July 29, 1918 
Parasites of the Brown-Tail Moth 
197 
a series of homologues with the intestinal tracts of other parasitic larvae, 
that a yet more important function is excretion. For the present the 
matter must rest here, but further study may throw more light upon 
the function of this curious structure. 
competition with other parasites wintering in the brown-tail-moth cater¬ 
pillars 
Since there are two other parasitic species that pass the winter within 
the small brown-tail-moth caterpillars there is naturally some competi¬ 
tion between the three. These other species are Zygobothria nidicola 
Townsend, a fly of the family Tachinidae, and Meteorus versicolor Wesmael, 
the other parasite discussed in this paper. It was determined from over 
13,000 dissections of hibernating brown-tail-moth caterpillars that when¬ 
ever A. lacieicolor enters into competition with either or both of these 
species it wins out; the other parasite or parasites present are killed 
before midwinter, evidently as the result of some toxic action induced 
by the Apanteles larva. Even when two larvae of A. lacieicolor occur 
in the same host, only one of these normally completes its development. 
Some very interesting cases of competition were encountered in the course 
of the dissecting: In one caterpillar were found two larvae of A. lac - 
teicolor , one of them dead, five dead Zygobothria maggots more or less 
encysted and no longer occupying their normal position in the jore 
intestine of the caterpillar, and three eggs of Meteorus versicolor , the 
development of which had been arrested; another caterpillar contained a 
living larva of A. lacieicolor , nine dead Zygobothria maggots, and one 
partly developed egg of M. versicolor , the embryo dead. Many similar 
cases were encountered, but in no case was a dead Apanteles larva found 
in the s,ame caterpillar with a living larva of some other parasitic species. 
This ability to win out over the species of parasites hibernating within 
the brown-tail-moth caterpillar strengthens considerably the position of 
A. lacieicolor. 
LATER ENDOPARASITIC LIRE 
In May, when the brown-tail-moth caterpillars resume feeding, the 
small larvae of A . lacieicolor within these caterpillars likewise become active 
and begin in earnest the task of destroying their hosts. The parasitic 
larva develops very rapidly; after a day or two of feeding it attains the 
length of 1 millimeter, or slightly more (PI. 20, D), and passes into the 
second stage, which differs from the first principally in that the mandibles, 
or structures corresponding to the mandibles, are bidentate and not 
chitinized, whereas in the first stage they were simple and heavily chit- 
inized (PI. 20, E). The anal vesicle is much more in evidence, being 
proportionately larger, but the horn beneath, so prominent in the first 
stage, is scarcely noticeable, not having increased in size at all. The 
almost invariable position of A. lacieicolor now is in the posterior half 
of the body of its host, the parasite being longitudinally disposed, its 
