Geographic distribution of imidacloprid tolerance in North Carolina

Neonicotinoid insecticides are a widely used family of active ingredients that mimic the action of nicotine and offer a systemic protection against green peach aphid (GPA, Myzus persicae) among  other piercing-sucking pests.  Over 95% of tobacco (Nicotiana tabacum) fields in North Carolina are treated with imidacloprid pre transplant, and resistance to imidacloprid is a concern to tobacco growers. We assessed the tolerance of field collected populations of M. persicae to imidacloprid.  We were also interested in the geographically distribution of tolerance and if color (green vs. red clones) polymorphism plays a role in tolerance. We collected aphids from four separate tobacco plants from four sites in North Carolina (Clayton, Oxford, Rocky Mount and Kinston). We measured LC50 for imidacloprid by exposing adult aphids to tobacco leaf discs dipped that had been dipped in 8 different concentrations of imidacloprid (0.5 mg/L - 100 mg/L). We counted number of live and dead adults after 72 hours and number of live a dead nymphs after 96 hours. Results show that tolerance to imidacloprid varied between populations ( LC50 ranged from ~1mg/L to ~10 mg/L) and that there was no influence from color or from geographical origin in the tolerance to imidacloprid in aphids feeding in tobacco in North Carolina.