Tolerance of Three Beet Armyworm Strains in Arizona to Methomyl12

Abstract

Tolerance levels of Spodoptera exigua (Hübner) to methomyl were investigated in Arizona. Laboratory cultures developed from feral collections in the Yuma, Mesa, and Safford localities were reared on a pinto bean diet. Acetone solutions of test grade methyl were topically applied with a standard microapplicator. Dosage-mortality data were obtained from 3rd instars held for 24 h after treatments. The Safford and Mesa strains were 3 times as tolerant as the Yuma strain. Dosage-mortality curves indicated a potential for resistance, but comparison with a 14-yr-old USDA strain showed that no methomyl resistance of any consequence is present in Arizona populations.