Forecasting potential risk for development of spiromesifen resistance in Tetranychus urticae (Koch): its genetics and cross-resistance

Tetranychus urticae (Koch) (Acari: Tetrancyhidae) is a notorious economically important pest due to its polyphagous behavior and strong capability to develop resistance, consequently, makes the chemicals applied as ineffective, in a short time. Considering these issues and to make chemical control effective, resistance risk, inheritance and cross-resistance to spiromesifen was studied in T. urticae. The spiromesifen resistant strain (SPIRO-SEL) showed 92.42-fold resistance after 20 laboratory selections compared with the Lab-colony. Reciprocal crosses (F-1 and F-1') showed no difference in concentration-mortality responses and exhibited a similar degree of dominance with DLC values of 0.57 and 0.70 for F-1 and F-1', respectively. The chi-square test of monogenic model showed significant differences between the observed and expected mortalities at more than half of the tested concentrations in the backcross which suggested that spiromesifen resistance is polygenic. Spiromesifen resistance in T. urticae was inherited as autosomal, incompletely dominant, and multigene. The SPIRO-SEL developed no cross-resistance to chlorfenapyr and very low cross-resistance to chlorpyrifos and spirotetramat. Realized heritability analysis showed that under a selection intensity of 10 to 90% the generations required to rise 10-fold spiromesifen resistance were 14 to 2, respectively. Herein, from a practical perspective, our investigations of spiromesifen resistance risk, inheritance and its cross-resistance with other tested pesticides could be favourable to provide sufficient insight for future implication of these results in devising a resistance management program against T. urticae.