Effect of Host Insect-Host Plant Associations on Selected Fitness Components of Encarsia formosa (Gahan) (Hymenoptera: Aphelinidae)

A decrease in hind tibia1 length was observed for Encarsia formosa (Gahan) when switched from Trialeurodes vaporariorum Westwood as a host on tobacco to Bemisia tabaci (Gennadius) as a host on poinsettia. Tibia lengths of the parasitoid E. formosa from commercial sources reared from tobacco decreased from 0.22 to 0.18 mm after at least 5 generations of the parasitoid on the new host. There was no significant increase in E. formosa tibia size when continuously reared on B. tabaci for at least 18 generations compared to the length after 5 generations on that host. After 18 generations on the B. tabacilpoinsettia association, E. formosa selected whitefly nymphs significantly longer than the whitefly nymphs selected by wasps reared on B. tabacifor 5 generations. Analysis of covariante demonstrated that there was a significant relationship between whitefly size and wasp size that was not significantly different for any of the whitefly/host plant associations. Standardization for whitefly size revealed a significant effect of origin on wasp size. Longevity of English E. formosa reared from T. vaporariorum on tobacco was significantly less than that of California E. formosa reared from B. tabaci on poinsettia after both 5 and 18 generations on that host. Emergence rates of E. formosa were not different for any host association examined, but there was a significant increase in the fecundity of E. formosa after 18 generations on B. tabaci on poinsettia. (C) 1991 Academic Press, Inc.