Effects of imidacloprid on Orius similis: assessing growth, development, and reproduction through age-stage two-sex life table analysis under contact and stomach toxicity treatments

Abstract

Although the use of chemical insecticides to control Frankliniella occidentalis is widespread, it may also affect its dominant predators such as Orius similis. To understand the consequences of imidacloprid on the growth, development, and reproduction of O. similis, we investigated its toxicity and selected the concentrations of LC₁₀ and LC₂₀ for both contact and stomach toxicity tests. Using the age-stage two-sex life table theory, we evaluated the impact of imidacloprid on the life table of the O. similis population. The results showed that the LC₁₀ and LC₂₀ values for each developmental stage of O. similis were lower under contact treatment than those under stomach toxicity treatment. After treatment with imidacloprid, the average oviposition by O. similis decreased compared to the control, and the net reproductive rate, gross reproduction rate, intrinsic rate of increase, and finite rate of increase were also lower than the control. The results also indicated that the peak value of age-stage-specific fecundity of O. similis was delayed by 1–2 days after imidacloprid treatment. Predictions for population growth of O. similis under unrestricted conditions showed that at 60 days, the population size of the control treatment was 2.06 times and 3.20 times that of LC₁₀ contact and stomach toxicity treatment, respectively. For LC₂₀ concentration, the control treatment's population size was 2.75 times and 3.87 times, respectively. Exposure to imidacloprid at different concentrations and treatment with contact and stomach toxicity had adverse effects on the growth and population growth of O. similis. Under imidacloprid stomach toxicity treatment, O. similis showed longer growth time and a slower population growth rate, indicating strong adaptability to the contact environment.