EFFECTIVENESS OF PARASITOIDS OF BEMISIA TABACI (HEMIPTERA: ALEYRODIDAE) ON COTTON CULTIVARS DIFFERING IN LEAF MORPHOLOGY

Field and laboratory experiments were conducted to determine resistance of cotton Gossypium hirsutum L. cultivars differing in leaf morphology (shape and pubescence) to the B biotype of sweetpotato whitefly Bemisia tabaci (Gennadius) and impacts on its parasitoids. Five cotton cultivars were evaluated in a field-plot experiment at Hastings, Florida. The pubescent cultivars, DP DES 119 and Stoneville 453, were significantly hairier than moderately hairy okra-leaf cultivar, Gumbo 500, and smooth-leaved cultivars NU COTN 33B and DP 51. There were significant differences among cultivars in eggs laid on the second and fifth node leaves. DP DES 119 and Stoneville 453 had greater numbers of whitefly eggs than did the glabrous cultivars. The okra-leaf cultivar, Gumbo 500, had greater numbers of eggs than the 2 glabrous varieties. There were significant differences among cultivars in numbers of first and second instars (young instars), third instars, unparasitized fourth instars and red-eyed nymphs on fifth node leaves, with higher populations occurring on pubescent cultivars and lower populations on glabrous cultivars. The abundant parasitoids were Encarsia pergandiella Howard, Encarsia nigricephala Dozier and Eretmocerus spp., however parasitism did not differ among the cultivars. The responses of Eretmocerus rui Zolnerowich & Rose and Encarsia formosa Gahan (Nile Delta strain) (Hymenoptera: Aphelinidae) as a function of density of the host were investigated in laboratory experiments on 3 cotton cultivars differing in leaf pubescence and shape (DP 51, DP DES 119, and Gumbo 500). Eretmocerus rui showed a type II functional response to second instars of the host with the mean number of parasitized hosts increasing as host density increased on all 3 cultivars. Encarsia formosa showed a type II functional response to fourth instars, where the number of hosts parasitized increased up to a density of 16 but remained constant for 32 and 64 hosts. Significantly more whiteflies were parasitized by both E. formosa and E. rui on DP 51, the smooth-leaved cotton cultivar, than on the hairy cotton cultivars. We conclude that glabrous cotton cultivars are likely to support lower whitefly populations than pubescent cultivars because of reduced whitefly oviposition and increased parasitoid foraging efficiency.