Abstract
Seasonal incidence of Plassey borer, Chilo tumidicostalis Hampson, and its larval parasitoid, Cotesia flavipes Cameron, was studied at Shillogani, Nagaon, Assam, during 2006-07. Population of C. tumidicostalis first appeared in the early part of May and peaked in the second fortnight of September in both the cropping seasons. Later it showed a declining trend till harvest. The activity of C. flavipes commenced from the first fortnight of June in both the cropping seasons and continued till the end of November, 2006 and early part of December, 2007. The extent of natural parasitism by C. flavipes varied from 2.10 to 39.43 per cent in 2006 and 1.33 to 48.30 per cent in 2007. Maximum parasitism (39.43 and 48.30 per cent) occurred during the first fortnight of October, 2006 and the second fortnight of September, 2007 in the two study years. The parasitism increased with the increase in incidence of C. tumidicostalis larvae and fairly synchronized with the latter's maximum incidence. The extent of parasitism had significant positive correlations with the incidence of host larval population and relative humidity, but showed non-significant correlations with temperature, total rainfall and sunshine in both the cropping seasons.
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