Seasonal Abundance and Within-Plant Distribution of Parasitoids of Bemisia tabaci (Homoptera: Aleyrodidae) in Peanuts

Abstract

Sweetpotato whitefly, Bemisia tabaci (Gennadius), was sampled on peanuts during 1991 and 1992 in Alachua County, FL, to determine parasitoid abundance and levels of parasitism. Common parasitoid species of B. tabaci in 1991 were Encarsia nigricephala Dozier, Encarsia pergandiella Howard, and Eretmocerus californicus Howard. E. nigricephala, E. pergandiella , and E. transvena (Timberlake) were the most abundant parasitoid species in 1992, whereas E. californicus appeared only rarely. E. nigricephala was the most common species in both years and accounted for 91% of adult parasitoids reared from whitefly-infested foliage in 1991, and for 54 and 71% of parasitoids reared from foliage at two sites in 1992. E. pergandiella , E. californicus , and E. transvena were more common during the late season, whereas E. nigricephala was most prevalent during the early season. Parasitism contributed significantly to whitefly mortality und, in 1992, 90% of all fourth instars were parasitized by 10 September at the second site and by 21 September at the first 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 (from the top of a lateral stem), and 91% were located on the lower leaflet 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 parasitism in peanuts could best be accomplished by examining both surfaces of a leaflet picked from the fifth leaf down from the terminal lateral stemleaf. The conservation of parasitoids to increase natural biological control of sweetpotato whitefly in peanuts is discussed.