Interference Competition and Optimal Host Selection in the Parasitic Wasp, Biosteres longicaudatus1

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Abstract
The influence of parasitoid female Biosteres longicaudatus Ashmead (Hymenoptera: Braconidae) densities on their mortality, oviposition, and superparasitization (>1 egg per host) and on progeny sex ratio was evaluated. Three tests were conducted. (1) One ovipositional unit test: each group of 150, 100, and 50 5-day-old, mated parasitoid females was given Anastrepha suspensa Loew (Diptera: Tephritidae) larvae (hosts) in single ovipositional units 20, 10, 5 cm in diameter, respectively, to provide corresponding densities of 0.5, 1.1, and 2.5/cm2. (2) Two ovipositional unit test: parasitoid and host numbers were the same as in (1), but two similar ovipositional units were used. (3) Similar to (2), but one of the ovipositional units contained house fly, Musca domestica L., larvae. Aggression, mortality, superparasitization, and male progeny increased with parasitoid density. Mean oviposition was inversely related to parasitoid density. Large females (>3.5 mm) laid more eggs than small ones (<3.5 mm) when only the preferred fruit fly larvae were provided. However, when house fly larvae were also available, small females oviposited primarily in these hosts to decrease competition. Thus, through this optimal foraging strategy, they laid as many eggs as large females.