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

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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.