June, 1922 bionomics of alphelinus semiflavus 



223 



This position was then held for several minutes without mov- 

 ing, during which the body of the aphid was noticed to slowly 

 collapse. After it was apparently sucked dry, Aphelmus would 

 withdraw and search out another victim where the same 

 maneuvers were repeated. Three small nymphs were thus fed 

 upon in half an hour, after which the parasite's abdomen 

 appeared quite distended with their contents. 



These dead aphids were later dissected, and it was found 

 that Aphelinus had deposited an egg in each. This would seem 

 to indicate that oviposition was the primary object in punctur- 

 ing a host, and that feeding was a secondary, acquired habit. 



Table III. 

 Effect of Different Food, Accessible, on Length of Life in the Adult Parasites. 



However, with this habit of feeding, the parasite defeats its 

 primary purpose by killing the host and preventing the develop- 

 ment of the egg immediately after it is deposited. 



Observations made in the course of other experiments show 

 that a single parasite ordinarily kills, in the above manner, 

 from three to five of the smaller instars per day. The very 

 young stages are almost always preferred, although it has been 

 noticed to feed on a third or fourth instar nymph. That the 

 older stages are seldom if ever attacked, has been demonstrated 

 in a number of instances where Aphelinus was confined with 

 adult aphids for various purposes. The parasite not only failed 

 to oviposit in these adults, but actually died with them for 

 want of food when the adult aphids did not produce young for 

 it to feed on. In all cases the aphid is very much weakened so 

 as to offer practically no resistance, before the parasite will 

 attempt to feed. While the feeding is going on, the aphid 



