Behavior Changes the Reproduction of Spalangia cameroni, S. endius, Muscidifurax raptor, and Nasonia vitripennis (Hymenoptera: Pteromalidae) at Increasing Fly Host Densities1

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Abstract
Attack rates and progeny production of several strains of 4 fly parasite species were observed under single-confined (forced) and multiple free-choice densities of Musca domestica L. puparia. Progeny production always increased with an increased host density limited by specific reproductive capacity. Female:male sex ratio increased with higher host densities when forced on single parasite females, but decreased when 10 competing ovipositing parasites were allowed free choice of densities in test cages. A parasite “contamination” principal was suspected. Two behavioral changes in Spalangia endius Walker might account for its increased rate of attack at higher densities. First, parasites spent less time examining puparia before ovipositing; and second, they laid more eggs in the same time period at a high host density than at a low. Superparasitism and probable differential sex mortality were also greater at the low density. Spalangia species demonstrated a greater searching capacity than Muscidifurax raptor Girault and Sanders or Nasonia vitripennis (Walker), and would be favored candidates for use as biological control agents. Experimental results indicated that small-number releases might be best at any immediate release site for maximum female F1 progeny production.