118 



under certain conditions, reproduce parthenogenetically. Observa 

 tions on breeding such minute insects are difficult to make, however, 

 and must always 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 only one, have been 

 bred. The adults live at most only about four days, and their av^erage 

 life is but one and one-half da3^s. During this stage 

 it is probable that they feed but little, although they 

 have been observed to feed on fruit juices in the lab- 

 oratory and might easily find food in nature at the 

 nectaries on the cotton squares or leaves. 

 ^ partrnzel^b^Tn^^^^^^^ ^or some two days after the eggs are stung by the 

 gramma pretiosa parasite they show uo external sign of parasitism, but 

 (original). generally on the third day they rapidly become dusky 



and translucent, which color changes to an opaque bluish black soon 

 after. This color , persists very 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 

 may 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 extremel}^ 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, by 

 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; antennae 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 by 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. 



