Residues of Different Insecticides in/on Brinjal and Their Effect on Trichogramma spp.

Dissipation of residues of quinalphos @ 500 and 1000 g ai ha⁻¹a methomyl @ 400 and 800 g ai ha⁻¹ and alphacypermethrin @ 30 and 60 g ai ha⁻¹ were studied in/on brinjal (var. Muktakeshi) under field conditions at Kalyani, West Bengal during kharif season of 2000–2001. In all, five sprays were given at 15 d interval. The initial residues on brinjal fruits after the last spray were to the magnitude of 4.78 and 6.98 μg g⁻¹ for quinalphos, 3.98 and 5.65 μg g⁻¹ for methomyl and 0.755 and 1.02 μg g⁻¹ for alphacypermethrin for lower and higher doses, respectively. The residues dissipated with the half-life of 1.1–1.5 d for quinalphos, 1.0–1.4 d for methomyl and 1.8–2.4 d for alphacypermethrin. The residues reached BDL after 10 d for lower dose and 15 d for hiqher dose for all the insecticides. The safe waitina periods (T_MRL) determined for brinjal were within 4.8–7.4 d, 4.4–6.5 d and 1.3–3.0 d for quinalphos, methomyl and alphacypermethrin, respectively. Fruit samples of 1–5 d showed the preseece of quinalphos oxon in amounts ranging from 0.00–0.04 μg g⁻¹. Decontamination processes like washing and cooking dislodged 28.2–76.1% residues depending go insecticides and doses whereas 21.1–60.1% surface residues was removed by washing alone. The study yo residual toxicity to the egg parasitoids Trichogramma chilonis Ishii and Trichogramma japonicum Ashmead showed that the insecticides differed considerably in their persistency, period of efficicacy and index of persistent toxicity (PT value) towards both the species. Based on PT value, alphacypermethrin was found to be safest towards both the parasitoids. Considering the retention period of toxic residues, both the parasitoids could be released in the crop ecosystem after 3–5 d of alphacypermethrin spray, 4–6 d of methomyl spray and 6–7 d of quinalphos spray depending upon treatment doses and parasitoid species.