April, "lo] 



McCOLLOCH: CHINCH BUG EGG PARASITE 



249 



Importance 



From the data thus far accumulated the egg parasite is an impor- 

 tant factor in the control of the chinch bug. In the spring of 1913 

 the emergence of chinch bugs from winter quarters was one of the 

 largest ever witnessed in Kansas and the indications were for serious 

 injury during the ensuing summer. Within two weeks after this emer- 

 gence the wheat fields were beginning to show considerable damage 

 and a few fields were entirely destroj^ed. Hundreds of eggs were de- 

 posited around nearly every wheat plant and it was thought that the 

 wheat and corn fields in many localities would be practically a total 

 loss. In two or three weeks it was evident that a large percentage of 

 the eggs were not hatching as the number of young bugs was far below 

 the expectation. At harvest when the bugs migrated to the corn 

 fields there was very little complaint of injury and throughout August 

 the number of bugs in the corn was exceptionally low. In the fall of 

 1913 the count's of the number of bugs in winter quarters showed only 

 one bug where there were from twenty-five to one hundred in the fall 

 of 1912. 



The climatic conditions during 1913 were favorable for the develop- 

 ment of the chinch bug. The drought during the summer prevented 

 the development of the chinch bug fungus and there was no known 

 factor except the parasite which could have caused this great reduc- 

 tion. In Illinois, where practically the same conditions existed as in 

 Kansas, with the exception that there were few parasites present, the 

 chinch bugs did a vast amount of damage in 1913 and were equally 

 bad in 1914. 



In 1913 the average parasitism at Manhattan during the summer 

 was 32 per cent and during the spring when chinch bugs were most 

 numerous it ranged from 20 to 40 per cent. In the experimental work 

 it was shown that the period of oviposition of the chinch bug covered 

 about two months, while the life cycle of the parasite extended over 

 a period of only two or three weeks. Thus the eggs of a single female 

 chinch bug were exposed to about three broods of parasites while the 

 eggs of one brood of chinch bugs were exposed to four or five broods 

 of parasites. From this data it is conservative to estimate the para- 

 sitism in the field during 1913 to have been at least 50 per cent. 



The number of chinch bugs in the fields about Manhattan in 1914 

 was exceptionally small and there was a marked reduction in the num- 

 ber of parasites. The parasitism in the early spring was considerably 

 below one per cent, but as the summer progressed it gradually in- 

 creased until in September it reached 25 per cent. Table I gives the 

 percentage of parasitism by months at Manhattan. 



