Lethal and Sub-Lethal Effects of Spirotetramat on Red Spider Mite, <i>Tetranychus macfarlanei</i> Baker and Pritchard (Acari: Tetranychidae)

The red spider mite, <i>Tetranychus macfarlanei</i>, is a serious pest of many cultivated crops in Bangladesh and other East-Asian and South-East Asian countries, in the Afrotropical, Oriental, and Palearctic regions. Sublethal concentration of pesticides, such as LC₁₅ and LC₃₀ (the concentrations that result in 15 and 30 percent lethality, respectively) impact reproduction, behavior, development, and physiology. This study assessed the effects of different concentrations of spirotetramat, an insecticide that disrupts lipid production, on the biological traits of <i>T. macfarlanei</i>. The LC₁₅, LC₃₀, LC₅₀, and LC₉₀ values were 2.16, 6.57, 20.54, and 332.81 mg·L⁻¹, respectively. Sublethal concentrations (LC₁₅ and LC₃₀) slightly reduced female fecundity but did not significantly affect development duration, pre-oviposition, oviposition period, or longevity compared to the untreated control group. Life table parameters differed between the treated and control groups, with significant reductions in the intrinsic rate of increase (<i>r</i>), the net reproductive rate (<i>R</i>₀), and the finite rate of increase (<i>λ</i>) for LC₁₅ and LC₃₀. LC₁₅ and LC₃₀ had negative effects on the intrinsic rate of increase for females. This study demonstrated that lower lethal concentrations of spirotetramat compromised survivability and negatively impacted the life-table parameters of subsequent generations of <i>T. macfarlanei</i>. These findings highlight the importance of sublethal effects in pest control, offering valuable insights for developing more effective and sustainable integrated pest management strategies.