Characterization of spinosad (Tracer~(R)) resistance in a laboratory strain of the tobacco budworm and development of novel diagnostics for resistance monitoring in the field

摘要

A highly spinosad-resistant strain of the tobacco budworm was developed in the laboratory by selecting each generation topically with technical spinosad. The LD_(50) at 15 days after treatment for the parental (susceptible) strain originally collected from North Carolina and reared in the laboratory on artificial diet was 0.131 #mu#g/larva. Resistance was detected as early as the 6th generation. In the 14~(th) generation, a dose of 100 #mu#g/larva produced 47.1 percent mortality, a resistance ratio >763 fold based on a comparison of the LD_(50)s. The parental strain demonstrated a similar susceptibility to spinosad as additional field strains from MS, LA, GA and NC. The susceptibility of the resistant strain did not revert back to that of the susceptible strain when reared for six generations in the laboratory in the absence of spinosad selection, immigration of new genes, and fitness challenges particular to the field environment. Spinosad resistance in the selected strain is present in both the larval and adult stage, validating the use of an adult bioassay for resistance monitoring in this strain. A larval feeding disruption assay was developed for spinosad resistance detection. One advantage of this assay is the rapid detection of resistance in neonates collected as eggs from a specific location or field prior to insecticide application. Other advantages of the feeding disruption assay technology are discussed.