Rami Horowitz, A., Department of Entomology, ARO, Gilat Research Center, M.P. Negev, Israel, Department of Entomology, ARO, Gilat Research Center, M.P. Negev, 85280, Israel
Gorman, K., Plant and Invert. Ecology Division, Rothamsted Research, Hertfordshire, United Kingdom
Ross, G., Agric. and the Environment Division, Rothamsted Research, Hertfordshire, United Kingdom
Denholm, I., Plant and Invert. Ecology Division, Rothamsted Research, Hertfordshire, United Kingdom

The inheritance of resistance to pyriproxyfen, an insect growth regulator (a juvenoid, with ovicidal and larvicidal activities), was studied in the whitefly Bemisia tabaci (Gennadius). Two parental strains, both belonging to Q biotype, were assayed with pyriproxyfen; a susceptible strain (AIM-1) originating from Spain and a pyriproxyfen-resistant one (Pyri-R) from Israel. The resistance ratio between the two parental strains was approximately 7,000-fold. Concentration-mortality lines for F1 heterozygous females from reciprocal crosses (SS♀ X R♂ and RR♀ X S♂) were derived by statistical modelling and proved intermediate to those of the parents. The pooled degree of dominance from both reciprocal crosses was +0.26, indicating that resistance was incompletely or partiolly dominant. Mortality curves for F2 males produced by virgin F1 heterozygous females displayed a broad plateau at 50% mortality, indicating that resistance to pyriproxyfen in B. tabaci is conferred primarily by a mutant allele at a single locus. The role of arrhenotoky in influencing the mode of inheritance of resistance, and its selection in field populations, is discussed. © 2003 Wiley-Liss, Inc.