TACHINID PARASITES OF THE GIPSY MOTH. 205 



information concerning the rapidity of dispersion of certain among 

 these flies and concerning the host relations of certain others. 



In an account of the methods used in conducting investigations 

 into the lives and habits of the tachinids, published by Mr. C. H. T. 

 Townsend three years ago, a good outline of the beginning of this 

 work is given. It has been found necessary to modify to a certain 

 extent the methods which seemed best at the time when this account 

 was written, and in one particular at least it seems advisable to 

 correct the statements therein made concerning the use of the large 

 out-of-door rearing cage for tachinid reproduction work and 

 investigation. 



In the beginning the use of the large cages, consisting of a wooden 

 frame covered with cloth or wire screen and inclosing a living tree, 

 was attempted upon a considerable scale. Cages of this character 

 had been so successfully employed in various somewhat similar 

 lines of work as to justify their consideration in this, and accord- 

 ingly a dozen or more were constructed and used for the confine- 

 ment of all sorts of introduced enemies of the gipsy moth or the 

 brown-tail moth, from Pteromalus egregius to Oalosoma sycopTumta, 

 including the tachinid parasites. 



The first of them, covered with wire gauze, was constructed in 

 1905 (PL XIII) and has been figured several times in various reports 

 upon and accounts of the work, but it was never given a thorough 

 test on account of the failure to secure parasites in any amount that 

 first year. In 1906 cheesecloth coverings were substituted for 

 wire and a number of cages, the general pattern of that figured 

 herewith (PL XIV), was constructed and used that year and in 

 1907, but with pretty generally unfavorable results. It was found 

 that only a very small number of caterpillars could be supported 

 by the foliage of the inclosed trees or shrubs, and that it was neces- 

 sary to feed them artificially exactly as was necessary in the smaller 

 cages. The impossibility of keeping a variety of native insects out, 

 as well as of keeping the foreign insects in, was another and only 

 too apparent fault. In an experiment with tachinid reproduction 

 in one of these cages in 1907, the number of flies introduced in the 

 beginning grew steadily less day by day, with no adequate explana- 

 tion for the disappearance of the missing individuals. 



Another disadvantage accrued through the fact that when a 

 caterpillar was in any way dislodged from the inclosed tree upon 

 which it was expected to remain and feed, the chances were infi- 

 nitely greater that it would find its way to the side, and then to 

 the roof of the cage, than that it would, unassisted, regain its former 

 position. The parasites, also, instead of staying about the tree 

 where their business was supposed to demand their attention, would 



