BIOCHEMICAL AND PHYSIOLOGICAL-MECHANISMS OF PYRETHROID RESISTANCE IN HELIOTHIS-VIRESCENS (F)

Pharmacokinetic and physiological assays were used to determine mechan isms associated with pyrethroid resistance in Heliothis virescens (F.) that were collected from two cotton growing regions in Louisiana. Com pared with those from a susceptible reference strain, levels of metabo lism and excretion of cypermethrin were higher in larvae from some (bu t not all) field collections, and were highest in populations sampled during mid to late season. Adult insects also exhibited levels of cype rmethrin metabolism and excretion that were higher than those measured in a laboratory reference strain but increased metabolism was not ass ociated with reduced levels of mortality. Reduced neuronal sensitivity was detected in larvae from all field collections tested. Frequencies of individuals expressing target site resistance to allethrin were hi ghest in an early-season (June) collection, but were reduced in late-s eason populations sampled from the same location. These results indica te that multiple mechanisms are associated with pyrethroid resistance in tobacco budworms, and that frequencies at which these mechanisms ar e expressed in populations of H. virescens may fluctuate during the gr owing season. (C) 1995 Academic Press, Inc.