42 EESULTS FROM GIPSY MOTH PARASITE LABORATORY. 



tiny tachinid maggot can, without inconvenience apparently, con- 

 tinue in its develo})mcnt with the Perilamjms larva boring about 

 within its body, and sometimes with not only one but five or six. 



What becomes of the planidium in case the caterpillar does not 

 contain a primary parasite is a question which has not yet been 

 answered, and to do so would require considerable care and patience. 

 There are two courses open to the Perilamjms in case it has selected 

 an unparasitized caterpillar. It may either wander about within the 

 body of the latter until it dies from starvation and exhaustion, or it 

 may make its way to the outside again and continue the search for a 

 host in another caterpillar. That it might possibly develop upon the 

 caterpillar itself is not to be considered. Even should it remain 

 within the caterpillar until the latter pupated,^ it is not hkely that 

 it could make its way through the hard pupal shell of Hyphantria, and 

 if this were possible the older Perilam-jMS larva is very much too 

 delicate a creature to be able to feed externally unprotected. 



In case the former alternative is what actually takes place, there 

 must be a great percentage of mortality due to the lack of a proper 

 host, for relatively only a small proportion of the caterpillars hatching 

 from the eggs ever reach an age sufficient to nourish a host for 

 Perilampus. Of those that do reach that age a great many are never 

 attacked by primary parasites and hence would not be available for 

 Perilampus. 



Just what is the effect upon the caterpillar itself which is infested 

 by Perilamjms but which contains no primary parasite is a matter for 

 conjecture. It seems likely, however, that its presence would not 

 prevent the caterpillar from reaching its full development and it is 

 probably only slightly inconvenienced if affected at all.^ 



Having followed the Perilam/pus planidium to its host wdthin the 

 caterpillar it is now necessary to trace out the slightly different modes 

 of development upon the various parasites of Hyphantna which are 

 subject to its attack. 



Life as a Parasite op Varich.eta. 



VaricJiseta aldrichi Townsend ^ has been by far the most common of 

 all of the parasites of the fall webworm in Massachusetts during the 

 past two years. As stated on a preceding page, it belongs to that 

 group of tacliinids which deposit Hving maggots upon the stems and 

 foliage in the vicinity of the caterpillars of their chosen host, a habit 

 first discovered by Mr. C. H. T. Townsend in the course of his work 



1 Later dissection of Hyphantria pupae, made in the spring of 1911, by Mr. H. E. Smith, discovered the 

 planidium alive and still "waiting for something to turn up." In one instance the planidimn was em- 

 bedded in the gonad of the Hyphaniria. — W. F. Fiske. 



2 The occurrence of the planidimn in the gonad, as noted in preceding footnote, suggests that partial 

 castration might possibly result. 



» Detenuinatioa furnished by Mr. W. R. Thompson. 



