Population dynamics of wheat aphids and their natural enemies

The abundance of aphids infesting wheat and their natural enemies was studied at the CSKHPKV, Palampur. The aphids (Rhopalosiphum padi and Sitobion avenae) population commenced from first week of January and reached a peak (30.40 aphids/shoot) during third week of March. Seven species of coccinellid beetles were recorded as predators, of which Coccinella septempunctata, Hippodamia variegata and Coccinella transversalis were predominant. Peak population of their adults (8.10 beetles/m2), grubs and pupae was observed during first week of April. As regards the syrphids, peak in population (13.00 adults/5 sweeps-Episyrphus balteatus, E. viridaureus, Ischiodon scutellaris, Sphaerophoria sp. and Melanostoma spp.) was during third week of April. Lacewing Micromus sp. started appearing from first week of March with its peak being during third week of March. The peak activity of Diaeretiella sp. was observed during first week of April with 16.6% parasitization. These natural enemies showed a significant positive correlation with aphid population, while with weather factors mixed results were observed. The predatory potential of coccinellids evaluated revealed that the adults as well as grubs have potential to suppress aphid population.