258 PARASITES OF GIPSY AND BROWN-TAIL MOTHS. 
something like 275 separate but similar experiments in their repro- 
duction in confinement in the laboratory. It is of course possible, 
since it was especially desired to continue the experiments as long 
as possible with individuals of known parentage, that the results are 
misleading. Possibly had American Trichogramma been collected 
in the open from a variety of sources, a race might have been found 
which was arrhenotokous, even as the similar search might have 
resulted in the discovery of a thelyotokous race in Europe. As it 
is, the American stock was once renewed. In 1907 a series of experi- 
ments was conducted with parent stock reared from brown-tail moth 
eggs collected in Maine, and in 1908 a similar but more extensive 
series with parent stock from eggs of the brown-tail moth collected 
in Massachusetts. In each instance the results were the same. 
The longest series of experiments with the arrhenotokous Euro- 
pean race was with the progeny of individuals reared from one lot 
of European eggs from the Province of Carniola, Austria. Similar 
experiments with one other lot of females upon another shipment 
of eggs from the same Austrian province and perhaps from the same 
locality resulted similarly, but the series was not nearly so long. In 
the first-mentioned series 13 generations were reared in the laboratory, 
all but the first three being parthenogenetic. Males were secured 
at one time, and for a limited number of generations, but soon dis- 
appeared, even from the progeny of mated females. The results 
of these experiments will be published in detail later. 
Importations of egg masses of the brown-tail moth which had been 
collected in the open in Europe were first attempted in the summer of 
1906, and from almost the first of those which were received at the 
laboratory a few examples of the pretiosa-like European form were 
reared. Mr. Titus attempted to secure reproduction in the labora- 
tory that first season, but as he had no supply of host eggs in which 
embryonic development was not considerably advanced, his attempts 
met with failure. 
In 1908 a larger number of egg masses of the brown-tail moth was 
imported from a great variety of European localities, and as before, 
the p? n etiosa-\ike Trichogramma was quickly secured. The failure 
of the previous season and its cause had early been taken into ac- 
count, and some time before a large quantity of fresh eggs of the 
brown-tail moth had been collected and stored at a temperature 
sufficiently low to prevent embryological development. When sup- 
plied with a quantity of these eggs the imported Trichogramma ovi- 
posited with the greatest freedom, and in the course of a few genera- 
tions had increased enormously, so that many thousands were lib- 
erated later in the fall. It was conclusively demonstrated that 
even though the host eggs were dead, abundant reproduction could 
he easily obtained under laboratory conditions. 
