Abstract
We examined relationships between larval weight and degree of resistance to cypermethrin in tobacco budworm,
Heliothis virescens (F.). Laboratory-reared larvae (9.0-175.4 mg) were treated with either 0.1 or 1.0 mg cypermethrin in acetone. Degree of debilitation of each larva was assessed at intervals from 0.5 h to 5 d after treatment cumulative scores incorporating degree of debilitation and survival time were used as a measure of tolerance (i.e. a continuous measure of resistance). at larval weights ( 100 mg, relationships between tolerance and weight were linear for both doses. At the rate of 0.1 mg per larva, tolerance reached an asymptote near 100 mg. Proportion of tolerance variation explained by weight decreased with size range, but we obtained significant relationships over weight ranges frequently used in
Heliothis studies. Weight and dose interacted; slopes of tolerance weight regressions were steeper at the lower dose (large larvae were disproportionately more tolerant than small larvae). These data indicate that the expression of tolerance and tolerance changes within populations are mediated by even small-scale weight variation, that relationships between tolerance and weight depend on dose, and that it my be possible to refine resistance predictions by account for weight variation in treated populations.
Keywords
Insects,
Heliothis virescens,
insecticide resistance,
continuous measure
Citation
Firko, Michael J.; Hayes, Janes Leslie. 1990. Quantification of larval resistance to Cypermethrin in tobacco budworm (Lepidoptera: Noctuidae) and the effects of larval weight. J. Econ. Entomol., Vol. 83(4): 1222-1228
