Effect of planting dates on dynamics of natural enemies of aphids infesting Brassica campestris, Brassicae oleracea var. capitata and Brassica oleracea var. botrytis

摘要

The impact of variation in planting dates on dynamics of predator and parasitoid of aphids was studied on brassica crops. The population was determined on early (3 October), mid (20 October) and late seeded (10 November) mustard, cabbage and cauliflower for two successive years (2011-12 & 2012-13). The mid and late seeded cabbage and cauliflower availed the maximum density of coccinellids (3.93 grubs/plant), syrphids (2.42 maggots/plant) and mummified aphids (10.33 mummies/plant). However, the earlyplanted mustard, harboured the relatively low population of both predators (2.93 coccinellids/plant, 2.07 syrphids/plant) and parasitoids (1.33 mummies/plant). The information inferred from variation in planting dates and its impact on incidence of natural enemies of aphids could be the significant outcome to achieve within-season mortality of aphids on late seeded brassica crops.