Effects of temperature on baseline susceptibility and stability of insecticide resistance against Plutella xylostella (Lepidoptera: Plutellidae) in the absence of selection pressure

Abstract

<i>Plutella xylostella</i> L. (Lepidoptera: Plutellidae) is an important pest causing significant losses to vegetables worldwide. Insecticides resistance in <i>P. xylostella</i> is a serious issue for scientists since last 30 years. However, deltamethrin and <i>Bt Cry1Ac</i> are commonly used insecticides against <i>P. xylostella</i> but studies involving development of resistance in <i>P. xylostella</i> against these two insecticides at different temperatures are lacking. The current study was aimed to find out the toxicity of deltamethrin and <i>Bt Cry1Ac</i>, and resistance development in <i>P. xylostella</i>. Results showed that the positive correlation between the temperature and toxicities of deltamethrin and <i>Bt Cry1Ac</i>. The results indicated -0.051, -0.049, -0.047, and -0.046 folds of deltamethrin resistance at 15 °C, 20 °C, 25 °C, and 30 °C temperatures, respectively from 1^st to 12^th generations. The toxicity of <i>Bt Cry1Ac</i> after 24 h was 2.2 and 4.8 folds on 1^st generation at 20 °C and 25 °C temperatures, respectively compared to the toxicity recorded at 15 °C (non-overlapping of 95% confidence limits). Based on the results of this study, it is concluded that the temperature has a positive correlation with the toxicity of deltamethrin and <i>Bt Cry1Ac</i> against the larvae of <i>P. xylostella.</i> This study suggests that deltamethrin and <i>Bt Cry1Ac</i> can be included in the management program of <i>P. xylostella</i> on many vegetable crops<i>.</i> The baseline susceptibility data might be helpful to understand the resistance mechanisms in <i>P. xylostella</i>.