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 " 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- 



