Modeling of aphid complex and its associated natural enemies in rapeseed-mustard in relation to climatic factors

Effect of climatic factors on population build-up of aphid complex of rapeseed-mustard viz. mustard aphid, Lipaphis erysimi (Kaltenbach), cabbage aphid, Brevicoryne brassicae (Linnaeus), and green peach aphid, Myzus persicae (Sulzer) and associated natural enemies (coccinellids, syrphids and a parasitoid, Diaeretiella rapae M’Intosh) was studied at Experimental Farm of CSK HPKV Palampur over a period of three years. Correlation coefficients indicated that the temperature favoured build-up of aphid population and their natural enemies while rainfall exerted negative impact. The population of coccinellids was negatively correlated with the population of L. erysimi and M. persicae while, positive correlation with B. brassicae was observed. On the other hand, population of syrphids was found to be positively correlated with aphid population. Predictive model using stepup regression analysis revealed that a weak relation in aphid population was attributed by weather parameters particularly minimum, maximum temperature and bright sunshine hours. Regression analysis revealed that 89 per cent variation in parasitization by D. rapae was attributed by minimum and maximum temperature, rainfall, relative humidity and bright sunshine hours.