Bulletin STATE OF ILLINOIS DEPARTMENT OF REGISTRATION AND EDUCATION DIVISION OF THE NATURAL HISTORY SURVEY THEODORE H. PRISON, Chitf Vol. XIX. BULLETIN Article VI. An Experimental and Observational Study of the Chinch Bug in Relation to Climate and Weather BY V. E. SHELFORD PRINTED BY AUTHORITY OF THE STATE OF ILLINOIS URBANA, ILLINOIS JANUARY, 1932 STATE OF ILLINOIS DEPARTMENT OP REGISTRATION AND EDUCATION M. P. Walsh. Director BOARD OF NATURAL RESOURCES AND CONSERVATION M. P. Walsh. Chairman William Trelease, Biology Johx W. Alvord. Engineering Henry C. Cowles, Forestry Charles M. Thompsox, Represent- Edson S. Bastix, Oeology ing the President of the Univer- William A. NoyEs. Chemistry sity of Illinois STATE NATURAL HISTORY SURVEY DIVISION Theodore H. Prisox, Chief H. C. OlCSTKliLI.NG. ICilitor SCH.XEPP & BAR.NES. rKl.NTKRS SPRlNGPirLD. II.L. 1931 G!U16—1,200 CONTENTS Page Introduction 487 E((uipment and oiieration 488 Length of Instars and the Life History 489 Methods and resuhs 400 Table L Aim-rhximatelv Constant Temi'f.kature 491 Table IL X'ariable Temperature 495 Lidividual variation 197 Effect of humidity 498 Table IIL Humidity Differences 499 Table IV. Simulation of Daily March of Temperature and Relative Hltmidity oOl Table V. Combined Velocity Values 503 Table \T. Length of Life Cycle 503 Velocit\- curves and charts 504 Table \TI. Cultural Conditions 505 Developmental totals 513 Overwintering 515 The Cultures 515 Vigor of stock 519 Effect of light 521 Abundance in Nature 5;!1 History in Illinois 531 W'eather relations 533 Conclusion 545 Bibliographv 546 Voi.niE XIX. AinicLE VI. AN EXPERIMENTAL AND OBSERVA- TIONAL STUDY OF THE CHINCH BUO IN RELATION TO CLIMATE AND AVEATHER V. E. SHELFORD Introduction The abundance of the chinch bug {Blissus leucoptcrus Say) has long been associated with variations and peculiar distributions of rain- fall and temperature in particular years or series of years. A desire for more detailed evidence from the experimental side led to this in- vestigation. Unfortunately, however, the chinch bug is difficult to study in this way, and at the same time the task could not be made the sole or primary work of even one investigator. Accordingly, gen- eral cultures instead of close observation of individuals had to play an important role in the work. The in\estigation reported in this paper is classifiable under three hc?ds: (1 ) the study of length of instars and of the life history in relation to different conditions of temperature, humidity, light, etc. ; (2) the study of the success of cultures under conditions similar to those under which the instars were studied; and (3) the study of the records of abundance, migration, rise, and decline of the pest in the State of Illinois since ISIO. The work on the chinch bug began with preliminary experiments in ]!)1G and closed with a few low-temperature experiments in li)2(). None of the liHG data proved to be of such a nature that conclusions could be drawn from them. Chinch bug cultures, however, were car- ried through the greater part of each summer for ten years. Unfor- tunately, this was an accessory bit of work, carried on chiefly in con- nection with codling moth experiments ( Shelford, !1)"^^ ) and made feasible by the fact that the apjiaratus was running. The .same cham- bers were freiiuently used for both insects in the earlier years; that is, codling moth pupae were put into the chinch Inig cages. The twu in no way interfered with each other. After the codling niolh work was conipleled, chinch bugs were run through the few additional summers to check on the preceding work, but in no case was it possible to improve very greatly the ])re- liminar\- work, 'i'be author gave three-fourths of his lime to instruc- [4S7] 488 Illinois Naivral History Survey Bulletix tion or other duties ; his assistants were devoting most of their time to the engineering curricuhim. This is unfortunate because if there is any insect requiring the undivided attention of investigators while the work is in progress, it is the chinch bug. Its persistence and viabiHty varies greatly from year to year. The variation in length of instar periods is much greater than that of most invertebrates. Its habits are such that obser\ation is difficult and special methods are necessary under many conditions. The populations of chinch bugs on the food plants will find their way below the surface of the soil and under the leaf-sheathes, so that nothing but a complete submergence of the plant will insure the observation of all the individuals. The general results of these experiments, therefore, must be re- garded as provisional, and it is hoped that they may afford a basis for intensive study by other workers. At least two observers, with the best possible equipment, should devote all their attention to such a study over a period of two or three years. Finally, of course, the authenticity of results will dejjend chiefly upon the observation of considerable numbers of life histories carried through under outdoor conditions in addition to cultures, the success of which is determined by the in- crease, decrease, or dying out of the population. Difficulties of main- taining the cultures are very great. Records of complete life histories of individuals, from egg to adult, are lacking in our work. The qual- ity of the food plants probably differs under different conditions, and identical results cannot be expected from bugs fed on plants actually growing under favorable conditions and those fed on cut plants. A great many observations on the rate of growth and success of any species under variable conditions are essential to bridge the gap be- tween the constant-temperature experiments and fluctuating weather conditions. It was on account of our experience with the codling moth, for which such observations were available, that the very im- portant connection between outdoor progress and the laboratory experi- ments could be provisionally established for the chinch bug in the form of trial velocity charts. Equipment and Operation The laboratory and the general equipment have been described and figured previously (Shelford, I'J^i), pp. 400-411). The principal chambers used in this work consisted of a two-room unit {op. cit., Figs, 169 and 170) designed to run at two approximately constant temperatiu-es, with humidity control for the separate rooms and with sockets for artificial lights. There were five other chambers (half as large as the improved form shown in Fig. 1T7) designed to give daily variations in tem]X'raluro simulating natural days. Some cages were Study of the Ciiinc ii Bug 489 also used in the glass-roofed house. For the study of length of instars it was necessary to isolate indix'idual nymphs and observe their UKinlt- ings. This was done in glass cages (Fig. ITS), each of which was ventilated by a suction pipe (Fig. 179). Ventilation in most of the other experiments was by means of compressed air from the Univer- sity Power Plant. The air flow, which was adjusted so as to be com- parable to that observed in the field, was measured with diajihragm chambers and attached gages (pp. 241-245). Moisture was removed by Crane oil separators (Fig. 100). In the approximately constant temperature chambers the temperature was controlled by means of recirculating ducts (Fig. 93), and the humidity was controlled by means of mixing tanks (perfected design shown in Fig. 176), to which dry air was supplied from the dehuniidifier (Fig. Ill) and moist air from a humidifier (similar to that shown in Fig. 109). The humidity control fur the variable-temperature units consisted of a spray chamber (Fig. 110), which gave a constant humidity at the temperature of the spray water and gave variation in the chambers as the temperature rose and fell. Livingston porous cup atmometers were used in practically all the experiments, though correlations with rate of evaporation did not prove to be important in this or other experi- mental work. The rate of evaporation represents a stnnmation of dififerent factors which often ha\e opposite effects on the rate of de- velopment of insects. i\ttenipts were made to vary the light surround- ing the chinch bugs, liut the equipment was not well designed for this purpose. The chamber windows consisted of either double or triple window glass, which shut out a large part of the light. Artificial day- light was provided with incandescent lamps and daylight ray filters in- side the cages. Arc lamps and lOOO-watt daylight bulbs were also used outside the cages. The exjierimental procedures, including the methods of recording the observations and calculating the results, as well as the concejits of developmental units and totals, have been explained in connection with the codling moth (.'^helford, 1927). Length of Instar Periods .\nd thic Life History The life cycle of the chinch bug is comjiriscd of the egg stage, five nymphal stages, or instars, and the adult stage ( from the time of moult- ing until egg-laying is finished). The determination of the length of the life cycle should be made with continuous observations of single individuals, and the difficulties here arc rather great. No individual was traced through from the egg to the adult condition in the experi- ments here re])orted. The reason for this is evident from an inspection of Figs. 14-25 and fr(]ni the following resume of the records. 490 Illinois Natiual History Si'Uvey Bclletix Mctlwds and Results In the year 1916, only preliminary experiments were carried on, and we were successful in getting the bugs to breed. In 1917 the bugs bred, but the conditions under which they were kept, coupled with the condition of the bugs themselves, were such that they in no case be- came at all abundant in the cultures, and most of the cultures died out early in the season. In 1918 the culture work went forward better than the preceding year. Attempts in these years to study the length of instar periods in U-chloride tubes through which a small amount of air was slowly forced, were generally unsuccessful. ^^//c:/ ^t?fJt ^t/cfan g^citJ^ ar >/Jj^ctt , A^e^^//^ by ^^a//^^ wan ' Fig. 1. Plan of tube used inside the culture cages to Isolate Indi- viduals for the study of length of iustars. Circulation was produced by suction. In 1!)11) over .")(H) iiidix iduals of different stages were put under observation, I)ut we were unsuccessful with all hut oH of the attempts to carry individuals through a complete single instar. It was thought in 1919 that a piece of cut grass could lie jilaced in a vial and corked with the young bug, but the evapdration from the food materials sat- urated the air in the small container, so that moisture was precipitated on the sides, and the younger bugs in particular became wet, stuck to the glass, and died. This was the chief cause of our losses, though the tubes with air forced slowly through them and the tubes to which suction was applied ( Fig. 1 ) did not yield a very large number of definite records. .\ large ex]K'niliuuc of energy gave few or no re- sults, and for some stages no recunls of length of stage were obtained in that year. In 19v'() the suction s\steni referred to in the description of the apparatus was put into n^e. the suction tubes being placed in the Stldy oi' Till'; CiUNi II Bug I'Jl cultures adjacent to the fuod plaiils. 'I'he rate at whicli the air was (h'awn out of the cage was adjusted so as to 1je approximately tlie same as the rate of tiow in the normal habitat of the insect. Extremes of humidity, both high and low, were avoided. The resuhs were much better than in i)revious years. About SO records were obtained out of 150 to 200 possibilities. In 1!)"21 the observations weru made by Dr. H. Yuasa, a well- known Japanese entomologist then em])loyed by the Natural History Survey and now of the Imperial Uni\ersity, Kyoto, Japan, and at least 75 records were obtained out of about 300 possibilities. The T.MILE I APPROXIMATELY CONSTANT TEJIPERATURE Showing length of stage for comparable groups of individuals subjected to small variations in temperature and relative humidity. The mean of the highest and lowest numbers of days in each grouping was used as the basis for calculating the percentage of variation. There were two observations per day in some cases, as indicated by half-days in some of the records. 492 Illinois NATiiiAi. Histohy Si'i:vkv Bi llktin Taiilk I—Cont'd Stiiiy of tiik Ciiixi II Bro Table I—Cont'd 493 494 Illinois NATtiiAL Hi.stohy SritvEV Bili-etix Tai!Le I—Cont'd Stluy of the Chixlii BfG 495 conditions, with a daily range of 1-7°C., and Silo were tmder more variable conditions, with a daily variation of lO-ltrC. These observa- tions were distributed as follows: egg, 31; first instar, 55; second, GT ; third, rn; fourth, 1!)0; fifth, 215. Tables I-I\" show selected data in connection with the length of instar periods, but only those that could be paired for comparison. The lengths of the several stages at 90% relative humidity and 23°C. mean temperature with 4° or 5° daily variation are estimated to be as follows: egg. 16.5 days; first instar, G.O days; second, 5.9 days; third, 5.7 days; fourth, G.l days; fifth, 11.2 days; the sum being 51. -4 days. The period from egg to adult, on the basis of the combined data shown in Fig. 10 and Table \', is 53.2 days. The average time obtained by taking the sum of the several stages at three combinations of temperature and humidity is shown in Table VL Table II VARIABLE TEMPERATURE Showing length of stage for comparable groups of individuals under more variable temperature than in Tat)le I but with only slight differences in mean relative humidity. The temperature conditions simulated the nor- mal daily fluctuations out of doors (10°C. rise and fall). Percentages were calculated as in Table I. Data for 1919 are omitted because there were no two comparable groups. 496 iLLi.Nois Natural History Survey Bulletin- Table II—Cont'd Stluy of thk Ciii.\( ii Big Tami.k II—Confd 497 498 Illinois Natural Histobv Sirvev Bllletix second stage ^.T^o, third stage 22.1%, fourth stage 17.4% and fifth stage 15.6%. A similar range of variation under more variable tem- peratures is indicated in Table II, where the average for the egg stage is 24.8%, for the first instar 16.8%, for the second 27%, third T.1%, fourth 12.2%, and fifth 10.7%, and the average for all stages 16.4%. These variations are rather large, as compared to the 8% devia- tion found in the codling moth pupae and percentages of the same order of magnitude in the other stages of the moth (Shelford. 1!>27). It is evident, therefore, that individual variation may render the re- sults in small series of observations quite irregular, and this considera- tion further lessens the weight to be given to the smaller number of cases. Effect of Hiiiuidity The study of instars brought out the great importance of moisture. While high atmospheric humidity is favorable, especially to the early instars, actual liquid water is detrimental or fatal. Data on all in^tars from the same stock which were kept under the same temperatures but different himiidities are presented in Tables III and IV to show effects of humidit}' upon length of stage. The average increase in the length of instars per 10% decrease in relative humidity is 25-35%. Generally speaking, the eftect of the lowest humidity is greatest in the first and second nymphal stages. The numerical relation of the length of life history stages of animals to atmospheric moisture (at any fixed temperature) has been but little studied. It is evident, hc)we\er, that none of the formulae used to express relations to temperature can ordinarily be used and that insects dift'cr greatly as to amount of eftect produced by a given difl'erence in atmospheric moisture, expressed as relative hu- midity in \Kr cent saturation, as saturation deficit, or otherwise. The effect of moisture on the length of chinch bug stages is relatively great. It approaches more nearlv a direct jiroportionality to per cent relative humidity than in many other organisms, .\ccordingly, to compare the dift'erent stages and gain a concept of the magnitude of the cft'ect of humidity on the rate of development of the chinch bug, the data have been reduced to a common basis of 10% difi'erence in relative humidity. This was necessitated by the great diftcreuces in humidity for the sur- viving stage-completing inii% relatixe humiflity and has a velocity \alue of 10 developmental units per hour. X^, is located on the same temperature (2i°C.) and 80% relative humidity and has a velocity value of S.5 — a decrease of 15% in rate of development. Again. X.,. on temjjerature 21 °C. and 90% relative humidity, has a velocity of ;j..-) ; and X,. on the same 510 Illinois Xatihal Histouy SriiVKV Billetix Fig, total of 6. Provisional chart for the third instar. based on a developmental S50 units. temperature but 10% lower luiniidity, has a \elocity of "2.."). Here the decrease in velocity is 10 oo, or 28.5%. It is noteworthy that the per- centage difference in velocity increases as the temperature is lowered. The curves show-n in Fig. 2 are in part a straight line (21° to 2S)°C.) and represent the rates of development under conditions indi- cated by the obh((ue line on I'lgs. ;>-S which runs from 100% relative humidity and approximately I'yC. to approximately 60% relative huniichtv and 'lO \'. luit varies somewhal as it is the actual average tor each stage. This c)bH(|ue Hue ihtis reiiresenls the average daily march Stldy of the CHixfii Bro 511 W4-_ 86- 512 Illinois Natihal History SnnKY Bilietin Fig. 8. Provisional chart for the fifth instar. based on a developmental total of 1400 units. The velocity cnivc .shown in Figure was checked against the vahies in Table \ . This velocity curve is indicated in each of the stages and rejiresents the cross-section of a ridge-like solid on which the e(|ual-velocity lines of Figs. 3-.S would correspond to contours. For a portion of each of these curves the relationship is a straight line (Fig. 2). and within this straight-line portion the product of time and tenii)erature above al])ha is a constant (Shelford lO^'T'). Stidy of thk Cmxt II Bi'O 513 514 Illinois Natural History Sirvf.y Bulletin Pig. 10. A composite chart, based on 6SO0 units as the developmental total for the egg and five nymphal stages. The pre-oviposition period of the adult is not included. found for the later stages. These separate iiistar totals for the more variahle temperature experiments were eheeked, howexer. with tables made from the charts of the various instars. By substitution of the values shown on the charts for the combinations of temperature and humidity (2-hour means), totals averaging close to the figures given were obtained for the more \ariahle temiierature. These figures are provisional because there were no outdoor records of instar periods with Icmiieratiue and hinnidity data available for checking them. Stidy of tiik Cinx( II Big 515 Ozrrz^'iiitcriuf/ A considerable iiuniljer of preliminary experinu-iUs with liiher- nating bugs had indicated that very cold conditions were not necessary ; hence, mild moist conditions were mainly tried. In nearly all the years in which cultures were maintained some attempt was made to carry bugs through the winter. In a few cases the bugs were alive in the early spring, but they did not breed. In 1921-22 an attempt was made to keep the bugs moist and uncler conditions similar to those out of doors. The temperature was lowered to about freezing in midwinter and then raised to a favorable point in March or Ajiril. The bugs were alive in March, but all died under favorable culture conditions. In the autumn of 1!)23 the bugs from the several cultures were ])laced in one culture cage in Chamber A on October 30, and 200 bugs from outdoors were placed in another cage. The temperature was reduced almost to freezing and held there for two months or more and then gradually raised. The humidity was 95%, and grass kept green in the cages. No li\c Ijugs were found after March 21. In the autumn of 1921 the cultures were all placed in the cold chamber, the air was kept very moist (90-95% R. H.) and the tem- perature lowered to freezing (O'C.J by the first of February. ]Most of the month of I-'ebruary was at, near, or below freezing, with the humiditv high. During March the temjierature was gradually raised, so that bv April 21 the conditions were good for the growth of bugs. It fell to ]S'C. at night and rose to 2';°C. dtu"ing the day. On April 10 the minimum was raised to a])]ir()ximately 20'^C. On April 23 mating was noted, but no eggs ajjpeared. Two out of three other cultures showed li\ing bugs but no breeding. ICach had contained from 15 tc; 50 bugs in the autumn. Till-; Cult I 'NILS The second ly]ie of investigatiun of chinch bugs consisted of set- ting up cultures under kiinwii condilions anrl obserxing them from dav to day to make records of the grnwth of the mniphal stages and tlie numlier of generations. In the e.\])eiiments of 19 1 i - r.)2.'!. wheat was planti'd in the con- tainers once or twice a week, depending upon condilions, and allowed to sprout, to sup])ly nourishment for the bugs. Some faihnx-s were doubtless clue to tlie deterioration of the foorl sui)]il\-, for occasionallv the wheat died rather suddenly, without sut'ficient time for a new supply to grow, especially in the drier ex])eriments. Sudan grass was used in 1921 and i:i25. with better results. 516 Illinois Natihal Histohy Siuvey Bii.lktix MAKCH APRIL MAY JUNE JULY AUGUST SEPTEMBER OCTOBER KOVEMSER DECEMBER JAN Stidy of thk Ciiin( II Bug 517 ^00 350 400 450 500 S50 TTlll Fig. 12. Curves showing the miilday light conditions in the experimental chambers (especially units A and B), indicated in percentage of the midday sunlight of clear days in early July, The measurements were made with screened photo-electric cells with the wave-length sensitivity shown below by the shaded pol- ygons. The Roman numerals on the curves are used in Figs. 14- 21 and in Table VII to designate the curves in their relations to particular experiments. adults by the tfiiili of |iil\-. l^rst-stage nymphs of the second genera- tinn tlicn ;i])|)caiT(l in the ciillurc, and the ridnlts iiractically (hsapjieared h\ July "'". liiciilcntally, the sex of tlmse i-i-iiiaiiiiiig was not deter- mined, liiit the presence of males is to lie e.\])ected and they wonl2 .BWWei EMWJ> ' Iff C Bdptt/ Fh- - rs _D -3ZII r".^ -Cr "MI " A. i±J_L I I I J_L _1_I_L Fig. 18. Curves showing planation see Fig, 14. success of all cultures in 1920. For ex- were supplied with ',?(i and grad- ually spread for four _\ears in patch-work fashion over the state. During most of this period Christian (^dunty was the center of devastating outbreaks. The chinch bugs ileclined in l!*"^."). and while they did some damage in VXVi they continued to decline to a minimum in 1929. This was followed by a very material increase din-ing the summer of 19:j(). though it came too late in the .season to do any damage to crops. Study of the Ciiini ii Bug 533 Ju.ne.1.71 Z-OB Chinch Bu& I P2Z Fig. 27. Map of Illinois showing reported areas of damage to crops by chinch bugs in 1922, together with inches of rainfall in Jlay (lower figures) and in June (upper figures) in each locality. Figs. 26-30 show the distribution of infested areas from 1D21 to 1925. The erratic shifting of the areas of abundance from year to year is characteristic and has to lie explained on the basis of favorable weather and either the perennial ])resence of the lings or their flight from infested areas. In the southern half of llu; state the former is the more likely explanation, ll'rallicr l\rlali(>iis The fluctuations in ;ibinulanre of chinch bugs ha\e long been associated with weather conditions. The early writers refer to late spring rains as causing the destruction of the bugs. It was i^ointed out 534 Illinois Natihal Histokv Suhvey Bllletix Chinch Bug- /9£3 ^evEPe MODCaA T£ Fig. 28. Rlap of Illinois showing reported areas of damage to crops by chinch bugs in 1923, together with inches of rainfall in May (lower figures) and in June uipper figures) in each locality. by Thunias (ISi!) ) that a dry May and June ami two dry siiniuicrs are essential to the development ot excessive minibers of these pests. Though they are apparently absent from large areas in spring, the small numbers which are jiresent in a gi\en area may develop rapidly if the season is very favorable and may increase to enormous numbers by autumn, and enough of them may siuvive the winter to build up a population that will do a great deal of damage in the following year even if the weather then is adverse. The variation in vitality and fecundity referred to above is, howexer. a subject for the most careful investigation from a jihysiological \iewpoint. Their decline is jirobably Stl'dy ov the Cium II Bug 535 Chinch Bug- I r~roo£f)A T£ I SLIGHT Pig. 29. Map of Illinois showing reported areas of damage to crops by chinch bugs in V)i\. together with inches of rainfall in May (lower figures) and in June (upper figures) in each locality. less closely correlated with external conditions than is their rise to abundance, but both are not so simple as was commonly supposed in the ])ast. In some years the bugs jjractically disappear from most localities in Illinois, so that sjieciiuens can hardly be found. In the last 20 years the only area in which it has Ijcen jiossible to find bugs at all times is an area in the suuthwestern part nf the state, east of St. Louis, reaching into the western half of Marion County and Fayette County, the southern half of Christian County, and the northern half of Wash- ington County. The im])ortance of late spring rainfall has been confirmed by the writer's examination of weather records for localities in Illinois and 536 Illinois Natukal Histoky Sii'-vkv Bi lleti.n /pa 5' &£-V£-^£- J3AMACE Fig. 30. Map of Illinois showing reported area of damage to crops by chinch bugs in 1925, together with inches of rainfall in May (lower figures) and in June (upper figures). elsewhere. An exhaiistive study was made of the data for periods of ahuiidance and scarcity of hugs as iniHcated hy reports of damage to crops in various parts of the state since 1853. Special analysis was given to a very large numher of cases in which a year of severe damage was followed liy a year of no damage, and to an almost equally large numl)er of cases in which tlie reverse was true. In each case a hyther- graph was made, according to the jilan tised in the study of the codling moth (Shelford, 1927), by plotting the mean temperature against the mean rainfall for each nmnth nf iJic year. The results are .summarized in Figs. 31-31. Stldv of the Chix< h Big 5:57 its' 538 Illinois Natuual Histoky Survey Bulletin 9^' Sttdy ok the CiiiNiii Bug 539 540 Illinois Natural History Survey Bulletin- Fig. 34. Hythergraph showing average conditions in years of no damage that were preceded by years of severe damage. Only a few exceptions to the usual seasonal trend were found. In 1!)19, after a year of no crop damage, the bugs became very abund- ant and caused severe damage in spite of the comparatively large amount of rainfall in Alay. The rainfall was distributed over Ki days of that month, and at man}' stations in the infested area it ranged from 5 to y inches, but it may ha\e missed the critical period of the bugs very generally. Other examples in which heavy spring rains failed to stop the progress of the bugs may be seen in the maps for 19'il and lO'i-i (Figs. 26 and 39), in which it appears that the rainfall was sometimes greater in the counties where the damage was severe than in the coun- ties where it was moderate or slight. There is no evidence that low temperatures or other conditions in the winter months have m.iterial effects on the alnmdance of chinch bugs in the following season. .\t least, winter temperatures as repre- Study ok the Chi.m ii Bug 541 OOOOOOOOQ— — — — — — — — — — «^C-J<^ic^oJC-J 542 Illinois Natiual Hlstouy Siiivey Blllktin OOOOooOOo — —— — — — — — — — r^c^t^o^'>'f-' 25 15 i '° " 5 S 5 o u 10 °15 ZO Z6 to . 15 -I Study of the Ciiixtii Brc r)4:i 'c:' IIBJUIPJ t»ii>Ul .2 ?; " " i •= : S3 m&- ving rat St. e th The 544 Illinois Natiual History Survey Bllletix chinch bugs are of such a character that they can be killed off in num- bers by the rain of a single night, and it is impossible to know the dis- tribution of rain from the older records, as the rain from day to day is not given. After gathering a large amount of information from litera- ture, from colleagues in other states, and from the records of the State Entomologist's Office, it was decided that further pursuit of this line of work was not advisable. Any further light thrown on this aspect of the chinch bug problem probably must come mainly from the de- tailed and whole-hearted efforts of investigators in a position to devote careful attention to the numbers of the bugs and to their relations to conditions as they occur in the field, and from the correlation of such findings with careful physiological studies. Our difficulty lies in the fact that except for a limited period we have no knowledge of the abundance of bugs in the autumn and again in the spring, or in early spring and again at the close of the crop season. In cases where data of this kind have been obtained the tendency is to confirm the findings of the writer and the older investigators. The exceptions usually indi- cate that the distribution and character of the rainfall is more impor- tant than its total amotuit in a given period. The writer accidentally discovered some evidence of apparent correlations between death rate in man and the abundance of chinch bugs. In some localities the chinch bug damage is great in years in which the human death rate is high. Analyses of the available data by simple comparison were carried out for a number of cities and over a number of years, with results as shown in Figs. 35 and 36 for six localities from 1900 to 1925. A more comprehensive comparison is afforded in Fig. 37, which represents the reported chinch bug damage throughout Illinois since 1840 in comparison with rainfall and death rate in two cities, Chicago, and St. Louis. The crop damage in each year was estimated by counties ; each county with severe damage was assigned a value of 3, moderate damage 2, and slight damage 1 : and then the sum of these assigned values for all the counties in the state was divided by 2 in order to obtain the rating for the year, and in that way the scale at the left of Fig. 37 was constructed. The lack of vital statistics for St. Louis and of weather records for Chicago in the earlier years made it impossible to ol)tain averages throughout the period covered by the records of the insect. It will be noted, however, that there is fairly close correlation between the jieriods of high death rate and great chinch bug abundance. The death rate usually rises in dry periods and falls in wet jieriods, and the chinch bug damage fre- quently follows these fluctuations rather closely, sometimes coinciding with them and sometimes lagging one year. In this connection it is Study of the Chinch Bug 545 worth repeating that variation in the vigor and fecundity of the bugs themselves is postulated as a factor not noted hitherto. CONCI-USION The chinch bug is a very sensitive insect. The immeasurable factors, such as quahty of food, presence of aphids or other insects, variations in the soil or in the food plants, and changes in the vigor of the bugs, interfered with the success of the cultures and so far over- shadowed the experimental differences in temperature, humidity, and light as partly to vitiate the results of experiments designed to deter- mine the effects of these factors. This same sensitivity of the insect also makes it difficult to draw conclusions from the data of field observers. While it is evident that young chinch bugs may be killed by rain, still a large total rainfall in a particular month does not always result in their destruction throughout an area, for the rain may fall too slowly or may be too localized in small showers. Field observations of outbreaks have not been exact, and in the absence of quantitative obser- vations on the abundance of the bugs, refinement of conclusions is not practicable. The results of the present study, however, may be sum- marized as follows : 1. Individual variation in the lengths of instars and life histories is very great, probably on account of the sensitivity of the bugs. 2. Low humidity aiTects the first in star strikingly and each suc- ceeding stage to a lesser degree. 3. The relations of the rate of development to temperature and humidity are expressible in developmental units, and for each stage an equal-velocity chart is presented, similar to those used by the author in his study of the codling moth. 4. The success of the bugs in a long series of cultures shows that their vigor varies from year to year. The bugs were very strong in lill!) and 1925, producing three or four generations in each of these years. They were weakest in VJ2i. This does not, however, corre- spond with the severest outbreaks of the bugs in the state. It does indicate the possible importance of internal factors not directly cor- related with the immediate surrounding conditions but determined earlier. It is necessary to consider unbalance in the bugs themselves as well as the unbalance in the system of nature of which they are a part. 5. In the early history of the outbreaks in Illinois there was a striking correlation between human death rate and chinch bug damage. \\ ith better developed agriculture and imi)roved sanitary couflitions this relation has become less striking. 546 Illinois Natihal History SrinKV Bllletix BIBLIOGRAPHY Davis. J. J. 1925. Insects of Indiana for 1925. Proc. Intl. Acad, of Sci., vol. 34, pp. 303-318. Fitch, Asa 1856. Noxious, beneficial and other insects, of the State of New York. Reports of the Xew York State Entomologist, no. 1 and no. 2. FOHBES, S. A. 1889. Studies on the chinch bug. II. 188.5-1888. 16th Report of the State Entomologist of Illinois, pp. 1-57. 1894. The chinch bug in 1894. Prospects for 1895. Contagious disease experiments. Other experiments. Plans and recommendations for next year. Office of the State Entomologist of Illinois. Bui. no. 5, pp. 83-89. 1916. The chinch-bug outbreak of 1910 to 191.5. Illinois Agr. Exp. Sta. Circ. no. 189, 59 pp. Harris, T. W. 1862. A treatise on some of the insects injurious to vegetation. 2nd ed., 640 pp., New York. Headlee, T. J., and McColloch, J. W. 1913. The chinch bug {Blissus leucopterus Say). Kansas Agr. Exp. Sta. Bui. no. 191. pp. 287-353. Howard, L. O. 1888. The chinch bug: a general summary of its history, habits, ene- mies, and of the remedies and preventives to be used against it. U. S. D. A., Div. of Entom., Bui. no. 17. 48 pp. Hyslop, J. A. 1922. Summary of insect conditions throughout the United States dur- ing 1921. U. S. D. A. Bui. no. 1103, 51 pp. Kelley, E. O. G.. and Parks. T. H. 1911. Chinch-bug investigations west of the Jlississippi River. U. S. D. A., Bur. of Entom.. Bui. no. 95, part in. pp. 23-52. LeBarox, Wji. 1872. Noxious insects of the State of Illinois. Second annual report of the State Entomologist of Illinois, pp. 41-71. Riley C. V. 1869-1877. Noxious, beneficial, and other insects of the State of Mis- souri. Annual Reports of the State Entomologist of Missouri, nos. 1-9. SlIELFOIil). V. E. 1927. An experimental investigation of the relations of the codling moth to weather and climate. Bulletin of the Illinois State Natural History Survey, vol. 16, pp. 311-440. 1929. Laboratory and field ecology. 60S pp. Williams & Wilkins Co., Baltimore. Md. Stliiv of tiik Ciii.NH II Bug 547 SWK.NK, M. H. 1925. The chinch bug aiul its control. Nebraska Agr. Exp. Sta. Circ. no. i!S, S4 pp. Thomas, Cykvs 1S7S. Noxious and beneficial insects of the State of Illinois. 7th Report of the State Entomologist of Illinois, 2yu pp. 1879. The chinch-bug. Its history, characters, and habits, and the means of destroying it or counteracting its injuries. U. S. Entom. Comm. Bui. no. 5, 44 pp. and map. 1S80. Temperature and rainfall as affecting the chinch bug. Periodicity in its increase. Amer. Entom., vol. 1, pp. 24-242. 1881. Noxious and beneficial insects of the State of Illinois. loth Report of the State Entomologist of Illinois, 238 pp. 1882. Noxious and beneficial insects of the State of Illinois. 11th Report of the State Entomologist of Illinois, 104 pp. Walsh, B. D., and Rii.ey, C. V. 1869. The chinch bug (Micropus leucoplrru.'i Say). Amer. Entom., vol. 1, pp. 169-177, 194-199. Wkhstek, F. M. 1896. The chinch bug ( BZi.s.s-H.v leucoptcrus Say). Ohio Agr. Exp. Sta. Bui. no. 69, pp. .59-79. 1897. The chinch bug and Hessian Fly. Extracted from Ohio Agricultural Report for 1896, 7 pp. 1897. Three years study of an outbreak of the chinch bug in Ohio. Ohio Agr. Exp. Sta. Bui. no. 77, pp. 33-41. 1899. The chinch bug. Ohio Agr. Exp. Sta. Bui. no. 106, pp. 237-248. 1907. The chinch bug. U. S. D. A., Bur. of Entom., Bui. no. 69, 95 pp. 1915. The chinch bug. U. S. D. A., Farmers' Bui. no. 657, 28 pp. INDEX Indexes and tabulations of species, with the exception of plankton specie tables in articles IV and V. are not duplicated in this index to the volume. The reader is referred to page 99 for an index to names of fish species, page 113 for a tabulation of Illinois birds, page 3S9 for an index of plant lice hosts and page 439 for an index of plant lice species. Accessory radial thickening—see New terms Actinastrum hantzschi 474. 4S0. 4S3, 4S6 Adams county 542 Algae 453, 454. 455. 474. 475. 4S0. 4S3. 486 Alona sp, 451. 466 Ambrosia trifida 13 Anabaena circinalis 460 planktonica 454. 460 spiroides 454, 460 Ankistrodesmus falcatus 461, 480. 486 Annureopsis fissa 485 Aplianizomenon flos-aquae 460 Aphanocapsa sp. 483 spp. 460 Arcella vulgaris 456, 457. 462, 479, 481, 484 Asplanchna 474 sieboUlii 464 sp. 479. 482, 485 B Bacillariaceae 460 Bald eagle 109 Beardstown, Illinois 470 Belleville, Illinois 541 Bernnida islands 60 Bidens cernua 13 frondosa 13 spp. 13 Bird waves 105. 112 Blissus leucopterus— see Chinch bug Boneyard 52. 57 Bosniina longirostris 451. 453. 466, 473, 474, 480. 482 obtusiroslris 466 Botryococcus sudeticus 461 Brachionus 454. 458, 473, 474. 477 angularis 457, 466, 474, 475. 479. 482, 485 budapestinensis 479, 482, 485 calyciflorus 466, 479, 482, 485 capsuliflorus 479, 482, 485 patulus 454. 456, 465, 479. 482 Callitriche sp. 13 Cass county 470 Catostomidae 18 Centropyxis aculeata 479, 481. 484 Cephalanthus occidentalis 13 Ceratium hirundinella 455. 464. 473, 474, 479, 481, 484 Ceriodaphnia lacustris 466 Champaign, Illinois 52 Champaign county altitude 5 area 5 drainage area 8, 16 basins 6 fish abundance 39, 41, 48. .JO ambient medium 39 analytical keys 18 collections 14. 16 diseases 39 distribution 41. 60 environmental factors 58 growing season 12 migration 6ii morphological adaptations 58 parasites 39 revised names 17 species 17 type habitats 34 intermorainal tracts 6 marsh 7 moraine 5 outcrops 6 [5491 550 Illinois Natckai. Histohy Sirvey Bullktix Champaign county—cont'd soils 7 streams 7, 469 topography 5, 6 water table 7 weather records 7 Chandlerville, Illinois 470. 471. 473. 474, 476, 478 Chicago, Illinois 542, 543, 544 Chinch bug apparatus 488, 522 correlation with human death 541, 542, 543, 544 cultures 515, 516, 519, 520. 521, 523, 524, 525, 526, 527, 528, 529, developmental total 506, 507, 509, 510, 511, 512, 513, 514 units 503, 506, 507, 508, 510, 511, 512, 513, 514 distribution 531 fecundity 534 food 490, 509, 515 hibernating 515 hythergraphs 536, 537, 538, 539, instars 489, 491, 492, 493, 4^4, 496. 497, 498, 499. 500. 501, 50 life history 489 moisture 489, 490, 498, 508 outbreaks 531, 532, 533, 534, 535. pre-ovipositiou period 513, 514 sex 517 stock ri20 velocity of development 504. 511. ventilation 489', 490 vitality 534 Chironomid 457 Chlamydomonas spp. 464. 484 Chlorophyceae 461 Christian county 520. 532. 535 Chroococcus spp. 460 Chydorus sphaericus 451. 467. 480 Cladocera 453, 466, 480, 482, 485 Cladophora crispata 13 glomerata 13, 53 Closteriopsis longissima 461 Closterium acerosum 451, 462. 486 acutum 480. 483. 486 gracile 462 monlliferum 462, 483, 486 472, rate 522, 530 508, 509, 540 495. 536 512 Closterium—cont'd strigosum 462 subtruncatura 462 venus 462 Codling moth 487. 488. 489. 498, 507, •508, 513. 536 Codonella cratera 453. 455. 464. 473, 474, 475, 476. 479. 481. 484 Coelastrum microporum 461, 480. 483, 486 reticulatum 461 Coelosphaerium kuetzingianum 451. 460 naegelianum 454. 460 Conochiloides dossuarius 451. 464 natans 482 Conochilus hippocrepis 464 Cook county 542 Copepoda 451. 45.3. 457. 467. 480. 483, 486 Copper slough 57 Coretbra 467 Cosmariuni botrytis 462 (lepressuni 456, 462 quinarium 462 sp. 486 Crane oil separators 489 Ciucigenia irregularis 461 Crystal lake 107. 108 park 52 Cyanophyceae 460 Cyclops liicuspidatus 451. 453, 455. 467, 473, 474, 477, 480, 483 leuckarti 467 serrulatus 4o7 viridis 453. 45."). 457. 467. 480. 486 Cyclotella spp. 486 Daphnia longispina 466. 473. 474. 4S0. 482. 485 Decatur Illinois 470. 471. 473. 474. 476, 477. 478 death rate 542 lake 471, 472. 473, 474, 475 sewage disposal plant 471, 472, 474, 475 Index 551 Dianathera americana 13 Diaphanosoma brachyurum 451, 466, 474, 480. 482, 485 Oiaptonius inississippieusis 451. 455, 467 siciloidps 473, 483, 486 Dictyosphaeriura pulchellum 461 Difflugia acuminata 457, 463, 481, 484 globulosa 451, 463 lobostoma 456, 463, 474, 475, 479, 481, 484 urceolata 451, 462 Dinobryon sertularia 451, 464, 479, 4S1 Distylla spinifera 485 Diureila stylata 465, 482, 485 tigris 465 Dorr separators 475 Duck hawk 109 Echo river, Kentucky 449 Elodea 10 canadensis 13, 53, 55 Embarrass (Ambraw) river 7, 14, 16, 50, 60 Epistylis 55 Equisetum hiemale 13 Euchlanis deflexa 465 Eudorina elegans 451, 464, 474, 479, 481. 484 Euglena acus 463, 479 acutissima 481, 484 oxyuris 463, 479, 481, 484 sanguinea 455. 456 sp. 479 spirogyra 456 tripteris 463 viridis 456. 463, 474, 479, 481, 484 Payette county 535 Pilinia longiseta 457, 46.".. 479, 482 (Triarthra) 474 Pislier, Illinois 469 Fissidens Julianus 13 Foosland. Illinois 469 Forestry, the 106, 107 Pragilaria 453 Prison, T. H. 54. 57 G Gibson City 57 Glaciers early Wisconsin 6 lUinoian 6 Glenodiniuni sp. 484 Golden eagle 109 Gonium pectorale 481, 484 Gyrosignia sp. 483 spp. 480. 486 H Harristown, Illinois 471, 472, 473, 474, 476, 478 Homer dam 56, 66 Hydrogen ion 452, 473 I Illinois fish commission 65 -Mississippi canal feeder 61 river 52, 455, 469' state water survey 452 Illiopolis, Illinois 471. 472. 473. 474, 478 Insecta 453. 467 Iroquois river 50 Jacksonville. Illinois 541 Juncus spp. 13 Jussiaea diffusa 13 K Kaskaskia (Okaw) river 7. 10. 14, IG, 50. 67, 469 Keratella 473 cochlearis 451, 453, 457, 466, 474, 475, 479, 482, 485 Kunz. Jakob 526 Lagerlieiniia sp. 461 Lecane ohioensis 465 siiinifera 479 ungulata 451, 465 Lemna minor 13 Lepadella acuminata 455, 456, 465 552 Illinois Natlual Hlstorv Sikvey Blllktix Limnodrilus hofmeisteri 55 Little blue heron 109 Livingston porous cup atmometers 489 Lyslgonium 453. 454 granulatum 460, 474, 477, 480, 483, 486 varians 451 M McLean county 469 Macbeth illuminometer 525 Mackinaw river 50 Macon county 470, 520, 542 Mahomet, Illinois 469, 471. 472, 473, 474, 475 Mallomonas caudata 463 producta 464 Mammoth cave 449 Marion county 535 Markus, H. C. 40 Mason county 470 Menard county 470 Micrasterias americana 451. 462 Micratinium pusillum 486 Mycrocystis aerunginosa 460 flos-aquae 460 incerta 460 Mills, R. W, 65 Mississippi river 476 state 454 Moina affinis 466, 473, 474, 480, 482 Monostyla bulla 465 lunaris 465 quadridentata 455, 456, 465 Monticello, Illinois 470, 471, 472. 473, 474, 475, 478 Myriophyllum 10 heterophyllum 13 N Nannoplankton 472 Navicula spp. 460 Nematoda 453, 457 Notrium di.gitus 451, 462 Now terms accessory radial thickening 129 Norton, E. A. .')0 Notholca longispina 451. 466 Nymphaea advena 13 Oscillatoria sp. 457 Ostracoda 453, 467 Pandorina morum 464, 474, 479, 4S1, 484 Pedal ia 474 mira 466, 480. 482 Pediastrum 454 duplex 46L 480. 483, 486 simplex 483, 486 tetras 461 Peridinium cinctum 453, 455, 464 sp. 456 Petersburg, Illinois 470, 471, 472, 473, 474, 475, 478 Phacus acuminata 463, 484 longicaudus 463, 479', 4S1, 484 pleuronectes 481, 4S4 Photo-electric cell 525. 526 Phytoplanktonts 454 Piatt county 61. 65. 470 Planktonts 452. 458 Platydorina caudata 481. 484 Pleodorina californica 464 illinoisensis 456, 464, 474, 479, 481. 484 Pleurotaenium sp. 451. 462 Pleuroxus haniulatus 466 sp. 467 trigonella 467 Pollution 470 Polyarthra 473. 474 trigla 451, 453. 456. 465, 474, 476. 479, 482, 485 Polygonum Hydropiper 13 Ponipholyx complanata 465 Potamogeton americanus 13 heterophyllus 13 pusillus 13. 53 zosterit'olius 13 Protozoa 453, 4,">5, 462, 479, 481. 4S4 I.N'DKX 553 Psychoda alternata 55 Pulaski county 450 Quincy. Illinois 542 Radicula NasUirtium-aquaticum 13 Rantoul, Illinois 57 Ranunculus aquatilis 13 ReeUoot lake, Tenn. 454 Richardson, R. E. 17, 46, 55 Riverton, Illinois 470, 471, 472, 47? 475, 47S Rock river 42, 46, 60, 61, 62, 455, 469 Rotaria neptunia 451, 464, 479, 4S5 Rotatoria 453, 464, 479, 481, 485 Rotifer tardus .^5 Runiex crispus 13 vcrticillatus 13 Sagittaria lieterophylla 13 St. Joseph, Illinois 54 St. Louis, Missouri, 543, 544 Salis spp. 13 Salt creek 470, 474 Salt fork 5, 7, 9, 11, 13, 14, 16, 48, 49, 50, 52, 55, 56, 58, 62, 63, 65, 66. 67, 107 east branch 7, 48. 50, 54, 56, 57, 63 west branch .j2, 54. 55, 56, 57. 65 Sandhill crane 109 Sangamon county 470, 520 river 7, 9, 11. 13, 14, 16, 42, 50, 61, 62, 63, 65, 66, 67, 469, 476 Sargasso sea 60 Scapholel)eris niucronata 466, ISO Sccnedesmus 454 arcuatus 461 liijuga 461 (limorphus 461, 480, 483. 486 (luadricauda 461, 480, 483, 486 Schizocerca divcrsicornis 466, 482 Schroederia setigera 486 Scirpis atrovirens 13 fluviatilis 13 vali