96 ASSOCIATION OF ECONOMIC ENTOMOLOGISTS. 



though all of lu}' assistants have repeatedlj^ observed the female 

 Polygnotus ovipositing in the eggs of the Hessian fly, and Mr. G. I. 

 Reeves has found larvse to the number of 28 in the matured maggot. 

 We have thus observed the ovii^osition in eggs of the fly and reared 

 adults from the " flaxseeds." If Doctor MarchaPs suppositions are 

 correct, and, as is very probable, our American species have similar 

 habits, their economic importance Avill be innnense, for it will be pos- 

 sible for a single female Polygnotus to place her supply of eggs 

 singly in those of the Hessian fly, and the number of her progeny 

 •would be limited only by the sustaining capacity of the host larvae. 



Another parasite with })olyembrvonic development is Plati/r/aster 

 herrie/iii Pack. Mr. Reeves has observed this also, ovipositing in the 

 eggs of the Hessian fly, and at another time, in a locality several 

 hundred miles distant, he counted ovei- 40 larva? in a single maggot. 



AMiethei" or not there are other species of Platygaster infesting the 

 Hessian fly it is just now impossible to state, but there are certainly 

 more than one species of Polygnotus engaged in this efficient work, 

 and the saving to the wheat ©rowers of North America through their 

 influences is innnense. 



The whole problem of polyembryony among parasitic insects is 

 exceedingly interesting and of the utmost economic importance. 

 AVlien Doctor Howard called attention to the enormous numbers of 

 Copidosoma that he had reared from a larva of Plusia hrasslcw in 

 1882, the number from a single individual, of ID larvre, being 2,528, 

 he was unable to learn by dissection that the female Copidosoma Avas 

 capable of laying more than 100 eggs. Later, in Ohio, I reared from 

 a lot of 5 larva' of this s^^ecies the enormous number of over 4,800, 

 and since that time Mr. C. W. Mally, in South Africa, reared 2,112 

 from a Plusia larva, while Monsieur E. Bugnion has reared over 3,000 

 individuals from a single host larva. Doctor Howard first thought 

 that more than one female Copidosoma had oviposited in a single 

 host larva, but this has since been found to be exceedingly unlikely. 

 In the case of some of our American species of Polygnotus and 

 Platygaster Jierrickii the female parasite positively refuses to ovi- 

 posit in eggs that have already been visited by another female. 

 Attention has also been called to the almost general phenomenon of 

 all iiidiA'iduals from a single larva being of the same sex, all of which 

 goes to iniply that l)ut a single ovum is placed in a single host, and 

 the extent to which the parasitic larvae will nudtiply from this is 

 only limited by the size of the host larva. Thus we have an expla- 

 nation of what has been a })uz7Je to entomologists, viz, the sudden 

 and almost complete disappearance of the Hessian fly between broods. 

 It also indicates the great value of these insects for use in introducing 

 parasites in section^ Avhere an outbreak of the host insect is seem- 

 ingly impending. How many of our parasites have this polyembry- 



