Effects of pyriproxyfen on three species of Encarsia (Hymenoptera: Aphelinidae), endoparasitoids of Bemisia argentifolii (Homoptera: Aleyrodidae)

Effects of the phenoxy juvenile hormone analog pyriproxyfen were evaluated in the laboratory on larvae, pupae, and adults of the endoparasitoids Encarsia pergandiella Howard, E. transvena (Timberlake), and E. formosa Gahan, as well as on their host, Bemisia argentifolii Bellows & Perring. Although B. argentifolii nymphs reared on sweet potato leaves and treated as 1st, 2nd, or 3rd instars with pyriproxyfen developed to the pupal stage; <5% adult emergence was observed. However, when treated in the 4th instar, adult emergence was greater than or equal to 70%, and when treated as pupae, greater than or equal to 97%. Of the 3 parasitoids tested, pyriproxyfen was least harmful to E. pergandiella and most deleterious to E. formosa. Concentrations of 1.00, 0.05, and 0.01 mg (AI)/liter applied to whitefly nymphs 6.5 d after parasitization caused significant reduction in subsequent adult emergence of E. formosa at the greatest rate, but not of E. pergandiella. Effects of treatment of whitefly nymphs containing E. formosa pupae (11.4 d after parasitization) were even more striking-73.5 and 44.6% reduction in emergence at the 2 highest rates, with wing deformations observed in a large proportion of emerging adults. Development time of all 3 Encarsia species was increased significantly by exposure to pyriproxyfen shortly after oviposition, and parasitization of B. argentifolii by E. formosa adults treated as larvae was reduced 21.4-56.8% compared with untreated parasitoids. However, residues of 2 higher rates reduced the progeny by 30.7-42.3% and rate of emergence by 11.2-27.6% with E. formosa, and to a lesser extent the progeny by 21.7-29.3% and adult emergence by 3.2-11.0% of E. transvena. Thus, pyriproxyfen proved to be effective against B. argentifolii, safe to E. pergandiella, and relatively safe to E. transvena, but relatively toxic to E. formosa, especially pupae.