2 BULLETIN 1088, U. S. DEPARTMENT OF AGRICULTURE. 



disease, before the parasites completed their development. Despite 

 the discouraging results of the breeding work, however, Z. nidicoJa 

 became established, and by 1910 had definitely taken its place in 

 our fauna. The trying experiences of the laboratory force, in their 

 attempts to establish this parasite, are interestingly recounted by 

 Howard and Fiske. 3 



DISTRIBUTION IN THE UNITED STATES. 



Because it evidently has no hosts other than the brown-tail moth 

 the parasite must necessarily remain within the area over which this 

 insect occurs; but within these limits it appears to be widely dis- 

 tributed, although it is relatively less abundant in the sections 

 where very low temperatures are reached during the winter. It has 

 been recovered from Rhode Island to northeastern Maine — very 

 abundantly in the former region, sparingly in the latter. This wide 

 dissemination, within some seven or eight years, is very largely the 

 result of natural spread, since there has been little artificial coloniza- 

 tion of this species. 



LIFE CYCLE OF THE BROWN-TAIL MOTH. 



Before taking up in detail the biology of the parasite it will be 

 well to review briefly the life cycle of its host. During July the 

 female brown-tail moth deposits her eggs on the underside of a 

 leaf of one of the favored food plants — apple, pear, oak, or wild 

 cherry. Usually the terminal leaves of the uppermost shoots of the 

 tree are selected for oviposition. The eggs hatch in about three 

 weeks and the small caterpillars feed on the epidermis of the leaves, 

 preferring the terminal ones, which they gradually tie together with 

 a large amount of silk. This process is slow, but ultimately a firm, 

 tough web, about 3 or 4 inches long, is formed. By this time the 

 majority of the slowly growing larvae are in the third stage and are 

 ready for hibernation. In the spring feeding begins as soon as the 

 buds open, and continues until the middle of June, when cocoons 

 are formed and pupation occurs. Moths issue during the first half 

 of July, and, after a few days, lay their eggs. There is only one 

 generation annually. 



LIFE HISTORY AND BIOLOGY OF THE PARASITE. 



EMERGENCE AND LONGEVITY OF THE ADULTS. 



Adults of Z. nidicola appear during the latter half of July. They 

 are very sturdy flies (Fig. 1) and endure unfavorable conditions 

 well, normally living for a period of at least several weeks. Some 



8 Howard, L. O., and Fiske, W. F. The importation into the United States of the 



PARASITES OF THE GIPSY MOTH AND THE BROWN-TAIL MOTH. U. S. Dept. AgV., Bur. Ent. 



Bul. 91, p. 289-295. 1911. 



