Chemical and toxicity bioassays

The spirotetramat (CAS No. 203313-25-1; Movento^® 240 SC; 240 g/L active ingredients) was obtained from Bayer Crop Science Co. Ltd. (Australia). The insecticide tested in this study is registered and being used in brassica crops in Pakistan to manage aphids. Toxicity bioassays were conducted with apterous adult aphids using the leaf dip method described by (Ullah et al., 2020) to measure the lethal and sublethal toxicity of spirotetramat. The distilled water was utilized to make spirotetramat concentrations (6, 3, 1.5, 0.75 and 0.375 mgL−1). Distilled water dipped leaf discs were used only for the control group. Brassica leaf discs were cut by a sharp metal cylinder and dipped in the dilutions of respective insecticide solution for 30 s. The treated leaf discs were placed at room temperature for 30 min to dry residual solution droplets on the leaves. The treated leaves were placed in plastic Petri dishes (size: 3 × 1.5 cm, with a biaxial surface downward) lined with moistened filter paper. Each concentration comprised three replications of 30 apterous adult aphids (≤24 h old) and five leaves were used for each replication. Mortality data were estimated at 72 h of spirotetramat exposure. Aphids were scored as dead if they did not exhibit repetitive (i.e., non-reflex) movement when gently probed with a soft camel hair brush (Moores et al., 1996). The lethal concentrations LC₅, LC_15, and LC₅₀ were calculated by using PoloPlus 2.0 software (LeOra Software Inc. Berkely, CA).