SB 818 eS 7 ENT 8 No. 43, SECOND SERIES. United States Department of Agriculture, DIVISION OF ENTOMOLOGY. THE DESTRUCTIVE GREEN PEA LOUSE. (Nectarophora destructor Johns.) RECENT INJURY. One of the most destructive and troublesome insects of recent years is a little green plant-louse which, from its injuries to peas, is known as the destructive green pea louse. Since it first attracted attention by its ravages in May of 1899 it has steadily increased in injuriousness, and has been the cause of great loss in the principal pea-growing regions of this country, especially where peas are grown for canning. It was, in fact, one of the most important of all insects that ravaged crops in the United States during the seasons of 1899 and 1900, and there appears to be little prospect, unless the unforeseen happens, of any decrease in its devastations. On the contrary, it is to be expected that it will widen its range geographically, as it has apparently already done to some extent. DESCRIPTIVE. This plant-louse is one of unusual size among those found infesting gardens, and the largest of the green species which attack the pea and related plants. The length of the body of winged, viviparous females is about i’¢ inch (4.5 mm.), and the total wing expanse about 7° inch (9 to 11 mm.). The general color of both the winged and apterous or wingless forms is uniform pea-green, the same color as the insect’s favorite food plant.! ! The eyes are prominent and reddish brown in color. The antennz are lighter than the body and the tubercles prominent; the joints are darker than the rest of the segments, the seventh joint filiform and fuscous. The legs are long and conspicuous; tarsi, distal ends of tibisze, and femora fuscous. The nectaries are fuscous at the tips, otherwise of the same color as the body. Note.—Several more or less comprehensive articles have been published‘on this insect, notably by Messrs. Johnson and Sanderson, of the Maryland and Delaware Agricultural Experiment Stations respectively, as well as by the writer. The for- mer gave it the scientific name which is used here, but the latter has recently given reason to show that this insect is in reality a European form known as Nectarophora pist Kalt. The question of the identity of the species, as well as other technical details, are necessarily excluded in the present circular, which is prepared as an aid to the correspondence of this office and is drawn, in the main, from matter already made public.—F. H. C. 2 A typical winged female of this insect is shown in figure 1 with wings expanded, showing venation at a, and a lateral view of the same with wings folded in their natural position when the insect is at rest or feed- ing is presented at b. Ate an apterous or wingless form of the insect is shown, and d illustrates the nymph in its last stage. The structure of the third antennal joint of the winged form may be seen at e highly magnified. DISTRIBUTION. From the fact that this species had remained unrecognized until 1899, and has not been found elsewhere than in the United States, the con- clusion was reached by some writers that it is indigenous to this country. Fic. 1.—Nectarophora destructor: a, winged female; b, same from side with wings folded in natural position when feeding; c, apterous female ; d, nymph in last stage; ¢, third joint of antenna of winged form—a-d, much enlarged, e, more highly magnified (author's illustration). Although this may be true, there are better reasons for believing it to have been introduced from abroad, probably from Europe, one being that injury of the severity noted by a species hitherto unrecognized as distinct from others of its kind is almost without a parallel in the his- tory of economic entomology. It seems probable, therefore, that we have in this pea louse a case analogous to that of the European gypsy moth, which was present in this country for about twenty-five years before it became a pest. The first notice of severe attack to pea that can with positiveness be attributed to the destructive green pea louse was reported to this office, in a letter dated May 16, 1899, by Mr. Thomas Bridges, Bridges, Va. 3 This was followed within the next few days by reports from Virginia and Maryland, and soon afterward injury was recognized in other States and Canada. During the previous season (1898), however, this pest was present in some numbers in certain fields in Maryland and was noticed on late peas in New Jersey. From present information it seems that this insect has been gener- ally injurious during the years 1899 and 1900, although somewhat locally in some States, from Noya Scotia south to North Carolina and westward to Wisconsin. At the time of writing, the insect’s occurrence in destructive abundance has been noted, by correspondents of this office, in Nova Scotia, New Brunswick, and Ontario, Canada; Maine, Vermont, Massachusetts, Connecticut, New York, New Jersey, Penn- sylvania, Delaware, Maryland, District of Columbia, Virginia, North Carolina, Michigan, Ohio, Illinois, and Wisconsin.! Injury to peas in the State last mentioned was not noticed prior to 1900. EXTENT OF INJURY AND METHOD OF WORK. This pea louse during the first season of its abundance overran and laid waste fields of peas from Nova Scotia and Maine to Virginia and Maryland, in the last as well as in some neighboring States destroying about 50 per cent of the annual output and doing similar injury the following year, in spite of the vigorous efforts that were made to control it. An estimate of the total loss for the year 1899 along the Atlantic Coast States reached the sum of $3,000,000. During 1900 the loss over the same area was placed as early as June 15 at $4,000,000. Sev- eral cases of severe damage were reported in Maryland, in which 80 or more per cent of the peas on farms of 500 or 600 acres were completely destroyed. In short, the pea growers of the Atlantic region and westward as far as Wisconsin suffered very severe losses, which gave rise to the expression that this country had been visited by a veritable scourge. The reasons why the species has become so conspicuous a pest are threefold—First, because of its ravages to a crop hitherto little troubled by insect attack, if we except the pea weevil, which has always been present in gardens and fields for upwards of a century and has come to be looked upon as a necessary evil; second, because it is a species never before noticed, so far as records go, as having been destructive to peas in this country; third, because of the great diffi- 1Mr. Sanderson has also recorded the species (assuming its identity with N. pist) as occurring in Minnesota and Nebraska. There is evidence that this species was observed on crimson clover in Delaware as early as 1890, and has perhaps been present along the Potomac River since, or prior to, 1886 (Bul. No, 26, n. s., Div. Ent., U. S. Dept. Agr., pp. 58, 72). t culty that has been experienced in its treatment, pea growers during the first year of its ravages having met with nearly complete failure in the remedial measures applied. Although garden and field peas are the crops most injured by this plant-louse, sweet peas, red and crimson clover, as well as vetches and tares! are affected, and in some cases have been damaged. Attack begins on the young vines; the lice gather in clusters at first under and within the terminals, and as the leaves become covered they attack also the stems, and by their numbers and voracity sap the life of the plant. Whole areas of vines are frequently seen cov- ered with the lice, which in a very few weeks are able to destroy a crop. Attack is seldom noticed until May? in the more southern States in which the insect is found, and a little later in its more north- erm range. The complete life history of this species is not known, but like other plant-lice it produces many generations each year. According to present knowledge, the pea louse hibernates on clover, particularly crimson clover, from Delaware southward. In the Dis- trict of Columbia it winters also on vetch. From these plants the lice spread by flight in April and May to peas, which they attack while young. As with other plant-lice, the females at certain perrods produce living young. These attain maturity in from ten to fifteen days, and possibly in less time in the hottest weather. Young that were born March 4 reached full maturity (winged form) March 16, or twelve days from the time of birth, and reproduced young three days later. As an instance of the rapid reproductive powers of this insect, Pro- fessor Johnson’s estimate is interesting. He states that females produce from 110 to 120 young; and that in one case where lice were observed on the first of May the fields were abandoned on account of ravages three weeks later. Calculating from the average number of insects produced each day, which is six, one individual would become the pro- genitor of 423,912 of these lice. NATURAL ENEMIES. The efficiency of natural agents in the destruction of plant-lice is so well known that it has been hoped that some one or more of the many species observed to attack the destructive green pea louse would 1A considerable number of aifennate food eat naa ee nena for Nectarophora pisi Kalt. in Europe. 2 The present year (1901) Mr. Samuel R. Haynes, Portsmouth, Va., reported the presence of this species in that locality about April 7. During the second week of May the writer found the insect numerous on crimson clover and vetches at Washington, D. C., and May 14 it was reported at work upon peas in the District of Columbia, near the Maryland State line. On increase in such numbers as to have an effect upon limiting its multi- plication. In spite, however, of the closest observation by a number of persons, the natural enemies have been found to produce only tran- sient relief, and this only in limited areas, as a rule late in the season, after damage has been accomplished. The present list of insects known to attack this plant-louse includes seven species of ladybirds, or “lady bugs’’ as they are familiarly termed,! three species of syrphus flies,” a lace-winged fly,’? a soldier beetle,t and a few minute four-winged hymenopterous parasites.” The ladybirds are destructive both as beetles and larvee; the syrphus flies only in the larval con- dition, which is true also of the lace-wing fly. The ef- ficiency of the syrphus flies is greatly curtailed by the { presence of a Braconid par- | asite,® which has been very prevalent during the last two seasons, sometimes al- most completely extermi- nating its host in many fields. Nearly all of the Fia. 2.—Megilla maculata : a, larva; b, empty pupal skin; species observed are well- c, beetle with enlarged antenna above—all enlarged (author’s illustration). known enemies of other plant-lice, and in fact greatly prefer as hosts the cabbage plant-louse and species found on weeds to this pea louse. The spotted ladybird (Megilla maculata) and a lace-wing fly (Chrysopa oculata) are shown in their different stages in figures 2 and 3 respectively. In addition to the natural enemies that have already been enumer- ated, several other insects attack this pea louse, among others a small, red mite (Rhyncholophus parvus Banks). Considering the inefficiency of all other natural agencies, if we except atmospheric conditions, in the control of this pest, it is hoped that a common fungous disease of plant-lice, known as Hmpusa aphidis, may become an important factor. As the development of this fungus is dependent upon rather warm, humid weather and is retarded by drought, it is fairly certain that atmospheric conditions, after all, are most 1 Coccinella novemnotata, Hippodamia convergens, Megilla maculata, Hippo- damia glacialis, Adalia bipunctata, Hippodamia 13-punctata, Coccinella san- guinea. *Allograpta obliqua, Syrphus americana, Spherophoria cylindrica. 3Chrysopa oculata. ‘4 Podabrus rugosulus. ° Aphidius washingtonensis, A. fletcheri, Praon cerasaphis, Isocratus vulgaris. © Bassus latorius. In the above list the species of each class are named in approximate order of abundance in Maryland, Virginia, and District of Columbia, and consequent efliciency as destroyers of the plant-louse in that region, 6 important in the limitation of this insect. It is within the bounds of possibility that the fungus might be cultivated artificially and be used, when weather conditions are favorable, in the control of this pest. METHODS OF CONTROL. In some instances natural enemies of this plant-louse have done efficient service. Seldom, however, do they destroy the insects suf- ficiently early in the season to save a crop. In the course of time, | v? Dy WE LULL a Fia@. 3.—A lace-wing fly (Chrysopa oculata): a, eggs; b, full-grown larva; ec, foot of same; d, same devouring pear-tree psylla; e, cocoon; f, adult insect; g, head of same; h, adult, natural size— all enlarged except h, which is natural size (from Marlatt). many years in all likelihood, these enemies may become more effect- ive; hence, in view of the fact that the extermination of the species even in a limited area is a practical impossibility, anything that can be done that will destroy the louse without harming its insect enemies is advisable. If this is to be accomplished it affords in itself a reason for the rejection of insecticides, none of which are in all respects satisfactory. ! Kerosene-soap emulsion, a standard remedy for plant-lice, care- fully prepared and diluted with about twelve parts of water, and ' For the benefit of some persons who are not wholly familiar with the feeding habits of this species it should be stated that it obtains nourishment by suction, and can not therefore be reached by means of internal or stomach poisons such as Paris green and other arsenicals. ~I sprayed upon the infested plants upon the first appearance of the lice, and so applied that the leaves are wet on both the under and upper surfaces, has thus far been found to be the most effective of the insecti- cides tried. A stronger solution than that specified is apt to scald the plant, particularly while the vines are young and tender. Sprays of whale oil and other soaps have been found less useful. The cost of the kerosene emulsion remedy, however, and the difficulty of under- spraying, its rapid evaporation, and the necessity of frequent applica- tions. are such as to hardly warrant its use. The brush and cultivator method.—The best remedy that has yet been devised is the growing of peas in rows sufliciently wide apart as to admit of a one-horse cultivator between them. The lice are brushed from the plants with boughs of pine with their leaves on, and a cultivator then follows down the rows as soon afterward as possible. For the perfect success of this method it should be practiced in the heat of the day, when the ground is dry and hot, and the repetition of the brushing is necessary every three to seven days until the crop is ready for picking. Such lice as are not buried in the ground by the cultivator will be killed by the dust which closes their breathing pores, while a considerable proportion is destroyed also by the force of the brushing. This method has the advantage of not being so destructive to the natural enemies as other means that might be employed, the louse being more fragile and delicate than any of its insect enemies. Moreover, peas planted in rows to permit of frequent cultivation suffer much less injury than when sown broadeast. As soon as the last picking has been made, infested plants should be promptly destroyed by plowing under.! The brush and pan method.—This method, which consists in jarring the lice from the vines into specially prepared, long, shallow pans in which a little kerosene is floating and which are dragged between the rows, has also given good results, the insects as they come into contact with the kerosene being all killed. A bushel of lice was caught to each row, 125 rods long, in one instance where this remedy was used. It is practicable only for small areas. Y Cultural methods.—Of cultural methods there is testimony to the value of early planting, the earliest peas seldom being infested, or at least only slightly injured. Very late plantings of peas to be used for canning have also escaped ravages in some instances, but it 1We have abundant testimony to the value of this method, but perhaps none more striking than that on the farm of Mr. C. H. Pearson, a Maryland pea- grower. During the season of 1900 a six-hundred-acre pea plantation was prac- tically saved by this method. After other means had failed, the fields were brushed and cultivated every third day fora period of two weeks. The previous season peas over the same area were broadcast; so that it was impossible to combat the pest in this manner, and as a consequence 480 acres were entirely ruined (Bul. 20, n. s., p. 94; Bul. 26, p. 57, Div. Ent., U. S. Dept. Agr.). ONIAN INSTITUTION LIBRARIES wing 8 3 9088 0127 may be that atmospheric conditions have had something to do with exemption in the cases which have come under notice. Rotation of crops is advisable, and it is unwise to plant peas in suc- cessive years in the same portion of a farm or garden, or in the vicinity of fields of red or crimson clover, or other leguminous plants, suchas vetch, which are likely to harbor this species. As has been said, this insect passes the winter on the plants mentioned, because peas are not available, and it might be possible to use small plats of some one of them as trap crops. Crimson clover would probably be best because of its conspicuousness and the early start that it gets in the spring. On the trap plants the lice could be killed by hand methods, such as brushing from the plants into pans and thus large numbers of the insects could be killed early in the sea- son before they had opportunity to spread to peas. In Delaware it has been shown that the practice of keeping the land well fertilized and frequently cultivated enables the peas, in spite of lice attack, to produce better crops than would otherwise be made. The subject of alternate host plants is an important one, since the pea, being an annual, is not available as food for this plant-louse during winter, and it is desirable to ascertain all of its host plants, and more especially weeds, as some one or more of these may be factors of importance in the life economy of the species. It might be necessary in the future, should the depredations of this insect continue as during the past two years, to limit the growing of clover and other legumes, as well as other alternate host plants, if such be found, in the vicinity of pea fields. If all of the principal alternate plants could be discovered this might furnish a solution of the problem of how to deal with this insect. F, H. CHITTENDEN, Approved: Assistant Entomologist. J. H. BRIGHAM, Acting Secretary of Agriculture. WASHINGTON, D. C., May 28, 1901. O 6 ;