Resistance mechanisms to some pesticides in a field strain of the two-spotted spider mite Tetranychus urticae

The two-spotted spider mite, Tetranychus urticae (Acari: Tetranychidae) is a major pest affecting crops worldwide, for which biological control has not yet been achieved, therefore, acaricides are commonly used to control it. Spider mites are sap-sucking and can cause leaves and flowers to wilt and die. The entire mite life cycle takes about 2-3 weeks. All life stages of spider mites are usually found on the undersides of leaves, which make early detection difficult. The overall aims of the study described in this work were to study the molecular biology of resistance mechanisms against certain acaricides which currently available in some Ismailia regions (Egypt). T. urticae were collected from five different sprayed districts, together with a strain collected from unsprayed districts. The laboratory tests were carried out to establish the probit analysis of the sprayed strains comparing with the laboratory susceptible strains using two acaricides (abamectin and chlorfenapyr). Results of LC50 for abamectin in resistant strains obtained from different regions (El-Qassasin, Ismailia, Abu-Sueir, Faied and El-Qantara Gharb) and in susceptible strains were 1.32, 1.54, 6.18, 11.03, 26.02 and 0.233 respectively, while for chlorfenapyr were 1.174, 1.47, 15.58, 26.25, 46.16 and 0.22 respectively. Results revealed that all treatments in significant reduction of the mean numbers of moving stages of the mite populations compared with that of unsprayed control. In all counts, abamectin was affected more than chlorfenapyr against the target pest. All field strains showed high resistant comparing with susceptible laboratory strain.