Comparative studies were conducted on the biologies and population growth potentials of Chelonus phthorimaeae Gahan, an indigenous North American parasite, and C. kellieae Marsh, an imported parasite from Costa Rica. Both species are primary, solitary, egg-larval endoparasites of the potato tuberworm, Phthorimaea operculella (Zeller).

Eggs of both species are hymenopteriform. In the laboratory, superparasitization was noted within the host egg; however, a single parasite larva develops within the haemocoel of the host larva. The parasite larva emerges before host pupation and constructs a silken-white cocoon within that of the host. There are three larval instars, the first being caudate-mandibulate, later becoming vesiculate-mandibulate. The second and third are mandibulate, with the third possessing spines and setae. The pupae are exarate. Developmental time from egg to adult female emergence is 22 days and 26 days for C. phthorimaeae and C. kellieae, respectively, at 26.7±1°C, 50% RH. Morphology of the immature stages and host relationships are presented. Parasitization of P. operculella by each species resulted in reduction of the size of the fourth instar host larvae. Optimum number and age of host eggs for maximum production of parasite progeny was 150 host eggs, 0-24 hours old, for C. phthorimaeae, and 50 host eggs, 0-24 hours old, for C. kellieae. Neither species host feeds nor are a carbohydrate source and free water prerequisites for progeny production. Females of both species require a carbohydrate source and free water for greatest longevity. Observations of the mating behavior disclosed males are polygamous and females monogamous. The mating ritual, searching, and ovipositional behavior are described. Both species are arrhenotokous with virgin and mated female C. kellieae producing approximately equal numbers of progeny, while mated female C. phthorimaeae produced a greater number of progeny than did virgin female C. phthorimaeae. Chelonus phthorimaeae and C. kellieae exhibited a preovipositional period of 2 hours and 4 hours, respectively, prior to production of female progeny.