Transgenerational effect of insecticides on zigzag ladybird beetle, <i>Cheilomenes sexmaculata</i> (Fabricius) (Coleoptera: Coccinellidae)

The effect of the insecticides at sublethal doses, recommended against aphid and pod borers in cowpea ecosystem was evaluated on the survival, development and reproduction of Cheilomenes sexmaculata (F.) (Coleoptera: Coccinellidae) by exposing the 0-24h old grubs via residue film method. The treatments for the assay were dimethoate 30 EC, flubendiamide 20 WDG, spinosad 45 SC, thiamethoxam 25 W, all at 1/10th of the recommended field dose along with the botanical component, neem oil emulsion at 0.3 per cent. Dimethoate induced complete mortality of the exposed grubs. Minimum survival at 18.33 per cent was with neem oil followed by 20 per cent in thiamethoxam in contrast to 82.50 per cent in flubendiamide, 84.17 per cent in spinosad and 94.17 per cent in absolute control. Exposure to thiamethoxam and neem oil extended the developmental time of the first and second-instar grubs. However, the mean duration of the pupa was shortened. Exposure to thiamethoxam, flubendiamide and neem oil significantly reduced the oviposition period to 47.88±3.45, 48.63±4.86 and 50±2.29 days, respectively, as against 55.88±1.15 days in control. Adult longevity was reduced drastically after exposure to thiamethoxam, neem oil, and flubendiamide. The fecundity and fertility were significantly less after exposure to all the insecticides. The hatchability of the secondgeneration eggs was minimal with flubendiamide (69.15%) followed by 71.10 and 71.97 per cent, respectively in thiamethoxam and neem oil as against 86.80 per cent in control. The results of the study indicated the direct mortality and indirect impact of dimethoate, thiamethoxam and flubendiamide at sublethal doses on the development and reproductive parameters of C. sexmaculata.