224 PARASITES OF GIPSY AND BROWX-TAIL MOTHS. 
It is yet too soon to begin to speculate upon what the actual out- 
come in specific instances will be. An investigation of the parasites 
of the fall webworm was undertaken in the fall of 1910 on the suppo- 
sition that Compsilura would find it an acceptable host, but although 
it is freely attacked when outside of its web in rearing cages in the 
laboratory, it was not at all commonly attacked in the open, as will 
be seen by reference to the brief summary of the results of the work 
in the concluding pages of this bulletin. 
There has never been a good opportunity to study the parasites 
of the Tachinidse, owing to the fact that some of the species pupate 
upon or beneath the surface of the soil, and are therefore difficult to 
find in sufficient quantities to make a comprehensive study possible. 
So abundant was Compsilura, however, as to make it possible to 
collect its puparia in considerable abundance and with comparatively 
little trouble at the base of trees upon which the gipsy-moth cater- 
pillars were common, and accordingly a number was so collected in 
the late summer of 1910. Not enough attention was given to the 
work to make the results as definite as is desired, but these were 
sufficient to indicate that secondary parasitism was undoubtedly of 
very common occurrence, and that it might be a factor of some con- 
sequence in limiting the effectiveness of the parasite. No less than 
six species of secondaries were reared, including Monodontomerus 
sereus, which was common, Dibrachys, another small chalcidid, a 
species of Chalcis, a proctotrypid, and a Phygadeuon. It is hoped 
that circumstances will permit of a more thorough study of this 
subject in 1911, and should the parasite show an increase propor- 
tionate to that which was indicated by its abundance in 1910 over 
that of 1909, the project should be very easy of accomplishment. 
It is fortunate that, under the present circumstances, with the 
gipsy moth and the brown-tail moth both exceedingly abundant and 
uncontrolled, there should be at least one parasite which was equally 
drawn toward both. It is easily possible that the first individuals 
which are reared upon the brown-tail moth as a host may attack the 
full-fed caterpillars for a partial second generation the same season, 
and then, together with the bulk of the brood coining from this host, 
turn their undivided attention to the gips} r -moth caterpillars. In a 
similar manner the first individuals to go through their transforma- 
tions upon the gipsy moth, together with the partial second genera- 
tion upon the brown-tail moth, may attack the less advanced gipsy- 
moth caterpillars for a partial third brood before the necessity for 
an alternate host becomes apparent. 
There is thus possible uninterrupted increase for two complete gen- 
erations at least, and probably for a partial third, but unfortunately 
the necessity for an alternate host , though delayed until no more than 
one such host is necessary in order that the seasonal cycle may be 
