BIOLOGICAL CONSTRAINTS ASSOCIATED WITH RESISTANCE TO PYRETHROIDS IN THE TOBACCO BUDWORM (LEPIDOPTERA, NOCTUIDAE)

Tests were conducted to detect reasons for the loss of pyrethroid resistance which occurs in laboratory and field strains of the tobacco budworm, Heliothis virescens (F.), in the absence of continuous exposure to pyrethroid insecticides. Larvae of a resistant strain (ICI) maintained in the laboratory developed more slowly than larvae of a susceptible laboratory strain. ICI females were less fertile and produced fewer eggs per individual than susceptible females in field tests. In addition, ICI females produced significantly less pheromone and attracted fewer males than did susceptible females. Field-collected susceptible females mated more frequently than field-collected resistant females; field-collected susceptible males were more attracted to pheromone traps than field-collected resistant males. These results indicate that biological constraints are associated with pyrethroid resistance in the tobacco budworm. Based on the origin and biochemistry of the insects tested, it was concluded that the differences in fecundity are probably associated with metabolic resistance to pyrethroids and that the deficits in reproductive success are probably associated with target site resistance to pyrethroids. These constraints may play a major role in pyrethroid resistance management programs which are based on avoidance of pyrethroid use early in the growing season.