A conserved amino acid replacement (A2′S) in RDL1 and multiple mutations in AChE1 were detected in the cotton aphid Aphis gossypii in Xinjiang China

The cotton or melon aphid (Aphis gossypii Glover) is one of the most important agricultural insect pests worldwide. Many populations of this pest have been documented to be resistant to multiple classes of insecticides in Xinjiang Uygur Autonomous Region of China. Understanding the molecular mechanisms behind resistance in field populations is crucial for making effective strategies for control of this pest. In this study, we investigated potential genetic mutations responsible for insecticide resistance in two insecticidal targets in four cotton aphid populations in Xinjiang. Our data showed that the classical A2′S mutation in the γ-aminobutyric acid (GABA) receptor RDL1 was present in the cotton aphid at frequencies ranged from 4.5 % to 50 %, indicating that the cotton aphids have evolved the Rdl-based mechanism of resistance to synthetic insecticides via a parallel mutation in Rdl1 even in the genetic background with the 2ʹS-carrying duplicated Rdl (Rdl2). In addition, three mutations (A302S, A332V and S431F) in the acetylcholinesterase AChE1 were found to be prevalently distributed in A. gossypii populations. Notably, the resistant 431F allele was fixed in the four examined populations, and all existing ace-1 alleles were resistant, carrying either one or two of the three mutations. The occurrence of resistance-conferring mutations in multiple insecticidal targets warns a risk of failure in aphid control using chemical insecticides in Xinjiang, the major cotton planting region of China.