Submitted to: Florida Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/13/2004
Publication Date: 9/20/2004
Citation: Gore, J., Adamczyk Jr, J.J. 2004. Laboratory selection for beet armyworm (Lepidoptera: Noctuidae) resistance to methoxyfenozide. Florida Entomologist. 87:4. Interpretive Summary: To aid the development of a proactive resistance management strategy, colonies of beet armyworms were developed in the laboratory with resistance to the insecticide, methoxyfenozide. Beet armyworm larvae were artificially selected in the laboratory by incorporating the insecticide into an artificial food source. Three colonies were selected at three different concentrations of methoxyfenzide. The concentrations represented low, moderate, and high selection pressures. Within seven generations, resistance of the beet armyworm colony selected at the low concentration did not increase compared to the original colony. In contrast, resistance to methoxyfenozide in the colonies selected at the moderate and high concentrations was approximately nine times higher than the original colony after seven generations. In addition, crosses made between susceptible and resistant individuals indicated that the trait for resistance of beet armyworms to methoxyfenozide was under genetic control. This information will be important for developing and implementing effective management strategies to delay the spread of resistance to this insecticide.
Technical Abstract: Beet armyworms, Spodoptera exigua (Hubner), were artificially selected in the laboratory for resistance to the insect growth regular, methoxyfenozide. A field collected beet armyworm colony was separated into three cohorts that were independently selected with three concentrations (0.033 ppm, 0.064 ppm and 0.125 ppm) of methoxyfenozide incorporated into meridic diet. These concentrations corresponded closely with the LC10 (0.033 ppm), LC50 (0.072 ppm), and LC90 (0.161 ppm), respectively, for the original colony. After seven generations of continuous exposure to methozyfenozide, resistance in the colony selected at the low concentration did not significantly increase. In contrast, LC50 values increaded 9.7- and 9.4-fold for the colonies selected at the moderate and high concentrations, respectively, over that of the original colony. Crosses between resistant and susceptible individuals indicated that the resistance was heritable. At 4 d after exposure, mortality of offspring from the reciprocal crosses was intermediate between mortality for the offspring from the parental crosses. When rated at 10 d, mortality of offspring from the reciprocal crosses was not significantly different than offspring from the cross between susceptible parents. These data will be important for developing a management program for beet armyworm resistance to methozyfenozide.