RESUMO
Aphid Lipaphis erysimi (Kaltenbach) infestation on mustard (Brassica juncea L.) account for considerable yield losses in India. Experimental data from six north Indian locations were used to study the role of weather on the incidence and development of mustard aphid. Temperature was found to regulate the aphid appearance and population build-up. In warm humid climate, time to attain peak population was relatively shorter than in cool climates. Aphids appeared mostly when the accumulated thermal time ranged between 810-847 degrees cd. Functional relations proposed in the present investigation between aphid incidence and peak population, using previous weeks weather and pest data for majority of the locations, could be used for taking any prophylactic/control measures.