Stability,cross-resistance and fitness costs of resistance to emamectin benzoate in a re-selected field population of the beet armyworm,Spodoptera exigua (Lepidoptera: Noctuidae) |
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| Affiliation: | 1. Biorational Pesticide Research Lab, Sichuan Agricultural University, Chengdu 611130, China;2. Plant Protection Station, Agriculture Department of Sichuan, Chengdu 610041, China;3. Agency of Protection and Quarantine, Agriculture Technology and Popularization Center in Central District of Leshan City, Leshan 614000, China;4. Chengdu Academy of Agriculture and Forestry Sciences, Chengdu 611130, China;1. Hubei Insect Resources Utilization and Sustainable Pest Management Key Laboratory, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan 430070, PR China;2. Department of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100081, China;1. State Key Laboratory for Biology of Plant Diseases and Insect Pests, Beijing 100193, China;2. Institute of Pomology, Chinese Academy of Agricultural Sciences, Xingcheng, Liaoning Province 125100, China;3. Laboratory of Integrated Pest Management in Crops, Ministry of Agriculture; Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing 100193, China |
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| Abstract: | Spodoptera exigua (Hübner) has a worldwide distribution with a high capacity for damaging a wide range of food, forage and fiber crops. It has been reported extensively from all over the world that populations of this pest species have developed field resistance against many insecticides. The objectives of this study were to determine whether an emamectin benzoate resistant field population of S. exigua re-selected with emamectin benzoate in the laboratory (Ema-SEL) showed cross-resistance to other insecticides, whether resistance was stable under laboratory conditions, and whether there were fitness costs associated with emamectin benzoate resistance. Bioassays at G1 for the field population, gave resistance ratios (RRs) of 220, 149 and 38-fold for emamectin benzoate, spinosad and lufenuron, respectively, compared with a susceptible laboratory population (Lab-PK). Resistance ratios were increased by 526-fold and 6-fold compared with Lab-PK and the unselected field population (Ema-UNSEL, G6), respectively after selection with emamectin benzoate (Ema-SEL) for five generations (G6). Selection with emamectin benzoate had no apparent effect on susceptibility of Ema-SEL to spinosad and lufenuron, instead toxicity to the latter insecticides reduced, suggesting there was no cross-resistance between these compounds. Analysis of various life history traits suggested that the Ema-SEL population had a lower overall fitness (0.38) compared with the Lab-PK (1.0). Lack of cross-resistance and the apparent instability of resistance to emamectin benzoate suggest that spinosad and lufenuron are suitable alternatives for use with emamectin benzoate in resistance management. In addition, the high relative fitness costs observed suggests that emamectin benzoate-resistant insects are at a considerable disadvantage to susceptible populations in the absence of selection pressure although this remains to be tested under field conditions. |
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| Keywords: | Emamectin benzoate resistance Fitness cost Cross-resistance |
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