Parasitization of aphids on cauliflower seed crop in relation to their population build-up in mid-hills of Himachal Pradesh.

Abstract

Continuous monitoring of aphid population on cauliflower seed crop from December to April revealed an increase in infested plants (23 to 48%). aphid population (8 to 131/plant) and parasitization (I to 3.8%) during January to mid-March, followed by a decline in aphid infestation and further increase in parasitization (to 7.4%) till April 6, despite prominence of coccinellid activity (0.8-9.5 beetles/plant). There was concomitant occurrence of Brevicoryne brassicae (Linnaeus) and Myzus persica (Sulzer), the former being predominant (65.3%) and their parasitization varied from 0.7-8.3 (av. 3.6 and 8-8.2 per cent (av. 4.4). respectively. Intra-plant distribution indicated that aphid infestation was maximum on inner whorl of leaves. followed by middle and outcr whorls. but number of mummified aphids did not vary significantly in respect of position of leaves. During mid-March to early-April also, H. brassicae outnumbered M. persicae on terminal bolts and thcil' parasitizlltion was 27.4 and 14.5 per cent. From the mummies of aphids collected from the cabbage fields during Decemher. and May-June, the arasitoid Diaeretiella rapae (M'Intosh) (Aphidiidae) and thc hypeqlanlsitoid Pachyneuron aphids (Bouche) (Pteromalidae) emerged. but the emergence was poor (5.6 and 6.3% respectively), The mummics from which the parasitoid emerged were bigger with oval and uniform emergence holes around cornicles than the mummies from which hyperparasitoid emerged, The emergence holes or the lattel was irregular, smaller and often towards anterior side of the body,