Population Dynamics of Mustard Aphid in relation to Humid Thermal Ratio and Growing Degree Days

Abstract

To determine the relative role of weather variables and accumulated heat units on mustard aphid Lipaphis erysimi (Kalt) population, field experiment was conducted at research farm of Indian Agricultural Research Institute (IARI) during the rabi season (October-April) of 2006-07. The study revealed that throughout the ascending phase of the aphid population right up to its observed peak, the maximum temperature showed downward trend till peak aphid population reached. During the descending phase of the aphid population, weather parameters were not found to be congenial. The maximum temperature started increasing after 27th January and later remained around 250C. Initially when aphid population started building up, HTR ranged from 2 to 3. The population started increasing gradually from 2nd week of December, reached peak population around last week of January in both of the varieties in 15th October sowing. In 30th October sowing aphid population started building up from 1st week of January and reached peak population around 1st week of February. It was observed that HTR as well as the aphid population increased, but as aphid population reached its peak the HTR values reduced. In both early (15th October) and late sown (30th October) crop the aphid population had a significant negative correlation with growing degree days (GDD), but positively correlated with humid thermal ratio (HTR). As the growth and development of insects mainly depends upon the accumulated amount of heat, GDD and HTR computation could be used for prediction of aphid population build up.