Effect of elevated CO2 and temperature on thermal constants and lower threshold temperatures of maize aphid, Rhopalosiphum maidis (Fitch.) (Aphididae:Hemiptera) on maize, Zea mays (Linn.)

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 degrees 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 degrees C to 35 degrees 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 degrees C under eCO(2) whereas it was 13.32, 9.41, 19.13, 30.48, 16.38, 22.88 and 20.89 degrees C under aCO(2) conditions,respectively. The mean lower temperature threshold for nymph was slightly higher (16.38 degrees C) at aCO(2) compared to that of eCO(2) (10.90 degrees C) whereas for adult the mean lower temperature threshold was slightly higher (23.22 degrees C) at eCO(2) compared to that of aCO(2) (22.88 degrees 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 eCO(2) conditions as against 111.11degree days under aCO(2) conditions. These estimated temperature thresholds and thermal constant can predict the pest scenarios and population dynamics of R. maidis.