Spider Mite Resistance to Dicofol in San Joaquin Valley Cotton: Inter- and Intraspecific Variability in Susceptibility of Three Species of Tetranychus (Acari: Tetranychidae)

Abstract

Following the discovery of dicofol-resistant Tetranychus urticae Koch in San Joaquin Valley cotton fields, studies were initiated to determine the significance of dicofol resistance in two other major cotton spider mite species, T. pacificus McGregor and T. turkestani Ugarov and Nikolski, and to establish a discriminating concentration of dicofol for surveying for resistance. The responses of resistant and susceptible types of T. pacificus to residual and topical dicofol treatments were determined. As with T. urticae, resistance in T. pacificus was manifested as the ability to survive very high concentrations of dicofol residues despite relative susceptibility to topical treatments. No resistant types of T. turkestani were found during 1981–1983, and the susceptibility of this species, the most damaging species to cotton, was measured with residual and topical bioassays. Analysis of the inheritance of dicofol resistance in T. urticae showed it to be an incompletely recessive trait. The significance of inter- and intraspecific variability in spider mite response to dicofol is discussed with respect to integrated pest management of cotton. A residual bioassay discriminating concentration of 1,000 ppm dicofol is suggested for surveying the frequency of dicofol-resistant spider mites in cotton.