Historic, archived document Do not assume content reflects current scientific l. Blaschke et Tscbemikh. [Translation.] Cardiophorus californicus: Elongate black, closely punctate, finely pubescent; thorax convex, subquadrate; dorsal surface of elytra de- pressed, feebly striate-punctate ; thorax beneath deeply punctate, convex; all joints of the tarsi and claws simple. Length lOf-9^ mm., width 3J-34 mm. Habitat, Cahfornia (Blaschke and Tschernikh). The Egg. The egg of Limonius californicus (PL 11, fig. c) is for the most part opaque white, though it shows small, irregular, semihyahne areas when placed on a white surface in dim fight. The surface appears smooth under the low power of the microscope, but under the high power it appears to be sfightly scaly. It reflects fight weakly from the fighted side. That the shell is quite tough is proven by the fact that even when the eggs are rolled about in the soil they are seldom distorted. The egg is elfipto-cyfindrical in shape. Both ends are broadly rounded and resemble each other. Measurements of 30 eggs gave an average length of 0.69 mm. and an average width of 0.5 mm. The length varied between 0.63 and 0.735 mm. and the width be- tween 0.473 and 0.53 mm. The Larva. The nearly mature larva of Limonius californicus (fig. 1; PI. II, fig. h; Pis. Ill, lY) is subcyfindrical in shape and shiny, waxy yeUow- ish-brown in color. The segments are very minut^ely and sparsely punctate. The head and venter are flattened dorsa../ and darker in color. There is a fight dorsal stripe on the posterior end of each seg- ment mth the exception of the venter. The head is depressed and considerably narrower in front. The mandibles are strong, notched, deep brown in color, changing to black at the tip. 1 Bui. Soc. Imp. Nat. Moscou, vol. 16, p. 238, 1843. DESCKIPTIONS. 15 The first thoracic segment is broad and long, being about equal in length to the venter. The other thoracic segments are short, being about equal in length to the first two abdominal segments. The remaining abdominal segments are a Uttle longer and quite similar. The legs are short and armed with heavy, short brown spines. The abdominal segments are slightly constricted where they join one another. There are from two to four hairs on the lateral side of each segment. The spiracles are bro^vn, conspicuous, and are situated in a poorly defined, fight lateral stripe. They are sUghtly nearer the anterior end of the segment. The venter is depressed dorsally, with raised edges. It is sparsely hairy around the edge. The caudal notch has a small tooth on each side pointing sfightly upward and backward. The margin of the notch varies from deep brown to black. The average length of the mature larva is from 18 to 21 mm., and the width is from 2.5 to 3 mm. The Pupa. When first formed the pupa is opaque white, but after a time the eyes show through as pale, dusky, blue spots. About this time the tho- racic segments become a pale waxy ye. 'ow, but no othr.i chrng^s take place until suo-^v be- fore emergence. The pupa (P,' ,>. vc^i^ much resembles the adult beetle in shape, except that thfej a^oCL'jnyen is sfightly longer in the pupal stage. The head is bent forward sli2:htly, and each anterior angle is armed with a long, heavy spine, which tapers regularly to a point. The mouth parts are conspicuous. The antennae are laid along the margin of the head on the ventral side, and their tips are behind the tibiae of the second pair of legs. On the underside of the head and near the prothorax are two short, heavy spines. There are also two short, stout spines on the dorsal side of the head near the posterior angles. The case covering the springing apparatus is plainly visible between the anterior coxae. The leg cases are folded similarly to Fig. 1. — The sugar-beet wire worm (Limonius calif ornicus): a, Head; 6, anal segment from above; c, same, lateral view. Highly mag- nified. (Original.) 16 THE SUGAE-BEET WIKEWORM. those of other Elateridae. All of the posterior pau-, excepting the tarsi, are covered by the wing cases, which are curved around and ahnost meet on the ventral side, at the distal end of the third abdomi- nal segment. The abdomen is contracted sharply at the seventh segment, so that the eighth segment is only a little more than haK as wide as the anterior end of the seventh. The anal segment . bears two long, heavy spmes on its posterior angles. These spines are shghtly divergent, are pitted, and the distal half of each is brown, changing to black at the tip. The pupae vary greatly m size. Measurements taken from sev- eral individuals give an average length of 11.5 mm. and a width of 3.6 mm. DISTRIBUTION. This wireworm is found quite generally throughout the western half of California. It is abundant in the lower sugar-beet lands of southern California.- The main districts affected by it are those of Ventura, Orange, and Los Angeles Counties. These three districts comprise probably the choicest sugar-beet land in southern Cali- fornia. The station for the study of this insect was located in Compton, in Los Angeles County, about 10 miles from the coast, and surrounded by about 12,000 acres of sugar beets. Limonius californicus has been reported from the following places, all in California: Kiverside, San Bernardino, Los Angeles, Lake, Monterey, and El Dorado Counties, by Prof. H. C. Fall; near Owens Lake, collected by Dr. A. Fenyes; Marin County, specimens in the collection of the University of California; Orange, Ventura, and San Diego Counties. (See fig. 2.) Prof. A. L. Melander, entomologist of the Washington Agricultural Experiment Station, Pullman, Wash., reports that in the collection there they have a single specimen which was collected in eastern Washington. It is thus seen that this species is fairly well scattered along the western half of California. It is probably not of economic impor- tance outside this State. FOOD PLANTS. The larvae of Limonius californicus have been noted to feed on the following plants: Sugar beet. Wild beet (5e^asp.). Potato (Solamnn tuberosum). Lima bean (all varieties). Corn (all varieties). Johnson grass (Sorghum halepense) . Dock {Rumex hymenosepalus) . Alfalfa (Medicago spp.). Pigweed {Amaranthus retrofiexus) . Chrysanthemum . Nettle (reported by H. M. Russell). Wild aster (reported by H. M. Kussell). Mustard {Brasdca niger). i Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. Plate V. I ^ t Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. Plate VI. Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. Plate VII. o -<**• i i FOOD PLANTS. 17 It is difficult to note a preference of this wireworm for any par- ticular food plant, as sugar beets, lima beans (Pis. VI, VII), corn (fig. 3), potatoes, and aKaKa aU seem to be favored. After these ^r Fig. 2. — Map of California showing counties from which the sugar-beet wireworm has been reported. (Original.) in order come Johnson grass and wild beets. The remaining food plants seem to be taken more from necessity than choice, and it is only occasionally that larvae are discovered feedmg on them. 6140°— Bull. 123—14 2 18 THE SUGAE-BEET WIEEWOEM. LIFE HISTORY AND HABITS. The Egg. time and place of deposition. The eggs (PL II, fig. c) are all deposited during the spring and in ^ the greatest numbers about the middle or latter part of April. (See diagram, fig. 4.) During the latter part of March immature eggs '^ to the number of from 25 to 40 could be dissected from the swollen , abdomens of the females. On April 9 the first eggs were laid. These were placed in the / loose damp soil of the rearing cages, about 1^ inches below the^ i Fig. 3.— Injury by sugar-beet wirewonn {Liwonius californkus) to field of sweet corn, Dominguez, Cal. (Original.) surface. It seems that it is intended that the eggs shall always be ~ placed singly, as out of about 8,000 eggs taken from the soil only a ; very few cases were noticed where several eggs were together. Never-J were more than three eggs in a group, and these were not held together , in any way. Food plants seem to have no effect on the place of deposition, as there were always as many eggs found at the edges of the cage as ^ there were surrounding the young beet plant at the center. At first this was supposed to be due to the fact that the tender root hairs J are scattered rather generally through the soil, but later tests seemed to indicate that the place of deposition is affected more by the con- , LIFE HISTORY AND HABITS. 19 dition of the soil, a loose damp soil being selected by the adults in preference to other kinds. Nearly all the eggs were placed in the first inch and a half of damp soU, and the greater part of these about 1 inch below the line of dampness. A small mite, which has been identified by Mr. Nathan Banks as (Gamasus) Parasitus coleoptratorum'L. (?), was commonly noted in the soil with the eggs but was never seen destroying them. NUMBER AND HATCHING OF EGGS. Complete records for the eggs could not be obtained, so the num- ber of eggs laid by a female of this species is still a question. One female which had been isolated after fertilization laid 71 eggs before death, and 11 were added by dissection, bringing the total to 82 eggs. Another female gave a total of 63 eggs by oviposition and dis- section. Two others gave 61 and 52 eggs. Twenty-five dissections gave the number of eggs as between 28 and 40, or an average of about A^^K Fig. 4.— Diagram showing the period eggs of the sugar-beet wireworm were in the soil, with temperature; season of 1912,. Compton, Cal. (Original.) " 34 eggs per individual. It is quite probable that 100 eggs or even more may be deposited by a single female. Practically all the eggs hatch. In the laborator}^ over 94 per cent of 5,000 eggs hatched successfully, even after they had been handled and kept under artificial conditions. Those which did not hatch were for the most part either allowed to dry out or were killed r by a fungus. Eliminating two cages — the one which dried out and the one in which the fungus appeared — it would be safe to say that i over 98 per cent of about 4,200 eggs which were kept under labora- tory conditions hatched safely. There is an optimum zone, in so far as the degree of dampness is concerned, for the hatchmg of the eggs. Some eggs kept in a dry ►, vial indoors, where it was not too warm, failed enthely to hatch and after a time shriveled up. On the other hand, the eggs which were kept too damp were subject to a fungous attack. Water itself 20 THE SUGAR-BEET WIEEWORM. seems to have little effect on the hatching of the eggs, as some which •were kept partiallT submerged part of the time hatched in good shape. As hatching time approached, large, irregular, hyaline areas ap- peared in the eggs m various places. At first nothing could be seen of the embryo, but about a week before hatching its outlines could be made out with difficulty. The embryo became little plainer, even at th-e time of hatching. LENGTH OF EGG STAGE. The length of the egg stage varied under laboratory conditions from 23 to 33 days, most of the eggs hatching in from 27 to 30 days, so that the length of the egg stage may be roughly considered as a month. It seems probable that the period might be shortened mate- riaffy under favorable conditions, out of doors, and eggs laid in the warm damp soil might possibly hatch in from 15 to 25 days. The Larva. emergexce from the egg. The larvae (PL II, Jig. h) emerge from the eggs by eating a small hole in the sheU and crawling out. In aU the cases noted the hole was very little larger than the body of the wireworm, so that it is a matter of a few moments for the young ^Treworm to leave the shell entii^ely. In the case of several which vrere timed, between two and seven minutes elapsed from the appearance of their heads through the sheU until they were entirely free. During the earlier part of the hatching season no eggshells could be found, and it was thought probable that the larva on emerging used the shell for food. Such did not prove to be the case, however, as later, when more eggs were hatching, it was observed that the larva on hatching leaves the old sheU almost at once. In a few cases the larvae crawled around the shells for a short time but did not attempt to eat them and always left them intact. TThere the eggs are hatchmg in the soil, the young larva remains for a short time in the cavity occupied by the egg. That the eggsheUs are quite tough was proven by the fact that the empty sheUs were able to retain thek shape for some time. THE XEWLY HATCHED LARVA. TMien fu'st hatched the larva (PI. II, Jig. b) is semiopaque white. The extreme tips of the mandibles are the only parts which show any color, and these are light yeUow. The general proportions of the newly hatched larva are very much like those of the older ones. They vary little in size. Theii^ average length is 2 mai. and the width is 0.27 mm. Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. Plate VIII. Fig. 1 .— Sugar-Beet Wireworms in Petri Dish, Killed by Bacteria in Cultures of Agar. (Original.) Fig. 2. -a Root Cage Used in Rearing Young Wireworms. (Original.) i t i i LIFE HISTORY AND HABITS. 21 When these larvae are exposed to a moderately subdued light they color quite rapidly and become noticeably yellow all over their bodies ui a day's time. When the newly hatched larvae are kept in darkness they color more slowly, and two or three days elapse before their bodies become yellowish. Their skin is quite tender, but in spite of this they can survive rather rough handling. REARING CAGES USED. Several styles of cages were used in an endeavor to find one in which the wireworms could be successfully reared and at the same time watched. Only three types gave any promise of success, and these will be reviewed briefly. The first type used was simply a petri dish with damp filter paper in it. Several sheets of filter paper were used so that when the larvse crawled between the sheets it w^as almost the same as if they were in damp soil. Slices of beets were placed in the cage and renewed daily. These were of use not only as food for the wireworms, but they also assisted in keeping the atmosphere of the dish damp and cool. These dishes were then kept in insect boxes to insure per- fect darkness and to assist in keeping the temperature even. This style of rearing cage was very successful for the first two weeks, and much was expected of it, but from that time on one bad point after another presented itself, and within a month the cage was given up as impractical. The two worst points in connection with this cage are that the amount of moisture can not be regulated and, secondly, that there is no drainage and the cage tends to foul easily. The cages were cleaned every day and fresh filter paper added, but in spite of all these precautions a red bacterium (PL VIII, fig. 1) made its appearance in several of the cages at about the same time, and as there seemed to be no way to check it this style of cage was given up. Another rearing cage (fig. 5) which was used was made of plaster of Paris, and was patterned after the Janet ants' nest, except that it was more simple. It is a plaster-of-Paris block with two depressions in it. Water is kept in one and the wireworms in the other. The water readily soaks through the block, and if the dish is covered with a tight-fating piece of glass the depression contaming the w^ire- worms is kept damp and cool. The cage is further improved b}' painting the glass plate black to exclude light. Dr. Chittenden sug- gested a coating of paraffin for the outside of the dish to cut down the excessive evaporation. This scheme worked well where only part of the dish w^as coated. Whenever the entire outside of the cage was coated, however, the drainage was cut off, the cage became foul, and the wireworms died. The great advantage of this cage, as pointed out by Messrs. Knab and Dimmock, is that it can be sterilized simply by heating. Most of the first trials of this cage were failures. 22 THE SUGAE-BEET WIEEWOEM. but it soon gave promise of being a simple and safe receptacle in which, to rear wire worms. The other style of cage was the common root cage (PL VIII, -B.g. 2), so often used for the study of underground msects. The cages used in these experiments had the glass walls very close together (one- eighth to one-fourth inch) so that there would not be much soil m which the larvae could hide. The root cages were not so successful as it was hoped they would be, for the larvae were usually able to conceal themselves and it seemed almost im- possible to wet the cages properly. Used in conjunction with the other cages, however, they gave fah success. The majority of the young wireworms were kept in large flower- pots, so that in case of accidents to the rearmg cages not all the larvae would be lost. These pots had an added ad- vantage in that they provided soil conditions quite similar to those out of doors. The flowerpots were emptied and exammed from time to time so that the larvae could be watched. Fig. 5. — Janet ants'-nest plaster-of-Paris cage, used in rearing sugar-beet wireworms. A, compartment for larvae; B, com- partment for water. (Original.) HABITS OF THE YOUNG WIREWORMS. The young wireworms are quite active, moving over smooth sur- faces or burying themselves in the loose soil with ease. Some placed in a root cage buried themselves almost at once, but were tempora- rily checked b}' a la3'er of compact earth about an inch below the surface. On the following day several had entered the compact layer and the next day one was noted at a depth of 4 inches. T\lien ver}' young the}' are unable to survive in dry earth even for a relatively short time. Some which were placed m a petri dish with dry soil were dead at the end of five hours, a few dying after the first hour and a half. These larvae shun the light and when exposed to it hide under any object which they can find. TThen placed in the petri-dish cages the}^ soon crawl between the layers of filter paper at the bottom. Experiments were made to test their ability to locate food, by placmg a slice of sugar beet m the cages and noting the time it took them to collect under it. The beet slice was not larger than a dollar and was LIFE HISTORY AND HABITS. 23 placed in the center of a large petri dish. Within 10 minutes all the wireworms were under it. This experiment was repeated by using a piece of damp cardboard the size of the beet slice and again timing the wireworms. In this test all the larvae finally gathered under the cardboard to escape the light, but a longer time was required before this took place. These tests were repeated several times as checks and always gave the same results, so it is evident that the larvae are able, to a small extent, to locate food. The larvae begui feeding noticeably, though lightly, very soon after hatching. A fresh slice of sugar beet was placed in the cage every day, and when each slice was removed the muiute black feedmg marks could be noticed. The depressions made by the feediag could be made out only with a hand lens, but the black staLa, so character- istic of wireworm injury, had spread out and was quite conspicuous. The wireworms grow quite rapidly duruig the first two or three weeks, and it might be added that this is the only time in their long larval life when their growth is apparent. They approxunately double in size in this time and then remain about the same size until they molt. At the time of their first molt they take a sudden jump in size and froij^ this time on then- growth is very slow. An attempt was made to trace the molts with these wireworms, but unfortunately it had to be abandoned. The death rate in the exposed cages was so high that it soon became apparent that none could be brought entirely through in this manner. Added to the difficulty was the fact that since their time of molting was so irregular only a few could be kept in a single cage. After about a thousand larvae had died in these cages it was concluded that it was impossible to carry the observations to completion with the forms of rearing apparatus at hand. The cast skins of the larvae could not be found, owing to their small size and transparency, and the only molts that could be traced were in the case of certain larvae which increased in size quite noticeably overnight. The increase in the width of the head was found to be the best test. From time to time the soil in the fiowerpots containmg the bulk of the wireworms was carefully examined to see whether anythiug could be learned concerning the feeding habits of the larvae under natural conditions. In every case the larvae were found scattered rather generally through the soil, and as many of them were found around the edges of the pot as directly around the beet root. Since the root hairs were scattered pretty generally through the soil it seemed prob- able that the larvae fed on them. This was further indicated by the fact that no feeding marks could be found on the main beet root. At any rate it is safe to say that, from the standpoiut of injury due to their feeding, the wireworms during the first year of their larval life may be disregarded. Larvae were generally found from 1 to 3 24 THE SUGAE-BEET WIREWOEM. inclies below the surface, but as the soil ui the rearing cages was kept clamp to the surface the}^ would evidently be found deeper under field conditions. Examination from time to time during the summer revealed no startling changes. Growth was very slow, but the wneworms be- came more active, and their skms a deeper yellow and noticeably harder. APPROXIMATE LEXGTH OF LARVAL STAGE. As the first larvae of this species were hatched from the eggs in the spring of 1912 there are no data concernuig the complete life histoiy or even of the way the larvae pass their first ^vinter. At the date of this writing (Oct. 15, 1912), however, it seems quite evident that this year's wire worms will turn out next sprmg to be the "small ones" which are always noted commg up to feed durmg February and March. At the time the beetles were bemg collected, in March, 1912, there was no vegetation of any kuid in some of the fields, and the wire- worms, coming out from hibernation, were attracted to the old beet roots which are found in greater or less numbers in all of the fields. Xearly all larvae collected at this time, to the number of over 3,000, were readily separable into two sizes. This has been reported before by other investigators.^ The smaller ones appeared to be about one- third grown, and very probably were the ones which had hatched the preceding spriag, and were consequently about a year old. The larger . ones showed more variation in size, occurring from three- fourths grown to practically mature. These larvae were probably 1 and 2 years older than those of the smaller size. That there is a difference in age in the wire worms of this latter group is proved by the fact that of 100 isolated durmg March only 17 pupated in the period from July to September, and the remainder, some of which at the time of TSTitmg (December, 1912), had recently molted, had gone deep into the soil in the cages and seemed prepared to spend the winter. Now, from the fact that none of these large larvae could have come from eggs the preceding sprmg it seems very probable that this species ^^'ill uphold the contentions of most of the American writers on this subject and spend three years m the larval state. To be exact, it would be a trifle over three years, as Prof. F. M. Webster ^ has pointed out, 'Hhe larvae hatching in the spring and pupatmg in the late summer." Larvae have also been carried in the laboratoiy from June, 1910, to April, 1912, without pupatmg, so it seems evident that the larval stage could not be less than three years. 1 Eleventh Report on the Noxious. Beneficial and other Insects of Xew York. By Asa Fitch. M. D.. 1S66. 2 Underground Insect Destroyers of the ^Mieat Plant. By F. M. Webster. Bui. 46, Ohio Agr. Exp. Sta., 1892. Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. Plate IX. M^Ki ^ -Ic^^flBI I^w ■E^ ft . HHHiJMyM ^ ^^g^ V V «l V 1 1 fl&4r -^ Ml Pm \^ ^Ttc # ^ V. ■i ' Work of Sugar-Beet Wireworms. Young Sugar-Beets, Showing Injury by WiREWORMS TO TAPROOTS; BLACKENED FEEDING MARKS VISIBLE ON END OF ROOTS. (Original,) Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. Plate X. Work of the Sugar-Beet Wireworm. Nearly Mature Beets Killed by wireworms; blackened feeding marks noticeable on taproots. (Original.) Bui. 1 23, Bureau of Entomology, U. S. Dept. of Agriculture. Plate XI. n f j|. 123, Bureau of Entomology, U. S. Dept of Agriculture. Plate XII. Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. Plate XIII. Bui. 123, Bureau of Er,tomolo?v, U. S. Dept. of Agriculture Plate XIV. Bui. 123, Bureau of Entomology, U, S. Dept. of Agriculture. Plate XV. ^ LIFE HISTORY AND HABITS. 25 HABITS OF THE OLDER WIRE WORMS. While these wkeworms were being collected in the fields there was a good opportunity to observe their feeding habits and their actions after emerging from hibernation. As the soil was wet to the surface by the intermittent rains, it was easy for the wire worms to reach the old beets which were scattered around on top of the ground. As the larvae had just emerged from hiber- nation they fed ex- tensively; with the result that whenever several wire worms attacked a beet root it was soon honey- combed with their channels. Many of the wireworms noted were buried far more than their own length in the half -rotted beets. These larvae are carnivorous on occa- sions (see fig. 6), even under field conditions ; especially is this so during the earl}^ period when they are feeding most busil}', and wlien at the same time they tend to be crowded. Under average field conditions, however, cannibalism is unimportant from an economic standpoint, as these larvae are veo^etable feeders ]:)V choice. P^IG. 6 V sugar-beet wii'eworm devouring one of its own kind; to illus- trate cannibalistic habit. (Original.) LOCATION OF FOOD BY THE WIREWORMS. AYhether or not the wireworms, under field conditions, can locate food at a distance, and, if so, at what distance, is more or less problem- atical. When wireworms were injuring beets in the fields it was found by careful digging that all which were near the beets were actually feeding on them. Wireworms noticed in fields containmg young beets were almost always found in the beet rows, in spite of the fact that the ground there is compact and unfavorable for them. These facts seem to carry out the idea gained from the experiments with the young larvae, that they can locate food at a short distance, though this is not proven conclusively. 26 THE SUGAK-BEET WIEEWORM. ACTIVITY OF THE ^YIREAVORMS. During the spring, when the soil is kept wet by the rains and loose by cultivation, it is probable that the wu-eworms are able to travel from one beet plant to another. Under laboratory conditions they have been noted to travel several inches daily, in the root cages, and the soil then is Terj apt to be compacted b}' wettmg. This pomt was tested by placing several ^\m'eworms in a root cage ^^'ithout food in order to compel them to move. The soil, which was quite damp at first, was allowed to become pretty thorougiily dry, and then the cage was watered. The water followed the channels of the vdre- worms, and in this wa}^ the wheworms could be easily traced by the wet streaks through the soil. These cages were 18 by 24 mches, yet in the week or 10 days the soil was drymg out the ^ii'eworms had been able to channel all thi^ough the soil. Late m the summer, vrhen the soil is more dry and compact, the}' move about much more slowly and are less anxious to feed, but as the}^ do all thek damage in the spring their actions at the latter time are of the utm^ost mipor- tance. From all the observations on their activity it seems not only possible but even probable that one wireworm can destroy several young beet plants in a season. The sugar-beet plants are from 6 to 8 inches apart in the rows. WIEEWORM INJURY TO BEETS. Durmg the latter part of February and m March and April the ravages of the ^Ti'eworms in the beet fields are very noticeable, especially so when the insects are present in numbers. In a year such as 1912, when their work was well scattered, injury can be noted, but it is possible to overlook it. When the young beet plants are attacked thej wilt, and upon examhmtion the root is found to be either badly scarred or entirely severed. (PL IX.) This injuiy generally takes place between 1 and 4 inches below the surface. There are two general types of mjury; in one the taproot is cut off clean, and the beet wilts and dies (see PL X) ; m the other the ^\Ti^eworm, after eatmg mto the root, turns and descends, eating off a side of the root as it goes down (see PL IX). This, of course, scars the root badly, and if the beet is quite young and tender it is apt to die. If, however, the beet is quite strong and the root is swollen a little, so that the mjur}' does not cut off the sap suppty, it will recover, though always remaining distorted and undersized. (See PL XL) In years when the wireworms appear hi numbers they are likely to be concentrated m certam spots. T\lien this occurs they kill off all the beet plants in these areas, causmg the characteristic ''bald spots." (Pis. XII-XV.) ^Yhell once they have collected in LIFE HISTORY AND HABITS. 27 this manner and liave cleared off the beets it is almost impossible to raise beets there during that year, even if replantmg is resorted to several times, as the wireworms kill them as soon as they germinate. The injury caused by the wireworms is characteristic and should never be mistaken. In the first place, if the injury is recent, an examination will reveal the wireworm near by in the soil. If no wireworm is present an examination of the wound will readily show whether or not it is wireworm injury. The wound itseh is stained black, as if rubbed with ink. Sometimes the black stain has pene- trated for a short distance into the sound beet tissue, but where it has not, it is considerably darker than the dry tissue surrounding an ordinary old wound. Effect of overflowing on the wireworm. — From the fact that wire- worm injury is often noticed in fields which have been overflowed in the latter part of the winter, it has naturally been supposed that overflowing of the land is favorable to wireworms. This has not been proven to be entirely true. A careful watch was kept on the fields which are subject to overflow, and from these observations it seems that overflowing the land is of account only as it aft'ects the character of the soil and is therefore secondary. In overflowed land which tends to be sandy the wireworms are likety to be destruc- tive year after year. On the other hand, flooded land which is a heavy silt and rich in humus is seldom so badly injured as is sandy unflooded land. One thing has been noticed, however, and that is that flooding the land does not seem to injure the insect in the least and therefore gives little promise as a control measure. Some of the beet fields which have suffered the most during the last few years are those which almost every year are quite thoroughly flooded for two or three days. TIME THE WIREWORMS CAN LIVE WITHOUT FOOD. Whether or not these larvae are able to find food in the soil is hard to determine, but judging from the length of time they are able to live without food it seems possible that they do receive some suste- nance from the soil, probably in the form of decaying vegetation. This is further borne out by the fact that where larvse are kept for a time in a cage without food all the lumps of leaf mold disappear and the soil in the cage becomes homogeneous. Several observers have reported that these larvae can survive long periods without food, and one example which was noted in the laboratory will furnish added proof. During June, 1910, Mr. H. M. Russell commenced a starvation experiment by placing several wireworms in a root cage, with ordinary soil, without food. In July, 1911, seven larvae were still alive and healthy. This cage was 28 THE SUGAE-BEET WIEEWOEM. watered regularly, except on two occasions, during the late summer of 1911 and was then allowed to become quite dry. As the larvse were killed by the dirying soil they were removed so that they would not furnish food for the survivors. On September 12, 1911, the cage was again examined and only one larva was found alive. Twp dead ones were found near the surface in the dry earth, and they had probably been killed by the drying out of the soil. This cage was then watered regularly and examined at intervals. The larva was stiU alive and active on April 15, 1912. During the latter part of April the cage, which was kept m the outdoor insectary, was blo^vn over by the wind and broken. Before it was noticed the soil had dried out to such an extent that the larva was dead. An / y^r^R / y^^R 3 /^O. 3 MO. 3A'^0. 3 MO. 3 MO. 3 MO. 3 MO. 3 MO. / 2 A „ ^ s 6 7 Fig. 7. — Diagram showing length of life of sugar-beet wireworm without food. (Original.) examination of the channels through the cage showed that the wire- worm had been quite active up to the time of its death. Wliile these larv83 might have secured a little food durmg the earlier part of the expermient they could not have done so later, as they were checked up and removed when they died. In this experiment seven wireworms lived over a year without food, and one almost two years,, as shown in the following diagram {^g. 7). These wireworms did not grow normally, for when the last one died after being in the cage two years it was less than hah size. This larva should have pupated that fall, as it was at least a year old when the experiment began, and therefore should have been mature. LIFE HISTOEY AND HABITS. 29 RELATION BETWEEN INJURY IN THE BEET FIELDS AND THE SIZE AND ABUNDANCE OF WIRE WORMS. As is the case with practically every destructive insect, the greatest harm is done by the maturing larvas. It is therefore only a matter of watching the progress of injury in the beet fields to tell whether or not there are many mature wireworms, and whether, therefore, there will be an abundance of beetles the following year. In every year during which observations have been made thus far it has beer a simple matter to foretell tliis point. In 1911 injury to the beets was quite heavy and general. From this it was reasonable to sup- pose that there were many mature wireworms in the soil and that the next year would see an abundance of beetles. Such proved to be exactly the case, and beetles were quite common in the fields; so much so, in fact, that it was no extraordinary feat to collect over 25,000 of them for the rearing work. In 1912, in the Adcinity of Compton, the wireworm injury, while quite general, was light, and using the same reasoning it was probable that there would be few beetles in the spring of 1913. This has been partially proven by the fact that very few of the larvae taken in the fields during 1912 pupated the same fall. The 300 wireworms collected in the summer of 1911 produced ahnost as many pupae in the fall of that year as the 12,000 wireworms collected in the summer of 1912 produced during the succeeding fall. MOLTING OF THE WIREWORMS. The wireworms molt in their channels, and wriggUng from their old skin (PI. Ill) they lie still for some time until their new skin has hardened. If the channel is larger in cross section at the place where the wireworms molt, it is so Httle larger as to be almost unno- ticed. When ready to molt the larvae he still for some time, in cer- tain cases for several days, before the skin spUts and they are able to free themselves. In a majority of the cast skins noted the skin had spht down the dorsum of the thorax. Where this occurs the process of molting is simple and seldom takes more than two or three hours. The cast skin is also in one piece. Now and then the skin spUts irregularly, and in these cases the molting process requires more time, sometimes several days. In one case noted the wireworm shed the skin from its head a fuU week after it had molted on its thorax and abdomen. In such cases the skin is quite apt to be torn into several pieces and is almost useless for study. Directly after molting the wireworm, with the exception of its mandibles, is a rather shiny opaque white. The mandibles are yel- lowish, shading to brown at the tips. The wireworms color quite wel] in from one to three days, but they often remain quiescent for weeks 30 THE SUGAK-BEET WIREWORM. after molting. This is especially apt to be the case in the fall, when they are sluggish. Most of the larvse observed during 1912 molted twice. A few were seen to molt once, although it is possible that a molt might have been overlooked in a few instances. In the case of a few others it was thought that a third molt was seen, but this is doubtful. From this it is impossible to give even the approximate number of molts with any degree of accuracy, but present indications are that they molt at least five or six times. The Pupa. pupation. In about July or August the mature larvae become shorter, and while they are not more constricted between the segments, they have the appearance of being so, as the segments swell slightly in the middle. At the same time there is a sHght change in color, the entire larva appearing sickly and of a dirty yellow color. During this period the wireworms lose most of their activity, and whatever movements they make are slow and weak. When pupation is only a short time off they are quite helpless, and if their pupal cells are broken open they are unable to make new ones. Several which were taken in this condition were able to pupate safely, the operation taking place in a Janet ants'-nest cage. THE PUPAL CELL. The pupal cell is simply an enlargement at the end of the larval channel, and is slightly elliptical in shape. It is unhned but is quite smooth and the soil is well compacted. The depth of the pupal cell below the surface varies between 4^ and 9 inches, but most of those observed were at a depth of about 6 inches. It is apparent that the wireworms move . very little preparatory to pupating, as pupae are often dug up with the wireworms close to the old beet roots. SOIL CONDITIONS AFFECTING PUPATION. The pupae (PI. V) are unaffected by a little dryness, but if the soil becomes quite dry for a long period they do not emerge. Many healthy pupae were dug up in the field in soil which contained only a Httle moisture. Those which came through best under laboratory conditions were from cages where the soil was kept only moderately damp. Where the soil was too wet a large percentage of the pupae sickened and died. Those found dead under these conditions were attacked either by a fungus or a bacterium, or sometimes by both. It was not determined whether these organisms were parasitic or sapro- LIFE HISTORY AND HABITS. 31 phytic. An attempt was made to rear some of the pupae in the plas- ter-of-Paris cages, but the cages seemed to be too damp, and all the pupae died. These appeared like those killed in the flooded cages, and the same bacterium and fungus infested them. VITALITY OF THE PUPA. The pupal stage is the most unprotected state in the life cycle of this insect, and is the one wherein the insect is most liable to mechan- ical injury. A small percentage of the pupae dug up out of doors were injured when their pupal cells were broken open, and conse- quently died. On the whole, however, the pupa is not nearly so susceptible to injury as is the popular belief. Such pupae as were unearthed in the field were kept under artificial conditions and handled quite roughly and often, yet most of them produced adults. The two pupae which were photographed for this bulletin (see PI. V) were handled several times with forceps, were exposed on a glass plate to light and temperature for hours, and on one occasion were dropped from the table to a chair, a distance of about 10 inches. In spite of this treatment both produced normal adults, and when last observed, October 14, 1912, were alive. There were several similar cases in which the results were the same as in the example cited. The pupae are quite helpless and are unable to make new pupal cells in case the old ones are destroyed. For this reason, probably, a large per- centage of those disturbed in the field die from exposure. The pupae are sensitive to light, heat, and contact, and when disturbed move their abdomens in such a way that the tip describes a circle. As the pupa becomes older it becomes more deeply colored and more sensitive and active. CHANGES IN COLOR OF THE PUPA. The first signs of coloration of the pupa are the eyes, and these appear as dusky bluish spots. The abdomen and thorax then be- come slightly yellow and the mouthparts and wing covers very faintly dusky. The tip of the abdomen remains whitish. About a week before emergence the entire pupa becomes darker, and just a few days before emergence the wing covers and mouthparts are quite dusky and the eyes assume a dusky color, the mouthparts, eyes, and wing covers remaining a little the darkest and being quite conspicuous. LENGTH OF THE PUPAL STAGE. The length of the pupal stage under laboratory conditions varied from 25 to 36 days, with most of the adults emerging in about 26 to 32 days. These were kept as nearly as possible under conditions which would compare favorably with field conditions. This gives, roughly, a period of a month for the pupal state. 32 THE SUGAE-BEET WIKEWOKM. The Adult. EMERGENCE OF THE ADULT. During the last few days before emergence the pupa becomes very sensitive to hght or contact, and when disturbed turns around in its pupal cell by moving its abdomen. An attempt was made to photo- graph one during this state, but in the hour and a half it was exposed it did not remain quiet long enough for an exposure to be made. The abdomen is drawn in and out as if the beetle were trying to break the pupal skin. This goes on for some time, often for more than a day, and finally the pupal skin splits down the dorsum of the thorax and is worked off. The beetle (PI. XVI), which has been quite active in shedding its skin, now becomes quiescent, and folding its legs and antennae as they were in the pupa, remains in the pupal cell. The cast pupal skin lies in the posterior end of the pupal cell along with the last larval skin, and helps form an obstruction between the pupal cell and the old larval channel. The cast pupal skin is semi trans- lucent white and thin, but at the same time quite tough. In two cases the legs of the beetle broke through the leg cases before the pupal integument split down the dorsum. Neither of these adults completely emerged, and after moving their legs feebly for a few days they died. PERIOD OF EMERGENCE. The period of emergence of the beetle from the pupa varies wddel3\ This was true both of those which were reared in the laboratory and of those pupae which were collected outdoors. Adults emerged be- tween early August and October in the laboratoiy, and pupae from the fields have given adults between the same dates. One pupa from the field transformed to adult October 6. Mr. Russell observed one adult emerge in the laboratory as late as October 17. Beetles disturbed dviring the fall are able to bury themselves and live if they are not injured. Several which emerged in the laboratory were constantly disturbed so they could be watched, but it seemed to have no ill effects on them. ACTIONS DIRECTLY AFTER EMERGENCE. As soon as the pupal skin is shed the adult, retaining the position it had held as a pupa, lies in the pupal cell. At first the beetle is a little softer and lighter in color, but soon becomes hard and fully colored. Since none of the pubescence on its thorax or elytra has been rubbed off, it appears grayish in color. At this time these beetles are totally different in their actions than the}^ are in the spring, when they appear on the surface, being negatively heliotropic and hiding under anything the}^ can find or burrowing into the soil when exposed to light. They also seek damp, cool quarters in Bui 123, Bureau of Entomology, U. S. Dept. of Agriculture. Plate XVI. X < h- z or O z Q - u i25 ^ < o > 2 , 5 z q: uj i> lU I- CQ > < -^ =5 < CO CO ir u O Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. Plate XVII. Fig. 1.— Beetles of the Sugar-Beet Wireworm iLimonius californicusi in Secondary Hibernation Under Slice of Sugar Beet. iOriginal.) Fig. 2.— Beetles of the Sugar-Beet Wireworm Photographed while Feed- ing on Slices of Sugar Beet. (Original. > HABITS OF THE BEETLES OF THE SUGAR-BEET WIREWORM ILIMONJUS CALIFORNICUS' LIFE HISTORY AND HABITS. 33 preference to the dry, warmer ones. The habit of feigning death, .so marked in the spring when they appear, is totally lacking at this time, and about the only way to make them move is to touch them. When they are dug up from their pupal cells, or from the ground in which they have been hiding, they become active in a short time, look for another hiding place, and as soon as they find it draw in their legs and antennae and resume hibernation. They are very sluggish, move slowly, and do not attempt flight. APPEARANCE OF BEETLES IN THE SPRING. In the early spring, during a period which covers two months, the beetles dig out of their cells, appear at the surface of the ground, and become partially active. That the time of this "emergence" is governed by several factors is strongly suggested by the diversity in the time of appearance. The average mean temperature is prob- ably the main factor, but such causes as the kind and porosity of the soil in which they have pupated, and the rains, certainly help in determining the time of their appearance. This latter point was sug- gested by the fact that beetles were always more abundant in the fields following a rain than they were directly preceding it. This might be explained by the fact that their cells became too wet and they had to dig out for safety. Just after their appearance in the spring the beetles are very sluggish and collect under rubbish of all kinds in the field. They still appear to be in a state of semihibernation and none are ever noted sunning themselves, feeding, or moving about. When their shelters are removed they are found in the same position they main- tain during hibernation, with their legs and antennae folded closely against their bodies. When the sunUght strikes them they slowly become active and search for another hiding place. In every respect their condition at this time resembles hibernation, except that they more quickly become active. To distinguish between this condi- tion and their true hibernation in the soil, the former for want of a better word was called ^^ secondary hibernation." This period lasted from about the middle of February, or a little earlier, tiU the middle of March. It is little more than a transition period betw^een their hibernation and their period of activity. During this time the weather was quite cold, with cloudiness and showers at intervals. BEGINNING OF THE PERIOD OF ACTIVITY. The beetles are so slow to show signs of activity and so sluggish during the earlier part of their active period that no hard and fast line can be drawn between the latter and their so-caUed secondary hibernation. Furthermore, under every beet active and inactive (5140°— Bull 123—14 3 34 THE SUGAK-BEET WIEEWORM. beetles may be found side by side. Now and then, about the middle or latter part of April, a beetle is seen sunning itseK at the edge of a beet under which it had been hiding. At about this time, also, it was noted that the underside of many of the beets which sheltered beetles was roughened and had the appearance of being shredded. At first no attention was paid to this until by chance a beetle was noted feeding on an old beet, and then it was seen that the roughened places on the beet were the feeding marks of the adults. TTheneTer a beet was turned over the beetles were for the most part active (PL XVII, 'G.g. 2), but a few were still in their secondary hibernation (PL XVII, fig. 1). The feeding marks on the beets become more and more noticeable but are never especially extensive, as the adults at the period of then- greatest activity are hght feeders. Even at this time the beetles are not entirely normal in their actions. This is most noticeable in regard to the habit of feigning death, so characteristic of most of the elaterids. ^Vhen a group is exposed by removing the beet under which they have been hiding, at least haK of them move about seai'ching for shelter. This is probably due to the fact that their senses are not very acute at this time, and the}^ consider only shelter. About a month later, however, when a gToup of beetles is exposed by removing the beet shelter, most of them remain quiet for some time, even though they may happen to be in an unusual position. VARIATION IX THE SIZE OF BEETLES. Among the beetles taken in the field there was a very noticeable variation in size. (See PL I.) The length was often found to vary between 9 and 12.2 mm., and the width between 2.5 and 3.5 mm. The larger ones outnumbered the smaller ones ahnost 2 to 1, since about 15,000 of those collected could be referred to the larger size to about 9,000 of the smaller, while about 2,000 or 3,000 were so nearly on the di^^ding fine between the other two sizes that they were unclassified. At first the large ones were thought to be females and the small ones males, so it was concluded that the females out- numbered the males about 2 to 1. Such did not prove to be entirely the case, for when copulation became general some of the smaU ones proved to be females, and not a few of the larger ones were seen to be males. Everything considered, it seems that sex is quite inde- pendent of size, for the males and females were seen to occur in about equal numbers. VARIATION IN THE COLOR OF BEETLES. From the outset it was noted that there was great -^^ariation in the color of the beetles. This difterence was most noticeable on the elytra, which varied from light buff to deep brown or dusky black. LIFE HISTOEY AND HABITS. 35 There seemed to be a rather plain dividing Hne between those with the buff wing covers and those with the brown ones, so they were separated. About 1,,500 or 2,000 could be referred to the former class. Some of these were sent to Dr. Chittenden for determination, and concerning them he wrote as follows : No. 495 (?) is Limonius sp. near calif ornicus . It does not appear to agree perfectly with the californicus with which I have compared it, and is not represented in our duplicate collection. The relationship of these beetles will be worked out in the future. The true adults of Limonius californicus also varied considerably in color, as some were found which were a relatively light brown. These color variations occurred in all sizes and both sexes, so color seems to have no bearing on the sex of the adult. FEEDING OF THE ADULTS, AND FOOD PLANTS. When the beetles were first collected the character of their food was unknown, and in an endeavor to find their natural food all the different kinds of foliage found in the beet fields were tried, but with- 1 out success. Adults by the hundreds were placed in cages contain- ing tender young beet plants, and while they climbed all over the plants they were never seen to feed on them, nor could any feeding marks be found on the plants. A close watch was kept on the adults collected in the field, and at last, as has been stated before, ^ they were noted feeding on the old left-over beet roots, now half > dried and partially rotten. When these were substituted for the beet foliage in cages, feeding was begun at once. A few instances were noted where the adults had eaten into the roots to such an extent that the head and thorax were hidden. Such cases, how- ever, were rather exceptional, and the beetles may be considered as light feeders. In addition to this, their feeding, from an economic . point of view, may be disregarded. The adult has been noted feeding on the following substances: Old beet roots. Alfalfa roots ( Medicago sp. ). Johnson-grass roots (Sorghum halepense). Wild beet roots (Beta sp.). II Young beet roots. The old beet roots are the favorite food, and it is only occasionally that beetles are noted feeding on the other substances listed. The beetles seem to be able to locate food readily and at quite a distance. In the laboratory whenever a shce of beet was placed in the cages the adults would be clustered about it in a very short time. In the field the beetles were always found at the old beets and always occurred in the greatest numbers where the beets were most plentiful. 36 THE SUGAE-BEET WIEEWOEM. In one field, which had a great many old beets on the surface, the beetles were taken from under almost every on'e, and sometimes in large numbers. It was a common matter to find from 30 to 70 adults under single beets, and as many as 243 have been found hiding under one beet. Another favorite shelter was afforded by the old beet tops (PI. XVIII) left in the field from the previous year's harvest. In the field which adjoined this one there were few or no old beet tops and beets for shelter, and here beetles were rarities. This field, just the year before, suffered more than any of the surrounding fields fro m ^\ireworm in- jury, so there must have been beetles which developed from the mature wire- worms that had caused the damage. In other fields, how- ever, which had suf- fered similar injury but m wliich the old beets had been al- lowed to r e m a i n , beetles were present in 1 a r g e numbers . There seems to be only one explanation for this fact, and that is that the adults had emerged from the cleaned fields and, not finding any shelter, had been obUged to move to other fields or be destroyed by the birds. This was further indicated by the fact that all the beetles found in the clean fields were mo\nng about. The state of aft'airs was found to be the same in other fields aggregating over 600 acres, where the conditions were similar. Fig. 8. — Screen cage used in obsennng oviposition of adults of the sugar-beet Tvireworm under field conditions. (Original.) STYLES OF REARING CAGES USED. Several styles of rearing cages were used, but only a few will be considered. The ones used indoors consisted of batter}^ jars, flower- pots, and flowerpots mth lantern globes. The highest death rate was found in the first, because there was no drainao-c and the contents Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. Plate XVIII. Secondary Hibernation of the Sugar-Beet Wireworm (Limonius cali- FORNicus). Beet Tops Used by Beetles as Quarters for Secondary Hibernation. (Original.) LIFE HISTORY AND HABITS. 37 tended to become foul. The two types last mentioned were about equal in efficiency, but the main difficulty lay in the fact that they were small and it was easy to overcrowd them. The cage used most successfully was a large screen cage of the common type, kept outdoors. (See %. 8.) Within the cage were several flowerpots, buried to the level of the ground, each containing young beet plants. The soil in the pots was kept loose and damp, and the soil around the flowerpots was tamped hard. This cage was large, well ventilated, and gave the beetles plenty of room in wdiich to fly about. Its best feature lay in the fact that the beetles all de- posited their eggs in the flowerpots, since this w^as the only place where they could bury themselves easily. It this way the eggs w^ere concentrated much more than they would have been under natural circumstances. As soon as one flowerpot contained a great many eggs it could be removed and another substituted. This cage also gave natural conditions, as the soil it contained was just as damp as that in the field, and since the cage was placed in the sun and was so airy the beetles were always kept at the field temperature. The death rate was very much lower in this cage than in any of the others and there were live adults in it for some time after all had disappeared in the other cages. DURATION OF LIFE UNDER VARYING CONDITIONS. To test the duration of life under varying conditions some adults were placed in various styles of cages and others were kept under various conditions as concerned the food and water supply. Some were kept without either food or water, some with food but ^^dthout water, and some with water but ^\dthout food. In every instance the beetles lived much longer than was expected of them and proved that they are not only quite hardy but can get along on little food. One hundred and forty adults were placed in dry battery jars without food or water, and the jars were closed with gauze. The results were as follows: Eighty-two adults died in from 9 to 12 days. Forty adults died in from 12 to 14 days. Eleven adults died in from 14 to 16 days. Five adults died in from 16 to 18 days. One adult lived 20 days. One adult lived 22 days. None of the beetles was very active after the twelfth day. These conditions were much more severe than any that they might encoun- ter under field conditions. The adults kept with water but without food were also kept in battery jars. These jars contained about 3 inches of soil, and this 38 THE SUGAR-BEET WIEEWOEM. soil was kept quite damp by additions of water from time to time. This cage presented very much the condition which ^'ould hold in the field if all the food could be eUminated. Five hundred and sixty beetles were used in this experiment, with the following results : About 60 died before 10 days. About 100 died before 10-15 days. About 200 died before 15-18 days. About ] 00 died before 18-22 days. About 60 died before 22-25 days. About 30 died before 25-28 days. About 6 died before 28-30 days. About 2 died before 30-31 days. About 1 lived for 34 days. One lived for 40 days. The last 10 to die were females. Their abdomens were quite swollen, but they did not lay any eggs — at least none could be found — and when they were dissected after death the ovaries, while containmg some eggs almost mature, were quite shrunken and dr}'. None of the beetles was very active after 15 days, and after 25 dhjs they were very feeble, the last few to die being unable to walk during the last days they lived. Many adults were separated and kept in xiols and given food but no water. Care was exercised to have this food as dry as possible. Out of 78 used in this experiment only 12 died during the fu^t 15 days, and the remainder were quite active. It was so difficult to obtain the food dry enough to affect them that the experiment was discontinued. LEXGTH OF TIME ADULTS CAX BE SUBMERGED. Several adults were submerged in water m a tube and kept below the surface by a smaller tube placed within the first one. The water was perfectly clear and care was taken to remove all the air. At the end of 15 minutes the beetles had ceased to move and at the end of 20 minutes they were removed. They seemed dead, but within a few minutes were moving about actively and seemed none the worse for their treatment. Another lot was submerged for 40 minutes and within a half hour after being taken out were as active as ever. The tests were not carried further, as these were considered as severe as an}^ they would be subjected to under field conditions. Twenty adults were floated on water for 15 hours and at the end of that time onh^ three were dead. From these results it w^as concluded that a majority of the beetles could survive a severe storm. LIFE HISTORY AND HABITS. 30 EFFECT OF TEMPERATURE ON THE ADULTS. The adults of many of the eastern species have been reported by some observers as being primarily nocturnal in habits.^ Other observers record them as flying readily both by day and night. The adults of Limonius californicus seem without exception to be warm- weather insects. They not only attain their greatest activity during the middle of the day when the heat and light are at the maximum, but during the morning and evening hours they are sluggish and quiet. Some specimens were kept in the writer's room during their entire life and none was ever observed feeding or copulating at night. On the warmest nights a very few were observed moving about sluggislily, but their activity at this time can not be compared to that which occurred during the daytime and especially when the temperature was over 75° F. Several experiments were conducted for determining the direct relation between temperature and activity. The apparatus used was very similar to that used in the boll weevil investigations,^ except that instead of the outer tube a flask was used, as it was believed that this would afford more even heating. The results agreed quite closely with those recorded in Bulletin No. 51 (pp. 101-102) and an approximation is given below: 48° F. Beetles quiescent. 54° F. Few crawling about sluggishly. 60° F. Beetles all moving about. 70° F. Beetles becoming active. 75° F. More active, few flying. 80° F. Many flying. 85°-90° F. All flying, very active, seem greatly excited. 93°-94° F. Period of greatest activity. 97° F. Few becoming quieter. Seem to be suffering. 99° F. Many becoming quieter. This experiment was varied slightly by placing damp filter paper in the inner tube so that the heat would not be so dry. The new results did not differ very startUngly from the preceding, except that the beetles did not seem to suffer so much at the higher tempera- ture and seemed less excited. Under field conditions 75° to 80° F. seems to be the optimum temperature for their various activities. At 70° F. they are quite active, but few are noted in flight, especially if there is a moderate wind blowing. At 60"^ F. very few are noted moving in the fields, and these are generally close around the* beets under which they have been hiding. The beetles are always more active on bright days than on darker days, even if the temperature is the same. This 1 Comstock and Slingerland, Bui. 33, Cornell Agr. Exp. Sta., 1891. 2 Bui. 51, Bur. Ent., U. S. Dept. Agr., PI. XVI, fig. 72, 1905. 40 THE SUGAK-BEET WIREWOEM. difference in their actions caused by light was very noticeable when cages w^ere removed from the insectary and placed in the sunlight. The beetles would fly about at once and before long many pairs could be taken in copulation. Wlien the cages were replaced ia the insectary activit}" would cease as suddenly as it had begun. ABILITY OF THE ADULTS TO WITHSTAND UNFAVORABLE CONDITIONS. The adults showed remarkable ability to withstand shocks of various kinds, whether occasioned by physical injury or by sudden and unfavorable climatic conditions. A few cases noted in the field w^ill shov/ their ability to withstand physical injury. When beetles were collected in the fields individuals were noted on several occasions to have been injured by their pre- daceous enemies, Calosoma cancellaturn Esch. and C. semilseve Lee, and these were separated from the others so they could be watched. Those which had merely lost some of then legs did not seem to be in the least inconvenienced. Others which were quite severely injured managed to survive as long as most of the other beetles. One, wliich had its abdomen so nearly severed near the anterior end that it had lost one of its elytra, lived for several da^^s. As to their ability to withstand unfavorable weather conditions, it may be stated that while over 25,000 beetles were collected from the field in a period which exceeded a month, very few were found dead. During this period there were sudden and great changes in temperature and several severe rainstorms. In view of the fact that the beetles seem to be so hardy in the field, it is difficult to explain the heavy death rate which w^as noted m all the cages about the time of oviposition. It seems that they must lose much of their vitality during their later life, so that by the time oviposition is about to take place they are comparatively weak. METHOD AND TIME OF MATING. When once the adults have attahied then- normal activity the}^ mate readily during the w^armer hours of mild da3^s. Beetles were taken mating as early as March 17, 1912, and as late as April 23, 1912. Every pair taken in copulation m the field was taken between 9.30 a. m. and 3 p. m. No pau's were ever found in copulation if there was a strong wind blowing or if the sky was cloudy or the weather cold and rough. The mated pairs w^ere generall}^ found near or beneath the beets under which they had been hiding and feeding; though one pair was found in a crack in the soil, about 2 inches below the surface. Temperature has a very direct effect on copulation, as was proved by tlie laboratory experiments. Battery-jar cages, when taken from LirE HiSTOBi' AND HABITS. 41 the cold rooms, contained only semidormant beetles, but after being placed in the sun for a time the beetles very soon became active and copulation took place. When the cages were returned to the cold rooms it was only a few moments until copulation ceased and the beetles became sluggish again. The method of mating of these beetles seems to be more or less unique. The male shows no signs of excitement until he comes in contact with the female, and then he rapidly attempts copulation. After the male has assumed his position he throws himself over back- ward so that he is on his back with his body in the same line with that of the female, but pointing in the opposite direction. The male then folds his legs and antennae close against his body and remains quiescent during the operation. If disturbed the female seeks shelter, walking slowly and dragging the male after her. The duration of the process varied greatly in the cases noted, covering from 7 to 19 minutes. After the operation the male was generally noted to be much more active than the female, but was not seen to attempt copulation a second time, even where the pair were confined in a small vial for some hours. Much of the copulation attempted in the cages was unsuccessful, about nine attempts out of every ten coming under this head. When- ever several males were attempting copulation wdth the same female at the same time they were noted to fight one another. About April 1, 1912, the abdomens of the females began to swell noticeably and a close watch was kept for the eggs. Every day about six females were dissected so that the development of the eggs could be watched. The immature eggs were small and disk-shaped, being little more than half as large as the mature eggs. They ap- peared as opaque spots in the translucent jellylike ovaries, which filled quite completely the ventral portion of the abdomen. The development of the eggs was relatively slow, the greatest change appearing in the ovaries, which increased rapidly in size until at the time of oviposition they practically filled the abdomen. ACTIONS OF THE ADULTS AFTER MATING. During the last week before oviposition the females spent all their time burrowing under the soil, and were never noted feeding or on the surface. Whenever they were dug up they immediately buried themselves again. If the ground was not allowed to dry out too much the females remained active and healthy, but in several cells in which the soil completely dried out the females died . The males did nothing but feed and crawl about on the surface. They lived, on the average, from two to four weeks after mating, so it seems possible that one male might fertilize more than one female. 42 THE SUGAK-BEET WIRE WORM. In one instance, when the female in a cell had been dug up she came in contact with the male. The latter attempted copulation, but unsuccessfully. OVIPOSITION. On April 9, 1912, the first eggs were deposited. These were laid in a vial which contained several females in which the development of the eggs was more advanced. These eggs were scattered through- out the soil. In only one instance was a female noted in oviposition, and that was under unnatural circumstances. Several gravid females had been placed in a glass, on the bottom of which was about half an inch of very compact soil. This glass was placed in the dark room for several hours, and when observed again one female was attempting oviposition between the soil and the glass. The beetle thrust her ovipositor down several times, and finally the egg was placed in the bottom of the hole made by the ovipositor. The ovipositor was then withdrawn slowly and then thrust back part way several times as if the beetle were trying to cover the egg. The entire operation took but a very short time. When the soil in the cages was broken up and examined for eggs it was seen that oviposition under natural conditions must be quite similar to that observed, as eggs were found at intervals under the channel made by the digging female. By the latter part of May the females became very scarce^ as they live but a short time after laying their eggs. The males for the greater part died during about the middle of the period of oviposition. Approximate Length of the Life Cycle. Considering the length of the egg stage as one month and the length of the pupal stage as the same, these, added to the length of the life of the adult, will give from five to eight months. If, as has been stated before, the larval stage lasts for over three years, it is seen that the length of the life cycle from egg to egg would be four years. SEASONAL HISTORY. Beetles from Emergence to Hibernation. The life of the adult, from emergence, through hibernation, until their appearance after hibernation, is governed to a great extent by conditions over which the beetles themselves have no control. The greater part of the beetles emerge from the pupse about the middle of September. The beets are plowed up for the most part during September and October, so the insect is in danger of being disturbed either during the pupal stage or soon after it has changed to the SEASONAL HISTORY. 43 adult. The plowing which the land receives at this time can hardly be called a plowing, but the ground is torn up to a depth of from 6 to 12 inches. As the soil is dry, that disturbed is for the most part in large clods, so there is little chance that many pupae or adults will be disturbed. Those which by chance are disturbed are either killed outright or have to live under changed conditions until spring. If they happen to be pupse the chances must be very much against them, and they will probably either be injured by the sharp particles of dirt or will dry out. If the insects are in the adult stage they will have a better chance of survival, but here also they may be compacted into the soil and killed, or be eaten by birds, since, living under unnatural conditions, they are obliged to appear earlier in the spring than they would otherwise. Even when kept under laboratory conditions many of those disturbed in the fall can not live till the normal time of their appearance. Hibernation. The adults pass the severest part of the winter in the soil. If disturbed they winter in their pupal cells, where they are well pro- tected, as these are on the average about 6 inches below the surface. This tempers the winter for them very well, and moisture can reach them only after heavy rains, and these seldom if ever occur except at the latter part of the hibernating period. When the beetles are disturbed in the fall they dig down into the soil for shelter. The depth to which they go varies. In some cases, where the soil is powdery, they go down only about from 1| to 3 inches, but when the soil is partially made up of clods and full of cracks they are sometimes found from 4 to 6 inches below the surface. M0RTA1.ITY During Hibernation. Under ordinary circumstances and where the pupal cells are undis- turbed, a large percentage of the beetles emerge safely — at least this is so under laboratory conditions. One cage was watered and kept outdoors so that the beetles were subjected to conditions as severe as the ordinary field conditions, yet all came through safely. Of those disturbed in the fall, not enough have been tested to give representative figures, but thus far almost a third of those treated in this way have died during hibernation. Gradual Emergence from Hibernation. The time of the appearance of the beetles in the spring is influenced to a large extent by artificial agencies, the most important of which is spring plowing. This plowing, which takes place as soon as possible 44 THE SUGAE-BEET WIEEWOEM. after the &3t rains, is quite thorough, averaging from 10 to 14 inches deep, and as the soil is damp and mellow at this time very few clods are left. This treatment disturbs most of the beetles, and these, unless the weather is too severe, may come to the surface and finish their hibernation in any sheltered place they can find. If the weather is severe and cold many of the beetles prefer to remain in the soil. It is due to these conditions that there is a variation in the time of appearance of the adults, as has been proven by systematic collec- tion in the fields. Collections were made in some of the fields day after day and tabulated. The beets which sheltered adults every day were marked, and the beetles which were collected from them every day were noted. The following table gives the number of beetles which were taken from under the same beet on the dates given: Table I. — Emergence of adults of the sugar-beet u-ireu-orm from hibernation in the field. Date. Xamber of beetles. ^■'''- ""iSies."' Feb. 29 Mar 1 2 1 7 3 17 2 1 1 0 29 47 13 Mar.l2 4 Mar 13 7 Mar 2 Mar. 14 . 1 Mar.3. Mai. 4 Mar.o Mar. G Mar. 7 Mar.lo 3 Mar. 16 SO Mar. 17 11 Mar.lS 0 Mar. 19 •'> Mar. 8 Mar. 23 1 Mar. 9 Mar. 24 srt Mar.lO Mai. 11 Mar.2(i 9 As these notes were tuken before the beetles were moving through the fi.eid very generally, it appears that the latter must have come from the soil near the beets which were used for hibernating cpiarters. Secoxdary Hibeexatiox. The beetles which are driven to the surface prematiu'ely seek what may be termed "secondary hibernation'' imder ahncst any shelter which can be found. The substances in the following Hst, under which beetles were foimd, are named in about the order of prefer- ence: (1) Left-over beets. (2) Old beet tops. (3) Wild beet roots. • (4) Alfalfa roots. (5) Johnson grass roots (Sorghum hale- pense). (6) Lambsquarters (Chenopodium sp.). (7) Pigweed stalks {Amaranthus retro- flexus) . (8) Wood. (9) Clods. (10) Cracks in soil. (11) Old sacks. (12) Manure. (13) ^liscellaneoiis rubbish. SEASONAL HISTORY. 45 Items 8 and 9 (wood and clods) sheltered practically all the beetles. The last-named item included paraffin roofing, old bottles, pottery, etc. The wide diversity of this hst shows that the beetles are not very particular about the character of their shelter. It is interesting at this time to note that no beetles were taken from under charred beets or wood ashes. This point was well illus- trated in the corner of one of the fields which proved to be the choicest collecting ground. It happened that in this place a large amount of rubbish had been burned the previous year, and about haK the old beets lying about on the ground were charred. Adults were taken in numbers from this corner daily, but not one was ever found under the beets which were charred. The same thing was true of the wood ashes. The numbers of beetles taken from single beets were much larger than might have been expected. As has been stated before, as many as 243 have been taken from under a single beet, and- on one occa- sion 187 were taken from under a single beet top which was less than 3 inches in diameter. The concave top was entirely filled with the beetles, which in some places were piled from 2 to 4 deep. Occurrence of Beetles in the Field. Up to the middle of March the adults are found close to their hibernating quarters, either feeding cr sumiing themselves. At about this time, however, there is a general dispersal ( f beetles, and their collection becomes a difficult matter. Flight is of common occur- rence, as is copulation. The writer watched many beetles which were moving about the fields, to see what they were doing, but to all appearances they did nothing except wander about. Some were watched to see if they would oviposit, but nothing of this kind was noted. ^ To judge from their actions in the laboratory cages, these adults were moving about preparatory to biUTowing into the soil for oviposition. Effect of Food in the Field on Dissemination. In the latter part of their secondaiy hibernation, and before they scatter through the fields, their presence depends very much on two factors, namely, food and hibernating quarters. Once they begin moving they feed very little, and food seems to have no effect on the direction or amount of their movement. As this is, economically, the critical point in the life of the adults — since where they collect, the eggs will be laid — they were w^atched carefuUy to see if there were any factors which governed their dis- persal through the fields. The amount of food and the size cf the 1 Subsequent rearing work in the laboratory proved that this was quite too early for oviposition. 46 THE SUGAE-BEET WIREWOEM. young growing beets were carefully taken into consideration, but the significance of these points, if there is any, is too slight to be notice- able. While the beetles have quite a strong flight, it was observed that they stay relatively near their hibernating places, so the most important factors at this period are the food and hibernating quarters which determined their presence earlier. These conclusions were arrived at from observations in fields aggregating several hundred acres. These factors, however, govern dissemination under normal conditions only. Other Factors Governing Dissemination. One factor which governs the direction of flight of the adults to some extent is the wind. This factor, however, has its limitations, as the beetles can fly mth ease against a very Hght breeze, and if the ^^ind is blomng too strongly they do not fly at all. The floods which are apt to occur during the time the beetles are in secondary hibernation, or a little later, are probably of some importance — at least they must be so locally, where the San Gabriel River spreads over many acres cf the beet fields almost every year. This river flows slowly and carries much rubbish, so that a large per- centage of the beetles carried along would probably survive. NATURAL CONTROL. Enemies and Checks to the Beetles. The adults of Limonius californicus, being slow in their movements and conspicuous, are quite subject to the attacks of predaceous ene- mies. The good work of these enemies is further helped by the fact that the fields are quite bare at the time they are present in the largest numbers, while the beetles are concentrated for a part of the time. Unfortunately no figures can be given regardmg the relations between the birds of the beet fields and the beetles, but a few observed facts may be given at this time. The only notes vrhich bear on the insectivorous habits of the birds locally were taken on examination of the excrement of the California shrike {Lanius ludovicianus gam- heli) during the month of April. This excrement was made up ahncst entirely of coleopterous ^v\.ng covers, and of these LiTUonius califor- nicus and Blapstinus sp. formed about 90 to 95 per cent. A very reasonable estimate would be that at least 70 to 80 per cent of the excrement examined was composed of fragments of Limonius cali- fornicus. Many observers have determined the fact that nearly all insectivo- rous birds eat different species of Elateridse readily, as the latter do not seem to be in the least distasteful to them. Following is a partial NATURAL COKTEOL. 47 list of the birds occurring in the beet fields, which have been proven to be insectivorous.^ Those marked (*) were especially abundant: Killdeer (Oiyechus vociferus). ^ Valley quail (Lophortyx californicus vallicola). Western nighthawk (Chordeiles virginianus henryi). Ash-throated flycatcher (Myiarchus cinerascens cinerascens). * Western meadowlark {Sturnella neglecta)? * Brewer's blackbird (Euphagus cyanocephalus). * Native sparrow. * California shrike (Lanius ludovicianus gambeli). Next to the birds as insect destroyers can be ranked the predaceous beetles belonging to the family Carabidse, or ground beetles. Only two were noted, Calosoma canceUatum Esch. and C semilseve Lee, but these proved to be important factors in the control of the beetles. Both of these occurred commonly throughout southern Cahfornia. Sometimes as many as 15 to 20 would be noted in a single collecting trip. Calosoma canceUatum occurred in the greater numbers. These predatory enemies are able to dispose of a large number of adults daily, as many outdoor observations proved. In one instance the examination of a large beet gave 31 live elaterids, 1 0. cancel- latum, and the remains of 117 elaterids. This beet had been exam- ined just two days previously, so this represented not more than two days' work. The rapidity of the work may be judged from the fact that the remains of a dozen of the elaterids were still moving their legs feebly when discovered. The carabids in feeding never touch the head or thorax, but bite off all or a part of the abdomen. As the abdomen, except when filled with eggs, contains little food it is readily understood how these ground beetles are able to destroy so many elaterids a day. The carabids did most of their feeding while the elaterids were in their secondary hibernation or early feeding period. They were especially valuable at this time, as they could dig under the beets and destroy the beetles collected there. These predaceous enemies — carabid beetles and birds — make a very good combination, as the beetles are an effective check early in the season, and later, when the elaterids are moving through the fields, the birds are at their best. Sudden and very severe storms probably act as further checks, but in a mild year, such as 1912, vexy few beetles were found to have been killed in the field. The adults are also attacked by a fungous dis- ease. This disease works well under laboratory conditions, but less 1 See Senate Document No. 305, 62(i Congress, 2d Session, p. 14, 1912. 2 Mr. Bryant, in the Pomona Journal of Entomology, vol. 4, No. 3, speaking of the western meadow- lark, says, "Ground beetles are taken each month of the year." He then names Limonius californicus among those taken. 48 THE SUGAK-BEET WIREWOEM. than 0.1 per cent were affected by it in the field. These two checks are of very little importance. Enemies and Checks to the Larv^. Two characteristics of the Avireworms, their thick skins and their underground Hfe, cause them to be almost free from enemies. Of the 10,000 larvae collected not one was noticed which was attacked by an internal parasite, although such parasites have been reported attack- ing Elateridse. Curtis ^ reports an ichneumon parasite en wdreworms in Great Britain, and says that Bierkander (of Sweden) also found them. Dr. S. A. Forbes ^ reports a single instance where a parasitic fly was reared from a wireworm. Very probably there are no eflacient parasites in this group. The sugar-beet mreworm is, however, eaten readily by several kinds of birds whenever exposed. During the spring, when several of the fields at Dominguez, Cal. (6 miles from the ocean), were being plowed, it was noted that sea gulls (Larus sp.) were very abundant in the fields and followed the plow much as chickens do. They occurred by the hundreds and, as they are known to be omnivorous, they must have eaten numbers of wireworms. At this time and earher crows were also very abundant in the beet fields. During this period the wireworms were feeding at the surface on the left- over beets, and it was easy for the crows to reach them. As crows are famed as wireworm destroyers it is only reasonable to suppose that they killed large numbers of the larvae. This point ^\dll be investigated thoroughly in the future work on this insect. Larvae of a large carabid, probably Calosoma cancellatum Esch,, have been found in the ground together ^Aith injured wireworms. In addition to bird and insect enemies one fungous and two bacte- rial diseases have been noted on this mreworm. The fungus is only observed occasionally in the field, hence it is probably of little impor- tance economicaUy. The bacterial disease of the mature larva was especially disappointing, as it seemed to work only in certain cages. This naturally led to the belief that its presence was probably more the result of unfavorable conditions than the cause of them. The bacterial disease of the young larva did not promise much, as it did not seem to attack mature larvae under any conditions. As has been mentioned under the headmg ^'Rearing cages used" (p. 21), many of the young Avireworms which were kept in petri dishes died of a bacterial disease. This disease spread very rapidly, and there seemed no way to check it. Wherever it appeared, all the healthy wireworms were removed to a sterile cage and the infected cage steriUzed. The cages were examined several times a day and all 1 Farm Insects. By John Curtis, IStiO, pp. ISl. 2 ISth Rept. State Ent. 111., pp. 47, 1891-92. NATURAL CONTEOL. 49 wireworms were removed just as soon as they showed traces of the disease. In spite of all these precautions the disease spread un- checked until, within 10 days of its appearance, it had killed every wire worm in the petri dishes, to the number of about 1,000. The disease spread in the same way every time, and the wireworms kiUed by it were so characteristically colored that they could never be mistaken. When a larva became diseased, there was a very faint reddish coloration in the anterior portion of its body. When placed under the microscope, it looked as if the head and thoracic segment contained Uttle, brilliant red, oil globules. The following day the spec- imen would be a deep blood-red all over its body and so putrid that when picked up on a pin point it would fall to pieces. The larvae immediately surrounding it would show the faint red coloration and the following day they would be red and putrid, while the larvae nearest them would be showing signs of infection. When the dishes were not sterilized, all the larvae in a dish would be killed in from three to four days. That the red bacterium was the cause of the trouble was very strongly suggested by the fact that whenever one infected ware worm was placed in a sterile cage the disease immediately made its appear- ance. This was further borne out by the fact that where a whole infected wireworm was used to make a culture on agar, a pure culture of the red bacterium almost invariably resulted. When the cultures were made on agar, the colonies showed in their true color — a beau- tiful rich blood-red. (See PI. VIII, fig. 1, p. 20.) It is interesting to note at this time that the mature wireworms which were exposed to infection by this bacterium were never affected by it. Everything considered, the larvae of Limonius californicus ^eem to be affected very little by their animal enemies and by their fungous and bacterial diseases, even when these latter are working under favorable conditions. Fungi Affecting the Pup^ and Eggs. A few piipae in the laboratory were attacked by a fungus and pre- sumably kiUed by it, as they died a short time afterward. As this occurred only in two cages and as no fungus-kiUed pupae were found out of doors, it is probable that this infection only occurs under arti- ficial conditions. Even if it did occur in the fields it would spread slowly, for during the time the insect is in the pupal stage the humidity is low and the soil in the fields is rather dry. A fungus which attacked and killed some of the eggs of Limonius californicus in the rearing cages in the laboratory would probably seldom or never occur out of doors. Even if it did it would not be 6140°— Bull. 123—14 4 50 THE SUGAR-BEET WIEEWOEM. of great economic importance, for when sound eggs were isolated in the cage in which the fungus was working they were seldom attacked, showing that the fungus must spread slowly. Its appearance was probably the result of unfavorable artificial conditions. REMEDIAL MEASURES. Historical. ]\Iost of the literature thus far devoted to the study of wireworms from an economic standpoint has been a consideration of remedies. Probably no other insects have had more remedies tried for their control and with less success. Some of the remedies have been par- tially successful, but generally their cost has been such that their use for average crops is entirely impractical. One which would come under this head was a method tried on a small scale in Europe some time ago and consists in baitmg the wireworms and collecting them. Eleanor A. Ormerod/ studying several species, gave as remedies (1) compacting the ground, (2) clearing off vegetation, and (3) making appUcations of gas Hme. vShe stated that crop rotation was of little value. John Curtis ^ suggested as remedies frequent plowing to turn up the larvae, and appUcations of soot and lime. Mary Treat,^ writ- ing on these insects, suggested spring and fall plowing and the trar>- ping of larvae. Fall plomng as a remedy was recommended by C. M. Weed.^ The two most important sets of recommendations based on actual exhaustive experiments and careful study were those of Comstock and Shngerland ^ at Cornell and S. A. Forbes ^ in Illinois. Their recom- mendations are quite different, Forbes suggesting a careful rotation of crops, while Comstock and Shngerland advise fall plowing for the destruction of the pupae and trapping the adults with poisoned bait. Tests of Suggested Remedies Against the Sugar-Beet Wire- worm. In testing remedies for the sugar-beet wireworm only those were tried which heretofore had promised at least partial success and which were at the same time thoroughly practical. attempts to destroy the adults with poisoned baits. Experiments with poisoned bait w^ere carried on against the adults, using the bait much after the method suggested by Comstock and 1 Manual of Injurious Insects and Methods of Prevention. By E. A. Ormerod, 1890, pp. 109. 2 Farm Insects. By John Curtis, 1860. 3 Injurious Insects of Farm and Garden. By Mary Treat, 1882. ^ Insects and Insecticide j. By C. M. Weed, 1891. 5 Bull. 33, Cornell ^gr. Exp. Sta., 1891. fi 18th Kept. State Ent. 111., 1891. REMEDIAL MEASURES. 51 Slingerland.^ These experiments from the first gave entirely nega- tive results, as the beetles could not be induced to feed on any kind of foliage, either in the poison or check cages. Further experiments were carried on, using such substances as bran, shorts, alfalfa meal, and ground beet roots. The last bait was the only one which gave any promise, and this proved successful only under laboratory conditions. Where the poisoned bait was applied in the cages a few beetles were killed by it, but where it was tested in the field it gave negative results. This was probably on account of the light , feeding habits of the adults and the abundance of food in the fields. The poisons used in the bait were Paris green, arsenite of zinc, arse- nate of lead, and strychnine. FALL PLOWING FOR DESTRUCTION OF THE PUPJE. The destruction of the pupse by cultivation, while probably it has never been tested under field conditions, has been recommended b^^ many students of this group because it is directed against the most helpless stage of the insect. From observations made of the results obtained by disturbing pupae in the laboratory cages, there can be no doubt that this remedy would prove beneficial, since not only would it break open many cells and kill the pupae mechanically, but 3't would also disturb the rest so that they would come out earlier in the spring and be subject to the attacks of their bird enemies. This fall plowing would have to be quite deep (9 to 10 inches), and very thorough, to be effective. The main objection to this remedy is that three or four years must elapse before the benefits derived from it become apparent. One point will serve to illustrate this. It was reported through Mr. R. S. Vaile, the horticultural commissioner of Ventura County, Cal., that in one instance, in a field which had been fall-plowed, the wireworms were worse than in any of the surrounding fields. This was doubtless true, and would have been possible had the plowing killed every pupa. The wireworms which do the main damage for at least the next two years are already in the soil at the time of the plowing and are unaffected by it. This is true because the wire- worms are not of sufficient size to be very injurious until the third year. Mr. Vaile states that it is a rule with many of the bean grow- ers in his county to fall-plow their fields; and that any benefits which might have resulted from such a treatment have never been notice- able. He adds, however, that the thoroughness of this plowing might be improved upon in many cases. 1 Bui. 33, Cornell Agr. Exp. Sta., 1891. 52 THE SUGAR-BEET WIEEWOEM. EXPERIMENTS WITH DETERRENTS AGAINST THE WIRE WORMS. A fairly exhaustive series of experiments was carried on, using repellent substances against the larvae. While some of these experi- ments are a repetition of the work done by Comstock and Slinger- land, the greater number are rather an addition to their work. From the start tliis work promised little, but was undertaken because, if successful, it would afford a remedy which would give immediate results, and this is most important with this insect. | A system was adopted regarding both the nature of the expeii- J ments and the times of application. Three tests were given each experiment in the spring, when the larvae were most active, and a 4 test was given in the fall just before their hibernation period. The last one was on a small scale and was carried on merely for the sake of added evidence. Flowerpots were the cages used in the spring experiments. It was found that if the hole in the bottom was stoppered with cork, none would escape in the time of the experiment. It was also noted that where about half an inch of dry soil was placed on top of the damp soil of the cages the wireworms would never come entirel}^ to the surface. This treatment, then, allowed the flower- pots to be buried to the surface of the soil out of doors, and with the exception that the larvae were a little crowded it gave outdoor conditions. In the first test of each experiment 50 larvae were used and the test covered 20 days. In the two remaining tests in the spring 25 i larvae were used each time and the experiment was allowed to run for 30 days. In the experiments with deterrents the following sub- stances were tested: (1) Carbolic acid. (2) Carbolic emulsion. (3) Turpentine. (4) Kerosene. (5) Kerosene emulsion. (6) Whale-oil soap. (7) Potassium cyanic! solution. (8) Potassium cyanid solid. (9) Copperas solution. (10) Copper sulphate. These deterrents were used on beet and lima-bean seeds, both of which are attacked by this species. It was hoped that in these ex- periments a deterrent could be discovered for protecting the tender roots until the plant had secured a fair start. If this could be ac- complished the injury due to wireworms would be materially lessened. (11) Potassium sulphid solution. (12) Tar water. (13) Ash water. (14) Nicotine sulphate. (15) Free nicotine solution. (16) Cresol (so-called coal-tar creosote). (17) Salt solution. (18) Lead chromate. (19) Dry sulphur. :^ REMEDIAL MEASURES. 53 CARBOLIC ACID. Some seeds were soaked in a 10 per cent solution of carbolic acid overnight, were allowed to dry for some time, and were then planted in the pots. Fifteen were planted in the cage which contained the 50 larvae. This cage was broken up in 20 days and examined, with the following results: Two seeds were destroyed before germination; seven after germination, and six were untouched; three larvae were dead. In the check cage three seeds were untouched; most having been destroyed just after germination, and one larva was dead. The check cages gave even less favorable results, so it seems clear that the carbolic acid has little effect as a deterrent. CARBOLIC EMULSION. Carbolic emulsion was made by using the following ingredients in the proportions named : ^ Crude carbolic acid gallons . . 5 Whale-oil soap pounds . . 40 Water (hot) gallons . . 40 The seeds treated were soaked in this emulsion overnight. After drying ^ in the sun for two hours they were planted. The results of the experiments are summarized in the following table: Table II. — Experiments with carbolic emulsion as a deterrent againU the sugar-beet wireworm . Larvae used. Seeds used. Seeds attacked. Seeds un- touched. Dura- tion of test. Before germina- tion. After germina- tion. i Experiment 50 50 25 25 25 25 15 15 10 10 10 10 2 10 1 4 3 4 7 3 7 6 5 2 6 2 2 0 2 4 3 1 3 2 1 5 0 1 0 I 0 Days. 20 Check 20 Experiment 30 Check .... 30 Experiment 30 Check 30 A glance at the foregoing summary shows that while carbolic acid might possibly be of value, it can not at this time be considered a practical remedy for wireworms. TURPENTINE. Seeds were soaked overnight in turpentine and after being allowed to dry were planted in the cages containing the wireworms. The turpentine had affected the seeds considerably and all of them were more or less ''blistered.'' ' Essig, Pomona Journ. Ent., vol. 2, no. 3, p. 252, 1910. 2 The seeds were dried in these experiments because, if used under field conditions, they would have to be treated in this manner before they could be used in a beet planter. This would be the only practical way the emulsion could be applied. 54 THE SUGAE-BEET WIREWORM. Table III. — Experiments with turpentine as a deterrent against the sugar-beet ivireworm. Larvae used. Seeds used. Seeds attacked. Seeds un- touched. Larvae missing. Larvae kiUed by fungus. Before germina- tion. After germina- tion. Dura- tion of test. Experiment Check Experiment Check Experiment Check 50 50 25 25 25 25 15 10 10 10 10 10 3 3 4 5 8 5 1 2 0 3 7 8 3 3 2 0 0 \ 4 0 0 0 1 2 1 Days. 20 20 30 3a 30 30 A glance at columns 6 and 7 of Table III shows that there is little difference between the treated and untreated seeds — too little to promise much for this method. KEROSENE. Kerosene was given a trial as a deterrent in spite of the fact that it gave negative results in the experiments of Comstock and Sliugerland. The seeds were treated by soakiug in kerosene overnight. The kero- sene in some instances removed part or all of the skin from the seeds. The results are summarized below. Table IY. — Experiments tvith kerosene as a deterrent against the sugar-heet wireicorm. Seeds attacked. Seeds un- touched. Larvae missing. Larvae killed by fungus. Diu-a- tion of test. Larvae Seeds used. ! used. ! 1 Before germina- tion. After germina- tion. Experiment 50 50 25 25 25 25 15 15 10 10 10 10 8 12 8 10 7 8 3 1 1 0 1 2 4 2 1 0 2 0 2 0 1 4 0 0 2 6 0 1 0 0 Days. 20 Check 20 30 Check 30 30 Check 30 This table shows that while treated seeds are a little less liable to attack before germiuation yet in the long run there is little difference between treated and untreated seeds. Germination tests carried on at the same time show that kerosene kills some of the seeds, so this would at least offset any benefits which might possibly be derived by protection. KEROSENE EMULSION. As the pure kerosene showed a weak tendency to keep the wu-e- worms away temporarily it was thought that if some distasteful sub- stance w^ere mixed with it the combination of the two might be more successful. To this end kerosene emulsion was prepared by using whale-oil soap. The seeds were soaked in this overnight and then KEMEDIAL MEASURES. 55 dried in the sun. The seeds did not dry thoroughly and tended to adhere to one another. This would be a great disadvantage, as it would be hard to run these treated seeds through a planter. The following summary further shows its impracticability: Table V. — Experiments udth kerosene emulsion as a deterrent against the sugar-beet wireworm. Larvae used. Seeds used. Seeds attacked. Seeds un- touched. Larvae missing. Larvae killed by fungus. Dura- tion of test. Before germina- tion. After germina- tion. 50 50 25 25 25 25 15 15 10 10 10 10 G 10 0 4 6 4 2 3 3 6 3 2 2 7 \ 0 1 0 2 2 5 2 1 0 0 0 0 Days. 20 Checlc 20 Experiment 30 Check 30 30 Check .. 30 WHALE-OIL SOAP. The seeds used in the whale-oil-soap experiment were treated in two different ways. At first they were coated with the soap, but this method proved impractical (1) because the seeds could not be used in a planter and (2) because they tended to rot. The seeds were then treated by soaking in a concentrated water solution of the whale-oil soap. This second method overcame the objections to the first method. The results are summarized below. Table VI. — Experiments with ivhale-oil soap as a deterrent against the sugar-beet wire worm. Larvae used. Seeds used. Seeds attacked. Seeds un- touched. Larvae missing. Larvae killed by fungus. Dura- tion of test. Before germina- tion. After germina- tion. Experiment 50 50 25 25 25 25 15 15 10 10 10 10 10 12 4 10 fi 8 2 1 3 0 4 2 3 t 0 0 0 0 0 0 0 6 Days. 20 Check 20 Experiment 30 Check 4 1 1 ! 0 0 1 30 Experiment Check. 30 30 This table shows that the treatment of the seeds with whale-oil soap holds little promise of success. TAR WATER. Since satisfactory results in seed protection by coating the seeds with tar have been reported, it was thought possible that similar results might be obtained by soaking the seeds in tar water. In this way it should give the benefits of coating the seeds with tar, 56. THE SXJGAK-BEET WIEEWOEM. and at the same time not have the disadvantage of causing the seeds to rot. This water is procured by allowing a mass of coal tar or pine tar to stand in water for some time. The water becomes slightly colored and smells very strongly of tar. A very little tar will suffice for treating a large amount of water. The seeds were treated by allowing them to soak in this water overnight, and they were then planted. They smelled quite strongly of tar even after they were allowed to dry partially. The results obtained are shown m the following summary: Table YII. — Experiments ivith tar ivater as a deterrent against the sugar-beet wireivorm. Larvae used. Seeds used. Seeds attacked. Before After germina- j germtna- Sseds un- touched. Larvse missing. Larvse Dura- killed by I tion of fungus.' ! lest. Experiment. Check Experiment. Check Experiment. Check Days. In spite of the fact that the table seems to indicate that tar water is ineffectual, this method is to be given a more extensive trial next spring. ASH WATER. Ashes have Ions: been used and recommended as a deterrent against various insects, and especially wireworms. It has been mentioned previously that the beetles appear to be driven out by ashes. About the only way that ashes could be used on a large scale would be to soak the seeds in water which had been used to leach out ashes. This method was used, the seeds being partially dried before planting. The following summary shows that any benefits which might have been derived from the use of this method are too small to be of much importance. Table VIII. — Experiments trith ash water as a deterrent against the sugar-beet wireworm. Larvae used. Seeds attacked. Seeds un- touched. Larvae missing. Larvae killed by fungus. Dura- tion of test. Seeds used. Before germina- tion. After germina- tion. Experiment Check Experiment Check Experiment Check 50 50 25 25 25 25 15 15 10 10 10 10 5 10 6 4 7 4 5 2 2 ti 1 2 5 3 2 0 2 4 0 2 1 ! 0 7 0 2 1 0 2 1 5 0 Days. 20 20 30 30 30 30 EEME0IAL MEASUEES. 5Y NICOTINE SULPHATE. Some seeds were soaked overnight in nicotine sulphate and dried before planting. This sulphate, which is advertised to contain 40 per cent nicotine, is a dark, viscous liquid and smells very strongly - of nicotine. When used pure it tended to rot many of the seeds- The best germination results were obtained when it was diluted ' about one-half with water. The summary shows that it could not be recommended as a deterrent. . Table IX. — Experiments ivith nicotine sulphate ns a deterrent against the sugar-beet W ivireivorm . Larvae used. Seeds used. Seeds attacked— Seeds un- touched. Larvae missing. Larvae killed by fungus. Dura- tion of test. Before germina- tion. After germina- tion. 50 50 25 25 25 25 15 15 10 10 10 10 8 10 6 10 8 7 3 2 0 2 0 0 0 0 1 0 1 4 0 0 2 1 1 1 (i 0 Days. 20 Check Experiment 20 30 Check 30 30 Check 30 free nicotine. Seeds were soaked in nicotine solution overnight. This fluid, which contains free nicotine in water, has a very sharp nicotine odor and is also 40 per cent nicotine. As the results obtained in two out of the three tests were negative, its value as a deterrent must be slight. Some of the bean seeds were riddled by the wire worms. The results are shown below: Table X. — Experiments tvithfree nicotine as a deterrent against the sugar-beet wireworm. Larvae used. Seeds used. Seeds attacked — Seeds un- touched. Larvae missing. Larvae killed by fungus. Dura- tion of test. Before germina- tion. After germina- tion. Experiment Check. 50 50 25 25 25 25 15 15 10 10 10 10 4 3 3 5 4 7 4 3 2 2 2 4 8 4 3 1 4 0 0 3 1 0 5 3 0 0 1 2 0 Days. 20 20 Experiment 30 Check 30 30 Check. . 30 CRESOL. Cresol, so-called coal-tar creosote, was tried in these experiments because it is used quite successfully in keeping dermestid larvae out of collections. It is a thin liquid, rather dark in color, and with a strong tarry odor. The seeds were soaked in it overnight. The 58 THE SUGAE-BEET WIEEWORM. results, which are summarized in the following table, do not promise much for the use of this substance in protecting seeds. Table XI. — ■Experiments with cresol as a deterrent against the sugar-beet ivireworm. Larvae used. Seeds used. Seeds attacked— Seeds un- touched. Larvae missing. Larvse killed by fungus. Dura- tion of test. 1 Before After germtna- germiua- tion. tion. Experiment Check 50 50 25 25 25 25 15 15 10 10 10 10 8 10 6 4 5 7 3 2 2 6 4 3 2 0 1 0 2 1 0 0 0 2 1 Days. 20 20 30 Check. 30 Experiment Check 1 0 0 4 30 30 OTHER SUBSTANCES TESTED AS DETERRENTS. The other deterrents will be considered very briefly, since, with the possible exception of two, none gave much promise of ultimate success. Copperas solution.— Seeds soaked overnight in a copperas solution, dried, and planted in the pots were almost as readily eaten as those in the check cages. Copper sulphate. — Copper sulphate did not give much promise as a deterrent, as the seeds soaked in a solution of it overnight were eaten readily by the ^vire worms, and with apparently no ill effects. Potassium sulpTiid. — Seeds treated with a concentrated solution of potassium sulphid appeared neither distasteful nor injurious to the wireworms. Salt. — The seeds treated by soaking in a salt solution seemed for a time to be partially immune to the attack of wireworms. By the time several tests were completed, however, it was seen that while they were more immune from attack just before germmation, enough were killed just after germination to make this procedure useless from a practical standpoint. Sulphur. — Some seeds were coated with, a paste made of equal parts of sulphur and flour, and after being allowed to dry were planted. When examined later many had rotted and the rest had been riddled by the wireworms. Some of the larvse were partially covered with sulphur, but did not seem in the least inconvenienced. It was con- sidered that this experiment would give negative results, since the sulphur, kept under the damp cool soil, would not give off fumes to any extent, and hence its best effect would be lost. Lead chromate. — Seeds treated as in the foregoing experiment, but using lead chromate in place of sulphur, were not protected in the least, nearly every seed being drilled through in several places. EEMEBIAL MEASUKES. 59 THE USE OF POTASSIUM CYANID AGAINST THE WIREWORMS. Potassium cyanid was one of the first remedies tested for the wire- worms, because it has the properties both of an excellent deterrent and a deadly poison. Used as a deterrent, the seeds were treated in two different ways. In the first the cyanid was used as a solid and drilled in with the seed. This method affords excellent protection to the seed, but the drawbacks connected with it have thus far made it impracticable. The cyanid burns the seed wherever it comes in contact with it, and when germination begins, it burns the tender roots. Another argument against its use for this crop is its cost. In the second method of seed protection the seeds were soaked over- night in a solution of cyanid in water, dried, and planted. In this method it was also quite effective as a deterrent, but unfortunately its effects on the roots were such that it could not be used. At the present time it seems very doubtful if the cyanid can be used in such a strength that it wiU keep away the wire worms and at the same time not harm the plants. This point is going to be tested further. While these experiments were being carried on it was noted that in some of the cages most or aU of the wireworms had been killed. These larvae had the appearance of having been kiUed by a fungus, but as their bodies were not filled with the fungus it w^as apparent that they had been killed in some other way. It was thought that perhaps they had been killed by the fumes of the cyanid, and later experiments seemed to bear out this point. With this in Adew, many experiments were carried on in an attempt to discover some good method for the application of the cyanid. From these, two plans were selected for final trials, one in which the cyanid was used as a solid, and the other in which it was used as a liquid. The results are given below. According to the first plan the cyanid was drilled into the ground much after the method used for fertihzers. This plan was finally given up, as the cyanid was not distributed evenly through the soil, and therefore had to be applied more heavily than was necessary in order to be effective. As the cyanid is very destructive to plant growth it is readily seen that it would have to be used as sparingly as possible. The method of using the liquid consisted in making a solution of the cyanid in water and applying it evenly over the land. This could then be made to permeate the soil to any depth by irrigation. By this method the cyanid is used sparingly, as it is evenly applied. Unfortunately it has been impossible to try this remedy thoroughly, up to the present time. In all the experiments where this method was employed its killing power was very good. To test it further, it was applied in a cage containing beets, with the result that both 60 THE SUGAE-BEET WIREWORM. beets and wireworms were killed. It was used several times more, and in weakened solutions, but invariably the results were the same. By this time the season was so far advanced that experiments along this line had to be given up for the year. The conclusions that seem justified from this experiment at the present time appear to be that the wireworms may be killed by applications of a solution of potassium cyanid to the soil, but that the beets are also killed by the same treat- ment. It is a question whether a certain strength of cyanid can be found which wiU kill the wireworms and spare the beets. Possibly, however, the wireworms can stand a stronger application of the cyanid than the beets can. As this is the only insecticide which has given promise of good results against the wireworms, it will receive further careful tests. The possible effect of this cyanid on the soil and future crops is also an interesting question, and one which will have to be investigated. There is a possibility that this cyanid might be applied directly after the crop is removed and before the wireworms have become dormant for the winter. EXPERIMENTS WITH POISONED BAIT AGAINST THE WIREWORMS. In the experiments in the use of poisoned bait against the wire- worms the points which were chosen for solution were, (1) to find a substance for the bait which would be very attractive to the wire- worms, and (2) to find a poison to go with it which would certainly kill the larvae. Thus far success has not been attained in the solution of either. The following materials have been experimented with as bait: Beans. Bran. Com. Alfalfa meal. Commeal. Shredded beets. Of these the only ones which have proved attractive enough to be used with the poisons were beans, corn, and shredded beets. Series of experiments were conducted using each bait with every poison, and checks were employed in each. The following poisons were used: (1) Lead chromate. (4) Paris green. (2) Potassium cyanid. (5) Lead arsenate. (3) Strychnine. (6) Zinc arsenite. The first four named, being insoluble, were applied to the bait in paste form with flour. In the case of every poison except the cyanid the wireworms were observed eating the bait, and if they suffered any ill eifects from it they failed to show it to a noticeable degree. The bait containing the cyanid was eaten sparingly on account of its deterrent qualities. Wireworms were found dead in some of the cages in wliich potassium cyanid was used, but whether their death Bui. 123, Bureau of Entomology, U. S. Dept. of Agriculture. Plate XIX. FiQ. 1.— Field of Young Beets at Age when they Begin to be Partially FROM Severest Injury by the Sugar-Beet Wireworm. (Original.) Safe Fig. 2.— Beet Field, Showing Conditions Favorable for Increase of Wire- worms. Weed Hedges which Shelter Adults in Secondary Hibernation. (Original.) j|. 123, Bureau of Enlomology, U. S. Dept. cf Agricul-ture. Plate XX. u. < < 2 > 2 < 2 o ~ q: Q O LU Q s I- cc < o o 5 -I > « CO t- 5ul. 123, Bureau of Entomology, U. S. Dept. of Agriculture. Plate XXI, -I cc ^ >- CQ < UJ CO UJ u < \- =) h- o « zO. < o of Entomology, U, S. Dept. of Agriculture. Plate XXil. Bui, 123, Bureau of Eirtomology, U. S. Dept. of Agricultur Plate XXIII. Fig. 1.— Beet Fields Separated By Strip of Alfalfa. (Original.) i; It r^ ^^J' -/, ' "" - ':^* -T' >•' * B ^^K. '-•V-T