Selection for abamectin resistance in colorado potato beetle (coleoptera: Chrysomelidae)

There was no difference in dose response to abamectin between a laboratory strain of Colorado potato beetle (Leptinotarsa decemlineata (Say))from North Carolina and a multiple resistant strain from Massachusetts (LD₅₀= 1.95 and 1.98 ng larva^?1, respectively). Two abamectin-resistant strains were generated by separate means. The mutagen, ethyl methanesulfonate, was used to generate an abamectin-resistant strain (LD₅₀= 29.4 ng larva^?1) from the susceptible laboratory strain. The other resistant strain (LD₅₀ = 45.3 ng larva^?1) was generated through an intense selection with abamectin of a field strain contained in cages set up in existing potato fields. Resistance ratios calculated from LD₅₀values for the two abamectin-resistant strains were 15-fold and 23-fold, respectively. Resistance ratios calculated from LD₉₇values (21-fold and 38-fold, respectively) were higher than those calculated at LD₅₀. Also, there were larvae in both resistant strains which were capable of surviving doses up to 100 ng larva^?1, while the susceptible strain had no survivors at 10 ng larva^?1. Although the logit mortality regression analysis produced statistically different lines for the two abamectin-resistant strains, the slopes of each appear to be the same. Both resistance factors were determined to be autosomal and incompletely recessive (0.26 to 0.4, respectively) via reciprocal F₁crosses to the susceptible laboratory strain.