2 75 



SCIENCE. 



[Vol. XIII. No. 323 



of the generations then breeding and hatching, and may operate 

 also to protect the crops of the following year, at a distance from 

 woodlands, by driving the adult chinch-bugs from the open fields, 

 and compelling them to resort to the grassy woods for food for 

 themselves and their young. 



Severe drought in a small-grain district has so thoroughly and 

 so early destroyed the corn-crop there, as to test practically the 

 effect of abandoning that crop as a defence against the chinch-bug. 

 In the case observed it was found that the injury the following 

 season was very much less than before. As the drought took effect, 

 however, on the field-grasses generally, and thus still further re- 

 duced the supply of insect-food, the result was not to be attributed 

 wholly to a lack of corn. 



A similar destruction of the corn by drought in midsummer, fol- 

 lowed by a general winter-killing of wheat, has shown that a suc- 

 cessive abandonment of these crops may greatly reduce the numbers 

 of the chinch-bug, even where other conditions are very favorable 

 to it ; this reduction amounting, in one such case, to one-half or 

 three-fourths of the number abroad the year preceding. 



Where wheat is abundant in a district very badly infested by 

 chinch-bugs, it is now certain that this insect may live and breed 

 very successfully in early spring in oats, in young timothy and blue- 

 grass meadows, and even in corn. 



A thoroughgoing investigation of the relations of chinch-bug 

 injury to the acreage of the principal farm-crops of Illinois in 1886 

 and 1887 shows, that, where the outbreak was but just beginning, 

 the wheat area had evidently much to do with the number and the 

 •rate of increase of the insects ; a rising gradation of injury ap- 

 pearing in correspondence to an enlarging area in wheat, the acre- 

 age of the other crops at the same time remaining nearly constant 

 or slightly declining. As the severity of the attack increases, how- 

 ever, the oats area begins to rise with the wheat, and may pres- 

 ently surpass the latter as a stimulus to the multiplication of the 

 chinch-bug, corn and grass finally showing a like tendency where 

 it has become excessively abundant and destructive. Here, when 

 the eggs of the winter brood are being laid freely onsall the food- 

 plants of the species, the wheat area may even decline as one 

 passes from districts where destruction is very great to those in 

 which it is complete. This may be due to one or more of the fol- 

 fowing circumstances : (i) the wJieat area may be purposely dimin- 

 ished by the farmers one year after another, as was certainly 

 sometimes the case in southern Illinois in 1887, where chinch-bug 

 injury had greatly lessened the yield and value of the crop for the 

 season or two preceding ; (2) a change of feeding-habits may arise 

 among the insects themselves ; or (3) there may be a spontaneous 

 gradual shifting of the centre of attack, due to a natural diminution in 

 the number of insects one year in places where they were the year 

 before the most abundant, and an increase in places where they 

 were then less numerous. This territorial propagation outward 

 from a centre of first excess is accompanied by a diminution in 

 numbers in the principal area of origin ; and a similar propagation 

 from districts where the crop most preferred and first infested 

 (wheat) is most abundant, to adjacent districts where the leading 

 crops are those freely fed upon, but less preferred (oats, grass, etc.), 

 is also highly probable, but less easily demonstrated. In both 

 cases the diminution in numbers is doubtless largely due to the 

 direct and indirect consequences of over-crowding, — a condition 

 which always arouses or intensifies the action of the natural checks 

 on excessive increase. 



Further comparison of the crop areas of 1886 with the injuries 

 of 1887 shows that a very decided diminution of the corn area has 

 had little or no effect to diminish the loss to small grain the follow- 

 ing year. 



From this we learn that the proper procedure respecting the 

 grass and the cereal crops in the presence of a chinch-bug uprising 

 is the prompt and early adandonment of wheat or a decided limita- 

 tion of its area, to be followed presently, if the attack continues, by 

 a diminution of the oats acreage also, and the sowing of clover, 

 whenever practicable, instead of the grass forage-plants. We also 

 find that these measures must be taken early or not at all ; since, if 

 too long postponed, they may easily do more harm than good. 



An analysis of the published opinions of economic entomologists 

 shows a general and rather indiscriminate dependence on the aban- 



donment of wheat-culture as a defence against the chinch-bug ; 

 this opinion being more positive, however, among the older ento- 

 mologists than among those who have studied the question re- 

 cently. A similar indiscriminate but not unanimous opinion as to 

 the advantage of the abandonment of wheat appears in the state- 

 ments of two hundred agricultural correspondents of the office, 

 eighty-seven per cent of the replies to an inquiry touching this mat- 

 ter being in the affirmative. 



From the miscellaneous experiments reported, it appears that the 

 worst-infested fields of small grain may be sustained under a 

 chinch-bug attack by heavy fertilization, if the land be originally in 

 good condition ; and that, in general, the damage done will vary in- 

 versely to the fertility of the soil and the support given by fertilizers 

 to the crop attacked. The best fertilizers for this purpose, on the 

 wheat-lands of the central part of southern Illinois, seem to be, 

 first, barn-yard manure ; and, second, the phosphates and nitrates 

 combined. . 



The kerosene emulsion, whose deadly effect on the chinch-bug 

 was first shown by Mr. Forbes in 1882, has repeatedly proven a 

 very valuable agent in the hands of farmers when applied in the 

 field for the protection of corn ; but it may best be used in combi- 

 nation with some obstruction to the passage of the chinch-bug 

 from small grain and grass to corn, — either ditches and furrows, 

 or belts of coal-tar along the border of the field. A mixture of 

 coal-tar with oil or grease, ten parts to one, will last, without har- 

 dening in the sun, from five to ten times as long as the pure tar, but 

 is too fluid to be poured directly on the ground. 



Tobacco-water was found frequently fatal to chinch-bugs of all 

 ages, but was apparently less effective than the kerosene emulsion. 

 An emulsion of coal-tar likewise gave promise of usefulness, having 

 the advantage in cost over the kerosene mixture, but being some- 

 what less convenient of application. 



On the other hand, infusion of lobelia, coal-tar water, turpentine 

 emulsion, lime-water, fresh gas-lime, arsenic, London purple, Paris 

 green, the " Egyptian insecticide," buhach, corrosive sublimate, and 

 steam, were applied to chinch-bugs with discouraging results. 



Some starvation experiments not begun until Sept. 4 were un- 

 satisfactory, because of the lateness of the period, and because 

 most of the bugs from the district where the specimens used were 

 collected, proved to be already weakened by disease. Adults and 

 young, some just hatched, confined on a dry surface and without 

 food, died in from one to six days. Other young, taken as they 

 hatched, lived from twelve to twenty-four hours. 



Careful studies of the contagious diseases of chinch-bugs, re- 

 vealed in August and September, t888, the presence of three dis- 

 tinct forms of fungous disease, two of them identical with those 

 reported by Mr. Forbes in 1882, and the third new. All these 

 were widely distributed through southern Illinois, with the possible 

 exception of the region bordering the Ohio River. 



Two of these diseases are produced by thread fungi (^Entomoph- 

 thora arid Botrytis), which make a rapid external growth after the 

 death of the insect, presently ernbedding the body in a snow-white 

 mould ; and the third is a bacterial disease, characterized by a 

 minute bacillus, which has its principal seat in the coeca (not the 

 Malpighian tubules) of the alimentary canal. Many and various 

 culture experiments with the latter were completely successful ; but 

 infection experiments could not be made for want of specimens 

 originally free from disease. On the other hand, culture experi- 

 ments with the E7itoniophthora and Botrytis v/ere tried without 

 success. 



Among various miscellaneous notes, Mr. Forbes reports the fail- 

 ure of an attempt to force the chinch-bug to feed on wild buck- 

 wheat {Polygonum dum.etoru7>i)\ the very early occurrence of the 

 chinch-bug in Edwards County, III. (in 1823, and again in 1828); 

 the prostration of wheat and corn as an effect of chinch-bug injury, 

 due to failure of development of the latest circle of " brace roots ; " 

 the harmlessness and uselessness of the flea negro bug, often found 

 associated with the chinch-bug in wheat; the place and time of 

 deposition of the eggs for the second brood ; the protective value, 

 under certain circumstances, of the sowing of timothy with wheat 

 in the fall ; the successful defence of corn-fields by ploughing and 

 ditching against an invasion from small grain ; and an important 

 modification of the mode of destruction by burning in the spring. 



