SEXUAL CHARACTERISTICS OF THELIA 549 
space between the abdominal terga and sterna; the fat distending 
the abdomen shows through laterally at this stage, but not in 
sexually mature individuals. 
In early June, when the young Thelia nymphs of first to third 
instar are abundant on the smaller branches, the female Aphe- 
lopus hurries nervously up and down the branches of the locust 
tree hunting its prey. Finding a nymph, she taps it with. her 
antennae, much as does an ant, and quiets it; she then climbs 
upon the dorsum of the nymph, feels its head with her large 
powerful mandibles, to test, I believe, whether or not the nymph 
is soon to molt. If the parasite decides to deposit an egg, she 
grasps the caudal part of the nymph’s abdomen between her 
mandibles, and, holding firmly with her legs to the abdomen of 
the host, tries to thrust her sword-like ovipositor cephalad 
through the intersegmental membranes of any two abdominal 
terga. The nymph struggles as the ovipositor pierces, and from 
the anal tube exudes a drop of liquid. This, the Aphelopus 
grasps In her mandibles and is gone in a second. If the nymph 
is a small first, second, or third instar, the whole act of oviposit- 
ing may take but a few seconds; but, when a fourth or fifth 
instar is attacked, a long struggle often follows and it may take 
several minutes before the small energetic parasite accomplishes 
her task. Having examined the nymph and decided to oviposit, 
the Aphelopus gets hold of a tibia with its mandibles and legs 
and hangs on, no matter how hard the Thelia kicks or even if 
both go rolling over and over. The parasite then tries to force 
its ovipositor through the soft membranes between the tro- 
chanter and femur or between the coxa and thoracic sternum. 
After ovipositing, the Aphelopus generally mounts the abdomen 
of the nymph to secure a drop of excrement. After a struggle 
with a large nymph, the parasite remains on the bark or on a 
leaf, cleans her wings, legs, antennae, and mandibles, and espe- 
cially rubs her ovipositor vigorously with her hind legs. The 
whole process of oviposition was watched many times in the 
laboratory under a binocular microscope by putting a female 
Aphelopus into a test-tube containing a locust twig upon which 
several Thelia nymphs were feeding. The parasite would hunt 
