Spatial distribution of cabbage aphid, Brevicoryne brassicae (L.) and its parasitoid, Diaeretiella rapae (Mc Intosh) under sub-temperate conditions of Himachal Pradesh, India.

Cabbage aphid, Brevicoryne brassicae (L) (Aphididae: Hemiptera) is one of the most serious pest of cauliflower throughout the world. Knowledge of spatial distribution is important for developing an effective sampling plan and ultimately for IPM strategies for a given pest. In the present study spatial distribution of B. brassicae and its parasitoid, Diaeretiella rapae (Mc lntosh) (Braconidae: Hymenoptera) was studied on cauliflower (Brassica oleracea var botrytis) under sub-temperate conditions of India during 2017. Both B. brassicae and D rapae assumed activity in the fourth week of January and remained active till May end with peak activity during fourth week of March, 2017. Dispersion indices like variance to mean ratio (σ²/X), David-Moore index (IDM = σ²/X-1), mean crowding (X*), Lloyd's mean crowding index (X*/X) and 'k' of negative binomial indicated that both the aphid and the parasitoid followed negative binomial distribution throughout the cropping season, Taylor's power equation was σ² = 1.7013X^0.5314 for B. brassicae and σ² = 2.2057X^1.4467 for D. rapae, while Iwao's patchiness regression equation was X*= 32.0099+1.7947X and X*= -2.0678+2.2746X for B. brassicae and D. rapae, respectively. Optimum number of samples required varied with the mean density and the desired precision level for both the aphid and the parasitoid. [ABSTRACT FROM AUTHOR]