July 29, 1918 
Parasites of the Brown-Tail Moth 
199 
spinning, and the old larval skin is pushed back upon the excrement 
previously voided. Gradually the pupa (PI. 21, B), yellowish white at 
first, blackens; then the pupal skin is cast, and the adult parasite 
emerges after first cutting out a perfectly circular lid at one end of the 
cocoon. The total length of the period spent within the cocoon is from 
5 to 8 days. 
The adults of the first generation of A. lacteicolor are found issuing 
from about the 20th of May to the middle of June in New England. 
Mating will take place almost at once, within 24 hours after emergence, 
and oviposition may begin within 48 hours. Laboratory experiments 
have shown females of this species unwilling to oviposit during the first 
24 hours, but they will do so very readily shortly after this. As is true 
with many parasites, fertilization is not necessary for reproduction, but 
unfertilized females produce only males. 
SUMMER HOSTS OF APANTEEES EACTEICOLOR 
Considerable effort has been expended by the writer to determine in 
what hosts this parasite passes the summer. The species has been reared 
frequently from small gipsy-moth caterpillars at the laboratory, and 
Howard (2, 3) emphasized the importance of the parasitism upon this 
species. The writer's observations in the field and experiments at the 
laboratory have convinced him that wherever brown-tail-moth cater¬ 
pillars occur in sufficient numbers to insure the presence of a fair propor¬ 
tion of A . lacteicolor , the parasitism upon the small gipsy-moth cater¬ 
pillars is considerable. These are attacked in the first or second stage 
and are killed by the parasite before they have passed the third (PI. 21, C). 
They are greatly retarded in their development when infested by the 
Apanteles, and when the development of the parasite is nearly complete, 
the caterpillars seek places of concealment on the lower side of leaves and 
limbs, in crevices of the bark, etc. Hence they are easily overlooked by 
men collecting caterpillars to determine the extent of parasitism. So far 
as the writer has been able to determine, the gipsy moth is the only host, 
acceptable to A. lacteicolor , which is available at the time of the appear¬ 
ance of the adult parasites of the first generation. Where the gipsy moth 
does not occur the Apanteles females evidently do not oviposit for several 
weeks, until various native host species, which this parasite will attack, 
appear. One much retarded caterpillar of Malacosoma americana Fab- 
ricius was attacked by A. lacteicolor , but no reproduction was secured, 
although, as was found later by dissection, an egg had been deposited. 
This species is normally too far advanced by the time of the appearance 
of A. lacteicolor to serve as a host of this parasite. 
The total period required for the development from egg to adult, in 
the case of the summer generations, averages 19 to 20 days, and it is 
during the last weeks of June and in early July that adults of the brood on 
the gipsy-moth caterpillars emerge. 
