An unusual abundance of cabbage butterfly, Pieris brassicae (Linnaeus) on various Brassica species in the environs of Delhi for locating sources of resistance among different cultivars

Cabbage butterfly, Pieris brassicae (Linn.), was recorded for the first time infesting Brassica spp., viz, B. juncea, B. napus, B. nigra and B. carinata at the National Bureau of Plant Genetic Resources Experimental Farm, Issapur, New Delhi, in February 1996. Its very high incidence was unusual, being primarily a pest in hills. Sixteen different Brassica spp. cultivars found infested were categorized on the basis of infestation index amongst 150 accessions (both exotic and indigenous). The late cultivars with green leafy stage coinciding with the period of pest activity were preferred while those with early maturity escaped infestation. Both intraspecific and interspeciflc variations in the acceptance of the food plants were observed. Amongst 12 B. juncea cultivars, the infestation index ranged from 1.25 in resistant Pusa Jai Kisan to 4.50 in highly susceptible EC-333568, EC-367885 and EC-333572 were moderately susceptible, whereas EC-322090, EC-367882, EC-322092, EC-333592, EC-367880 and EC-322093 were susceptible to P. brassicae. Other highly surceptible B. juncea cultivars included EC-333571 and EC-333594. B. napus cultivar, BEC-335 exhibited moderate susceptibility, the infestation index being 2.13, while B. nigra cultivar EC-289660 was susceptible (3.30). B. carinata cultivar EC-223405 was susceptible but EC-151995 A was highly susceptible to the pest. The physical factors of the host plant ruch as leaf texture and leaf colour were unrelated with the larval preference. Probably, the chemical factors of the host plant acting both as phagostimulants and phagodeterrents influenced host plant selection.