Age-Specific Interaction Between the Greenhouse Whitefly 1 and Encarsia formosa: 2 Influence of Host on the Parasite's Oviposition and Development

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Abstract
The parasite, Encarsia formosa, oviposits in all 4 instars, including the late 4th instar and the pharate adult (=pupa of previous workers), of the greenhouse whitefly, Trialeurodes vaporariorum. When each host stage is exposed individually, percentage parasitism is significantly greater in 3rd instar, “early” 4th instar, and transitional substage whiteflies than in 1st instars, 2nd instars, or pharate adults. Although E. formosa's eggs develop and hatch within all sessile whitefly stages (i.e., 1st to pharate adult), the parasite's larval development does not proceed past the 1st instar until after the host reaches the 4th instar. Subsequently, E. formosa completes its life cycle and emerges as an adult from 4th instar whiteflies. A comparison of the four host instars showed that 3rd instar, “early” 4th instar and transitional substage whiteflies are the most suitable for parasitization because they give (a) the highest percentage E. formosa emergence, (b) the greatest parasite survival, and (c) the lowest host mortality (including host killing). Also, E. formosa egg and larval development is significantly faster in the 3rd instar, “early” 4th instar and transitional substage than in earlier host stages or the pharate adult stage. These results are directly applicable to increasing the efficiency of mass-rearing and colonization of E. formosa by allowing precise timing of parasite introduction.