Behavioral evaluation of Greece and Nile strains of Encarsia formosa Gahan (Hymenoptera: Aphelinidae), parasitizing the silverleaf whitefly, Bemisia argentifolii Bellows & Perring (Homoptera: Aleyrodidae), were performed on Hibiscus (Hibiscus rosa sinensus) in the laboratory under four temperature regimes: 16°, 21°, 26°, and 31°C. Behaviors evaluated included: (1) walk-ing, (2) drumming, (3) preening, (4) ovipositor probing, (5) parasitization, (6) stationary, (7) feeding and (8) walking off the lower leaf surface.

Analysis of the mean time and mean percent time that each E. formosa strain spends in each behavior, mean frequency of behaviors, and percentage of individuals performing the specified behaviors, all indicated that the E. formosa strains represent two climatic-ecotypes, with the Greece strain optimally adapted to a cooler climate (21°C), and the Nile strain optimally adapted to a warmer climate (26°-31°C). This appears to be the first behavioral evidence for two strains of E. formosa based upon temperature optima. Biological control implications are discussed.