Sal Seed Infestation and Adult Emergence of <I>Sitophilus rugicollis</I> Casey (Coleoptera : Curculionidae) in Midnapore (West Bengal)

Abstract

Seeds of Sal (Shorea robusta) are an industrially important seasonal forest product of India. These seeds on the forest floor as well as in the godown are often found to be infested by the weevil Sitophilus rugicollis Casey (Coleoptera: Curculionidae). Rates of seed infestation were studied from the Sal seeds collected from different forest floors in Midnapore, West Bengal, India during April to July to 1983-85. The rate of Sal seed infestation was very low (10.13 ± 3.77%) in April. The incidence rose steeply from May-July (24.98 ± 5.47%; 60.51 ± 9.76% and 97.70 ± 1.55% in May, June and July respectively). At the end of July the maximum number of seeds on the forest floor were infested by the weevil. The rate of adult emergence usually shows a little higher trend under laboratory conditions (7.65 ± 1.68 per seed) then under natural conditions (6.03 ± 1.69 per seed). Thus, even a small cluster of seed is capable of producing a considerable weevil population either in field or in godown. And due to their higher intrinsic capacity of damage, the weevil causes a tremendous economic loss in the area during each and every year.