Abstract
Selection for spirodiclofen resistance was done in the laboratory with a susceptible strain of the citrus red mite, Panonychus citri (McGregor). Successive selections for spirodiclofen resistance through 42 generations resulted in a high level of resistance and the resistance ratio at LC50 was 103 compared with that of the original susceptible strain. In the selected strain, the level of resistance to spirodiclofen was high at all developmental stages except eggs and P. citri adult infertility caused by spirodiclofen was decreased. Cross-resistance to spirotetramat was detected but not to 10 other acaricides. Synergist experiments indicated that,piperonyl butoxide (PBO), S,S,S-tributyl-phosphorotrithioate (DEF) and diethyl maleate (DEM) synergized the toxicity of spirodiclofen in the selected strain by 3.3, 2.3 and 1.6 fold and the resistance ratio decreased from 103 to 38, 45 and 65, respectively, but no synergism was found in the susceptible strain. Key words: Spirodiclofen, laboratory selection, cross-resistance, synergism,Panonychus citri.
Highlights
Spirodiclofen belongs to the acaricidal group of spiroyclic tetronic, which are the acid derivatives newly discovered and developed by Bayer CropScience
This study investigated the levels of resistance at each developmental stage of the mite and the spectrum of cross-resistance to other acaricides in the spirodiclofen-resistant strain
P. citri was shown to develop resistance more slowly to spirodiclofen than other acaricides when selected continuously with increasing concentrations under laboratory conditions
Summary
Spirodiclofen belongs to the acaricidal group of spiroyclic tetronic, which are the acid derivatives newly discovered and developed by Bayer CropScience. Spirodiclofen has excellent efficacy against all developmental stages of mites, including agriculturally important pests such as Tetranychus urticae, Panonychus ulmi, Panonychus citri, Aculus schlechtendali, Phyllocoptruta oleivora and Brevipalpus phoenicis (Bretschneider et al, 2007). Spirodiclofen reduces the fecundity of adult female mites; the number of eggs laid is greatly reduced and those laid by females that had been exposed to sublethal doses of spirodiclofen are infertile. Spirodiclofen does not show cross-resistance to conventional acaricides (Rauch and Nauen, 2002) and has been used worldwide to control phytophagous mites, including various pesticide-resistant mites, in citrus fruit, pome fruit, stone fruit, grapes and nuts under an integrated pest management system. The citrus red mite, P. citri (McGregor) (Acari: Tetranychidae), is an important pest of citrus trees(Zhang et al, 1994).
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