Studies on the influence of biotic and abiotic factors on aphid, Lipaphis erysimi Kalt. population under mustard ecosystem

Attempts were made to study the influence of biotic and abiotic factors on aphid, L. erysimi Kalt. population under mustard crop ecosystem during rabi season of 2015–2016. The correlation studies of aphid population with bioagent population showed negative impact with ‘r’ value of -0.5446 with a regression coefficient 0.1550 and is observed to be statistically non-significant even at p ≤ 0.05. The regression equation fitted with the bioagent revealed that for every increase of one unit of bioagent there would be a decrease of 0.1550 number of test insect. The occurrence of bioagent population was observed during third week of January when the mean aphid population was varying between 10.07 to 21.67 aphid/10 cm terminal shoot. During 3^rd week of January the mean of bioagent population was observed to be 0.04 per plant on 20.01.2016. However the effect of abiotic factors (temperature, humidity, rainfall) with aphid population revealed that maximum and minimum temperature were found to be statistically non-significant with a regression coefficient of -0.1807 and 0.3191, maximum and minimum relative humidity were also statistically non-significant with a regression coefficient of 0.0521 and -0.0761 and rainfall have negative correlation with aphid population r = -0.7650 with a regression coefficient of -0.0098. The maximum and minimum temperatures on day of observation were 19°C and 11°C and the maximum and minimum relative humidity were 94 per cent and 69 per cent, respectively. On successive days of observation at an interval of 7 days the bioagent population gradually increased till 24.02.2016 reaching to a peak of mean population of 1.52 per plant.