Population Dynamics of Mustard Aphid Lipaphis erysimi Kalt. on different Varieties of Indian Mustard and their Relationship with Prevailing Weather Parameters

An experiment was conducted during Rabi 2008-2009 and 2009-2010. Aphid appeared in first week of January when the maximum temperature was (15.8-16.10C) and minimum temperature (5.3-8.00C) along with relative humidity 93.0-95.3 per cent maximum, 66.0- 82.9 per cent minimum and wind speed 2.6 km/h during 2008-09 and 2009-10, respectively. The peak intensity of aphids on different varieties of Indian mustard during 7^th standard week (Feb., 12-18) in respective years, when the temperature was 23.1-25.10C maximum and 9.4-12.50C minimum along with relative humidity maximum 89.0-91.0 per cent and minimum 43.0-69.0 per cent during 2008-09 and 2009-10, respectively. The aphid population was completely wiped out from mustard crop in the last week of February and first week of March, when the crop age was 118 days. At this stage, temperature was 29.7-31.70C maximum and 12.7-15.70C minimum along with relative humidity maximum 73.0-78.0 per cent and minimum 34.0-36.0 per cent during 2008-09 and 2009-10, respectively. Simple correlation co-efficient of aphid with weather factors showed a positive relationship with temperature (r=0.226-0.645 and 0.900-0.961) and wind speed (r=0.434-0.651 and 0.599-0.684), while negative impact with relative humidity (r=-0.579 to -0.765 and -0.526 to -0.633) during both the years.