6 



BULLETIN 1088, U. S. DEPARTMENT OF AGRICULTURE. 



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 pviposition 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 body, 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, b). 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 

 days and feeds on the fat body of 

 the slowly developing caterpillar. 

 Then it enters the oesophagus and 

 remains here throughout its hiber- 

 nation period of about nine months. 

 It may lie longitudinally disposed 

 or it may lie obliquely ; apparently 

 no particular part of the oesopha- 

 gus is preferred, but usually the 

 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 against 

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

 at all. 



Rather severe competition is encountered from two hymenopterous 

 parasites, Apanteles lacteicolor Viereck and Meteorus versicolor 

 Wesmael, which also hibernate in the small brown-tail moth cater- 

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

 with Zygobothria produces the death of the latter. The exact 

 nature of this peculiar influence exerted by the h} T menopterous para- 

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



Fig. 2. — Zygobothria nidieolo: a. Mouth 

 hook of first-stage maggot, dorsal as- 

 pect ; b, mouth hook of first-stage 

 maggot, lateral aspect ; c, mouth hook 

 of second-stage maggot : d, mouth 

 hook of third-stage maggot. 



