176 TRANSACTIONS OF THE ILLINOIS 



Another method is to use a hook at the end of a pole, as suggested by 

 Dr. Le Baron. I mention these little facts because they may not occur to 

 many of you, and I know many of you may profit by them. 



There are many indirect ways of fighting this insect — first of all, by 

 encouraging its parasites. I have discovered that two parasites prey upon 

 the codling moth. Some of the college students before me may want to 

 know what I mean by parasites. If I told you of a bug that deposited its 

 eggs on the bodies of sheep or other animals; that that egg hatched out 

 into a serpent, which fed and flourished in the fatty portion of the sheep, 

 without injuring it, for a time, apparently ; that on the contrary, the 

 sheep so infested would be able to live without food, whereas without the 

 parasite it would die ; that after a time the serpent ate its way through 

 the sheep, burrowed into the ground, and after remaining there an indefi- 

 nite time, would struggle through the earth and issue as a bird, like its 

 parent, the story would appear ridiculous. Yet it is hardly more wonder- 

 ful than the actual facts of parasitic insect life. 



But I will illustrate the parasitic theory of the insect world by show- 

 ing you the tomato worm. 



[Here the lecturer illustrated, at some length, the curiosities of parasitism by means 

 of drawings on the blackboard, which cannot be produced here.] 



In referring to the common tomato worm, he remarked : 

 There is a peculiar little microgaster, a little fly that comes along 

 and invariably settles on the back or head of the worm, knowing ver}- 

 well that it cannot there be injured. It punctures the skin of that worm 

 and inserts an egg, or perhaps forty or fifty. The maggots hatched from 

 these eggs feed on that worm — which in time becomes sickly, until at 

 last the little parasites are fully grown, and then they spin cocoons on the 

 back of the worm, from which, eventually, little black flies, like the 

 parent, issue. Now, this is primary parasitism ; but there are secondary, 

 tertiary and even quaternary parasites. And so it is, in the language of 

 Swift : 



" So naturalists observe a flea, 

 Has smaller fleas that on him pre)' ; 

 And these have smaller still to bite 'em, 

 And so proceed, ad infinitum.'''' 



We frequently have no less than four distinct parasites feeding on 

 one another, and all of them on a vegetable feeder. 



Mr. Galusha — Is it invariably the case that parasites are much less 

 in size than those upon which they prey ? 



Mr. Riley — True parasites, as distinguished from cannibals, invari- 

 ably and necessarily are. I have mentioned two parasites on this apple 

 worm. I will try to describe one : it is the macrocentrus delicatus. This 

 fly punctures the worm while yet in the heart of the apple, and spins its 

 cocoon inside the cocoon of the apple worm. This is a yellow fly ; the 

 other is a black fly, pimpla annulipcs. Instead of destroying it before it 

 has assumed the chrysalis state, it does not destroy it until after. 



