Cross-Resistance Pattern and Genetic Studies in Spirotetramat-Resistant Citrus Red Mite, Panonychus citri (Acari: Tetranychidae)

In the laboratory, an acaricide-susceptible strain of the citrus red mite, Panonychus citri (McGregor) (LS-FJ), was used to screen for resistance to spirotetramat. A spirotetramat-resistant strain (ST-NK) obtained after continuous selections through 15 selection cycles (45 generations) exhibited 1668.4-fold greater resistance when compared to the parent generation. Instability of the spirotetramat resistance in the mites was observed during 11 months under spirotetramat-free laboratory conditions. Cross-resistance to spirodiclofen and spiromesifen was detected both in eggs and larvae, but not to five other tested acaricides. Probit lines for F1 heterozygous progeny indicated that the resistance to spirotetramat in the mites was autosomal with neither sex linkage nor maternal effects. The degrees of dominance were 0.15 and 0.23 for the diploid F1 of LS-FJ♀ × ST-NK♂ and ST-NK♀ × LS-FJ♂, and 0.07 and 0.13 for haploid F2 of LS-FJ♀ × ST-NK♂ and ST-NK♀ × LS-FJ♂, respectively, which indicated that the resistance was incompletely dominant. The χ2 analyses from the response of a backcross of crossed F1 progeny and ST-NK and F2 progeny showed that multiple genes are responsible for resistance to spirotetrama