Target-site insensitivity to some acaricides in a field population of Tetranychus urticae Koch (Acari: Tetranychidae) from Egypt

The control of the two-spotted spider mite (TSSM), Tetranychus urticae Koch, a worldwide agricultural pest, is largely dependent on pesticides. However, their efficacy is often encountered by the development of resistance. The present study was conducted to evaluate resistance levels to five pesticides with different modes of action in field population of T. urticae collected from tomato plants grown in open fields at Bernasht village, El-Ayat, Giza Governorate, Egypt, using leaf-dip technique. These pesticides were dimethoate, chlorpyrifos, and ethion (organophosphates), etofenprox (pyrethroids), and abamectin (avermectins). Moreover, the common resistance mutations associated with different groups of pesticides in T.urticae was identified by quantitative sequencing. Very high resistance levels of TSSM to organophosphate pesticides were observed in Eg-Bernasht population. Also, the nucleotide sequences were aligned, megablasted, and compared for similarity with the corresponding genes in different databases such as NCBI nucleotide collection (nr/nt). Of the five common mutations associated with organophosphate and carbam ate pesticides, three mutations were identified in Eg-Bernasht population: a threonine residue was replaced by alanine (T280A), glycine was replaced by alanine (G328A), and phenylalanine was replaced by tryptophan (F331W). One of the three common mutations associated with pyrethroid pesticides, alanine was replaced by aspartic acid (A1215D). Further two substitutions of amino acids, leucine to valine (L988V) and aspartic acid to glutamic acid (D1569E) were also identified. The common mutations associated with the target site of avermectins (glutamate-gated chloride channels, GluCl1, GluCl3) and etoxazole pesticide (chitin synthase, CHS1) were absent in Eg-Bernasht population. Also, with glutamate-gated chloride channel genes in one clone of Eg-Bernasht population, two substitutions of alanine to leucine (A308L) and valine to leucine (V309L) were identified. The results obtained from the current investigation indicated that four common mutations associated with pesticide resistance were present in the field population of T.urticae. These mutations were T280A, G328A, and F331W in the acetylcholinesterase (AChE) gene and A1215D in the voltage-gated sodium channel (VGSC) gene. An improved understanding of acaricides resistance in TSSM is important to maintain the efficacy of these chemicals for the control of this pest in tomato and other crops. We recommend focusing on the use of integrated pest management programs and pesticide alternatively to manage resistance.