Selection of Aphis craccivora (Hemiptera: Aphididae) for Resistance to Thiamethoxam Insecticide under Laboratory Conditions1

Abstract

Abstract The cowpea aphid, Aphis craccivora Koch (Hemiptera: Aphididae), is a polyphagous pest that causes yield losses in a variety of crops worldwide. Its management relies mainly on the use of chemical insecticides. This study followed the development of resistance to thiamethoxam in A. craccivora under laboratory conditions for 24 generations. The initial median lethal concentration (LC50) of thiamethoxam in a susceptible laboratory population of A. craccivora was 2.62 ppm. Exposure of surviving aphids in each generation to thiamethoxam caused an increase in the LC50 with each successive generation. After 24 generations, the LC50 had increased to 225.83 ppm, an 86.2-fold increase over the initial LC50. Resistance, as indicated by the increasing LC50, appeared as early as the second generation with a 1.4-fold increase over the initial generation. By the 14th generation, the LC50 had increased by 29-fold, and by the 16th generation, it had quickly increased by 69.4-fold. Our results indicate that A. craccivora populations repeatedly exposed to thiamethoxam in a cropping system can lead to rapid development of resistance to the insecticide. Any overuse or other misuse of the pesticide may lead to an even more rapid development of high levels of resistance to thiamethoxam within a short period of time. Elevated levels of the detoxifying enzymes, carboxylesterase, glutathione-S-transferase, and mixed function oxidases, in aphids exhibiting resistance as compared with the initial susceptible population indicated that the detoxifying enzymes, especially the carboxylesterases, are likely involved in facilitating the development of resistance to thiamethoxam in A. craccivora.