256 



JOURNAL OF ECONOMIC ENTOMOLOGY 



[Vol. 8 



Double Parasitism. — The female parasite does not seem to be 

 able to distinguish between parasitized and unparasitized eggs and 

 double parasitism often resulted. If double parasitism occurs at 

 about the same time it results in the death of both larvse, while they 

 are in the first larval stage. If the second parasitism occurs when 

 the first parasite is in the pupal stage, the second parasite makes no 

 development and the first parasite emerges. 



In the case of simultaneous double parasitism the eggs hatch in 

 about the normal length of time but the resulting larvae develop slowly 

 and never reach the second larval stage. These larvae may live from 

 nine to twelve days, usually one of them dying two or three days before 

 the other. 



Parthenogenesis. — Eumicrosoma benefica can reproduce partheno- 

 genetically but the percentage of eggs parasitized and the number of 

 eggs parasitized per female is usually low. Twenty-three unfertilized 

 females were supplied with eggs in the life history work. Of the 620 

 eggs supplied 239, or 38.5 per cent, were parasitized, an average of 

 ten eggs per female. Two hundred and ^even parasites were reared 

 and 206 were males. 



Proportion of Sexes.— In the study this year the number of fe- 

 males greatly exceeded the number of males. Of the 4,474 parasites 

 reared during the past summer 3,176, or 71 per cent, were females, 

 while 1,297, or 29 per cent, were males. Sexual reproduction, how- 

 ever, seems to be the rule, for of the 468 parasites bred from eggs col- 

 lected in the field, 336 were females and 132 were males. In the lab- 

 oratory studies unmated females always produced males. 



Effect of Oviposition in Different Stages of the Host Egg. — 

 The parasites show a decided preference for chinch bug eggs that are 

 from one to three days old and the best results were obtained in lab- 

 oratory studies when eggs of this age were used. A number of experi- 

 ments were conducted in which parasites were supplied with eggs 

 ranging in age from two to fourteen days. Parasitism occurred in all 

 of these eggs but the percentage of parasitism decreased as the age 

 increased. 



Host Relations. — Numerous experiments were conducted again 

 this year in an effort to rear Eumicrosoma benefica on some host other 

 than chinch bug eggs but all proved negative. The parasites were 

 supplied with eggs of Nysius angustatus, Geocoris sp., and of several 

 species of Jassidse. Large numbers of these eggs were also collected 

 from grass containing parasitized chinch bug eggs and these were care- 

 fully examined for parasites but no evidence of parasitism by Eumi- 

 crosoma benefica was noted. 



Length of Life. — The length of adult life was found to vary from 

 a few hours to seventy-eight days. Temperature is probably the most 



