Abstract
During a three year study in rapeseed-mustard crop, the response of two ladybird species, Coccinella septempunctata and Menochilus sexmaculatus was dependent upon density and time of appearance of their prey. Mustard aphid, Lipaphis erysimi appeared during the second (2000 and 2001) and last (2002) week of January. Aphid appearance was highly dependent on the pheno- logical stage of the host plant. It appeared earlier in rapeseed, Brassica campestris var. BSH-1 than mustard, Brassica juncea var. RH-30. The ladybird beetle's eggs were observed in the last week of January, 4-5 weeks before the maximum aphid population. A correlation between aphid number and the abundance of ladybirds' life stages (egg, larva and beetle) on these host plants revealed that the egg and larval density was positively correlated to aphid numbers. Adult beetles, however, did not show significant positive correlation with aphid numbers during all the three years of study. Coccinella septempunctata was more abundant than Menochilus sexmaculatus in these crops. Menochilus sexmaculatus population disappeared earlier than Coccinella septempunctata which was abundant until end of the crop season.
Highlights
Oilseed Brassicas contribute substantially to the oil economy of the world including India in the form of oil yield and their by-products for industrial use (Bharti et al, 2002)
The alates settled on rapeseed during standard week 3
The results of the present study in northern plains of India have shown that mustard aphid is a predominant pest of rapeseed and mustard crops frequently varying in its numbers
Summary
Oilseed Brassicas contribute substantially to the oil economy of the world including India in the form of oil yield and their by-products for industrial use (Bharti et al, 2002). Lipaphis erysimi (Kalt.) inflicts major losses to the rapeseed and mustard crops in India. It sucks on the phloem of different plant parts including inflorescence and seed pods resulting in substantial yield losses (Kennedy & Abou-Ghadir, 1979). Use of insecticides for the control of this pest leads to serious environmental hazards in the form of pollution, biological control is of vital importance in oilseed Brassicas. The aim of this study was to record the density dependent response of C. septempunctata and M. sexmaculatus towards their aphid prey in rapeseed-mustard crops in a tropical region of India
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