A laboratory bioassay (topical application) was conducted to evaluate the relative toxicity of ten insecticides against third instar larvae of fall army worm, Spodoptera frugiperda (J E Smith). Emamectin benzoate was found to be the most toxic with least LC50 value (1 ppm). The order of toxicity was emamectin benzoate (1 ppm) > spinetoram (1.2 ppm) > chlorantraniliprole (1.8 ppm) > novaluron+ emamectin benzoate (7.7 ppm) > novaluron (18 ppm) > novaluron + indoxacarb (31.7 ppm) > flubendiamide (33.8 ppm) > indoxacarb (42.3 ppm) > lambda-cyhalothrin (77.2 ppm) > chlorpyriphos (184.7 ppm). Emamectin benzoate, spinetoram, chlorantraniliprole, novaluron+ emamectin benzoate, novaluron, novaluron + indoxacarb, flubendiamide, indoxacarb and lambda-cyhalothrin showed 184.70, 153.92, 102.61, 23.99, 10.26, 5.83, 5.46, 4.37 and 2.39 folds toxicity over chlorpyriphos, respectively at 72 hr after treatment.
The pink bollworm Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae) has recently emerged as a serious menace on Bt cotton in India. Extensive roving surveys were conducted in 12 locations of three major cotton growing districts of Andhra Pradesh, India, to assess the level of pink bollworm infestation in Bt cotton during 2018-19 and 2019-20. The dynamics and severity of flower damage due to pink bollworm during the 60-135 days’ crop period were evaluated based on a random sampling of flowers. Survey results revealed a widespread infestation of pink bollworm on Bt cotton flowers across the surveyed sites in a range of 11.8-19.50%. With the advancement of the crop season, a progressive increase in the flower damage was observed till 120 DAS then declined. Reasons for the enhanced flower damage and implications are discussed in this article.
The objective of this study was to examine the development of corn leaf aphid,Rhopalosiphum maidis Fitch (Aphididae: Hemiptera) on maize Zea mays Linnaeus at elevated and ambient concentrations of CO2 (550 and 380ppm ± 25 ppm, respectively) at six temperatures (20, 25, 27, 30, 33 and 35°C) and to estimate thermal constants and lower temperature thresholds for the forecasting models based on heat accumulation units which could be developed for use in forecasting. The duration of different growth stages of R.maidis were reduced with an increase of temperature from 20°C to 35°C under both ambient and elevated CO2 conditions. The lower development threshold for first nymphal instar,second nymphal instar, third nymphal instar, fourth nymphal instar, adult duration and total development period required 10.1, 5.04, 13.42, 26.96, 10.9, 23.22 and 20.20°C under eCO2 whereas it was 13.32, 9.41, 19.13, 30.48, 16.38, 22.88 and 20.89°C under aCO2 conditions,respectively. The mean lower temperature threshold for nymph was slightly higher (16.38°C) at aCO2 compared to that of eCO2 (10.90°C) whereas for adult the mean lower temperature threshold was slightly higher (23.22°C) at eCO2 compared to that of aCO2 (22.88°C). The thermal requirement of R. maidis from first nymphal instar to adult (total development period) was found to be 100.00 degree days (DD) under eCO2 conditions as against 111.11degree days under aCO2 conditions. These estimated temperature thresholds and thermal constant can predict the pest scenarios and population dynamics of R. maidis.
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