Experimental studies in insect parasitism. I.—Introduction and technique

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Abstract
Although the numbers of most animals are partially regulated by spp. which prey upon them, experimental data that might serve as a basis for an understanding of how or to what extent this is true are almost entirely lacking. Trichogramma evanescens was bred on the moths Sitoiroga cerealella and Ephestia knehniella. The procedure was, in a constant physical environment, to subject host eggs to parasitism by attaching them to sheets of graph paper which made it simple to regulate their spatial distribution, the parasite and host eggs being placed in petri dishes. When a number of parasites were distributed among an equal number of hosts, there resulted neither the 100% parasitism to be expected from a perfect distribution, nor the 63% to be expected from entirely random distribution, but something between them. Discrimination between parasitized and unparasitized hosts is evident as is also the tendency to refrain from oviposition when the host is already parasitized. This faculty seems to be widespread among the parasitic Hymenoptera. Trichogramma [female][female] are able, at least for a time, to retain their eggs rather than deposit them in parasitized hosts. When the number of hosts was limited, the parasite would sometimes lay 2, 3, or 4 eggs in one host, but the number of cases of superparasitism was far smaller than would be expected from chance distribution. Larger hosts were selected for superparasitization.

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