OF WASHIXGTOX, VOLUME XV, 1913 129 



the development of the resulting adult flies; (4) what species of 

 Tachinidse were involved. 



The only species reared wa< Winthemia quadripustidata Fabr. 

 Fourteen caterpillars were selected, each bearing from one to 

 twelve of the conspicuous eggs of this fly. Each larva was placed 

 in a single small cage and kept under similar conditions. Two of 

 them designated respectively as F and G died after entering the 

 ground from causes undetermined, no flies issued from them, they 

 may therefore be eliminated from consideration. In the re- 

 maining twelve cases parasites emerged from each, resulting in the 

 destruction of the host, thus apparently indicating a very high 

 degree of effectiveness for this species of parasite on the last instar 

 of Laphygma. 



The largest number of flies to issue from any one host was three 

 and this occurred only in one instance. In five cases two flies 

 emerged. In the remaining six but pne fly each resulted. It may 

 be seen by consulting the appended table that the largest individ- 

 uals each and all emerged from hosts which had borne but a single 

 egg of the parasite. In these cases designated as A. G and L the 

 flies averaged 10.5 mm., all males. In case M (the only example 

 remaining in which but two eggs were borne by the host), the 

 resulting fly, a female, measured 9 mm., indicating apparently that 

 there is a distinct economi- loss to the fly when more than one egg is 

 deposited. And this idea is well borne out by the results obtained 

 from the other examples where a large number of parasitic eggs 

 were found. In cases C and D where six eggs occurred the result- 

 ing flies, two males and one female, averaged 8.5 mm. In cases I 

 and X where 7 eggs occurred we have an average of 8.59 (two males 

 and one female). In cases E and K where as many as 12 eggs 

 were present on the host the average is but 7 mm. (three males and 

 one female). In both the latter cases but two adults issued in 

 each cage. It appears obvious from the foregoing that in this spe- 

 cies at least the size of the adult fly may bear a direct relation to the 

 number of eggs deposited on the host caterpillar by the parent. 

 It would be interesting to know what effect if any this diminish- 

 ment in size has upon the reproductive powers of the resulting indi- 

 viduals. The three largest individuals are all males. But the fact 

 that size bears no relation to sex in this species is apparent from the 

 results here obtained, that is to say. the two smallest individuals 

 reared (see case K) are also males. 



AYe might speculate at length upon what occurs in those cater- 

 pillars where -everal eggs are deposited. But one thing is plainly 

 evident, namely, that a struggle for survival ensues among the para- 

 sites. One result of which is diminished size and therefore possibly 

 a lessening of reproductive vigor in the issuing adults. 



