118 
under certain conditions, reproduce parthenog-enetically. Observa 
tions on breeding such minute insects are difficult to make, however, 
and must alwaj'S be attended with some uncertainty. The sex of the 
parthenogenetically produced individuals was not determined. From 
a parasitized egg there emerge, on an average, about two parasites, 
although often as many as four, and sometimes onh^ one, have been 
bred. The adults live at most only about four da^^s, and their average 
life is but one and one-half days. During this stage 
it is probable that they feed but little, although they 
have been observed to feed on fruit juices in the lab- 
orator}^ and might easily find food in nature at the 
nectaries on the cotton squares or leaves. 
^'v^l^^zfa^j'-^ich!- For some two days after the eggs are stung by the 
g r a m ma pretiosa parasite they sbow DO Bxtemal sign of parasitism, but 
(ongina ). ^ generally on the third day they rapidly become dusky 
and translucent, which color changes to an opaque bluish black soon 
after. This color persists ver^^ distinctly, even after the parasites 
have emerged, and alwaj^s serves to distinguish a parasitized egg. 
Their exit is accomplished by cutting a rounded, often jagged, hole in 
the shell of the host egg (see fig. 21). Although several parasites 
ma}^ come from a single egg, generally but one exit hole is present, it 
being in most cases on one side. Copulation usually takes place 
within a few hours after emergence and oviposition follows almost 
immediately. 
DESCRIPTION OF TRICHOGRAMMA PRETIOSA RILEY. 
Trichogramma is an extremely minute Chalcis-fly, scarcely visible 
to the unaided eye, and resembling closely the numerous other species 
belonging to this group. It can be recognized readily, however, b}^ 
the characteristic arrangement of the hairs on the front wings, i. e., 
in regular rows, and by the presence of only three tarsal joints. 
Length 0.3 to 0.43 mm., the males being usually the smaller. Color pale yellow, 
as a rule, although some specimens are almost black. Eyes dark red and wings 
hyaline. Head wider than the thorax; antennse eight-jointed, pedicel about two 
thirds the length of the scape, one small ring joint, the two joints of the funicle equal, 
together shorter than the pedicel, club conic ovate, a little longer than the scape; 
funicle and club beset with many long hairs in the male and with short ones in the 
female. Hairs of the front wings arranged in about fifteen lines. Abdomen not so 
wide as the thorax, but as long as the head and thorax together. 
Eggs attacked b}^ this little parasite have been obtained at various 
localities in South Carolina, Georgia, Florida, Alabama, Texas, and 
Arkansas, so that there can be no doubt of its very general distribu- 
tion throughout the cotton-growing States. It is also a very useful 
parasite of the eggs of the cotton caterpillar. 
