The Ichneumon Flies 



cross-sectioned and is shown at c in the accompanying figure. 

 When fall comes and the feeding and breeding season is past, all 

 living individuals of this particular parasite will be found snugly 

 packed away in the larval state within the bodies of some host 

 insect and the winter is passed by them mainly in the larval con- 

 dition in their cocoons. With the approach of spring, however, 

 they transform to pupae and about the time when the young 

 host caterpillars begin to hatch from their eggs the adult para- 

 sites emerge ready for the summer's campaign. 



In this act of emerging it is interesting to notice that as with 

 many other parasitic Hymenoptera and in fact with many other 

 insects the males as a rule issue before the females and wait with 

 impatience for the companionship of the fair sex. From one lot 

 of cocoons studied by the writer in the spring of 1896, forty-nine 

 males issued between March }d 

 and nth before a single female 

 put in an appearance. On March 

 i jjth and I4th a single female 

 issued each day; on the I7th 

 eight more; on the i8th three 

 more; on the I9th fourteen more, 

 and on the 2Oth twenty more. 

 In the meantime the number of 

 males issuing had rapidly fallen Flg - 

 off and they eventually ceased 

 to make their appearance. The number of members of both 

 sexes was approximately equal. 



A curious fact may be noticed concerning the cocoons from 

 which these early spring individuals issued, that is to say, the 

 over-wintering cocoons. We have seen that an entire generation 

 may be produced in a space of fifteen days in midsummer, but, 

 of course, in colder weather the development is slow and the time 

 may be much extended. Again, in the absence of proper host in- 

 sects the females may live for several weeks without having oppor- 

 tunity to deposit their eggs. The midsummer cocoons are rather 

 fluffy and although more closely spun than are the cocoons of the 

 tussock moth caterpillar, they are still rather loose and the outer 

 silk in particular is loosely spun. With the over-wintering co- 

 coons, however, it is at once noticed that they are of a closer, 

 tougher and more parchment-like consistency. There is less of 



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