Relative Susceptibility and Resistance of the Tobacco Budworm to Methyl Parathion and Synthetic Pyrethroids in Southern California1

Abstract

Various collections of Heliothis virescens (F.) from different locations in southern California were tested for resistance to methyl parathion, fenvalerate, and cis-permethrin using the topical application methods on 8 mg larvae. Baseline levels of susceptibility for these 3 compounds were established in 1975 at 6.16, 1.01, and 0.35 μg/g, respectively. The resistance level for these compounds for larvae collected from cotton in the Imperial Valley increased gradually during both the 1977 and 1978 seasons although there was a notable decrease in these levels between the 2 seasons. At the end of the 1978 season, resistance levels as high as 9.8, 8.5 and 13.7X, respectively, were monitored. Larvae from other areas of southern California were susceptible to these compounds.