation of the Bureau of Kntomology, was able to determine that the weevils had been prac- tically, if not completely, exterminated in that portion of the 1904- infested area lying east of the heavy line shown in the map, running from the southwestern corner of Caddo Parish, through about the

third of Calcasieu and Gauacen parishes, ae parallel to jae W ei ern boundary of the State. In other words, through the unfavorable climatic conditions following the Miematsion! of 1904 the weevil was exterminated throughout practically two-thirds of the area in Lou- isiana which had first become infested by the weevil dispersion of that year. From the reports from Louisiana of the Weather Bureau for 1904 and 1905 it appears that killing frosts occurred generally through the State about November 13 to 15, 1904. The temperature and rainfall conditions within the infested area from that time till the end of December were not far from normal, though the rainfall _ during December was very heavy east of the infested area. During | January the temperature in the infested area averaged about 5 degrees below the normal, while in February it reached an extreme departure, averaging 9 degrees below normal. During these two months the rainfall in this area was very heavy, averaging more than 10} inches. Though this appears to be not more than 1 or 2 inches in excess of the normal rainfall during these two months, it is far more than the weevil has been obliged to withstand, as a usual occurrence, in Texas, and in conjunction with the very exceptionally low temper- atures it probably explains in large measure the extermination of the weevils through practically all of the territory entered by them in the fall of 1904 after the latter part of August. It remains to be seen whether the heavy winter rainfall which normally occurs in this Louisiana territory will, as a usual thing, prove to be an impor- tant factor in reducing the number of weevils hibernating successfully within this area. A somewhat similar reduction of infested area occurred in northern _ Texas coincident with that in Louisiana, buts owing to the demands of other lines of investigation in Texas, it was impracticable to make as thorough:an investigation to determine the limit of infestation in July, 1905, in Texas as was done in Louisiana.

As the weevil seems to be acquiring a greater power of resistance to low temperatures as it spreads farther northward, the value of this factor for any locality now included within the weevil-infested area would seem to be gradually decreasing. The efficiency of winter cold is very largely affected by the coincident humidity and by the abundance and favorable character of the opportunities for shelter which may be obtained by the hibernating weevils.

Besides the direct effect upon weevil survival, winter climatic conditions exercise an indirect effect upon weevil injury during the following season by their influence upon the survival of cotton roots. This is an especially important consideration in southern Texas, where during many seasons a considerable proportion of old roots survive,

11575—Bul. 74A—07——-2

18 NATURAL CONTROL OF THE COTTON BOLL WEEVIL. |

giving rise in the spring to what is variously termed sprout, stubble, or seppa cotton. These sprouts arising from roots which are already established begin growing, as a rule, before cotton is planted. Their growth is exceptionally vigorous, so that these plants frequently produce squares several weeks in advance of the average planted crop. This source of food supply, occurring so early in the season, serves to sustain a large number of hibernated weevils from the time of their emergence until after the planted cotton becomes suscep- tible to their attack. It also furnishes early emerged weevils with opportunities for reproduction, which may produce a large number of first generation weevils by the time planted cotton begins to form squares. It has been noticed that durmg seasons when an excep- tional amount of sprout cotton occurs weevil injury has, as a rule, been exceptionally severe. The increased injury during such seasons is undoubtedly traceable to two primary causes: (1) The climatic conditions which are most favorable to the survival of cotton roots are also as favorable to the survival of hibernating weevils; (2) the large numbers of weevils surviving under these conditions are pro- vided with an abundant food supply and with early opportunities for reproduction by the sprout cotton which occurs.

During winters when the climatic conditions are unfavorable both for the survival of weevils and for the survival of old cotton roots the smaller number of weevils emerging in the spring find no other food supply than that provided by the planted cotton, and can not begin their reproductive activity until such time as the squares upon the planted cotton may be about one-half grown. Under these con- ditions the crop has a fair opportunity to set before weevils become sufficiently abundant to destroy a large proportion of the rapidly forming squares.

It is difficult to understand why so many planters fail to appreciate the importance of preventing entirely the appearance and growth of sprout cotton. The only way in which its occurrence may be posi- tively prevented in all seasons and in all parts of the infested area _ is by the uprooting of the old plants. Itis plain that the most effective time to do this, so far as securing a reduction in the number of weevils is concerned, is immediately following ‘the maturity and picking of the crop. This prevents further multiplication of weevils at that time and removes the available food supply of those which are adult as long as may be possible before they can hibernate successfully. Extensive experiments and observations have shown that if the stalks be thoroughly destroyed (as by burning) from three to four weeks before the occurrence of the first frost in the fall and if the eround be kept clean, so that favorable opportunities for shelter are removed, the number of weevils surviving hibernation may be very greatly reduced. If by any chance sprout cotton appears in

CONTROL BY WINTER CLIMATIC CONDITIONS. 19

the spring, every plant of it should be destroyed to prevent its nourish- ing the weevils which may have survived. The practice of allowing

sprout cotton to grow in a field of planted cotton can not be too strongly condemned. Certainly if planters could appreciate the fact that these occasional plants will, under usual conditions, enable the weevils to do much greater injury to the main crop, they would be very careful to destroy them. If planters in southern Texas fully appre- ciated the importance of this menace, there would soon be developed a strong public sentiment which would compel every planter to adopt methods which would prevent the occurrence of sprout cotton. It is entirely possible in a great majority of cases for the planter to insure for himself the beneficial effect of a large reduction in the number of weevils surviving hibernation, such as would result from occasional winters of unusual severity, even during seasons which would be favorable for the survival of large numbers of weevils. This, then, is the part of cultural practice which may be made to regularly supplement or possibly supplant the beneficial effects which are occasionally experienced by an exceptionally large degree of natural control through severe climatic conditions during the winter. RELATIONSHIP OF FACTORS OF CONTROL.

It is evident that these factors, which are but the extreme fluc- tuations in climatic conditions, will only occasionally exert their maximum effect, and that under normal conditions of temperature and humidity other factors, having a more constant average effi- ciency, May surpass climatic variations in their controlling effect upon the weevil. It is to a study of some of these average factors that the present paper will be mainly devoted. Among the factors concerned in the natural control of the boll weevil in the United States to which especial attention has been given may be mentioned heat or drying, native ants, proliferation, parasites, the limitation of the weevil’s food supply by the work of the cotton leaf-worm (Alabama argillacea Hbn.), and birds.

In this bulletin special consideration will be given to the effects of heat or drying, native ants, and parasites. Proliferation® was

@ ** Proliferation,’ as the term is used in connection with cotton, refers to a phe- nomenon which frequently follows the attack of weevils or other insects in cotton squares and bolls. It may be defined as the development of numerous elementary cells from parts of the bud or boll which are themselves normally the ultimate prod- ucts of combinations of much more highly specialized cells. The resulting product is thus composed of comparatively large, thin-walled cells, which are placed so loosely together that the formation is of soft texture and has a granular appearance which may be seen with the naked eye. Proliferous formations lack the distinctive texture which is characteristic of the normal parts of either bud or boll. The consistency of

the formation is soft and yielding, resembling somewhat a rather soft gelatin. From

this apparent resemblance the term ‘‘gelatinization” is sometimes used instead of proliferation.

1 04 st

20 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

studied extensively in 1905, and the most important results of the investivation have been published.¢

The work of parasites and the possibility of making them even more valuable in the fight against the weevil is considered fully by Mr. W. D. Pierce in another bulletin of this Bureau.’ The relation- ship of birds to the boll weevil has been treated in several publica- tions, principally by the Biological Survey.°¢

The study of the influence of the leaf worm upon weevil control will require at least. another season before the results can be suffi- ciently complete for publication.

The work with proliferation was continued in 1906 only as far as seemed advisable to confirm preceding results and conclusions. It was found in 1905, in over 8,000 examinations, that proliferation produced an increase in weevil mortality, averaging, for squares and bolls together, about 12.5 per cent. From the data following in these pages it appears that there is an average mortality not attributable to heat or drying, ants, or parasites, among over 80,000 obser- vations of squares and bolls together, averaging slightly over 12 per cent. The confirmation of previous conclusions is evident, but in reference to both it should be stated that the figures recorded must be considered as a conservative statement of the value of this factor, since it must be admitted that it may become effective in many cases even before the hatching of the weevil eggs and that it is practically impossible in a large series of examinations to determine whether an egg or very small larva of the weevil may have been destroyed. It must also be considered that proliferation resulting from feeding punctures of the weevil and of other insects frequently proceeds to such an extent as to itself accomplish a destruction of both squares and bolls entirely disproportionate to the severity of the feeding injury which originally incited the proliferation. The value of pro- liferation as a factor in controlling the weevil is therefore offset in some degree by its tendency to continue beyond the remedial point and by its abundant formation under certain conditions of irritation when no weevil stage is present.

The work with parasites has been sufficiently extensive to form a very reliable basis for further investigations which promise to give increasingly valuable results. The actual records of parasitism and the comparisons between this and other factors of natural control are given herewith, while the more special consideration of the con- ditions favoring parasite abundance, the biological study of the species found, and the possibility of increasing their effectiveness

« Bul. No. 59, Bureau of Entomology. (See p. 8 for bibliography of proliferation. ) > Bul. No. 73, Bureau of Entomology. ¢ Bul. No. 51, Bureau of Entomology, pp. 150-153; Buls. Nos. 22, 25, and 29, Biolog- ical Survey.

RELATIONSHIP OF FACTORS OF CONTROL. oT

may be found as given by Mr. W. D. Pierce in Bulletin No. 73°of the Bureau of Entomology. -

For manyyyears the cotton leaf worm (Alabama argillacea) has been considered as an important cotton pest throughout the South, though the severity of its injury to the crop has been less during recent years than it was formerly. It now appears in destructive numbers only during the latter part of the season, usually after the crop begins to mature, and is not infrequently a welcome visitor. _ Especially in rank late cotton its destruction of the foliage enables

light and air to penetrate more readily, thus preventing the decay of bolls lying on or near the ground and greatly facilitating the maturity of the crop. For this reason comparatively few planters now look upon the leaf worm as a pest to be controlled by the application of insecticides. Succeeding generations of the caterpillars remove an increasingly large proportion of the foliage until the plants may be finally stripped bare repeatedly before the close of the season.

The significance of the leaf worm in the control of the boll weevil rests directly upon its effect upon the food supply of the latter species. As the weevil has no other food plant than cotton, its final multi- plication before the end of the season is usually limited directly by the abundance of squares and bolls within which it may breed. The defoliation of the cotton by the leaf worm stops immediately the formation of squares and the subsequent possibility of the setting of bolls. Further development of the weevils is thus abruptly checked. The maturing bolls may continue to give out weevils for some weeks, and previously infested squares may add’ to the number of adult weevils for from one to two weeks, but the sudden removal of the food supply and of the shelter usually enjoyed by the adults causes great mortality among them. Many weevils leave the bare fields in search of food, and thus, in various ways, the number of weevils in a field where the leaf worms work abundantly and thoroughly becomes very greatly reduced. If the leaf worms continue to strip the cotton until late in the fall there will be no possibility of an increase in the number of weevils. The leaf worms may actually accomplish what is practically a more or less complete early destruction of the cotton plants and a cleaning up of leaf rubbish in the field. Where this is the case it is safe to assume that so few weevils will survive or hibernate that a very positive benefit may be experienced during the following season, and if climatic conditions should favor the growth of cotton, a crop may be secured with comparatively little injury by the weevil.

Defoliation by the leaf worm may be especially effective if it should happen to be followed by winter climatic conditions which are exceptionally severe, so that only those weevils which found the most favorable hibernation shelter would naturally survive. The leaf worm does not, however, often occur abundantly during two succes- Sive seasons in Texas. Its work is often local and only partial in the

e fi e P.;

22 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

field attacked. Frequently the plants leaf out and form squares after having been defoliated. It. must, therefore, be placed rather low in the list of factors concerned in the natural contrpl of the boll weevil.

It is possible that something can be done to increase the efficiency of this factor or to render it of more constant value, especially in such regions as the Red River valley of Louisiana, where the worm occurs with considerable regularity. It is evident, however, that the planter should not rely upon the leaf worm to secure the destruction of his stalks at as early a date as the picking of the crop may render possible. At present in the bulk of the infested territory it may be considered as an occasionally valuable factor, but the completeness of the con- trol resulting from its occasional work is a most valuable demonstra- tion of the effect which it is possible for the planter to secure quite regularly by himself destroying the food supply of the boll weevil early in the fall.

The irregularity of the leaf-worm attack makes it necessary that final conclusions as to its value in controlling the weevil be based upon observations extending over a number of years, but the data already collected show conclusively that with these two important pests of cotton present in abundance the leaf-worm work is a most positive benefit to the planter; and if it secures continuous defoliation until too late in the season for the weevil to resume its breeding, this may result in the practically complete control of the insect for the following season.

There can be no doubt that birds are an important factor in pre- venting the extraordinary multiplication of many species of insects. Considerable attention has been given to the determination of the value of various birds as destroyers of weevils, and this important work is being continued by the Biological Survey. These records show that birds do not yet constitute a very important factor in controlling the boll weevil. There are several reasons for this. The habits of the weevil are such that the adults are but slightly exposed to the attack of birds, except during the season of the fall dispersion.

In Cuba Mr. E. A. Schwarz has determined that a bird (/cterus hypomelas) has learned to tear open the fallen squares and eat the weevil stages infesting them, but in the United States no bird has yet acquired such a habit. The season at which birds capture most weevils is during the dispersion in the fall months, when the weevils are flymg most abundantly. The destruction of a large number of weevils late in the season can not, however, be as effective in con- trolling the weevil as would be the capture of a comparatively few during the hibernation season or in early spring, but during the first half of the season very few birds frequent the cotton fields. For these reasons birds must be ranked low among the controlling factors,

a RELATIONSHIP OF FACTORS OF CONTROL. 93

but it is possible that they will gradually acquire an increasing importance the longer the weevil remains abundant.

There are other factors which are, or may become, of relatively great importance in the fight against the weevil. Some of these have been but slightly investigated. It is safe to assume that the factors which have been mentioned include those which have thus far proved to be of greatest importance in holding the weevil in check to some extent. 4

The relative value of these factors is certain to change suddenly, and when one assumes a position of predominant influence the others must undergo a readjustment of relative position. It is certain that the efficiency of predaceous enemies and of parasites is gradually increasing, while it is probable that the gradual adaptation of the weevil to its new environment is rendering it more resistant, espe- cially to the effects of the adverse climatic factors. Additional observations of the effects of these opposing tendencies should bring to light facts which will be of general significance in connection with the study of many other pests besides the boll weevil.

The area infested by the boll weevil in. the United States now reaches a total of between 175,000 and 200,000 square miles. Of course but a small percentage of this enormous acreage is actually devoted to cotton culture, but the range in geological conditions is naturally great. Thus in Texas cotton is cultivated extensively on five or six very distinct geological areas each furnishing more or less distinctive conditions of environment affecting faunal, floral, and shelter conditions which may at any time prove to have an impor- tant significance in the weevil status.

INVESTIGATIONS SHOWING CONTROL BY HEAT, ANTS, AND PARASITES.

Observations of the effect of various natural factors in controlling the weevil have been accumulating since the beginning of the boll weevil investigation. The earlier records, however, were not made to include the simultaneous effect of several factors, and the records presented in this connection are therefore confined to the observa- tions made during 1906.

Heat and drying are considered together, as their effects upon the immature weevil stages are coincident and inseparable. The effi- ciency of this factor naturally follows seasonal variations, but it is largely affected by the distance between rows, the size of the plants and density of their foliage, the season of occurrence in relation to the state of the cotton crop, and by cultural conditions.

Whenever ants are referred to in succeeding pages it should be understood that no reference is intended to the Guatemalan ‘‘kelep”’ (Ectatomma tuberculatum Oliv.), which has failed to maintain itself in Texas.

>

24 NATURAL CONTROL OF THE COTTON BOLL WEEVIL. |

The native ants concerned in the control of the weevil are princi- - pally of the genus Solenopsis and varieties of the species geminata (fig. 2).

The principal points in the characterization of this species are as follows: There are two distinct nodes or scales in the slender petiole of the abdomen. All forms but the male have a sting (Pl. I, fig. 2). The antenn (PI. II, fig. 3) are ten-segmented; the club is formed of the last two segments, of which the terminal one is the longer. Maxillary and labial palpi have each two segments. The clypeus has two longitudinal ridges and the sting is very large. The color varies, but the workers usually seen are of a dark reddish brown, the color of the abdomen being often considerably darker than that of the head and thorax. Length of workers from 2 to 3 mm. ;

These ants form nests near the surface of the ground. All stages of development and forms of adults may be found in these nests practically throughout the summer season. The individuals which are most active, if not in fact those which are alone concerned in the attack upon the weevil, are the smaller workers which are commonly to be seen outside of the nests. In Plate II, figures 5 and 6, are shown some of the. immature stages of this species. The queen larve are very much larger than the worker forms as is shown in the illus- tration. The pup are naked, and as they approach maturity the color gradually changes from a translucent white to a dark brown. The active worker form is shown Fic. 2.—Solenopsis geminata, ant ene- jn Plate dole figures 1 and 4.

EE aera arse weed Uctrs species shows a tendency to nest a. within the shade formed by the plants, and is to some extent out of the reach of ordinary cultivation by being close to the middle of the rows. The breaking up of a nest, however, does not seem to drive them away or to interfere seriously with their activities. In Plate III, figure 2, are shown cotton squares which have been entered by these ants and in which weevil stages-have been destroyed. A comparison of the external resemblance of these entrance holes with the exit holes made by weevils is shown in Plate III, figures 1 and 2.

Since, in external appearance, the emergence holes made by adult weevils in escaping from squares resemble very closely the entrance holes made by the Solenopsis ants in obtaining access to the weevil stages in a square, it seems advisable to add a brief explanation of the manner in which these two classes of squares may be positively separated. In all cases the final determination as to the class in which a square belongs rests upon an examination of the interior. As

Bul. 74, Bureau of Entomology, U. S. Dept. of Agriculture.

STAGES AND CHARACTERISTICS OF SOLENOPSIS GEMINATA Fig. 1.—Adult, small worker form. Fig.

Fig. 2.—Sting of worker. Fig. 3.—Right antenna of worker. 1—Adult workers, various sizes from workers minor to workers major. Fig. 5.—Larve and pup of small forms of worker. Fig. 6.—Larvee of queens compared with larva and pupa of small forms. Fig. 7.—Workers dragging off adult boll weevil which they have killed. Fig. 1, enlarged to 7 diameters; figs. 2 and 3, to 40 diameters; figs. 4 to 2 diameters. (Original.)

fig. 7,

5, and 6, to 4 diameters;

PLATE Il.

ee eas ee = SS ee. ee ee ——— —=

OGL aimee ee ee oe - a a . a cease = ——

ths i ai P a “«

ae CONTROL BY HEAT, ANTS, AND PARASITES. 25

al hing g the emergence hole made by the weevil Crk TUT tie: 1) 2 regular in outline and somewhat larger in area than are the nce holes made by the ants. Upon opening the square carefully 1 Il be found that if a weevil has reached full development therein emerged, there will be found present three definite signs which are t ae in cases where ants have destroyed the weevil stage. One f these signs is the delicate white skin which is shed by a pupa ag the weevil transforms from that stage to its adult condition. . II, fig. 5a.) This is usually so shriveled and twisted as to have no Bitemblance whatever to the outlines of a living pupa and is fre- quently more or less hidden in the débris which constitutes the second sign. This is a rather abundant mass of fine particles which have been torn from the square by the weevil in cutting its emergence hole. hese are not eaten by the weevil but are left within its cell (Pl. III, figs. 3 and 5b). The third sign of adult activity consists of a number of particles of white excrement which are almost invariably deposited by the adult weevil before its emergence from the square (Pl. II, figs. 3 and 5c). These three signs are absent in cases where ants have entered and destroyed the weevil stages (Pl. III, fig. 4). _ The value of a study based upon statistical dae becomes easily apparent to one engaged in a thorough study of such a subject as this. Without it there is a strong probability that the general impressions formed may not give proper credit to the influence of the various factors. Conélusions which are based upon the total effects of the various factors in a large series of observations must necessarily be more reliable. This must be especially true of the general average of _ results from a considerable number of localities and under a consider- able variety of geological and climatic conditions. The first division in the data as obtained has been secured by sepa- _ rating the cotton fruit into several classes, each of which may contain weevil stages which have been exposed to similar conditions. But four of these divisions have been retained in the arrangement of the data shown in Table III. These are, (a) hanging, dried bolls; (5) hanging, dried squares; (c) fallen bolls; (d) fallen squares. As a rule infested squares and small bolls are shed by the plant in from seven to twelve days after the weevil attack. Many small bolls, especially, are shed normally, even though they may have suffered no injury from insect attack. This happens most commonly within a few days after the withering of the flower and before the young boll has made any growth. It may result from a failure in fertilization of the flower or the inability of the plant to sustain an excessive load of fruit. With both squares and small bolls, the shedding is accomplished “naturally, just as is the shedding of leaves in the autumn, by the for- - mation of an absciss layer of corky cells which cuts off the fibrovascu- lar bundles through which the sap is supplied, thus destroying the vital connection between the bud or boll and the plant branch. The

Id

« ~

.*

26 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

exact location of this cork area is shown by the scar left by a fallen leaf or square. It frequently happens, however, that for some reason the severance is incomplete and that the square or boll remains’ slightly attached to the plant though cut off as far as the vital con- nection is concerned (Pl. IV, figs. 2 and 3b). The difference in these two conditions may be seen and better understood by reference to — Plate IV, figures 1 and 2.

The tendency to retain dead squares and bolls seems to be a charac- | teristic of individual plants in nearly all varieties, but is most strongly marked in those which approach the limbless, cluster type of growth. In some fields the hanging, dried forms may be found very abun- dantly, while in others at the same time they may be very rare.

The retention of squares and bolls bears no definite relationship to the boll weevil injury, as many of the small bolls, especially, have never been attacked.

It is evident that the immature weevil stages in those forms which remain hanging upon the plant will be subjected to very different influences by the factors of natural control from those in fallen forms. This difference is especially marked as regards the exposure to the effect of sunshine and to the attacks of predaceous and parasitic enemies, and should be kept in mind in considering the data pre- sented in the following tables.

An explanation should also be given regarding the counting of stages. Besides each weevil stage, living or dead, which was actually found, one stage was counted for each case where there existed unques- tionable evidence of its previous presence. This evidence would include the emergence hole made by an adult weevil, the cell within a square or boll from which some stage of the weevil had been re- moved by ants, and also the cases of parasitism. Since dead stages accumulate through a considerable period of time, or so long as the forms remain intact, and will be found and counted upon examina- tion, it becomes necessary in determining percentages of mortality to count emergence holes as representing living adults which, of course, is really the case.

It would require too much space to give the detailed results of each of the examinations made. For each locality, therefore, all-the obser- vations made have been combined. This means in most cases that the figures given in these tables represent an average of several fields in each locality, and in seventeen of the twenty-eight localities where observations were made the figures combine the results of examina- tions upon from two to nine dates.

NATURAL CONTROL IN VARIOUS CLASSES OF FORMS.

In collecting the forms for these examinations all were taken as they came, whether fallen, or dried and hanging to the plants. The green, growing forms were not examined. Separate collections were made to secure hanging or fallen forms.

ee Se ae | Bul. 74, Bureau of Entomology, U. S. Dept. of Agriculture. PLATE III

SIGNS DETERMINING BOLL WEEVIL EMERGENCE OR ENTRANCE OF ANT SOLENOPSIS GEMINATA.

Fig. 1.—Emergence hole of boll weevil in cotton square. squares. Fig. 3.—Evidences of adult activity in Fig. 4.—Clean interior of square entered by ants.

Fig. 2.—Entrance holes of ants in square from which weevil emerged. Fig. 5.—The three evidences of adult weevil activity, removed from square: a, Shed pupal skin; 6, refuse formed in cutting emer- sence hole: c, excrement of unfed, voung adult. All, except fig. 2, enlarged to 4 diameters; fig. 2, enlarged to 2 diameters. (Original.)

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i NTROL OF THE COTTON BOLL WEEVIL.

NATURAL CO

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r a a

80 - NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

From a study of the totals in each section of this table it appears that the highest average percentage of mortality from all three causes considered was found among the fallen squares, where it reached 60.5 per cent. The next highest average mortality occurred in the hanging, dried squares, with 52.6 per cent. The mortality in the two classes of bolls is very similar, with 33 and 30.4 per cent.

The data include only examinations of cotton forms which had been destroyed by some cause. In the majority of cases the de- struction of the form could be attributed directly to weevil attack. The data upon this point are stated in subsequent tables. (See pp. 64-72.)

-A comparison of the mortality records in hanging versus fallen forms (including both squares and bolls) shows that among the 9,663 stages found in hanging forms there was an average mortality of 40 per cent, while among the 29,328 stages in fallen forms there was an average mortality of 56 per cent. In hanging bolls the mor- tality is 30.4 per cent; in fallen bolls, 33 per cent; in hanging squares, 52.6 per cent; in fallen squares, 60 per cent. These figures show a consistent difference in favor of the fallen forms.

Parasites work more freely in the forms that remain attached to the plants than in those which fall to the ground, but in neither class of forms is their work as important as is that of the ants or even the effect of heat or drying. From many observations as to the stage of the parasite at the time of examination and from a general knowledge of the time that must have passed between it and the parasite attack, it appears that, as a rule, the parasite egg is deposited at about the time the square or boll withers. If this be the case, it is probable that the increased length of time during which the forms that remain attached and dry upon the plant are exposed to the parasite attack may explain the greater percentage of parasitization found in the hanging forms. In hanging forms parasitization amounts to 9 per cent, while among fallen forms it averages only 2.8 per cent.

The average total mortality among all classes of forms caused by the three factors was 52 percent. As the weevil does not pass beyond the influence of these factors of control until after it has become adult and emerged from the square or boll, it is evident that among the 13,000 living stages found present there might still have occurred a very con- siderable mortality before all could have become adult and emergence taken place. The larval and pupal stages, which number over 80 per cent of all the living stages found present, are especially susceptible to the influence of the three natural factors of control under considera- tion. It would be very conservative to assume that fully one-half of the living stages present would have been destroyed had the forms been allowed to remain exposed to the influence of the factors of con- trol until all surviving adults could have emerged. This would have

*

RETENTION OR SHEDDING OF INFESTED FORMS. >. St

sased the destruction of weevil stages by these factors to about 68

.

Still another arrangement of general results may serve to show a

comparison between the four classes of forms and between hanging

J rTty\ be . . . = 7

and fallen forms. This arrangement is given in Table IV. It may

‘serve to indicate for the entire infested area whatever general advan-

iF tage there may be to the plant in the shedding or in the retention of its infested forms. :

Tasie LV.—Summary of mortality results shown in Table IIT, hanging and fallen forms.

Weevil stages

dead. Cause of death. Pro- Total ———<—___—_—|——___- por- num- | Total Heat or ae her Se . ber of | weevil Per drying. se 2 ale ately | Pa Class of fruit. | forms stages | ‘Total cent of| : | es exam- | found.| num- | total |Num-| Per | Num-| Per |Num-| Per | Sacv ined. ber. |stages| ber of|cent of, ber of \cent of! ber of |cent of weevil found. | stages) total | stages | total | stages) total | stage killed.|found.| killed. found. killed. found. | j Hanging forms: | Dried, hanging | | bolls.......- 17,359 | 5,433 | 1,650; 30.4| 426] 7.8) 902] 166! 322) 6.0} 3.20 Dried,hanging squares... ... 7,004 | 4,230} 2,227) 52.6 804 19.0 | 883 | 20.9] 540] 12.8 1. 66 Totals, hang- | ' lee ing forms ...| 24,363 | 9,663 | 3,877} 40.2] 1,230) 12.9) 1,785 | 18.7 | 862 | 9.0 2. 52 Fallen forms: | ; are cals fino 2, eer he Fallen bolls...) 22,685 | 4,618 | 1,523 | 33.4 527 | 11.4 951 | 21.0 45 1.0 4. 91 Fallen squares | 39,908 | 24,710 | 14,885 60.8 | 6,201 | 24.7} 7,806] 32.8 (Oe ioLe 1. 62 Totals, fall- | : | | en forms...) 62,593 29,328 | 16,408 | 56.4 | 6,728 | 23.0} 8,757 SOLON 823: 2.8 2. 13 Summary of all | *. SA sigh sag sek | YuRy | forms: | al Hanging forms| 24,363 | 9,663] 3,877] 40.2] 1,230| 12.9] 1,785] 187] 862] 9.0} 2.52 Fallen forms. .| 62,593 | 29,328 | 16,408 | 56.4 | 6,728 | 23.0] 8,757 | 30.0 823 2.8) 2.53 Totals, all | | | | LOUIS: .. -~ 86,956 | 38,991 | 20,285 | 52.3 | 7,958} 20.5 | 10,542 27.2 | 1,685 4.3 2.23 }

The possibility of weevil damage having any relation to the reten- tion of forms by the plant may be settled by a study of the proportion of weevil stages to each class of forms.

The last column of the table shows the average proportion of each class of forms to one weevil stage found. It must be borne in mind that many squares and bolls are destroyed by the feeding of the weevils in which no eggs have been deposited. Undoubtedly in a great many cases a young larva may have died when no trace of its presence could be found at the time the examination was made. This would especially apply to the hanging forms. From the pro- portions given it appears that, among hanging forms, twice as many bolls were examined for each weevil stage found as in the case of squares, while among fallen forms the proportion is three to one. This indicates that there is practically no difference in the proportion

32 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

of weevil stages to squares, whether hanging or fallen, but that there is a natural tendency on the part of the plant to shed a large number | of uninfested bolls soon after their formation and before weevil — attack has taken place. Many of the dried hanging bolls also fail to show any sign of weevil attack. The attack of the weevils upon squares is, therefore, of much greater importance in their multiplica- tion than is their attack upon bolls: Here again the importance of natural control is shown by the mortality in all squares, amounting to almost 60 per cent, whereas in all bolls it was but 31.6 per cent.

These figures show a remarkable similarity in the degree of infes- tation for the corresponding classes of fruit. This agreement is so — close as to lead to the conclusion that the attack of the weevil has practically no effect upon the tendency of the pppaut to retain a portion of its surplus fruit in this way.

The proportion of hanging to fallen forms is not accurately shown by the figures given here as no effort was made to collect the hanging and fallen forms from the same areas at each examination made. This proportion varies very greatly in different fields and during dif- ferent periods of the season, but it is safe to say that in the exami- nations recorded a much larger proportion of hanging, dried forms was collected than would be found in any ordinary field of cotton, unless it were of some limbless variety, such as the Dickson. Among the forms examined, nearly 70 per cent of the squares and bolls had fallen. “These fallen forms contained somewhat more than 70 per cent of all the weevil stages found. The proportion of weevil stages to forms is very closely similar in hanging and in fallen forms, but the percentage of mortality in hanging forms averages 40, while in the fallen forms it averages over 56 per cent. ‘The relative importance of the mortality in the two classes of forms as related to the whole question of natural control is shown to a fair degree by a comparison of the percentages of mortality in hanging versus fallen forms, based upon the total number of stages found in the total number of forms examined. In this way we fad that among the 38,891 weevil stages found the 3,877 dead in hanging forms constitute approximately 10 per cent, while the 16,408 dead in fallen forms constitute 42.1 per cent. Since, as has been stated, the hanging forms examined are in a greater proportion to the fallen forms than actually occurs in the average field, it follows that it is conservative to say that, as a rule, the total mortality in fallen forms will average to be, at least, four times as great as that occurring in the hanging forms. Consequently the factors of natural control which affect especially the weevil stages in the fallen forms must be given a correspondingly high rank as compared with those which affect more especially the stages in the hanging forms. Figuring in this way for each of the three factors of natural control given, we find that heat or drying caused a mortality of 3.2 per cent in hanging forms and 17.5 per cent among fallen forms,

i <e a. _-——sS RETENTION OR SHEDDING OF INFESTED FORMS. 33

iD ts caused a mortality of 4.6 per cent among hanging forms and 22.4 per cent among fallen forms, while parasites caused a mortality of 2.2 per cent among hanging forms and only 2.1 per cent among fallen orms.

The conclusions may also be drawn from a study of the proportion _ of weevil stages found dead in each class of forms, in connection with the factors causing death and the proportion of forms to weevil ~ stages in each class examined. In this way it appears that the low- - est total mortality was found in the hanging bolls which dried upon the plant, being in this case 30.4 per cent. For fallen bolls this per- centage was 33.4, in hanging squares there was a mortality of 52.6, while in fallen squares it amounted to 60.8 per cent. Taking next a comparison of hanging and fallen forms, it appears that there was an advantage during the season of 1906 of 16.2 per cent greater total mortality among the fallen forms.

As to the factors which were most effective in producing this mor- tality, it appears that among hanging forms ants produced 46.5 per cent of the total mortality found, while in fallen forms they were responsible for 53.2 per cent of the total mortality. It is evident, therefore, that in either hanging or fallen forms Solenopsis ge minata was the most important summer factor in 1906 in controlling the weevil. When it is considered that a large majority of the infested forms fall, it becomes still more certain that the effectiveness of the factors naturally tending to control weevil multiplication is greater when the infested forms are shed than when they are retained by the plant.

From these data it appears that it is more desirable that plants shed their infested forms completely and quickly after the infesta- tion takes place than that they should retain them, allowing the weevil stages therein to develop under the smaller influence of natural control to which they would then be subjected.

i i

MORTALITY IN BOLLS VERSUS SQUARES.

It should be stated that in these examinations no attempt was made to determine the mortality among weevil stages in large bolls which continued their development in spite of the weevil attack. In such bolls it is obvious that heat or drying can have had little if any effect upon the weevil stages. Ants do not enter green, growing bolls, though they frequently destroy weevil stages which become more easily exposed to their attack through the opening of the bolls. Instances have been found of parasitism of weevil stages in large bolls. Proliferation is, however, an active factor which has been found in the examination of more than 12,000 locks to produce an increase in mortality of weevil stages amounting to between 6 and 7 per cent.

11575—Bul. 74—07——3

34 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

For this comparison the figures given in Table III are combined .

Several general conclusions may be drawn from the study of these figures. In bolls nearly two-thirds of all the stages found were alive, while in squares the living stages constituted but slightly more than one-third of the total stages found. Heat is about two and two- thirds times as effective against the weevil stages in squares as against those in bolls. Ants are also much more effective in raising the mortality in squares. Parasites are slightly more active in attacking weevil stages in squares than in bolls, but the difference in this case is much less than in the case of ants or heat. From the combined effect of these three factors there is a total mortality averaging in bolls a little less than one-third, and in squares nearly three-fifths, of all weevil stages present.

Among the 38,991 weevil stages found, 63.5 per cent of this total number occurred in fallen squares. It is evident, therefore, that the factors of natural control which are most effective in destroying weevil stages in fallen squares are the most important in restricting the summer multiplication of the weevil. It appears that the Solen- opsis ants and heat are the two most important factors in-this con- nection.

In these examinations it was impossible to account for eggs and very small larvee, as the drying of much of the material and the decay present in another large portion would inevitably efface all traces of these stages even in cases where the work of the living larve was not sufficient to have done so. In the absence of positive data showing the mortality in these young stages, no attempt will be made to esti- mate the mortality that undoubtedly does occur early in the weevil’s development. It is certain that the average of the smallest larve found would not be more than one-third or possibly one-fourth crown, but the data given for the stages above the one-third grown larva are thoroughly reliable.

It is therefore safe to say that the mortality of the boll weevil throughout the infested area, as represented by twenty-eight well- distributed localities, during the period from June 16 to October 15, 1906, from the effects of heat or drying, ant, and parasite attack averaged not less than 65 or 70 per cent of all the weevil stages sur-

MORTALITY IN BOLLS VERSUS SQUARES. 35

viving beyond six or seven days from the deposition of the eggs. - If to this percentage we add the 12 per cent which were found dead _ from some cause other than the three under consideration, but prin- _ cipally due to proliferation, we have a total mortality of from 75 to 80 per cent.

The average length of the developmental period from June to October is shown in Bulletin 51, Bureau of Entomology, page 94, to be between eighteen and twenty days. The mortality shown by these records occurs, therefore, during the last two-thirds of the period between the deposition of the egg and the emergence of the adult weevil. When it is considered that a considerable proportion of eggs

7"

and very young larve must also be destroyed, it becomes increasingly apparent that but a very small percentage of the total number of eggs deposited by the weevils in a field of cotton produce adults.

It may seem that this tremendous destruction of weevil stages would be sufficient to bring the weevils under practical control so that the comparatively small remainder would produce little injury to the crop. Such, however, is not the case. The fact is that in nearly if not quite all of the fields examined the weevils were so abundant as to destroy a large portion of the crop, and in most cases it is probably true that the multiplication of the weevils was finally limited by the amount of food supply present rather than by the destruction of the weevil stages by all these factors of natural control. This does not mean that the crop did not benefit by the destruction of weevil stages accomplished, for had it not been for this checking of the possible multiplication of the weevils few of the fields could have produced a crop that would have been worth the picking.

Were it not for the fact that in nearly all cases the destruction of the weevil stage occurs only after the weevil has destroyed the cotton form, the crop might be much more largely benefited by this natural control. Without’ the natural control existing, cotton production within the weevil-infested area would be impossible; with it alone, the continuance of cotton culture may still be possible; but only by sup- plementing the work of nature by the most practicable methods known ean the balance be thrown largely in favor of the planter in producing a very profitable crop.

FETE eR A tM Rie

“

Te a ae. a

NATURAL CONTROL IN VARIOUS LOCALITIES.

In the sections of Table III the data are divided according to the class of forms examined in order to make apparent the varying dif- ferences in the effects of the several factors of natural control upon the weevil stages in each class of forms. In studying the combined effect, which is really the measure of control in any locality and for any period of time, this separation into classes is no longer necessary. For this reason the figures given in Table VI represent a combination

* 36 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

of the four classes given in Table III. It is proposed to show for each locality the proportion of the total mortality due to each of the three factors, a comparison of the mortality in each stage of the weevil— larva, pupa, and adult—and the general climatic conditions prevail- ing during the period covered by the examinations. In this way it may be possible to show whether any particular combination of cli- matic conditions prevailed in coincidence with the highest percentages of mortality found, or whether the percentages may vary widely under similar climatic conditions so that the real explanation for the variation must be due to other causes than climatic differences. In this table, as in Table III, the percentage of mortality in larval, pupal, and adultstages is based upon the total numbers of those stages which were’ found alive or which had died from the effects of heat or drying. It seemed impracticable to attempt the determination of the stage of the weevil destroyed by ants and parasites, though in many cases it would have been possible. The ‘‘total of weevil stages found” includes those found alive, those killed by heat or drying, and those which had died but probably from some other cause than heat, and each weevil cell emptied by ants as well as each instance of parasite occurrence.

In the column showing ‘‘total mortality from three causes”’ it may be seen that the range is from 0 to 84 per cent, with the average at 52 per cent. Eleven localities show a mortality above the average and seventeen below it. For the eleven the average mortality is 63.2 per cent, while for the seventeen the average is but 34.2 per cent. It is noticeable that nearly all of those showing the higher percentages are located below or south of the center of cotton culture in Texas. The figures in Table V1 show the conditions for mortality by these three factors, and also give in each locality and in a general way the climatic conditions prevailing during the period of examination and for ten or fifteen days previously. In cases where no records are available, those are used for a near-by locality having weather con- ditions probably similar to those of the locality in which the examina- tions were made. The totals in this table show the general facts concerning mortality under average conditions in the twenty-eight localities representing in a general way the infested area. Besides the comparison as to mortality by each of the three factors repre- sented there is a general record showing the mortality found in each stage of the weevil from heat or drying. The records of the four principal classes of forms examined are combined in this table.

It is shown that the mortality from heat in the larval stage amounts to 52.6 per cent, in the pupal stage to 18 per cent, and in the adult stage to 6.3 per cent. Nearly 70 per cent of all the mortality caused by heat or drying occurs, therefore, during the larval stage. An early shedding of infested forms is plainly very desirable,

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38 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

Ants (Solenopsis geminata) accomplish a greater destruction of weevil stages than heat and parasites combined. Parasites are decid- edly the least important of the three factors.

So many conditions influence the effect of sunshine especially that it is difficult to determine whether there exists anything like a con- stant relationship between the maximum temperatures at a locality and the mortality from heat or drying. In some cases a relationship is evident which can not be regarded as merely accidental. The localities in which a comparatively small series of examinations was made should not be considered in this connection.

The highest proportion of rainy days occurred at Calvert during July and August, being twenty-five in sixty-one days. The influence of each factor of natural control seems to have been greatly reduced by the excessive amount of rain (10.22 inches) distributed over so many days. The total mortality was but 15.1 per cent, distributed among the factors as follows: Heat 3.9 per cent, ants 9.3 per cent, parasites 2. 1 per cent. The high maximum temperatures occurring were evidently prevented from exerting their usual influence by the almost continu- ously wet condition of the ground. This produced a high percen- tage of relative humidity which would naturally favor the development of the weevils.

Fortunately for this portion of our study an automatic self-regis- tering combined thermograph and hydrograph had been located at Calvert early in the season of 1906, and the records from this machine furnish valuable data regarding humidity conditions which could not otherwise be obtained. ‘These records may be used in connection with Weather Bureau reports for the locality of Calvert and some interesting facts will appear.

Around Calvert very light rains fell early in June, but from that time until June 25 there was no rainfall. The period from June 5 to June 25, 1906, shows an average relative humidity® amounting to

@ Relative humidity is the term used to denote the proportion of atmospheric mois- ture which actually exists as compared with the amount of moisture which it would be possible for the air to contain at any given temperature. If the air contains all the moisture possible, it is said to be “saturated” and this is the condition during fogs and sometimes, though not always, during rains. It is the condition of the air at a given point when dew is deposited. The relative humidity under this saturated condition is 100 per cent. The condition opposite to this extreme is a perfectly dry air in which the relative humidity is 0. The amount of moisture, or water vapor, which it is possible for a given amount of air to contain is much greater if the air be warm than if it be cold. Thus, taking a certain quantity of air containing a definite quantity of water vapor, the percentage olf relative humidity will increase as the tem- perature is lowered and decrease as the temperature is raised. A low percentage of relative humidity naturally promotes evaporation owing to absorption of the moisture by the drier air, while evaporation ceases, even from a water suriace, when the air becomes saturated. During the summer in central Texas the relative humidity increases at a few. icet above the ground during the nights until it reaches, as a rule, a maximum of between 90 and 95 per cent. During the day it decreases until in the warmest part of the afternoon it reaches a minimum of between 30 and 50 per cent.

NATURAL CONTROL IN VARIOUS LOCALITIES. 39

about 69 per cent. From June 25 till after September 10 showers _were of frequent occurrence and the records show during this period an average relative humidity of 75 per cent. Doubtless very signifi- cant facts might be learned if for other localities data similar to those obtained for Calvert were available for comparison.

INFLUENCE OF CLIMATIC CONDITIONS ESPECIALLY.

:

l

| In further determining whether climatic conditions were the most important factors affecting the total mortality percentages, con- - clusions may be more readily drawn by arranging the data in three _ groups, ranging from the highest total mortality to the lowest. 5 Group A may include the eleven localities having a total mortality above the average of 52 per cent, ranging from 84 to 52.5 per cent. Group B may include seven localities having a total mortality ranging from 51.4 to 39.4 per cent. The division between Group B and _ Group C is made because of the rather large difference in percentage of total mortality shown between 39.4 per cent, the lowest in Group B, and 28 per cent, the highest in Group C. Group C includes ten local- ities with the total mortality percentage ranging from 28 per cent to vero. Each group is summarized to facilitate a general comparison - of the average results of the observations made and of the average climatic conditions prevailing. The data are presented in Table VII.’

40

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42 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

From the eleven localities in Group A 52,334 forms were examined This number constitutes 60.2 per cent of the total of the three groups In these forms were found 23,947 weevil stages. This number consti tutes 61.4 per cent of the total number of weevil stages found in the three groups. The proportion of weevil stages to forms examined in each of the groups varies but slightly. When we come to the total number of weevil stages killed by the three factors, we find in Group A 15,145 dead, which number is 74.7 per cent of the total mortality occurring in the three groups. This shows that in Group A there was actually an increase of nearly 15 per cent in the total mortality above | the average proportion which might have been expected in this group. The average mortality occurring in Group A is 63.2 per cent. The — percentage of mortality in Group A from each of the three factors is somewhat greater than the average shown in Table VI. For heat and drying this increase amounts to 6.3 per cent, for ants to 4.5 per cent, for parasites to 0.5 per cent. The greatest increase is therefore attributable to heat or drying and it might naturally be expected that the climatic records would show a considerably higher maximum temperature to account for this increased mortality. A comparison of the mean maximum temperature records for Group A with those for Groups B and C shows, however, an average difference of less than 2 degrees. Between A and C there is an average difference of but 0.1 degree. In group A 27 per cent of the weevil stages found were destroyed by heat or drying, while in Group C, having almost identic- ally the same mean maximum temperature, the mortality from this cause is but 7.1 per cent—a decrease in Group C of 19.9 per cent.

The percentage of mortality from ants shows an even greater dif- ference between Groups A and C than has just been shown for heat, amounting in this case to a decrease of 22.8 per cent. Certainly this difference can not be attributed to the variations in temperature shown for these groups.

While unquestionably an unusual defdfonk® of rainfall is very important in checking the development of w eevils, the difference shown in this table for the average monthly rainfall in each of the three sections can not account for the difference found in the total mortality from-any of the three factors. Thus in Group A, having a monthly average of 3.39 inches, which is 0.89 of an inch above the average normal rainfall for the localities given, and an average of 6.2 rainy days per month, the mortality from heat or drying averages 27 per cent. In Group B, for seven localities the average total rainfall is 2.6 inches per month. For these localities this is a deficiency amount- ing to 0.72 inches per month. We have here five rainy days per month and the mortality from heat or drying is but 13 per cent, or less than one-half the mortality found in Group A. Similarly, in Group C, with a mean maximum temperature approximately the same as

INFLUENCE OF CLIMATIC CONDITIONS ESPECIALLY. 48

at in Group A and a total rainfall for each month averaging 3.75 1es, which is 1.92 above the normal, there is a total mortality from ll three causes averaging but 19.1 per cent, while that from heat alone verages but 7.1 per cent. A comparison of the mortality from ant rork between Groups A and C shows in C a decrease which is very arly proportional to that found for heat, while the reduction in arasite work is comparatively slight.

_ These facts seem to point to the conclusion that other factors than ¢limatic conditions must explain the variations in mortality which » shown in this table. Undoubtedly extreme variations in tempera- . e and rainfall are exceedingly important; but it is obvious that the “average variation in these factors does not produce a corresponding variation in the mortality figures, such as might be expected. Eyvi- dently there are other factors modifying or neutralizing the effect of ‘climatic variations, which if acting alone might produce more consist- ; ent results. — ; INFLUENCE OF CULTURAL CONDITIONS.

High temperature can affect the weevil stages only after the forms have fallen or been so cut off from vital connection with the plant _ that the sap flow is stopped and a drying of the form results. The effect upon the weevil stage will then depend upon the conditions of exposure to the heat. If the square or boll remains hanging or dries upon the plant, the temperature in it will not rise as high as if those forms were exposed directly to sunshine upon the surface of the ground. If the square or boll falls to the ground, its position in

regard to the shade of the plant will determine largely the degree of exposure to the heat of the sun and, consequently, the probability as to _ the survival or destruction of an inclosed weevil stage. The direction in which the rows run, and more especially the open distance between plants, will affect the exposure of the fallen forms to the direct action of the sun. The dryness of the surface soil is another factor which will largely affect the drying of the forms and the mortality resulting from heat. The work of the living larve naturally produces a larger degree of moisture in the infested forms than will be found in those _ which contain no weevil stage. If the conditions are such as to _ insure a very rapid and complete drying of the form within a few days after it falls to the ground, there is a strong probability that the weevil stages affected will be destroyed by heat or drying. If climatic or environmental conditions favor the weevil’s development until the pupal stage is reached, the condition of the form is then much more favorable for the entrance and attack of the ants. The ants seem to be able to recognize the presence of a living weevil stage within a form and rarely, if ever, enter forms in which the stages have pre- viously been destroyed by heat. If ants destroyed both parasite and weevil stages no evidence of the parasitism might remain. It is

~

44 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

possible that the indiscriminate work of ants may explain, in part / at least, the fact that fallen forms have invariably yielded a smallei

percentage of parasites than have hanging forms. Referring Table III, this difference in the percentage of parasite attack is shown as follows: In hanging bolls, 6 per cent; in hanging squares, 12.8 per cent; in fallen bolls, 1 per cent; in fallen squares, 3.2 per cent. As the ants are already distributed in the cotton fields throughout the weevil-infested area, it is evident that their relative abundance in different localities may explain to a considerable extent the variations which have been found in the percentage of mortality resulting from ant attack. | ; ¥

It has been found that all of the parasites which attack the weevil are native species having some other host which lives normally in some part of the vegetation surrounding the cotton fields. In no case can the weevil be considered as the primary or preferred host of any of | these species. It has been found that in many instances the occur- rence of other weevils, living under such diverse conditions as in the buds, flowers, fruit, seeds, stems, roots, or in galls formed by the attack 9 of some other insect, a large variety of weeds, or other common plants and of trees, directly influences the abundance of parasite species and explains variations which have been found in the extent of parasite | attack upon the boll weevil. It is plain, then, that the abundant occurrence of some plant supporting a large number of other weevils which do not at all affect cotton may produce indirectly an abundance of some parasite species whichis capable of attacking the weevil. It is to be hoped that some of these parasites may ultimately develop a preference for the boll weevil as their host. This would seem to be a possibility, because the boll weevil presents a continuous series of stages for parasite attack throughout the season, whereas in many cases it is known that parasites are forced by the short breeding sea- son of their original host to change from one host to another in order to continue their own reproduction throughout the season. The tendency of parasites to adapt themselves to this change in possible host conditions demands continued careful investigation.

The note records concerning cultural conditions in the various fields investigated are not as complete as is desirable for this study, but a general summary of conditions as noted will be given to determine the possibility that cultural conditions may explain some of the variations which have been found in mortality. In Table VIII, Group A, the cultural notes are given for most localities recorded in Table VII, Group A. The same arrangement in regard to total mortality is retained.

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a el _ INFLUENCE OF CULTURAL CONDITIONS. 47

‘

From ‘a careful study of Table VIII it is quite evident that no igle e cultural factor will be found to explain the varying mortality. he character of the soil in each group varies from sandy postoak to lack river bottom. * The direction of the rows fails to show any con- ent relationship to the proportion of weevil stages destroy ed. fhe condition of cultivation was recorded for but few fields, and may practically be disregarded because of the lack of data. In the column for spacing of plants among the remarks are some points which were undoubtedly influential in producing the mortality results shown. Table VIII should be studied in connection with Table VII. At Beeville it was noted that the stand was poor and that only one-half of the ground was shaded where the stand was good. A large propor- tion of the squares were infested as early as July 12, and fallen,

drying squares were abundant on the ground. Referring to Table VII in connection with Table VIII, it will be seen that under these conditions, with only fallen squares and bolls examined, the mor- tality from heat was quite large, but that caused by ants was relatively more than three times as great. Had the ants not been so active, it is very likely that the percentage of mortality from heat

would have been very much greater. As it was, so many weevil stages were destroyed by the ants soon after the forms had fallen that the mortality from heat was kept comparatively low.

At Beeville about the middle of July the cultural notes indicate that the stand was uneven and that at best only about one-half of the ground was shaded. During July and August the climatic records show that the temperature averaged 1.5 degrees below normal, while the rainfall amounted to 1.42 inches above normal. Doubtless the excess of rainfall and the deficiency of heat are correlated. Under these conditions, however, there occurs the highest total mortality found in any locality, i. e., 84 per cent. Of this total mortality heat and drying was responsible for 20 per cent, while ants destroyed 62.8 per cent. In this case, therefore, it is evident that the ants were far the most important factor in producing the highest recorded per- centage in mortality, and it would appear that their work was favored by the conditions of open spacing, medium heat, and much moisture. | At Overton the ants caused an even greater proportion of the total - mortality than is shown above for Beeville. At San Antonio the examinations were not extensive, but the ants were responsible for the entire mortality found. In these three cases of highest total mortality the climatic factors would seem to have been much less important than was the abundance of the ants, which might have been influenced by local conditions.

At Corpus Christi all of the examinations were made on July 10. The notes show that at that time the ground was about two-fifths

= \ * : i Ve ee ee 4 - we

48 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

shaded, while it was very dry and had cracked deeply. The tempers ture records at Corpus Christi (Table VII) show far less range temperature than is found at most of the other localities, which ¢ all situated farther from the coast. The mean maximum tempera. ture, therefore, appears to be relatively low, although the mear average temperature is 1.3 degrees above the normal for that locality The weather records for May show that the temperature averages 1.3 degrees above normal, while during that month the rainfall was 1.78 _ inches below normal. June records show that the temperature averaged 1.7 degrees above normal, while rainfall was 1.63 inches ~ below normal. July was also warm and dry, so that in this case the 40 per cent of mortality ascribed to heat or drying is very evidently the result of the extreme drought which had prevailed during the preceding eight or ten weeks. The high total mortality at Corpus — Christi appears, therefore, to be largely a direct result of the extreme drought in a very open field, together with the active assistance of the ants.

At Hallettsville during August occurred the highest mean maximum J temperatures found in any locality except Kerrville, although the — mean average temperature was only 1.1 degrees ebove normal. The rainfall recorded was 1.54 inches below normal for the month. The full effect of this drought was probably not realized because of the fact that during the month there were traces of rain upon eleven days, when the precipitation was not sufficient to be measured. The cotton was dying in places and green in patches, so that forms must have been largely exposed, and the high temperature and drought should have produced _an even higher mortality than the 31.7 per cent found for this factor. The effect is probably also modified by the fact that dur- ing July nearly the normal amount of rain had fallen, so that the ground during August was not nearly as dry as it was at Corpus Christi during July. At Hallettsville, also, ants were responsible for more than the average percentage of mortality. An explanation of the reasons for the great difference shown in the effect of heat, especially between Hallettsville and Kerrville, may be given at this point. A direct comparison of the Weather Bureau records will show at a glance how the influence of one important factor may be essentially affected by other related factors, and in this case it will afford an ample explana- tion of the mortality from heat, amounting to 31.7 per cent at Hallettsville, with a mean maximum temperature of 95 degrees, and ‘only 3 per cent at Kerrville, with a similar temperature of 95.3 degrees.

a

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INFLUENCE OF CULTURAL CONDITIONS. er \!) is /

LE 1X.—Explanation of variation in temperature effects at Hallettsville and mf : Kerrville, Tex.

Temperature conditions. Rainfall and cloud conditions. Absolute max-_ ; | & = : imum, Average. = 5 Rainfall. Cloudiness. aes — =. & rs Si | | Be | On | of Is le. em |e x > * A «cc } war ~ of bo Bh ppm c L faa | &'9 S s | 2@& eal | oll =| we a eee — © S = e Tid ie = wh | ~ ~ a la Bel a oo |. | 3 5 |%6]#e u 2g | 2c |PAp) os QS so Trt, = oo PAT T A ; ad. |, SLB A,zt-°e HO > bo = BE ie ss = ~Ha lg? ids lapel ae we | SE i S oy ae eo ee ee ee ey ee ® | SOR 3 A= D © © | OSE | Fa) S54 |505/ 33 ’ _— — — ~ e 7_ ’ > we > . = ig = a |a '2 e 1A A | Ae iz x, ee Sa Pao eal | | a We eae sas | Sih “By In. | Inches. Hallettsville..... 99 5] 95.0] 74.1 | 84.6 |+1.1] 0.85 | —1.54 3 6 i 14 meerrvilie........| 98 2 95.3 | 69.5 | 82.4 |4+1.2 | 3.47 | +1.90 9 14 13 4

Such differences as those shown in rainfall and cloud conditions are entirely sufficient to explain the difference in the effectiveness of similar maximum temperatures. At Cuero the month of June was extremely hot and dry, showing a temperature averaging 4.6 degrees above normal and rainfall 2.04 inches below normal. These conditions are probably responsible for the major portion of the crop that was set in that locality. During July there was an excess of rainfall amounting to 2.63 inches, while during August the excess amounted to 0.77 inch. While the mean average temperature for August was 1 degree below normal, the

mean maximum temperature ranged very high. In this case it

appears that the mortality from heat or drying, amounting to 29.5

per cent, was due not so much to drought as to the fact that the

maximum temperature experienced during the month reached 95

degrees or higher upon nineteen days. In this case, apparently, heat

may have been the important factor rather than drying.

‘At Waco, Junction, and Victoria, Tex., the mortality is very evenly divided between heat and ants, the excess at Waco being due to a much larger percentage of parasitism. At Brownsville a large proportion of the mortality appears to have been due to heat, and this would seem to be a natural condition for that locality.

The study of the data shown in Tables VII and VIII for the locali- ties in Group B indicates similar conclusions for those shown for Group A. At Mineola, in a total mortality of 51.4, 31.5 per cent was due to heat or drying, and the remarks state that it was ‘“‘very dry and hot” at the time the collection was made.

At Trinity, with 50.5 per cent mortality, but 10.4 per cent was due to heat, while the destruction of stages by ants amounted to 37.7 per cent. The remarks show that although a large portion of the leaves had fallen from the plants because of a fungous disease, the excessive amount of rainfall would naturally prevent a large mortality from heat or drying, while the presence of ‘‘many Solenopsis”’ directly explains the large proportion of the total mortality which was due to

11575— Bul. 74—07——4

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explaining the low mortality from heat or drying.

The remaining localities given in Group B and those which have been included in Group C show a continual decrease in total mortality. The decrease is more evident from the effects of heat or drying and from ant attack than it is from the attack of parasites. Thus in Group B the average weighted percentage of mortaiity from the para- site attack is 3.8, while in Group C it is 3.3 per cent. From ant work in Group B there is a weighted average mortality of 26 per cent, while in Group C it averages 8.7. Mortality from heat or drying in Group B is 13 per cent, while in Group C it is but 7.3 per cent. It is evident that the extent of ant and parasite attack will be directly influenced more by the abundance of the species concerned than by the climatic conditions under which they may work. It is impossible to determine whether ants or parasites are particularly abundant-in any locality except by determining the proportion of weevil stages which they have destroyed, but the primary actual cause of their abundance may depend upon very different conditions.

It is possible that the ants might be quite abundant and still attack the weevil stages but little if some other food supply were more easily available. It is manifestly more difficult to determine why mortality is low in a field than it is to determine what are the effective factors when it is high. From acomparison of Groups A and C in Table VIII it would appear that in Group A the predominant type of soil is sandy, while in Group C the soil is heavier and probably would tend to give a ranker growth of weed. This conclusion seems to be borne out by the remarks given for Group C, which indicate a heavy growth and a large degree of shade. This condition would decrease the efficiency of sunshine, and it is quite likely also that the soil conditions in these fields were not as favorable to the ants as in the more sandy locations.

It has been generally considered that the weevil has done greater. damage in river bottoms than in upland fields. This has been held to be due to the greater moisture of the bottom lands and the ranker growth of the plants grown thereon. From the considerations which have been mentioned it would appear that this idea is well founded, but that the difference is due in a possibly equal degree to the absence of ants in the river bottoms. If this be true, then the importance of strictly cultural methods in controlling the weevils in the bottom lands may be even greater than it is on uplands, since as a general rule the factors of natural control may be less effective in such locations. It is evident, however, that there is no definite line of division between the localities in which natural control will be most effective and those in which it will be least so. Only by continuing observations for several years will it be possible to determine at all definitely the class ,

or _

INFLUENCE OF PERIOD OF INFESTATION.

f locations which will benefit most largely by the average effectiveness

of these factors of natural control.

INFLUENCE OF PERIOD OF INFESTATION UPON NATURAL

CONTROL.

A rearrangement of the data given in Tables IIT and V may be used

to give a comparison of the results according to the classes of forms

~ examined for Louisiana and for Texas. The separation of the data

for the two States is made to enable a comparison as to mortality in a recently infested area, as in Louisiana, with an area which has been

infested for a considerable time, as is the case with nearly all the

- localities examined in Texas.

TasLe X.—Summary of results showing mortality in Louisiana and Texas resulting

from heat or drying, ants, and parasites.

} | | Tot: Tot: Tot: Tots ; Total Total Total Total Heat or dry- |

Weevil stages killed.

number number number, mor- Lae. Ants. Parasites. State and class of of of of tality B-

fruit. forms | weevil | weevil) by ; ry: 7. =

exam- | stages | stages. three |. Hex, : Perit Per

ined. | found.!| dead. |causes.| Num-} cent | Num-| cent | Num-}| cent | ber. joftotal| ber. joftotal| ber. of total stages. stages. stages.

Louisiana: | Per ct. Hanging bolls... .. 2eSb5r «1, 163 458 39. 4 137 11.8 252 ZN 69 6.0 Hanging squares. .| 1,268 | S47 519 61.3 175 20. 7 274 S240 | 70 8.3 Fallen bolls.......- 2,606 599 200 33. 4 54 9.0 14] 23.5 5 0.8 Fallen squares... .-. 4,170 | 2,508 | 1,031 41,1 160 6.4 859 35.7 12 OL7 Total, Louisiana.| 10,999 | 5,117 | 2,208 43.2 526 10.3 | 1,526 2ORSule 156 3.0 Texas: = — a — - —— — — — — = — ———} | —<— | — — Hanging bolls. .... 14, 404 4,270 1,192 27.0 289 6.8 650 15. 2 253 6.0 Hanging squares..) 5,736 | 3,383 | 1,708 50.5 629 18. 6 609 1872'4, 4705) 13.9 Fallen bolls........ 20,079 4,019 1,323 32.9 473 11.8 $10} 20.2 | 40) 1.0 Fallen squares. ...-.| 35,738 | 22,202 | 13,854 62.7 | 6,141 27.8 | 6,947 | 31.3] 770 3. 5 Total, Texas. ...| 75,957 | 33,874 | 18,077 53.5 | 7,532 22.31 9,016] 26.7 | 1,533 4.6 Total, Louisiana | |

and Texas..... 86,956 | 38, 991 | 20, 285 52.0 | 8,058 20.7 10, 542 Die | 1, 689 4.3

Naturally the examinations in Texas cover a much larger number of forms than do those in Louisiana, amounting to 87.4 per cent of the total for the two States. The Louisiana forms show a slightly greater proportion of weevil stages to forms examined than do those from Texas, in the former case the proportion being one weevil stage to each 2.15 forms, in the latter State one weevil stage per 2.25 forms. This difference is, of course, but slight.

In comparing the mortality results for the two States it appears that in Texas the total mortality averaged fully 10 per cent higher than it did in Louisiana. The smaller mortality found in Louisiana, being inevitably connected with a higher proportion of weevil develop- ment, doubtless explains sufficiently the slightly higher proportion of weevil stages to forms examined which was found in that State. A comparison cf the mortality from each of the three factors shows that in Texas the mortality from heat or drying and from parasites exceeds that from these causes in Louisiana, while in the latter State

_ the proportion of mortality due to the work of ants is slightly greater

~“

o2 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

than that found in Texas. Nearly all of the excess in total mortality found in Texas is shown to be due to heat or drying. A sufficient explanation for this difference in the effect of heat in the two States is not brought out by the notes. By reference to Table VII it may be — seen that only one locality in Louisiana (Mansfield) is to be foundin Group A, which contains those localities having a total mortality greater than 52 per cent. In that case it is quite evident that ants — were responsible for about three-fourths of the total mortality found. It is also evident that the mortality from heat in that locality was — greater than at any other locality examined in Louisiana. This was doubtless due to the early defoliation of the plants by rust, but even — in this case it was hardly equal to one-half of the average mortality — from heat found in Group A. In Table VIII it is shown that all of — the fields examined in Louisiana had a sandy soil. This soil condi- tion may have been related in some way to the larger mortality from ant work and to the smaller mortality from heat or drying, but further observations are needed to definitely determine the correctness of this supposition. It is noticeable that parasites are somewhat more active in Texas than in Louisiana, and the difference shown probably indi- cates fairly correctly the degree of adaptation to weevil conditions which the Texas parasites have undergone. This seems especially true in view of the fact that a general average of observations upon parasite attack made in Texas four years ago also showed 3 per cent, as do the Louisiana localities in 1906.

In comparing the figures given for each class of forms in the two States some peculiar conditions are noticeable. Among hanging forms in Louisiana the total mortality averaged 48.6 per cent, while for the same class of forms in Texas the total mortality averaged but 37.9 per cent. On the other hand, for fallen forms in Louisiana the average was 39.6 per cent, while in Texas it was 57.9 per cent. The reason why the percentage of mortality is higher in hanging forms than it is in fallen forms in Louisiana while it is higher in fallen than in hanging forms in Texas is not apparent. A tabular statement of these differences presents them most clearly:

Mortality caused by—

rater een); fbi State and class of forms. Pava= mortal- Heat. Ants. re! ity. (Hanging ca. 2252 ence eee ee eee eee eee ere | G39 26. 2 6.9 48. 6 PODISIATIAN tiaras 21, kk Coke ee | eee 6.9 32.2 0.5 39. 6 T Hanging is osae: ke eee te ce ee ee eee 12.0 | 16.5 9. 4 37.9 OX88--=-\ Wallen. cst oce. yas ES hae GRE LIE ES Ae 25.3 | 29.7 ah 57.9

The conclusion that is strikingly apparent is that, for some reason, the mortality among the forms on the ground is much greater in Texas than it is in Louisiana from the factor of heat or drying. As is shown in Table VII, the temperature differences are not sufficient

INFLUENCE OF PERIOD OF INFESTATION. 538

iccount for the disparity if the conditions of exposure to the sun- line were at all similar. The difference of 3.5 per cent among the anging forms is not great and it seems reasonable to assume that a yenerally more dense shade may have protected the fallen forms in ouisiana. This would possibly favor ant work but be unfavorable for destruction by heat and by parasites in fallen forms. ~ From Table X, as a basis of comparison of areas which have been infested for different periods of time, it appears that in the territory infested but about two years the parasite attack amounts to only about two-thirds as much as it does where the weevils have been present for an average of five years.” In neither case are they sufli- ciently abundant to be considered as a factor of great importance at present, but recent experiments indicate that it may be possible to greatly increase their utility in the future. The Solenopsis ants do not seem to require a long period of time to become accustomed to the weevil’s presence, but attack the stages readily and probably in proportion to the abundance of the ants. It would seem ‘that the effectiveness of heat may have been increased by the methods of cultivation of cotton which have been adopted by the planters in the older infested region in Texas.

EFFICIENCY OF NATURAL CONTROL IN VARIOUS SECTIONS.

In the sectional reports of the Weather Bureau for Texas the localities from which observations are reported are divided into seven sections, according to their geographic location and their simi- larity in regard to climatic conditions. In making a more detailed locality study of the natural control of the boll weevil, it seems advisable to group the localities which have been examined upon the same general basis as has been done in grouping them for weather observations. The first two groups, western Louisiana and eastern Texas, have very similar conditions of climate, soil, flora, and fauna. In the group designated as southern Texas are found those localities which are included in the Weather Bureau reports as in the ‘‘coast”’ district, together with Cuero and Hallettsville from the ‘south- western’”’ district. These localities would seem to be more closely identified with the conditions of the coast district than with those of southwestern Texas so far as weevil conditions are concerned. For our present purposes, therefore, we have formed five groups of localities in Texas and one in western Louisiana. It is somewhat unfortunate that the limitations of the printed page prevent the association of all the data which should be considered in a study of this kind, and it is also realized that it is a difficult matter to make comparisons and to draw conclusions from a table even as extensive asis Table XI. Webelieve, however, that it is better to present these data, so that anyone who may care to study the subject more fully than can be done in this bulletin may have the opportunity of referring to these figures.

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nj pe" a _ . Fan

60 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

A casual examination of the data given in Table XI will be suffi cient to show that considerable variation exists in the mortality pro- duced by each factor in the same class of forms in even the most closely associated localities. This seems to prove the influence of local conditions affecting the mortality produced by the different factors. From several considerations this would seem to be an encouraging fact, indicating that it may be possible to change unfa- vorable conditions or to take advantage of those which are most favorable in regard to environment, cultivation, soil, ete. It is noticeable that in all classes of forms, in practically all localities, a large proportion of the mortality from heat occurs during the larval stage. In southern Texas alone does the larval mortality in hanging dried squares fall below that in any other class of forms. In that case three-fourths of all larvae found in fallen squares were killed by heat, while in the hanging squares slightly more than one-half were thus killed. As a general average for the entire area about 53 per cent of the larve, 18 per cent of the pupe, and 6 per cent of the adults had been killed by heat. These percentages are very nearly in the ratio of nine, three, and one. -It appears that the nearer the weevil stage approaches maturity the less susceptible is it to the adverse influence of heat or drying. This shows how important it is that the spacing of the plants be such as will submit the largest pos- sible proportion of fallen forms to the direct influence of sunshine. Whatever spacing may have been found advisable where weevils were not present, there can now be no question about the general soundness of the recommendation for increasing the space allowed each plant wherever the weevil is present in abundance. It is true that the efficiency of this factor under similar cultural conditions may vary widely during different seasons, and during different portions of the same season, but in any case the data given would seem suffi- ciently reliable to prove that under nearly all conditions, with the weevil present, wide spacing is advantageous.

It was found impracticable to determine the effect of ant attack upon the various stages of the weevil. It may be stated that, m general, parasites were found to attack the weevil during the last few days of the larval stage. A considerable number of parasitized pup were found, and in a very few cases the weevil had become adult before death was caused by the parasite. As the parasite causes the death of its host very quickly after beginning its attack, the time required for the egg stage of the parasite should be taken into con- sideration in determining the time of attack, but it has been impos- sible, as yet, to determine the egg stage for any of the parasites of the weevil.

MORTALITY IN EACH CLASS OF FORMS FOR EACH SECTION.

Some additional points in the comparison of the general results shown in Table XI may be more conveniently shown by such arrange- ment of the totals and average percentages as is given in Table XII.

a

~: Ss a ~~ i, : “ ie f f , ’ 4 <

ss MORTALITY IN EACH CLASS OF FORMS. oF

"lee

Bie XIT.—Comparison of mortality results by class of forms and section of State.

Total Total number of | Mortality per- / ; num- Total stages destroyed. centage. Total | ered Dass of fruit and section! ber of | 1" | |mortal-| tion by f State forms | €T ° | ity— | o at. stages Para- P | tk , | total exam- fond | Heat. Ants. sites, | Heat.! Ants. | Frain [ tare | mor- ined. st ae et aan dehy ae iy m4 tality. c® cy: PTS a ‘Dried hanging bolls: LP. cel Bs.ch i Po cts |) Pet Western Louisiana...) 2,955 1,163 | 137 252 69 | 11.8] 21.7 6.0 39.4 | 2 Eastern Texas... .... ree 621 29 | + 74 6°40 ILO) Tal gan 5 Southern Texas...... | 2,361 928 49 109 27 5.3} 11.6 2.9 20.0 (ee Central Texas........ 4,906 | 1.358} 144 234 113 10.4; 17.2 8.4 28.8 3 Northern Texas...... 4,604 | 1,362 | 67.) 282 7 4.9| 17.0 4.9 26.9 4 Southwestern Texas. .) 310 1 0 i 0 0.0 100.0 0.0 100.0 1 17,359 | 5, 433 426 | 902] 322 7.81 16.6) Gol S0.4ie tee ° ’ ———— = ——_——-- — — | = ———— Dried hanging squares: ° | Western Louisiana...) 1,268 S47 175 274 70 | 20.7 52.3 | SB: 61.3 2 Eastern Texas....... 800 604 102 119 70 17.0 19.7 1053. |" “48:2 3 Southern Texas...... 3,028 | 1,848) 322) 301; 235] 17.3] 16.3] 12.7] 47.0 4 Central Texas........ lact-276 | 706 180 128 1544), 26.5-). 8;1-| BER 65.4 1 Northern Texas...... 225 110 Is 19 9 16.4 17.3 8.2 41.8 6 Southwestern Texas. .| 307 115 7 42 2 6.1 | 36.5 Lea 44.3 5 | 7,004 | 4,230 804 883 540 | 19.0] 20.9] 12.8 52.6 | ey ‘ S - Fallen bolls: oe Ka Re te ay ae Western Louisiana...) 2,606 599 54 141 5 9.0 23.5 Q.8 33.4 2 Eastern Texas... .... | 5,570] 1,204 165 452 5| 12.8! 36.2 4.0 50.0 1 : Southern Texas..._-.. | 8,280 1,315 | 190 211 17 14.4 16.0 1.3 31.8 3 Central Texas........ | 4, 466 796 Q2 106 9 11.6 13.3 1.1 26.0 4 Northern Texas ...._. 1,127 | 177 | 14 19 i 8.0 10.7 0.6 19.2 5 Southwestern Texas. - 636 | 437 | 12 22 8 7a | 5.0 1.8 9.6 6 ; | 22.685 | 4,618 27 | 951 45| 11.4] 21.0| 1.0 ay. 4 i ee Fallen squares: ide wae RAE he Lea Fa Western Louisiana...) 4,170 2,508 | 160 859 12 6.4] 34.2 0.4) 43.0 5 Eastern Texas....... 4,340 | 2,820} 296 820 34 10.5 |} 39.1 2 |) 2e 408 6 Southern Texas....../ 23,411 | 15,583 | 5,009 | 5,280 bee} wlez |) 386.0 3.6 70.7 1 Central Texas... ..... | 5,976] 2,939 | 640 669 16h wise PL ar | 5.7 50.0 2 Northern Texas. ...-- 1,216 573 |. 147 106 Oe eae Oo ulie ies 1.5 44.9 3 Southwestern Texas. .| 795 287 | 49 52 yf RH by da Hi set 825: 43.5 4 39,908 | 24 710.) 6/30) | 7;7964. 778 | 25.5 | 328) 3.3} 60.8|.cc.. ac

| |

In Table XII one of the most striking points is the rather uniformly high percentage of parasitism in each section found in dried hanging bolls and squares. By far the highest percentage of parasitism is the 21.8 per cent shown in dried squares in central Texas. Western Texas leads in the percentage of parasitism in fallen squares, but when the comparatively small number (287) of weevil stages found is con- sidered, it would appear that 8.5 per cent may be largely in excess of the percentage which would have been found in so extensive a series of observations as was made in central or southern Texas. A similar exception should be noted for the 100 per cent of mortality from ant work in dried hanging bolls in western Texas where only a single weevil stage was found. In dried hangmg squares the mortality | from heat, as a general rule, very nearly equals that from ant attack, | while in other classes of forms ants destroyed many more stages of the | weevil than did heat and parasites together.

In regard to ant work, it is evident that the high percentage shown among fallen squares in each of the six sections examined is very important. This is especially so because of the fact that these per- centages apply to the largest series of examinations made, the number

a ais ee ?

62 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

of weevil stages found in this class of forms being somewhat mor than 60 per cent of the total. Eastern Texas, southern Texas, and. western Louisiana seem to have profited most by the work of the ants in fallen squares, and these same sections show the highest percentages of ant work in fallen bolls, as might naturally be expected.

The wide diversity of conditions under which the ants successfully attack the weevil is another one of the encouraging features shown by — this work. It proves in a very reassuring way the general distribution of this species of Solenopsis and their activity in destroying weevil stages in every class of forms and in all parts of the infested area. The value of the work which they do in restraining the weevil multi- plication can not be estimated. Their work henceforth will be more fully appreciated and a careful study will be made of the life history of the species and of the possibility of producing an increase in its efficiency.

SECTIONS PROFITING MOST BY NATURAL CONTROL.

Still another arrangement of this same series of results will show most plainly a comparison of the total mortality in the four classes of forms for each of the six sections into which the localities have been grouped. In Table XIII are shown the general results of the examinations.

TaBLe XIII.—Comparison of total mortality results according to section.

A

Weevil stages alive. | 7 : : Total | Weevil stages dead Mortality from heat, cone | \ dult from heat or drying. etc., by stages. Section. - : raae\| xa), \Larva.| Pupa.| [ara a ty ined. |+:45Va. ae) 2 el ee patie Larva. Pupa. Adult. Larva. Pupa. Adult. at | | : ue ee ld” Perct.: P.ct.| Perck. Western Louisiana -..| 10,999 576 672 365 | 1,070 | 293 138 105 | .50.9 | 20.5 Tas Eastern Texas....... | 12,933 | 1,374 883 259 397 492 76 94] 35.8} &6 ahi Southern Texas....-.} 37,080 | 2,311 ; 1,665 ; 1,033 | 1,407 | 4,812 | 603 155 | 67.6 | 26.6 6.0 Central Texas....... 16,724 | 865 923 462 686 820 | 131 105 | 48.7 ; 12.4 8.4 Northeastern Texas*! 7,172 | 430 376 258 334 137 77 32 | 24.2 {17.0 aaa | Southwestern Texas. 2,048 | 396 126 30 48 62 3 3 1.6) 2.4 3.8 86,956 | 5,952 | 4,645 | 2,407 | 3,942 | 6,616 1,018 424) 52.6, 18.0 6.3 ? Killed by heat | x; ey. Killed by Rak or drying. Killed by ants. | Darasites. Total | of sec- " Total | percent Hons E Par Per number of mor- per- SE Num- | Fer oe Number | Cent of | Num- | cent of poh ee pally cent- ber of | . el _| total | ber of | total Fpetn ats % age of . | Stages | of stages. eo be teres |i rey b bes ls three stages. found | Stages | stages. | stages causes mor- ; found. found. we” ) ay: Western Louisiana .- . 526 10.3 1,526 | 29.9 156 3.0 D, 117 43.2 3 Eastern Texas....... 592 1H teak 1,465 | 27.4 155 2.9 5,339 41.4 4 Southern Texas...... 5,570 28.3 5, 921 30.0 811 4.1 19, 674 62.6 1 Central Texas...2 + 1,056 18.2 | 1,137 | 19.8 443 7.8 5, 799 45.5 2 Northeastern Texas . 246 heal 376 | 16.9 86 3.9 2, 222 31.9 5 Southwestern Texas. 68 8.1 117 13.9 34 4.0 840 26.0 6 8, 058 20. 7 10, 542 27.0 1, 685 4.3 38, 991 52.0 1.22258

Dy / SECTIONS PROFITING MOST BY NATURAL CONTROL. 63

Many of the conclusions which might be drawn from Table XTIT ave already been stated in connection with preceding tables. The ast column shows that southern Texas enjoys the benefits of natural control to a larger degree than does any other section. In that section 62.6 per cent (nearly two-thirds) of all stages found had been de- stroyed. One half of this mortality was accomplished by ants, the other half by heat and parasites combined. Central Texas stands next, with a total mortality of 45.5 per cent. In this section, while the effectiveness of heat and of ants had decreased, that of parasites had considerably increased. The increase in parasite attack, however, was by no means sufficient to counterbalance the decrease from the other two factors. Western Louisiana and eastern Texas, with 43.2 and 41.4 per cent of total mortality, respectively, show very close agreement in the proportions of mortality from each factor. This close agreement might be anticipated because of the similarity in soil, climatic, and cultural conditions prevailing in those adjacent sections. The principal reason for separating the localities into these two sections was to facilitate a comparison of the recently infested territory of Louisiana with the older-infested sections of Texas. In this respect, also, but little difference exists between east- ern Texas and western Louisiana. In analyzing the factors producing the closely similar total percentages of mortality in western Louisi- ana and in central Texas it will be seen that there were very essential differences. In western Louisiana nearly 70 per cent of the total mortality found was due to ant attack, while in central Texas only 43.5 per cent was due to ants. It is evident that in central Texas may be found the conditions which are most favorable to parasite attack. An extended study is being made of the entire field of para- -sitic attack upon the boll weevil, and part of the results previously obtained may be found in Bulletin 73 of this Bureau. By far the lowest proportion of total mortality is that found for southwestern Texas. Most of the localities included in this section have but recently become infested. It would appear, however, that in the higher altitude of those localities heat may not be quite as effective and that ants may not be as abundantly distributed as they are in other sections of the State. The observations in this locality have not extended over a sufficient period to justify any general conclu- sions regarding the result of the smaller degree of natural control which would appear from the observations made. It is quite possible that other factors than these which are here considered may serve to check the weevil in this section. Such a condition as a much larger mortality during the hibernation period might hold the weevils largely in check in spite of the smaller mortality during the summer.

x > cL a ~ ae

64 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

DESTRUCTION OF COTTON FORMS BY WEEVIL ATTACK OR B’ NATURAL CAUSES.

It seems advisable in connection with this study of factors con cerned in the natural control of the boll weevil to place on record som of the data which have been obtained, showing the proportion: o squares and bolls which have been found to be destroyed by weevil attack or which were shed by the plant from natural causes without insect injury.

COLLECTIONS OF FALLEN FORMS IN 1905.

During the season of 1905 quite extensive experiments were made to determine the value of a thorough collection of fallen forms in checking the injury done by the weevil. These experiments showed a net loss. The cost of collecting fallen forms exceeded by several dollars per acre the slight increase in yield shown by the plots from which collections were made as compared with plots under similar conditions, but in which no forms were collected. No examinations were made of these forms to determine the proportion which had been attacked by the weevil, but from sample lots as shown in Table XIV the proportion of squares and bolls was determined.

a

TaBLE XIV.—Proportion of squares and bolls among fallen fruit, Texas, 1905.

Squares. Bolls. Total q z Mi Locality. Date. forms ex- : J ieee = Per cent 4, Per cent amined. | Number. of total: Number. | of total. nrley, Tex. 22.0. eat ot Aug. 10-12... 498 | 147 29.5 351 70.5 OI Se ee ne aE AOE he Mek Aug. ieee 2,442 411 16.8 2,031 83.2 HB) eet St ee BE RS has See BE Alp. 19! 2222s 775 239 30.8 536 69.2 1DY0) Sees Seer eR ee ae eae AUS lees 650 240 36.9 410 63.1 QOunlom exces.) sess hose hones AUS 24 eee 2, 542 472 18.6 2,070 81.4 MERC OMLC Rn Mi eee oe AUIS lee 4, 036 1, 269 31.4 2, 767 68.6 Total or average........... eat pa Poets 10, 943 2,778 25.4] 8,165 74.6

It should be stated that the lots for which figures are given in Table XIV were from the last collections made in those experiments. The picking began early in July,-and doubtless a test at that time would have shown a considerably larger proportion of squares. As it was, the average proportion among the nearly 11,000 forms exam- ined was approximately one square to every three small bolls. In the field at Gurley five collections were made in about six weeks. This work extended over one-half of the 16-acre field. Upon this 8 acres about 730,000 fallen forms were collected. According to the proportions shown in Table XV, it would seem conservative to esti- mate that in this field at Gurley there were collected fallen squares containing from 100,000 to 125,000 weevil stages, and in the fallen bolls from 100,000 to 115,000 stages. From this 8 acres, therefore, there were collected, during July and August, 1905, in all probability from 200,000 to 250,000 weevil stages. If we apply to this number

DESTRUCTION OF COTTON FORMS,

65

ages the proportion shown by Table VI to have reached the h It Bes 3 in Louisiana and Texas in 1906 (i. e., about 17 per cent), it would appear that this work of collection prevented the emergence of from 34,000 to 42,500 adult weevils upon an area of 8 acres. When it is considered hat i in spite of this large destruction of weevils the resulting increase in yield averaged hardly 50 pounds of cotton “per acre, the reader will be able to realize more clearly than he could without such a comparison the tremendous importance of the factors _of natural control which do, under exceptionally favorable conditions, make it possible to produce a very profitable crop, because of their direct effect in reducing the number of weevils which reach maturity. It will be understood, also, that the total mortality resulting from all factors must become very large indeed in order to reduce the damage done by the small percentage which do survive, so that the develop- ment of the crop may far outstrip the insect attack.

COLLECTIONS OF FALLEN AND OF DRIED HANGING FORMS IN 1906.

In Tables XV and XVI are presented some of the results from the work of 1906. In these tables, however, it is possible to include a statement of the number of weevil stages found in each examina- tion. In the collection of this material there was no particular selec- tion of squares or bolls, but all forms were taken as they occurred.¢ Special collections were made, however, for hanging and for fallen forms, so that the proportion of hanging and of fallen forms could

_ not be considered as an indication of the proportion which actually existed upon the area from which collections were made. This explanation applies both to Table XV and to Table XVI.

TaBLE XV.—Proportion of fruit destroyed by insect injury or by natural causes,

Louisiana, 1906. pee ee ed | en aah 2) |W oy il stages aad Infested by weevil.

Class of fruit examined, and | - .,. |Lotal ex- 5 Saal aah | SaETLS.

locality. Date: | amined. : Per cent | Potal

| Number | of total |S impber. J Percent | weevil

of forms.| exam- | of total.| stages

ined. | found.

Fallen bolls: | WOW) Aug. 24 450 392 87.1 58 12.9 58 ST GLE (OS | Aug. 24 100 300 75.0 100 25. 0 106 Wa CCG Es i er Sept. 29 372 332 89. 2 40 10.8 47 DOG ee Aug. 23 555 402 72. 4 153 27. 6 153 Lo LU pate A ng Aug. 534 396 74. 2 i38 25.8 168 Wraupevilless......-..---.,. Aug. 145 109 75. 2 36 24.8 36 OS UC Sept. 30 150 | 119 79.3 31 20.7 31 MOmuls, sete DOS. .o-22.)2.2.5..... 2, 606 | 2, 050 78. 7 956 21.3 599 Fallen squares: Johnsous Bayou........... Aug.22-27 300 | 78 26.0 122 74.0 225 Lo) a Aug. 24 100) | 193 48. 25 07 51.75 207 EN ete ok Aug. 24 525 268 51.0 257 49. 0 257 Mansfield....... , Sept. 29 37 20 54.1 17 45.9 17 PEE Me sik s - = = Aug. 23 | 875 336 38. 4 539 | 61.6 539 re Aug. 23 | 1, 133 407 39.9 726 | 64. 1 728 Orangeville Aug. 23 400 142 35.5. | 258| 64.5 259 4 Smenmovile..*........-.... Aug: 23 500 332 66.4 | 168 | 33.6 176 Totals, fallen squares....|.......... 4,170 1,776 42.6 | 2,304 57.4 2, 408 = =|

11575—Bul. 7

* ’ 66 WATURAN CONTROL OF THE COTTON BOLL WEEVIL.

TABLE XV. —Proportion of fruit destroyed by insect injury or by natural causes, Louisiana, 1906—Continued.

Weevil stages not Infested by weevil

fous.

Class of fruit examined, and ie a. arent Bareant | Total

y Number | of total | Numpber.| Percent weevil

‘of forms. exam- of total. stages

£' ined. | found. Hanging bolls: | | MGrishialA A): SS RES | Aug. 24 1, 412 965 68.3 447| 31.7 479 MATIBACIO oe oe eee ae | Sept. 29 293 190| 648 103 | 35.2 145 Mange 2 us. Sees ee | Aug. 23 125 74 | 59. 2 51 40.8 54 Marys 2 oso. eo eae te |} Aug. 23 800 450 | 56. 3 350 42.7 380 Mang Pte ene ee | Aug. 23 325 228 | 70. 2 7 29.8 105 | —<$<——— Totals, hanging bolls. - - a pee: 2,955 1, 907 | 64.2 1,048 35.8 1,168 Hanging squares: ny

Mansheld #2" hea eae | Aug. 24 | 430 186 | 43.3 244 56. 7 244 Mansfield! ? 52:32 os | Sept. 29 | 5 3 | 60. 0 2 40.0 2 MANY ise bene eee ee | Aug. 23 | 115 27 23.5 88 76. 5 88 ETI ee ee eel Seer |} Aug. 23 | 466 136 29.2 330 70.8 330 Man yn Seicmes shoe see cee | Aug. 23 252 69 | 27.4 183 | 72.6 183 Totals, hanging squares .|-........- 1, 268 AM-| 33.2 847 66.8 847 Totals, all forms=2. >. | Ap eee et 10, 999 6, 154 56.0 4, 845 44.0 | 5, 017

As is shown in the last line of totals, giving the average percentages for the four classes of forms oe 56 per cent of the 11,000 forms contained no stage of the weevil. Among 5,561 bolls, including both

thanging and fallen bolls, 71 per cent contained no weevil stage, while in the remaining 29 per cent, 1,604 bolls, there were 1,762 weevil stages. This means that in the bolls found to contain weevil stages there were an average of 1.098 stages per boll. Among the 5,438 squares, 40 per cent contained no weevil stage. In the 3,241 squares containing stages there were 3,255 found. In squares, therefore, there were about 1.004 stages for each square. This shows how strictly the multiplication of the weevil is limited by the available supply of squares. An average of squares and bolls shows but 1.035 weevil stages for each form which was found to contain them. Among all bolls but 30 per cent contained a weevil stage, while among all squares 60 per cent were infested. While it is probable that few of the 30 per cent of squares which failed to show some stage of the weevil had really escaped all form of weevil injury, it is equally prob- able that a very small portion of the 70 per cent of bolls which were found to contain no stage of the weevil had ever been attacked in any way. Thus, while few squares perished regardless of weevil attack, probably more than one-half of all the small bolls which perished had not been attacked in any way by the weevil, though it is possible that in many cases there had been some form of injury to the square or bloom connected with that boll.

In the examination of material from Texas there are so many local- ities represented for each class of forms that it seems advisable to divide the table into a section for each class.

Te, ss Vf I ’ . ss DESTRUCTION OF COTTON FORMS. 67 s XVI.—Proportion of fruit destroyed by insect injury or by natural causes, Texas, 1906.

A. HANGING, DRIED BOLLS.

vit | eacilateres | Bolls with weevil stages.

Total ~ —-— ~ bolls ry . Number amined. |. | Percent | ,; ‘er cent of weevil

Number, | of total, | Number.) o¢ total. stages

*| found. “Gl es eee 208 192 92, 1 16 7.9 16 a ae 311 246 | 49.1 | 65 20.9 | 70 ee e's haem 157 137 87.3 20 12.7 20 Vp Set ISRO Ae = ne 225 170 75.8 55 24. 2 | 75 PER sa = wc OAS tnt ewan 450 391 $2. 4 59 17.6) 59 2 ee Se eer S800 675 84.4 125 15.6 117 Soe A eee 26 20 | 76.9 6 23. 1 6 6S 250 138 | 55. 2 112 44.8 | 183 =~ TE al eee 232 206 | 88.8 26 | Wee 26 op ie ee 511 408 80. 0 103 20. 0 103 Sg. 5 ea ner ee 571 475 83. 2 96 16.8 107 gt ee eee 450 358 | 80.0 92 20. 0 95 J Ae Se eae 323 220 | 68. 3 103 31.7 157 - MR Ee ae ae 498 | 344 | 69. 1 154 30.9 190 - Se 505 389 | EUS 116 33.0 125 sol [je ee 510 425 83.3 | 85 16.7 96 ce che SS es ee 494 354 | yflyahy 140 38.9 216 oie 9f a EE eee 510 430 | $4.3 | 80 15: 7 247 ts i ESE eee 165 132 80.0) 33 20.0 33 1 le! ee ee ae 125 68 54. 4 | 57 | 45. 6 103 Sunt Ah es, Se Se ee ae 240 ibe Filey 46.2 | 129 53.8 | 129 RASMOCULAVING.-......-.-4...-.-- 370 274 | 74.1 96 25.9 | 96 PIAveVUS VIG! 220202 S252. -. +: 870 700 | 80.0 | 170 | 20. 0 | 177 5 Se eee 173 133 76.9 40 23.1 52 Mtn: Sak sas 210 121 57.6 89 42.4 89 234K 282 ae eee 510 299 58. 6 211 41.4 211 Bee SSS once ok om oko 9 6 66.7 3 33.3 9 1) ee eee 75 74 98. 7 1 | 1.3 i 5 aiy SO eee, eo eae 125 85 | 68. 0 40 | 32.0 40 42. 2 ee ee Eee 605 463 76.5 142 23.5 142 i Bie ee ee 725 603 83. 2 122 16.8 | 127 22 ee eee 315 157 50. 0 158 50. 0 201 J ach See eee 434 412 95.0 22 5.0 | 22 ooh See ae Se SO 160 144 90. 0 16 10. 0 16 2 ee eee 795 | 613 ibaa 182 22.9 | 252 12. 2 Se ee 370 243 65. 7 127 34.3 153 2p ee SO eee 29 17 58. 6 12 41.4 12 SO ne ps cle ee 200 | 144 72.0 56 38. 0 | 66 oe. a Se 34 18 53.0 | 16 47.0 | 16 1 eae 169 | 109 4. 5 60 35. 5 | 79 See Meee Sr, SS, Sac 100 | 17 17.0 83 83.0 | 112 Sat ae ees 339 170 50. 0 169 50. 0 233 ee oc ee ee 14,178 10, 691 75. 4 | 3, 487 24. 6 | 4,279

68 NATURAL CONTROL OF THE COTTON BOLL WEEVIL. |

Taste XVI.—Proportion of fruit destroyed by insect injury or by natural caus _ Texas, 1906—Continued. ,

'B. HANGING, DRIED SQUARES.

Paneres ideo Squares with weevil stages. Total Date. Locality. pe Soe tac ss : P : Nomiey er cen er cent | of weevil - ined: | Nuntber. of total. | Number. of total. | stages © present. Bug. 22) Calvert. -- 26-22-25 -p eee eare 103 97 94.2 6 5.8 6 PATTIE oe. |) CANT RED (2 cies eae, Eee ee } 62 14 22. 6 48 77.4 48 AES Ol Calvert a tao ne he cece ae ee ae 18 4 22. 2 14 77.8 14 papt..13:|‘Calvert.- 29.522 te ee ass 24 13 54. 2 il 45.8 13 Aug: 23.) Corsicanaa 03 825-2 a ee. RE 72 18 25. 0 54 | 75.0 55 | Avie? 23 | Gorsicang,-(3*- =i) oa a a. 2 ae 53 23 | 43. 4 30 56. 6 30 | Arie: 29 Cuero ns eri oo ee oe = eee eo 106 15 14.2 91 85.8 91 AVNeL SI CUClO Soe Seek 5. . Soca eee $25 481 58. 3 344 41. 7- 347 Ano: 29) al lais 8 aes cee ee ee 61 47 ioe 14 2259 12 Sepia lc allags - Foca es ee ee oe 31 17 54.8 14 45. 2 14 Gepinis))| Batias ies as ote eae oy | 100 36 36.0 64 64.0 64 Oct? 2 Dallas: ose 2 2. ees Bee 11 3 27.3 | 8 | ear 8 Oct: 260), Dallasss ee ees Eee oe 8 5 62.5 3 | 37.5 3 Oct GilaDallas=. ees Sree 1 See 5 1 20.0 4 80. 0 4 Oct= 16) "Dallags 5-5.) fe tee eee 9 4 44.4 5 | Bo6 5 ATI ie OMAG: = 2 en no nee Ree ee 35 12 34.3 | 23 65. 7 23 Sept, ol eGollad <2 eels aa ee 152 68 44.7 | 84 55. 3 84 SODts von ACOA ss. ai are ae | 150 48 32.0 | 102 68. 0 102- Are. 19 \ealiettsvilles.—. 22. ees ee ee 122 37 | 30.0) 85 70.0 85 Agvip~-30))|) Fallettsvilles: ---: eee 2 ae 480 167 34.8 | 313 65. 2 314 ANI OS OIC ES NL cy oye Se et = Ba 12 | 8 66.7 4 33.3 5 ATIP 2 2h| OVENtONe ocke acon aah eee 56 11 19. 6 | 45 80. 4 45 Avo 10/4 sPalestinesone: 325} este 468 78 16. 7 | 390 83.3 390 Sept-25 |ROOseyel tia - ot ee ee 216 136 | 63.0 — 80 37.0 81 AIS Sanya TONOs > a oe oe ee 6 | 5 81.7 1 18.3 ul mp 165) UaVlON ces sree cos sas e ec See 116 37 32.0 79 | 68.0 | 81 oy Fgh * (LS Ra 6 ry eC RE 216 78 36.1 138 | 63.9 | 138 JNCFERS a} 0001 | Sl Ur oh my fe ee ee el eee Sere ee 60 29 48. 3 31 51.7 | 31 epee ls iehorige 2200. 2. Pees a eae 938 293 31.2 645 | 68.8 | 654 Suily. Sen AVILCLOLI Gass Ao ee anes 220 82 31.3° 138 62.7 | 148 DiLilyarcOs| ACO Slee 2. ee ae ne 254 155 | 61.0 99 39.0 | 99 SUING NV COME eS et ee ee ue 54 32 59.3 22 |- 40.7 | 22 IPS Dea WiCOM osc sc) ots eee 213 75 35. 2 | 138 | 64.8 | 138 PRUE 20 AIO WWELCO> ase See ne mee nee eh eee 200 | 108 54. 0 92 46.0 | 92 DOD ORV RCOs Saree mes ot oe Sees ee 20 35. 0 13 | 65. 0 13 Sepuseloai WRCOle sae wade ee. wo ene 43 | 27 62.8 16) 37.2 | 16 BODE OUMWiaCOre ee. 528 oe eae eae 11 9 81.7 | 2 | 18.3 | 4 Sepb+20 hk WACOs ss oe ee ee as 90 | 35 38.9 55 | 61.1 55 EDU ZON|MNVACO Rome San aoe eee ae 43 19 44.2 24 | 55.8 | 24 TCU ES ee le RN ae OA tare SMO. 5, 663 2, 334 41.2 3,329 58.8 3, 359

TABLE XVI.

Locality.

July | MURR ee) eee a ~ os os ass oS ==> Aug. 8 | Beeville..........------------- ‘Aug. 13 | Raeville. ....2...-.-.---------- Beant. 3 | Beeville..........------------- Diy 28 | Beeville...-..---.------------- Sept. 5 | Beeville...--.-...------------- me. 25)| Calvert....------------------- Sept. 13 | Calvert....------------------- July 10 | Corpus PINE cases scek~- 5 ~'<-= Sept. 18 | Corsicana...------------------ Aug. 31 | Cuero.....-.----------------7+ Aug. 29 | Dallas. .--.------------------- eee ay | mullexs -. -:-------------+---"- Sept. 3 | Goliad....-------------------- Sept. 3 Pela on. 2 sts ----------+5--- Aug. 30 Hallettsville. ....--.---------- Aug. 30 Hallettsville.......----------- Sept. 24 | Junction....-.--------------- Aug. 26 Korrville......---------------- Sept. 3 Korrville. ....----------------- Sept. 26 | Lula....-.-.--------------0-"" Aug. 22 | Marshall..-.-----------------° Oct. 2 |-Mimeola...-.------------------ eas | Overton. -- == ---- 66 -----o eee eas sOWErtON .. 22 ---------=---- >" Aue. 10 | Palestine------------------*-- Sept. 4 Palestine.--------------------| Sept.” 24 Roosevelt ...-.---------------- Aug. 15 | San Amtoniowes.)-=-*=------=- Bee i bayiOl.. 20 ~~ 6 s> $< 2-6-=-~ =" --- Sept. 19 | Morrell. :.-.-----------------"° muiaiee @ WA tinity.~~----- o02---->----->- Aug. 9 DOTA ee oo en opeee ee Meee a0 |) Prinity---2------->----*->-°* "| Maer ead |) Urinity -.----=-----2----7----" | Tune 23 Victoria. --------------------- | June 28 | Victoria..-.----------------*- Soly. 5 \ Victoria..-.-.----------------

Fuly18-20 | Victoria...-----------+-----"- Matbeee MICLOTIA {25-5 =~ sear eon

Sept. 1 RPUOLIneee = - = = -=-- nteaert) WECO------=2-------2 6 ooo Aug. 17 | Waco-...----- 50 Ae ee ere Moseas |, Waco. -----------------7"

Aug. 29 | Waco...--.-- ----- Sle ee eS

Total bolls ex-

amined.

—Proportion of fruit destroyed by Texas, 1906—Cont inued.

Cc. FALLEN BOLLS.

Bolls without weevil stages.

Per cent

DESTRUCTION OF COTTON FORMS.

69

insect injury or by natural causes,

Bolls with weevil stages.

Number. of total. Number.

140 | 13 93.6 sf] 78 5Y 75.6 19 310 278 90.0 32

1, 588 | 1, 328 83.6 200 35 | 30 85, 7 5 1,785 1, 428 80.0 357 573 469 85.3 104 340 173 50.9 167 32] 301 93.8 20 310 277 89. 4 33 282 219 Or a 63 367 327 89. 1 40 382 | 378 99. 0 4 133 104 78. 2 29 355 280 80.0 75 540 469 86.9 71 362 | 349 96. 4 13 44 28 63.6 16 232 | 132 56.9 100 268 | 136 50. 1 132 46 19 41.3 27 227 210 94.1 17 158 109 69.0 49 145 108 77.9 37 230 | 181 78.7 | 49 460 | 266 Hy Cite) 194 118 | 104 | 88.1 | 14 46 12 Doe 34 235 PATS 100 0 | QO 211 180 85.3 | 31 220 176 80.0 44 908 $21 90. 4 87 580 517 | 89.1 63 1, 452 803 | 55 3 | 649 1, 450 1, 293 89.2 157 10 10 100.0 | 0 135 135 100 0 | 0 R85 843 95. 3 42 420 341 S1ez.\| 79 533 442 83.0 91 472 404 85. 6 | 68 691 639 92.5 52 315 291 92 4 24 932 829 89. 0 | 103 490 4\1 83.9 79 260 233 89 6 27 241 175 (ON 66 20,315 16,683 | 82:1 3,632

Per cent of total.

Number of weevil stages found.

70 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

Taste XVI.—Proportion of fruit destroyed by insect injury or by natural causes, Texas, 1906—Continued.

D. FALLEN SQUARES.

Squares without

ee weevil stages. Squares with weevil stages. Date. | Locality. ee s - Number = . er cent Percent of weevil

| found. Sule 10: | Beeyille-casen sete aes 900 O34. 260ual? BABA) opel 656 Ap? 1S. | Beeville 2s o oe e 512 76 | 14.8 | 436 | $5.2 436 Ano: 134] Beeville os ois ear. 2s ee Re 1,000 126 12.6 | 874 87.4 874 Bent. (33) Peavilles sone oes eee 90 222 24.7 678 75.3 | 678 Jive 28 | Srownsvilles<= -.. <eeres ae 2,524 957 37.9 1, 567 62.1 1,568 Aue: 3. | BTOMNSVINet soc. cheer eae 130 17 | 13.8 | 113 86.2 115 Sept.) 5) DrOnmsvilles: oe see eo es 4,032 2, 889 70.3 1,143 | 29.7 1,147 sept. 29'| Brownsvillés.:.: 2.scteee e+ oy 456 199 43.6 | 257 56.4 265 AM. 28> | Caliverl:: 3.228. 2o ee 353 40 11.3 313 88.7 315 Septee133 i Calivent. e260 5--2..2 a see eel 1,033 341 33.0 692 67.0 722 ony, 10) (*Conmpus) Christine. ---ecee see 718 | 283 39.4 | 435 | 60.6 438 SeptalS)|(Consicanaec 2:5. 4-s ee 26 | 10 | 38.5 | 16 61.5 | 16 AIP eS | ACUCTON! = oS. cece ec nske eee oe oe 1,550 495 | 32.0 | 1,055 68.0 1,059 Ais 2On Malas: so etn cin Oe ee ee es 111 BT 51.4 54 48.6 | 54 ARIS elif c | Woes! 542.02" ee oo poe eee 100 79 | 79.0 21 21.0 | 21 Sept: «3° Goliad -22 26. ose eee 430 154 35.8 276 64.2. 281 Sepie cos Golale cease see stk Rees es 875 347 39.7 | 528 60.3 | 540 AE 30) eballettsvilles: 5.226 ens esne 1,150 250 21.8 900 78.2 | 903 Aue. 30)| Hallettsville: =... 22222... 230. | 93 40.4 137 59.6 | 137 Septeec4s | unehion fs a. See eS 383 254 66.3 | 129 33.7 | 129 Er 26! IMOTNVIN Gime tno os «ate eine 29 6 20.7 | 23 69.3 23 Sapte -ar| Kenrvillesst.2. 0. js Sab es 17 | 5 29.4 | 12 70.6 | 12 NODE 2GON | Watlare res: meee cero e cues 278 228 82.0 | 50 18.0. 54 AUIS 235 | AMES HA leo em 2 ioe aaa ee 52 | 29 55.8 33 | 44.2 23 ANI O10) Mime alaman oe as eee 100 88 88.0 | 12 | 12.0 12 Ane O:| Mineola 254.0% o-eceeeeele. s 120 38 | 317 82 68.3 87 Oetry 2:| Mineolak: 802 5 2"! top ase als ee 697 353 SOr zal 344 | 49.3 347 PAIS 525) Overtons- m2 2: =. 2. seo ose 148 | 35 23.7 113 | 76.3 113 AIS 29237) (OVertONine. tot ocean eee eee 164 80 47.6 | 84 | 52.4 84 AVIS a LOs isles tine set a. 5-42 ae eee sBPy, 285 21.5 | 1,042. 78.5 1,042 sept. 4° (SPalestine - ise... :s235 ee cee 8 2 25.0 | 6 75.0 6 Bepuse4 | Roeseveltece. o9- orn ee ee 88 25 28.4 63 71.6 69 AIC Lon Moa DeAMEONIO ns eet eae oe 83 53 63.9 | 30 36.1 33 Ae GO Mavyloracce osc acse sess 79 35 45.6 | 44 54.4 | 44 Sep lor | Merreliiesse eo k oes er Seon 88 35 40.0 | 53 60.0 | 53 PT amen | Pen Gye eee fee ae eee nee 900 | 347 38.6 553 61.7 | 553 JM Fags XQ VN ML Sto UN Aa en ere eee ine a? 887 | 393 44.3 494 | 55.7 | 494 PSUS DO) anys ween oe eee 614 225 36.6 389 63.4 | 390 TI sO) | AGING Ys oe Le ee ce eee ss, 240 124 50.2 116 | 49.8 | 116 Dalricwel Olle VICTONIaa 2 asec ee = eee ae 980 | 116) BEY 864 86.3 4 864 ORE 5 | ) Q7 5 : 7 stad {Victoria bs De hy Cs: 3. 496 518 | 14.8 | 2,978 85.2 2,978 F aR | 95 | 5 7 5 July 5-9 {Victoria ne ne te eee ae 1, 405 355 25.3 | 1,050 74.6 1,050

7 ES = | 9 | ) -

ae 18 {Victoria ho) a vate fa 679 | 197 | 29.0 | 482 71.0 494 Seyee a 24 MVICGOTIN tanec ee ee ee 302 215 7122 87 28.8 87 SED ieee MV CCOLIA@ ae: nel se ee ea 1,142 129 11.3 1,013 88.7 1,026 itil yemeoo |AVWELCOR oC aea tne o1 eee on eae 737 480 65.1 257 34.9 | 259 BOLT eas | ORVVIRCO serene oe eens Cee nea 170 131 AW) 39 23.0 | 39 AIS SAV ACO! cs yee ee see et ee 742 431 58.1 311 41.9 | 311 ASU Oh LVS. CO Sata heen eo eC meee 1,300 711 54.7 589 45.3 | 591 wb At) EY Co eRe Ree aa pean, «Oe SN 785 477 60.8 308 39.2 308 OCG SA Ze EWiACO sso acces tee eee eee Gee 1, 284 1,032 80.4 252 19.6 253 Ota |i ace ee aoe ee eee 36, 354 14, 301 39.3 22,053 | 60.7 | 22, 169

From Table XVI A, hanging, dried bolls, it appears that three- fourths of the number examined contained no weevil stage. In this case there were found 1.227 weevil stages for each boll which was found to contain any. The percentage containing some stage shows an exceedingly wide variation between the 1.3 per cent for San Antonio, where the infestation was slight, and the 83 per cent at Waco on September 20, where the infestation was very heavy. It

SP ee!)

DESTRUCTION OF COTTON FORMS. 71

seems that the presence or absence of a weevil stage has little, if any- thing, to do with the retention by the plant of a portion of its surplus fruit, but that the abundance of weevils in proportion to their food supply may be largely responsible for the variations which appear in the percentage of these dried, hanging bolls which contain some weevil stage.

In Table XVI B, among the hanging dried squares, nearly 59 per cent of these examined contained some weevil stage. In this case there were found an average of but 1.01 stages per square. The per- centage containing weevil stages varies somewhat, as it did in the case of dried bolls, but the variations are not exactly parallel. One reason for this apparent lack of agreement may be found in the fact that weevils show considerable preference for squares, and therefore attack them to a much larger extent than they do the small bolls. Among the bolls an average of 24.6 per cent contained some stage of the weevil, while among the dried squares there were 58.8 per cent.

In Table XVI C, fallen bolls, it appears that an average of only about 18 per cent contained some weevil stage. In this case there were found 1.106 weevil stages for each boll found to contain any. Examinations in three localities failed to reveal any weevil stage in a total of 380 bolls. Two of these examinations were made at Victoria in June before weevils had become sufficiently abundant to attack bolls to any extent. The third case was at San Antonio, where, as is indicated by observations in the other classes of forms, the infestation was comparatively light. It is probable, however, that a more extensive examination would have revealed some weevil stages in fallen bolls at San Antonio.

In Table XVI D, fallen squares, it is shown that slightly over 60 per cent contained some weevil stage. In this very large series of examinations there were but 1.05 stages for each square containing any. As would naturally be expected, there is not quite so wide : range between the extremes in the percentage of total squares which were found to contain a weevil stage as in other classes of forms. The importance of fallen squares, as compared with other classes of infested fruit, is shown by the fact that, in the 36,354 fallen squares examined, were found 22,169 weevil stages; whereas, in the 40,166 forms in the other three classes for Texas, there were but 11,666 weevil stages. While 60.7 per cent of the fallen squares were found to contain some stage of the weevil, an average of the three other classes of forms showed stages in but 26 per cent. The special signif- icance of these comparisons, from the standpoint of natural control of the weevil, may be appreciated when it is considered that the total mortality in fallen squares is much greater than in any other class of forms.

72 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

This may be more clearly understood if we consider a concrete illustration based upon the actual average percentages shown in Table III. In addition to the percentage of weevils found dead at the time of examination, it is reasonable to assume that had the stages been left in the undisturbed forms until all surviving weevils might have emerged, there would have been an increase in mortality fully equal to one-half of the percentage shown by the examinations. Based upon this mortality, a hypothetical illustration shows in a striking way the influence which the class of form may have upon the proportion of weevil stages reaching maturity therein.

TABLE XVII.—Illustration of effect of natural control, as found, upon weevil develop- ment in each class of forms.

: Number

= ying as by | Additional +

Reo ed of | Proportions |_ number ap z

Class of forms. ge Seki found at /likelystillto| ° seve anaedi & examinations) die before Wee eee rem given emergence. | “™€Tsing- herewith.

Dried hanging pollss.".-- 2.2.2 ee ; 100 30 15 | 55

Dred hanging squares... 2-145. 6 soso eee 100 53 27 | 20

WaTIGMsDOlS ces sere sence rae cee cs te ee nt nat aera 100 33 17 50 Motaltor si Glasses above --5--52- 2 300 116 59 125

it _ _ —_-

From this illustration it may be seen that the chances for a weevil to reach maturity are greatest in hanging bolls, second in fallen bolls, third in hanging squares, and least among fallen squares. Starting with three hundred stages, distributed equally among the first three classes of forms, between 40 and 45 per cent may be expected to become adult, while an equal number of stages in fallen squares may probably yield not more than 10 per cent of adults.

It is fortunate that under normal conditions a large majority of weevil stages develop in squares which fall to the ground. Because of this fact it is possible for the most important factors of natural con- trol to exert their greatest influence in checking the multiplication of the weevils. Without the large degree of natural control, such as has been shown to have existed in 1906, the profitable production of cotton would, apparently, not be possible. Understanding something of the influence of these factors, as we now do, we can appreciate in some measure our indebtedness to them for making it possible to continue the culture of cotton throughout the area which still, in spite of the damage actually done by the weevil, produces more than one-third of the annual crop in the United States. We can appreciate also the importance of following such methods in the culture of cotton as are found to promote in the greatest degree the efficiency of any factor in the natural control of the weevil.

SUMMARY AND CONCLUSIONS. 73

SUMMARY AND CONCLUSIONS.

_ If there be a fair amount of moisture in the soil up to the time squares begin to form, and there then ensues a period of from four to six weeks of hot dry weather, with mean average temperatures ranging from 75 to 85 degrees F., it may be expected that the weevils, though abundant _ theretofore, may be so effectively checked as to do little injury to the crop of that season.

An entire season of extreme drought, even without exceptionally high temperatures, will greatly reduce the number of weevils, but the crop will be small because of the continued lack of moisture. This condition may show little benefit from weevil control during that sea- son, but will greatly favor the production of a large crop, if weather conditions be favorable, during the following season. The difference in effect of a drought during squaring season alone and during the entire season lies in the widely different effect which those conditions exert upon the number of weevils developed in the fall, upon the food sup- ply available to the weevils until time for them to enter hibernation, and upon the shelter obtainable by the weevils during winter. In the former case many weevils may survive, in the latter few weevils will survive to attack the succeeding crop.

Winter conditions of unusual severity with frequent low tempera- tures and much rainfall have a beneficial effect by reducing the num- ber of weevils surviving hibernation and by preventing the survival of old cotton roots.

By cultural practices it is possible to secure regularly as great reduction in weevil injury during the following season as occurs occasionally after winters of extreme severity.

Defohation of cotton by the cotton leaf worms, if thorough and repeated, may be a very important factor in reducing the number of weevils in a field which may enter hibernation, or which are likely to survive. The planter can usually secure regularly much of the good effect of irregular leaf worm defoliations by destroying the cotton stalks early in the fall.

Fallen forms contain fully 70 per cent of the weevil stages develop- ing in a field. These stages are exposed to the most effective action of heat and of ant attack. Only in case of the fallen forms is it pos- sible to vary cultural practice:so as to increase the effectiveness of these factors. The mortality occurring in fallen forms is fully four times as effective in controlling the weevil as is that in hanging forms.

Less than one-half of all the weevil stages were still alive when found. If these had been allowed to remain undisturbed, under the continued influence of the three factors of natural control studied, it is very probable that the total mortality resulting would finally have

— ee eat: | 74 NATURAL CONTROL OF THE COTTON BOLL WEEVIL. amounted to fully 70 per cent. From 10 to 15 per cent of mortality occurred from other causes than those given in the tables.

All factors of natural control seem to operate more effectively against weevil stages in squares than against those in bolls. Ants and - J heat or drying are the most important factors in each class. In ball ) about two-thirds of the stages found were alive, while in squares but two-fifths were living. ’

The data used in this bulletin include examinations in twenty- eight localities, in several fields in each locality, and in seventeen — places examinations upon from two to nine dates between June 15 and October 15, 1906. More than 86,000 forms were examined and 39,000 weevil stages were found.

Nearly all of the eleven localities having an average total mortality above the average for the twenty-eight localities examined are situ- ated south of the center of cotton production in Texas.

Ants of the species Solenopsis geminata are more important in the summer control of the weevil than are heat and parasites combined.

The effectiveness of heat from sunshine is largely influenced by spacing of plants, which should be wide for best results, and by the coincident dryness of soil or atmosphere. The mortality from heat in two groups of localities having almost identical mean maximum temperatures varies as widely as between 7 and 27 per cent. Exact reasons for this great difference are not apparent. Average climatic variations do not appear to produce a corresponding variation in the average mortality of weevil stages.

Ants seem to enter only forms containing living stages of the weevil. Variations in mortality from ant attack may be due to vary- ing abundance of the ants in different fields or localities. Their activity is evidently influenced by climatic conditions and may also be affected somewhat by cultural conditions.

All parasites attacking the weevil have other hosts. Parasite attack is much greater in hanging than it is in fallen forms. The abundance of parasites seems to depend largely upon the proximity of some other plant than cotton in which their usual hosts abound. Their attack upon the boll weevil is a promising adaptation to a new host and may increase in effectiveness.

Climatic and cultural conditions seem to have been less influential in producing the three highest percentages of mortality than were the ants alone.

The highest mortality from heat or drying was found at Corpus Christi, Tex., in coincidence with comparatively low average max- imum and average mean temperatures, but after an exceptional drought extending over some eight or ten weeks. This occurred also in a well-tilled field where not more than one-half of the ground was shaded.

SUMMARY AND CONCLUSIONS. 75

The proportion of clear to cloudy days and the relative rainfall seem to influence in considerable degree the effectiveness of high temperatures.

Comparison of mortality records in localities infested for not : more than two years with those in localities infested for from three

to ten years shows a total mortality averaging about 10 per cent

greater in the section longer infested. This increase was due princi- pally to the greater effectiveness of heat and parasites, while in the recently infested area ants were exceptionally effective. The princi- pal reasons for these differences were probably the more moist cli- mate and the more abundant ant distribution in the recently infested area.

Nearly 70 per cent of all mortality found from heat or drying occurred during the larval stage. The ratio of mortality percent- ages in each weevil stage from heat is: Adult 1, pupa 3, larva 9. An early shedding of infested forms is very desirable.

Whatever spacing may have been found advisable where weevils were not present, these records prove the general soundness of the recommendation for increasing the space allowed each plant where the weevils are abundant. Central Texas shows the high average mortality of 21.8 per cent by parasites in hanging squares, 8.4 per cent in hanging bolls, and 5.7 per cent in fallen squares. Owing to the small number of observations made in southwestern Texas, western Louisiana should really be ranked first, with 39.4 in average percentage of total mortality among hanging dried bolls, while cen- tral Texas is second, with 28.8 per cent. Among hanging dried squares central Texas stands first, with 65.4, and western Louisiana second, with 61.3 per cent. Among fallen bolls eastern Texas ranks first, with 50 per cent mortality, and western Louisiana second, with 33.4 per cent. In eastern Texas alone did the number of fallen bolls examined exceed the number of fallen squares. Among fallen squares southern Texas has a long lead in total mortality, with 70.7 per cent, as compared with central Texas, with 50 per cent. The high percentage found in this class is based upon much the largest series of examinations made for any class in any section, and the figures are therefore exceptionally reliable and significant.

In degree of benefit from natural control, the six groups of locali- ties rank as follows in average percentage of total mortality

Per cent. ALLER de a Stee Pia OT DOS. Et tion 62.6 CSREES Sc spe PLO hpi ed SE ka 15.5 EL TBE MTT h Rp a eg ey gs eee kee el 43.2 SRC MR SRS oe 5 ot a Ss FL Bg, BY aah es SL Sie, Miia teh pipiniiel ithe te 11.4 MEE Rata NA geo PRET Saigs.a = te <b Woe Hee eee mee mia 31.9 DREMEL (MEMOS «yoo gti Sod bie iwinie dt aracie we ce eee mec 26.0

76 NATURAL CONTROL OF THE COTTON BOLL WEEVIL.

In examination of about 11,000 fallen forms collected between August 10 and August 31, 1905, 25 per cent were squares and 75 per cent were smalf bolls. The proportion between these forms varies ereatly with the stage of growth in each field. In the examination of 62,593 fallen forms collected between June 15 and October 15, 1906, 64 per cent were squares and 36 per cent bolls. Among 24,363 hanging forms examined in 1906, 28.6 per cent were squares and 71.4 per cent bolls. The

In a test of the effect of hand picking of infested fallen forms in 1905, it is probable that between 34,000 and 42,500 adult weevils were thereby prevented from emerging upon an area of 8 acres. In spite of this large destruction of weevils, the increased yield of seed cotton upon the test area averaged only abouf 50 pounds per acre as compared with a check area of similar size. This shows the tre- mendous importance and effectiveness of natural control, which frequently produces much greater increases in yield than 50 pounds of seed cotton per acre.

In the examination of 11,000 forms from Louisiana in 1906, only 44 per cent were found to contain a weevil stage. The balance of 56 per cent included many which had been injured by feeding of the weevils. Among the bolls 30 per cent and among squares 60 per cent contained some stage of a weevil. Probably few of the remainder of the squares had escaped some form of weevil attack, but a large proportion of the 70 per cent of bolls perished without any injury by the boll weevil.

In examinations of forms collected in Texas in 1906 among more than 14,000 dried, hanging bolls, hardly 25 per cent showed any stage of the weevil; among over 20,000 fallen bolls only 18 per cent had any stage; among 5,600 hanging dried squares nearly 60 per cent and among more than 36,000 fallen squares slightly over 60 per cent contained a weevil stage. Practically two-thirds of all weevil stages found in Texas were in the fallen squares.

The proportion among 100 weevil stages starting in each one of the four classes of forms which may be reasonably expected to reach maturity and emerge is as follows: Hanging dried bolls, 55; fallen bolls, 50; hanging dried squares, 20; fallen squares, 10.

Evidently we are indebted in a very large degree to the effectiveness of natural control for the possibility of continuing cotton production. Such cultural methods should be followed as shall exert the strongest influence upon hastening the maturity and increasing the yield of the crop. In addition to this, such cultural methods should be followed as will promote the highest efficiency of the factors in this natural control of the Mexican cotton boll weevil.

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@ 4 INDEX. Alabama argillacea. (See Leaf-worm, cotton.) Page. SIE AY CONNTOR OF DO1L WEEVIL... oo. ee we cee ete cence cnc ccc cece 19, . 24-25, 27-29, 30, 31, 33, 34, 37, 38, 40-41, 42, 43-44, 45-46, 47, 48, 49-50, 51-53, 54-59, 60, 61-62, 63, 74, 75 a lS A Re a (5 Birds, factor in control of boll weevil..... sp eS, Se ieee eae ane) 19) 20am Bolls, fallen, boll weevil mortality............. *.... 28-29, 30, 31-33, 51, 54-60, 61-62, 75 proportion destroyed by boll weevil versus natural causes....... 65-66, oe 69, 71, 72, 76 hanging dried, boll weevil mortality...........-.. 27, 30, 31-33, 51, 54-60, 61, 75 proportion destroyed by boll weevil versus natural causes. 66, 67, 70-71, 72, 76 remaron amon fallen cofton forms. .........:/.....20.5-220-e2 eee nee 64, 76 retention by plant of those dead..... BRC RES AIO LETS Ghee A 26 Meee squares, mortality of boll weevil......-..........0..-..2-..02 33-35, 74 Boll weevil, abundance and injuriousness as affected by humidity............ 11-12 PePMESTeGuH UICC SLACES... 2 <n. vee es se cena ee obec wccee 23 PUT ee fe etm ne rue eee oo. Lod ete 19, 24-25, 27-29, 30, 31, 33, 34, 37, 38, 40-41, 42, 43-44, 45-46, 47:48, 49-50, 51-53, 54-59, 60, 61-62, 63, 74, 75 UNE EM haa MRD oh eG a Age Rd Aa 19, 22-23 GINA GRMN IROTIS. <4 ch leas le eee 11-19, 37, 38-43, 74 © eollection-ol fallen forms... Jc2.( eee. oe eek eee 64-65, 76 PIUEURIROOUOUOTESY faethe ty. te ee, le 43-51, 74 destruction of cotton stalks in fall.....-.-.....-.-.. 18-19, 73 VET SCE CCR yc i Re a ae i a a a ee NN el OE td 19, 23, 27-29, 30, 31, 32; 34-35, 36, 37, 38, 40-41, 42- ! 43, 47-50, 51-53, 54-59, 60, 61, 62, 63, 74-75 leaf-worm (Alabama argillacea)......-....--- 19; 20, 21-2273 PEDATASILOR: 0. teh Sots, 19, 20-21, 23, 26, 27-29, 30, 31, 33, 34, 37, 38 40-41, 42, 43-44, 49, 50, 51-53, 54-59, 60, 61, 62, 63, 74, 75 PRAT rat oe eae a eo wee nas eal a 19, 20, 33, 35 UMM DS TS GCNMILTS ais nck ns eo pi Sale eens anh act oe 33 (See also Ants.) wide spacing Of cOLlon. Planis.....2--2--52-4te---=4 45-47, 75 MITEL CONGIIONS 1 LOUISIANA. 2.2.42 seen ecw dee a < LOM developmental period, average length..................--.---+.-- 35 PMO En POMC cs esc. a) ek SOARS st alee ee 16 emereonce Signs In Cotton Square... ......--.2- 22-222 -s eens eens ZED in Louisiana, control by winter conditions....:..........-------- 16-17 MOLE CTE LES CT pee = cele See aE fe OE ae RN 8 16 MEMEO, DUICCTOU TDN: FAMMIAN Ge Canc ats oa ales ie wee be enw ae See 13-15, 17, 37, 38-39, 40-41, 42-43, 47-50, 75 temperature...... 11-19, 37, 40-43, 47-50, 73, 74, 75 77

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- eee 78 NATURAL CONTROL OF THE COTTON BOLL. WEEVIL.

Page,

Boll weevil, mortality 10 all classes of forms, 0222 = Ue eee 30-31 | bolls versuysquares.<. 2017.) 1 33-35, 74 each class of forms for each Bechion:) #20. eee on 60-62 fallen holla 532.2 ae . 28-29, 30, 31-33, 51, 54-60, 61-62, 75 FOTO So cts eigen oc oa ee ee 73-74 diane. 6520 3s sae eee 31, 33, 51 heat and drying........... 31, 32, 51 parasites: << Sstewte Shs eee 31, 33, 51 PU ARES or rhtre = -aveae anes. ohne ee 29, 30, 31-32, 33, 44, 47, 51, 54-59, 60, 61-62, 75 hanging dried bolls.__. -:-- 27,305 31=33, 51. 54-60, 61-62, 75 BEG Etec an ne ae eee 27-28, 30, 31-32, 33, 44, D1, 54-59, 60, 61, 75 forms: 525, So Meu tee ee oe 73-74 from ants. .i2 el, Ween ee eee 31, 33, 51 heat and drying............___ 31, 32, 51 DATARILOR ay pad Ne 31,33, ar Louisiana, western..................._. 04-55, 61, 62-63, 75 aAuUareS Menus bolls: stay ieee eee eee 33-35, 74 Texas; -centralh. <8.) ya eee 2. S758. 61. 62-63, 75 CaSvern. ci soit ee yl ey 59, 61, 62-63, 75 northeastern....__. See a ee ee 08-59, 62-63, 75 MLOTUD CBR 3d Togstien ich 8 oak de ite ae 61 SOULHSrR 4 Assn ety se A ee 56-57, 61, 62-63, 75 southwestern 4).¢2-5. eh eUen ety 59, 61, 62-63, 75 of adults "in’cotton ions: "s1.0 2 0 han eae a 27-29, 37, 38, 40-41, 43, 54-59, 60, 62, 75 lapvee-im. cottom fommgs,a:7 1 esa ea 27-29, 30, 37, 38, 40-41, 43, 04-59, 60, 62. 75 Pupee in cotton foruise) s12 Sesiaek eae ae 27-29, 30, 37, 38, 40-41, 43, 54-59, 60, 62. 75 natural control in various localities...............__ 35-38, 53-59, 61-63 parasites more abundant in hanging than in fallen forms.......___ 30 proportion of stages which may emerge from fallen bolls.......__. 76 BQuaress fs. Jue 76 hanging dried bolls... 76 Squares 76 Climatie conditions in control ol bellyweevile’ <6 oo 11-19, 37, 38-43, 74 Control, natural, of boll weevil, climatic factors involved....___. 11-19, 37, 38-43, 74 conclusions and SUBLMABY? 3. .0 ES aha 73-76 conditions requiring consideration......._____ 11-12 defihiticn=ia: sah. akerer nh se gees 6

influence of dry season on succeeding season 14-15, 73 period [duration] of infestation. 91-853, 75 short drought in same season... 12-14, 73

winter climatic conditions... 15-19, 73

in various classes of forms ---------. 26-31) 60-62, 75 localities. 009 39-38, 53-59, 60-63, 75

localities where BRCOTCRL Sos s 8 5 Oe ee 74 relationship of factors......................_ 19-23 summary and conclusions................._.. 73-76

Cotton forms (see also Bolls and Squares). fallen, mortality of boll weevil......................._. 30, 31-33, 73-74

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INDEX. 79 Page, tton forms hanging, mortality of boll weevil...................... 30, 31-33, 73-74 proportion destroyed by natural causes versus boll weevil attack. 64-72 retention by plant of those dead........................-.-02-- 25-26 versus shedding for control of boll weevil.......... 2... 31-33

leaf-worm. (See Leaf-worm, cotton.) retention by plant of dead squares and bolls.......................... 25-26 stalks, fall destruction for control of boll weevil................. 0... 18-19, 73 P. wide spacing for control of boll weevil............................. 45-47, 75 5 Cultural conditions in control of boll weevil............................... 48-51, 74 practices, value in control of boll weevil...................... 18-19, 73, 76 Ectatomma tuberculatum, failure to maintain itself in Texas........0..00.2202-. 23

Gelatinization. (See Proliferation.)

Heat and drying, factor in control of boll weevil............. 19, 23, 27-29, 30, 31, 32

34-35, 36, 37, 38, 40-41, 42-438, 47-50, 51-53, 54—59, 60, 61, 62, 63, 74-75 Humidity (see also Rainfall).

as affecting abundance and injuriousness of boll weevil......... 2... 11-12

ES SS GIES Fo ec 39

mn nnamens, enemy of boll weevil..........-........2.--..---.----00-- 22 “Kelep.”’ (See Ectatomma tuberculatum.)

Leaf-worm, cotton, factor in control of boll weevil...................- 19, 20, 21-22, 73

Louisiana, boll weevil control by winter conditiong.......................-.- 16-17

SEI SMGNGE kt, Pee Was OL A See ad iad ea deeek weate 16

weber, Doll weevil mortality ....-..-....-..-.-..-.. 54-55, 61, 62-63, 75

Parasites, factor in control of boll weevil.........-..-- 19, 20-21, 23, 26, 27-29, 30, 31,

33, 34, 37, 38, 40-41, 42, 43-44, 49, 50, 51-53, 54-59, 60, 61, 62, 63, 74, 75

of boll weevil more abundant in hanging than in fallen forms... ... 30

Promieraton, factor in control of boll weevil...................-...-.. 19, 20, 33, 35

Rainfall (see also Humidity). aegiine mortality of boll weevil. .........-2-- 22.22 et eee ee 13-15,

17, 37, 38-39, 40-41, 42-43, 47-50, 75 Solenopsis geminata (see also Ants).

PEP DOL WEO YIN nla cote tse kl elke este ee Ses 24-25, 33

Squares, fallen, boll weevil mortality...... 29, 30, 31-32, 33, 44, 47, 51, 54-59, 61-62, 75 proportion destroyed by boll weevil versus natural causes.... 65,

70, 71, 72, 76

Raneme dred, boll weeyil mortality.......-..-..---.--------..---- 27-28,

30, 31-32, 33, 44, 51, 54-59, 60, 61, 75 proportion destroyed by boll weevil versus natural

aCe ot) te alg SCD 5 alle tea en Re a 66, 68, 71, 72, 76

proportion amonp fallen cotton forms. -...........-.--.-----------%- 64, 76

meuemnncneaye plarin Of LHOse dead... 2.2.52. ee lee eee eee 25-26

mene Dols, mortauty Of Doll. weevil.....-....-----------.---..- 33-3), 74

Statistical data, value in study of natural control of boll weevil. ........-.---- 25 Temperature (see also Heat and drying).

as affecting mortality of boll weevil.... 11-19, 37, 40-43, 47-50, 73, 74, 75

Wexae central, boll weevil mortality.......-...---....-.-.---.--- 57-58, 61, 62-63, 75

Pane eOll Weevil WOrality._-.-.--. 226+ -- anne teen} --- 55, 61, 62-63, 75

northeastern, boll weevil mortality. .....................---.- 58-59, 62-63, 75

SEL MMOLE, WEC VAL INOUE 2 os tein. tao. oe eee ee eee eee eee ne ok 61

southern, boll weevil mortality..........-.......-...-...- 56-67. 61, 62-63, 75

southwestern, boll weevil mortality..............-..-.-.---- 59, 61, 62-63, 78

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