Evaluation of the lethal and sublethal effects of fenpyroximate on Scolothrips longicornis, a non-target predator of spider mites

Understanding the lethal and sublethal impacts of pesticides on biocontrol agents is crucial for the successful implementation of integrated pest management (IPM) programs. This study investigated the sublethal effects of fenpyroximate, a broad-spectrum acaricide/insecticide, on the fitness of Scolothrips longicornis Priesner (Thysanoptera: Thripidae), a key predator of the two-spotted spider mite, in controlled laboratory environments. Adult predators were exposed to pesticide residues on leaf discs to estimate parameters of concentration-mortality response models for females and males and calculate median lethal concentration (LC50) as well as sublethal concentrations (LC10, LC20 and LC30) used in subsequent bioassays. The estimated LC50 values for female and male predators were 18.32 and 15.49 µg a.i./mL, respectively. Results of sublethal concentrations experiments did not reveal any significant impact on the development of each stage or the survival rate of S. longicornis juveniles compared to those in the control group. However, the longevity of adult males and females was significantly lower at all sublethal concentrations than in the control. Moreover, the fecundity decreased significantly at all sublethal concentration treatments. With one exception (LC10), both the adult preoviposition period and total preoviposition period increased with increasing sublethal concentrations compared to those of the control. The shortest oviposition period (9.30 days) was observed at the LC30. For the life table parameters of S. longicornis females treated with sublethal concentrations, a significant decrease was found in the intrinsic rate of increase, net reproductive rate and finite rate of increase, whereas the mean generation time in the LC10 treatment was lower than that in the other treatments. This underscores the imperative need to consider sublethal concentration effects of fenpyroximate in the strategic design and implementation of IPM systems.