178 Annals Entomological Society of America [Vol. XI, 



HOST KILLED BEFORE OVIPOSITION OF PARASITE, 



The one point in this hfe history which seems to be of 

 unusual interest and perhaps practical importance is the fact 

 that the parasite stings the host before depositing eggs upon it 

 and oviposits only on dead or inactive larvae. 



The question naturally arose as to whether the larvae were 

 killed by the parasite or died from other causes. 



Larvae which had just died were examined by C. W. Howard 

 of this Division, who was unable to find any indication that the 

 caterpillars were killed by disease. After the larvae had been 

 dead one or two days, small brown spots appeared on the skin 

 presumably at the points pierced by the ovipositor. These 

 spots rapidly increased in size. 



Larvae, after being stung, but while still alive and active, 

 were injected with a 1% solution of trypan blue and after 

 about an hour were opened and the stain washed out. On 

 examination, the skin and tissues immediately surrounding each 

 puncture made by the ovipositor were found to be stained blue. 

 Larvae which had never been stung when injected in a similar 

 manner, showed no such stained- areas. It was thus possible 

 to determine the number of times a larva had been stung by the 

 parasite. The number of punctures in a single larva ranged 

 from 6 to 38. There seems, therefore, to be no doubt that the 

 parasite actually stings the larva. 



In order to prove that this stinging kills the larvae of the 

 wax moth, forty healthy larvae were placed in a glass jar con- 

 taining no parasites. They spun their cocoons and at the end 

 of three days were all perfectly normal. Then twenty of these 

 were removed from their cocoons and placed in another similar 

 jar where they again spun cocoons. Thirty parasites were then 

 introduced into the first jar where the larvae had been undis- 

 turbed, since spinning their cocoons. These parasites were 

 observed to move actively about and sting the larv«. In less 

 than a week every larva in this jar was dead. The larvae in the 

 second jar were all alive and eventually eighteen out of the 

 twenty reached maturity. This experiment was repeated three 

 times with similar results in each case. This experiment showed 

 that the larvae were undoubtedly killed by the sting of the 

 parasite, but whether death was the result of mechanical injury 

 or of a poison injected by the parasite was the subject of further 

 investigation. 



