Adult Emergence Interval and Reproduction in Parasitic Hymenoptera Influenced by Host Size and Density1

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Abstract
Observations on the developmental periods of 1 endo and 4 ectophagous solitary parasites of 2 species ofdipterous hosts, Hippelates collusor (Townsend) and Musca domestica L., showed that adult parasite emergence occurred over a spread of 6–9 days for each species of parasite when parental oviposition was limited to a 24-hour period. Two observed differentiating pathways were the differential development of immature stages and the differing propensities of adults to bite their way out of the host puparium. When ectophagous species ovipositedon small hosts at high host densities, emergence of their progeny was hastened, an effect not markedly evident in the endophagous species. The effects of host density on the rate of parasite development could have been produced by behavioral and physiological changes in the parent female, among which changes varied amounts of yolk in the deposited eggs are considered. Generally, the greatest total oviposition in 24 hours was correlated with high host densities and large hosts. Divergencies from expected sex ratios are explained on the basis of a differing optimum parasite adaptability to certain ranges in host size. Although the average massof an endophagous species varied with host size, that of the ectophagous species was not changed, eliminating the phenotypic effect of a limited food supply during larval development. A characteristic average size forectophagous species was manifested. The theoreticaleffects of developmental variation on host regulation are discussed.

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