6 



BULLETIN 1088, U. S. DEPAETMEXT OE AGEICULTUEE. 



brown-tail moth caterpillar was completed within 10 minutes after 

 the egg had been deposited. From many observations it appears 

 that normally 20 to 30 minutes elapse between oviposition and the 

 entrance of the parasitic larva into its host. Often the caterpillar 

 makes vigorous attempts to destroy the maggot before the latter 

 has made its way inside, and occasionally these efforts are suc- 

 cessful, particularly if the egg of the parasite was deposited near 

 the posterior end of the host. In this case the brown-tail moth 



larva, by doubling its bodj^, can reach the parasite 



and crush it with its mandibles. 



FIRST-STAGE MAGGOT OF THE PARASITE. 



The most striking thing about the parasitic mag- 

 got at the time it enters the caterpillar is the strongly 

 chitinized mouth hook (Fig. 2, a, h). It is 

 simple in this stage, consisting of a single 

 apical tooth and comparatively narrow,, 

 divided, posterior plates, the entire mouth 

 hook being one solid structure. A pair of: 

 rather indistinct spiracles open on the last 

 body segment. 



After entering its host the parasite lives 

 free in the body cavity for about 10 to 14 

 daj's and feeds on the fat body of 

 the slowly developing caterpillar. 

 Then it enters the oesoiDhagus and 

 remains here throughout its hiber- 

 nation period of about nine months 

 It may lie longitudinally disposec; 

 or it may lie obliquely ; apparently 

 no particular part of the oesopha 

 gus is preferred, but usually thf 

 head of the parasite is directed to 

 ward the anterior end of its host 

 From dissections it appears that the maggot lies in a cyst agains 

 the inner wall of the intestine. Here, of course, it does not fee( 

 at all. 



Rather severe competition is encountered from two hymenopterou 

 parasites, Apcmteles lacteicolor Yiereck and Meteofus versicolc 

 "Wesmaeh which also hibernate in the small brown-tail moth cater 

 pillars. The presence of either of these parasites in the same hof 

 with Zygobothria produces the death of the latter. The eXac 

 nature of this peculiar influence exerted b}'^ the hymenopterous par? 

 sites upon the dipterous larva has not yet been demonstrated. Deat 



Fig. 2. — Zyoohothria nidicola: a. Mouth 

 hook of first-stage maggot, dorsal as- 

 pect ; i, mouth hook of first-stage 

 maggot, lateral aspect ; c, mouth hook 

 of second-stage maggot ; d, mouth 

 hook of third-stage maggot. 



