Impact of acequinocyl exposure on life history traits and demographic parameters of Tetranychus urticae Koch (Acari: Tetranychidae)

Abstract

Understanding the sublethal effects of pesticides is crucial for evaluating their ecological impact on pest populations. This study investigated the demographic responses of Tetranychus urticae Koch (Acari: Tetranychidae) to sublethal concentrations of acequinocyl, which is widely used to control T. urticae. We examined the effects of LC10 and LC25 concentrations of acequinocyl on key life history traits, including developmental duration, longevity, fecundity, and population growth parameters, using an age-stage, two-sex life table approach. The experiments were conducted under controlled laboratory conditions, maintained at 27 +/- 1 degrees C, 70 +/- 5% relative humidity, and a 16:8 light: dark cycle. Phaseolus vulgaris served as the host plant for T. urticae throughout the study. Although there were statistical differences in some periods of pre-adult development in females and males compared to the control, the total pre-adult period was found to be the same as the control in both sublethal concentrations. Female longevity was significantly prolonged at the LC25 treatment, whereas male longevity decreased. No significant differences were observed among treatments for APOP and TPOP durations, but egg production was significantly higher in the LC25 treatment. Similarly, the oviposition period was extended in the LC25 treatment. Life table parameters revealed no significant differences in the intrinsic rate of increase (r), finite rate of increase (lambda), or net reproductive rate (R0 ) among treatments. However, the mean generation time (T) was significantly longer in the LC25 treatment. The gross reproductive rate (GRR) was significantly higher in the LC25 treatment relative to the control, while the offspring per female ratio (Nf/N ) was significantly lower in both sublethal concentrations. The results demonstrated significant concentration-dependent effects on T. urticae. These findings highlight the dual impact of acequinocyl: while it enhances reproductive output, it simultaneously suppresses population growth by reducing survival and altering sex ratios. This underscores the critical need for careful evaluation of sublethal concentrations in pest management strategies, as they can significantly influence the population development of T. urticae both in the short and long term.