61S MISC. PUBLICATION 657, U. S. DEPT. OF AGRICULTURE 
Famity APHELINIDAE 
Most members of the family Aphelinidae are minute insects that 
parasitize the diaspine coccids. or aphids, although occasionally other 
orders are attacked. Many species are very important from an eco- 
nomic standpoint. 
Aphytis mytilaspidis (LeB.) is the most common parasite of the 
oystershell scale (Lepzdosaphes ulmz) in the United States and other 
parts of the world, and it also attacks many other diaspine coccids. 
Griswold (205) studied this parasite at Ithaca, N. Y., where high 
percentages of parasitization were obtained. The adult is a minute 
insect less than 1 mm. long and is bright lemon yellow, with black- 
ish eyes. The winter is spent as a full-grown larva beneath the scale 
of the host, and aduits emerge during the first 2 weeks in June, or at 
the proper time to oviposit on second-stage host larvae. The female 
pierces the scale and usually deposits one egg on the surface of the 
host. The larval stage, during which the parasite feeds externally, 
lasts about a month. The pupal stage is passed in the same position. 
Second-generation adults emerge during August and deposit eggs on 
the surface of sexually mature hosts or ‘lay their eggs among those of 
the scale insect. The resulting larvae complete “feeding and over- 
winter. Male parasites are very rare. 
Famity TRICHOGRAMMATIDAE 
The Trichogrammatidae are a small family of extremely minute 
insects, all of which are egg parasites. 
Trichogramma minutum Riley is such a well-known egg parasite of 
many species of Lepidoptera, and has been so extensively. propagated 
for biological-control work in this country, that only very brief notes 
will be made regarding it. The adults are extremely minute insects, 
measuring a litttle less than 0.5 mm. long. ‘Two strains or var ieties 
are commonly recognized, a yellow strain. (pretiosa) occurring in the 
colder regions, and a dark one (minutum) in the warmer parts of the 
country. This parasite spends the winter as a partly developed larva in 
the host egg. The number of individuals that may develop in 1 egg de- 
pends upon the size of the egg. Patterson (346) recorded a maximum 
of 37 and an average of 29.5 adults emerging from eggs of the pandora 
moth (Coloradia pandora). Eggs are inserted directly into the host 
egos, and normal development of the host embryo ceases immediately. 
The parasite larva hatches within a few hours, and lives free within the 
liquid contents of the egg. Temperature is an important factor in 
determining the life cycle. During warm weather from 9 to 16 days 
is usually sufficient for development from egg to adult. Approxi- 
mately 13 generations occur per season in New Jersey. Early in the 
summer the parasite is usually scarce, whereas late in the summer it 
may be abundant. 
Famiry MYMARIDAE 
The species of the family Mymaridae are all exceedingly minute, 
and, as in the Trichogrammatidae, all are egg parasites. The Hem- 
ie ‘a-Homoptera, Corrodentia, and Rhyncophora are commonly at- 
tacked, whereas Orthoptera, Odonata, and other orders are also para- 
sitized. The species are mostly black or yellowish and devoid of 
metallic colors. 
