Comparison of Foraging Behavior, Interspecific Host Discrimination, and Competition of Encarsia formosaand Amitus fuscipennis

The foraging behavior of Amitus fuscipennisMacGown & Nebeker and Encarsia formosaGahan was studied on tomato leaflets with 20 Trialeurodes vaporariorum(Westwood) larvae in the first or third stage. Ten of the whitefly larvae were previously parasitized and contained a conspecific or a heterospecific parasitoid egg or larva. The host type (host stage and/or previous parasitization) did not influence the foraging behavior of either parasitoid species. The residence time on these tomato leaflets was about 0.9 h for A. fuscipennisand 1.9 h for E. formosa. Amitus fuscipennishardly stood still and fed little, while E. formosashowed extensive standing still and feeding. As a result, the time walking while drumming was similar for both parasitoid species. The numbers of host encounters and ovipositions per leaflet were similar for both parasitoid species. However, the residence time of A. fuscipenniswas half as long as that of E. formosaso the rate of encounters and ovipositions was higher for A. fuscipennis. Amitus fuscipennisis more efficient in finding and parasitizing hosts under these conditions. The walking activity and host acceptance of the synovigenic E. formosadiminished with the number of ovipositions, but not those of the proovigenic A. fuscipennis. Encarsia formosais egg limited, while A. fuscipennisis time limited because of its short life span and high egg load. Both parasitoid species discriminated well between unparasitized larvae and self-parasitized larvae, but discriminated poorly those larvae parasitized by a conspecific and did not discriminate larvae parasitized by a heterospecific. Self-superparasitism, conspecific superparasitism, and multiparasitism were observed for both parasitoid species. Superparasitism always resulted in the emergence of one parasitoid and multiparasitism resulted in a higher emergence of one parasitoid of the species that had parasitized first. The data suggest that A. fuscipennisis a good candidate for use in biological control of high-density spots of T. vaporariorumwhen we consider its high encounter and oviposition rate.