280 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 
them. During this operation the caterpillars, stirred into unusual 
activity, were crawling over everything in the immediate vicinity, but 
more particularly over the outside of the cage and the person of the 
operator. 
If a sufficient number of these caterpillar parasites were to be reared 
to make possible satisfactory colonies another year, it was obviously 
exceedingly desirable to devise some other means of feeding the 
caterpillars than that afforded by the closed cage, and accordingly, 
in the winter of 1907-8, when the first active caterpillars began to 
emerge from the nests which had been kept in the warmed part of 
the laboratory for the purpose of securing Pteromalus, all sorts of 
experiments were made in the hope of discovering some method 
whereby the disadvantages above recounted might, at least in part, 
be obviated. The feeding tray illustrated herewith, was the result of 
these experiments, and as soon as it was found to be practicable, 
enough to accommodate several thousand caterpillars were con- 
structed, and one wing of the laboratory 11 annex/' illustrated in 
Plate XXVI, figure 2, and Plate XXVII, was fitted for their accom- 
modation. 
In all respects these trays were a success. There was occasionally 
some trouble caused by the caterpillars finding or constructing a 
"bridge," by which they passed from the interior of the tray directly 
to the frame above the concealed band of "tanglefoot," but when 
sufficient care was used in feeding and in searching for bridges before 
they were completed this was almost completely done away with. 
It was manifestly impossible to feed more than a very small part 
of the caterpillars from the many thousands of nests which had been 
imported during this winter, and accordingly the caterpillars from a 
few nests in each lot were fed in small trays in the laboratory during 
the late winter and early spring, and the extent to which they were 
parasitized by Apanteles was thus determined. The most highly 
parasitized nests were saved, and the larger part of those less highly 
parasitized were destroyed forthwith, since it was no longer desired 
to save the Pteromalus which might be reared from them. 
A good many Apanteles were reared in the course of this work, and 
since they issued long before the resumption of insect activities out 
of doors they were used in a series of reproduction experiments upon 
active caterpillars of the brown-tail moth feeding upon lettuce indoors. 
It was found to be easy to secure reproduction when caterpillars 
which had not molted since leaving the nest were used as hosts, but 
if they had molted once successful reproduction was secured with 
great difficulty or not at all. The adult Apanteles were very far from 
being as strong and hardy as the adult Pteromalus and could not be 
kept alive to deposit more than a small part of their eggs. There 
were, other reasons, too, why reproduction upon caterpillars in confine- 
