These flies are of medium to large size, with long often partly clouded wings. They are solitary or gregarious internal parasitoids of adult scarab beetles. Davis (1919) studied Pyrgota undata Wied., a nocturnal species attacking nocturnal hosts, Phyllophaga spp. To oviposit, the female alights on the dorsum of a feeding beetle, causing the latter to fly. At this time she inserts the ovipositor through the thin exposed integument of the abdominal dorsum. Female beetles are more often attacked than males, and the host dies 10-14 days after parasitoid oviposition. The puparium is formed within the dead host. There is a single generation per year, and winter is passed as pupae.
In India, Adapsilia flaviseta Ald. commonly parasitizes beetles of the genus Popillia (Clausen et al. 1933). Adults are dirunal as are the ost. Oviposition behavior is similar to Pyrgota undata, but male beetles are preferred (ca. 88%) early in the season. Later only 60% of males are parasitized as their abundance diminishes. Eggs hatch 3 days after oviposition, and the larval period is 12-15 days. The beetle is killed by the parasitoid larva soon after its second molt, which is 12-14 days after oviposition. There is a single generation per year, and hibernation occurs in the puparium within the bodies of dead host beetles in soil.
Clausen (1940) referred to unpublished reports of R. W. Burrell containing information of the habits of Maenomenus ensifer Bezzi, as a parasitoid of adult beetles of Anoplognathus olivieri Dalm. in Australia. The oviposition bvehavior differs from the above examples in that attack occurs while the host rests on foliage, the ovipositor being broght forward between the legs and inserted through the intersegmental membranes, or through the anal opening. There are generally 10-20 parasitoids able to mature in each host, but a maximum of 33 was obtained. Pupation occurs externally between the elytra and abdomen of the dead host in soil.
It was concluded by Clausen (1940) that on the basis of information available on behavior of Adapsilia and Pyrgota, that these and other species of similar habit can be of very little value in the natural control of scarab pests. The long larval period makes it probable that a portion of the oviposition potential of female scarabs is realized before death. The pronounced preferences of Adapsilia for male hosts reduces its value, because the portion of its effective reproductive capacity expended on the male sex is wasted. Death of male beetles contributes nothing to population reduction of the following generation, even though it perpetuates the parasitoid (Clausen 1940/62).
For detailed descriptions of immature stages of Pyrgotidae, please see (Clausen 1940/62).