Toxicity, Joint Action, and Mean Time of Mortality of Dipel 2X, Avermectin B1, Neem, and Thuringiensin Against Beet Armyworms (Lepidoptera: Noctuidae)

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Abstract
Toxicity of Dipel 2X, avermectin B1, and neem to beet armyworm, Spodoptera exigua (Hübner), was determined using neonate larvae in a diet-incorporation bioassay. LC50’s for Dipel 2X, avermectin B1, and neem in diet medium were 196 μg/ml, 0.814 μg (AI)/ml, and 0.116 μl/ml, respectively. Combinations of ABG-6162 (an experimental formulation of thuringiensin) and Dipel 2X resulted in potentiation, whereas combinations of neem with avermectin B1 or Dipel 2X produced an antagonistic effect. There was no significant linear relationship in mean time of mortality across all concentrations within a toxicant except for ABG-6162. Mean time of mortality was significantly different among toxicants. These times for Dipel 2X, avermectin B1 neem, and ABG-6162 were 3.06, 4.13, 5.42, and 6.23 d, respectively. Mean time of mortality for toxicant combinations was variable and provided insight into modes and sites of action for compounds applied individually or jointly.