Population fluctuation of aphid (Aphis craccivora Koch.) infesting som plant leaves (Machilus bombycina King) and its management

Som plant (Machilus bombycina King), useful for rearing of muga silk worm (Antheraea assama ww), is susceptible to various insect pests of which Aphis craccivora Koch. causes heavy damage to tender leaves of the plant. Initially its population was recorded as 10.88–12.79 aphid/leaf during January-February and then declined. Higher population (17.45–24.98/leaf) was maintained during 2^nd week of September to 1^st week of October. Aphid incidence showed positive correlation with temperature and relative humidity. Immidacloprid, was the most effective in providing more than 80% aphid suppression followed by azadirachtin. As som plant leaves provide the major food component of muga silk worm rearing, toxic synthetic insecticide should not be used. Polygonum extract was very effective against the aphid (>60% suppression).