SEASONAL ABUNDANCE AND WITHIN-PLANT DISTRIBUTION OF PARASITOIDS OF BEMISIA-TABACI (HOMOPTERA, ALEYRODIDAE) IN PEANUTS

Sweetpotato whitefly, Bemisia tabaci (Gennadius), was sampled on peanu ts during 1991 and 1992 in Alachua County, FL, to determine parasitoid abundance and levels of parasitism. Common parasitoid species of B. t abaci in 1991 were Encarsia nigricephala Dozier, Encarsia pergandiella Howard, and Eretmocerus californicus Howard. E. nigricephala, E. perg andiella, and E. transvena (Timberlake) were the most abundant parasit oid species in 1992, whereas E. californicus appeared only rarely. E. nigricephala was the most common species in both years and accounted f or 91% of adult parasitoids reared from whitefly-infested foliage in 1 991, and for 54 and 71% of parasitoids reared from foliage at two site s in 1992. E. pergandiella, E. californicus, and E. transvena were mor e common during the late season, whereas E. nigricephala was most prev alent during the early season. Parasitism contributed significantly to -whitefly mortality and, in 1992, 90% of all fourth instars were paras itized by 10 September at the second site and by 21 September at the f irst site. Vertical distribution within plants of sweetpotato whitefly stages, unparasitized and parasitized, was assessed in 1992. Red eye nymphs (late fourth instar) were most common on leaves 4, 5, and 6 (fr om the top of a lateral stem), and 91% were located on the lower leafl et surface. Parasitized fourth instars were most prevalent on leaves 5 , 6, and 7 and were found on the lower leaflet surface 79% of the time . All life stages were equally distributed among the four leaflets of the compound leaf. These data indicate that monitoring for whitefly pa rasitism in peanuts could best be accomplished by examining both surfa ces of a leaflet picked from the fifth leaf down from the terminal lat eral stem leaf. The conservation of parasitoids to increase natural bi ological control of sweetpotato whitefly in peanuts is discussed.