@article{roe_young_iwasa_wyss_stumpf_sparks_watson_sheets_thompson_2010, title={Mechanism of resistance to spinosyn in the tobacco budworm, Heliothis virescens}, volume={96}, DOI={10.1016/j.pestbp.2009.08.009}, abstractNote={Topical laboratory selection of tobacco budworm larvae, Heliothis virescens, with technical spinosad for multiple generations resulted in larvae 1068-fold resistant to topical applications of the insecticide and 316.6-fold resistant to insecticide treated diet as compared to the parental strain. The penetration of 2′-O-methyl[14C]spinosyn A across the cuticle of the susceptible (parental) and selected (resistant) tobacco budworms increased with time 3–12 h after application. A trend of reduced penetration in the resistant strain was found but the differences were not statistically significant. 2′-O-methyl[14C]spinosyn A when injected into the hemocoel was not metabolized 96 h after treatment in both the susceptible and resistant strain, suggesting that a change in metabolism was not the mechanism of resistance. Electrophysiological studies indicated that dose-dependent spinosyn A-induced currents occurred in neurons from spinosyn resistant and susceptible (adult) tobacco budworms. At both 10 and 100 nM spinosyn A, however, the amplitude of these currents in the resistant insects was significantly smaller than the amplitude of currents observed from neurons from susceptible tobacco budworm adults. This suggests that neurons from resistant insects have decreased sensitivity to spinosyn A. However, the reduced inward currents in the resistant strain may or may not be related to the mode of action of the spinosyns. No statistically significant cross-resistance was noted for the spinosad resistant tobacco budworms for topical applications of permethrin (Pounce®), profenofos (Curacron®), emamectin benzoate (Denim®), or indoxacarb (Steward®). A statistically significant reduction in susceptibility to acetamiprid (Mospilan®) in artificial diet as determined from a resistance ratio of 0.482 was found.}, number={1}, journal={Pesticide Biochemistry and Physiology}, author={Roe, Richard and Young, H. P. and Iwasa, T. and Wyss, C. F. and Stumpf, C. F. and Sparks, T. C. and Watson, G. B. and Sheets, J. J. and Thompson, G. D.}, year={2010}, pages={8–13} }
 @article{wyss_young_shukla_roe_2003, title={Biology and genetics of a laboratory strain of the tobacco budworm, Heliothis virescens (Lepidoptera : Noctuidae), highly resistant to spinosad}, volume={22}, ISSN={["1873-6904"]}, DOI={10.1016/S0261-2194(02)00153-9}, abstractNote={Tobacco budworm larvae, Heliothis virescens (F.), were collected from the field in North Carolina in 1996 and 1997 and established as a laboratory (parental) strain. When a subset of these insects was selected by the topical application of technical spinosad (a mixture of spinosyns A and D) every generation for 13 generations, they became highly resistant to the insecticide. The resistance ratio for topically applied spinosad based on differences in the LD50 between the parental (susceptible) and the resistant (generation 19) strain was 669-fold when fourth stadium larvae were treated. The susceptible strain LD50 18d after treatment was 0.11μg of active ingredient per larva while the LD50 for generation (G) 19 of the resistant strain was 73.55μg per larva. Reciprocal single pair matings between the resistant and the parental strain and backcrosses of F1(R×S) females with resistant males indicated that a non-sex linked, (partially) recessive single gene was responsible for spinosad resistance. The F1 larvae were only slightly (5.3–5.6-fold) resistant compared to the parental strain. The stability of resistance was tested by removing spinosad selection for five generations. In the absence of immigration of susceptible budworms into the population and insecticide treatments, the LD50 decreased only 1.4-fold. The only differences noted in the biology of the parental and resistant strain was that the resistant males developed slower as larvae and emerged as adults later than the susceptible males and had a slightly smaller 1d old pupal wet weight. However, when 80% highly resistant and 20% parental moths of both sexes were allowed to mate freely, the majority of the offspring (84.6%) were susceptible to spinosad. This suggests a reduced reproductive competitiveness for the resistant strain.}, number={2}, journal={CROP PROTECTION}, author={Wyss, CF and Young, HP and Shukla, J and Roe, RM}, year={2003}, month={Mar}, pages={307–314} }