Seasonal abundance of aphid, Rhopalosiphum maidis (Fitch) and its natural enemies on barley ( Hordeum vulgare Linn) and Predatory potential of major coccinellid predators on aphid ( Rhopalosiphum maidis )

The aphid, R. maidis was found to be the major insect pest causing damage to the barley crop. The population of aphid started in the first week of January, increased and reached to peak (114.02 aphids/ tiller) at 22.0 0C maximum temperature, 6.3 0C minimum temperature, 65 per cent relative humidity and 9.5 sunshine hours in the first week of February, thereafter, the population declined gradually and completely disappeared in the fourth week of February. The maximum temperature had significant negative correlation (r=-0.76) and relative humidity had significant positive correlation (r=0.80) with aphid population, other abiotic factors were no significant. The population of ladybird beetle, Coccinella septempunctata Linn. On barley crop reached to maximum (5.98 per five plants) in the third week of February at 31.1 0C maximum temperature, 12.7 0C minimum temperature, 55 per cent relative humidity, and 9.0 sunshine hours. The maximum temperature and sunshine hours had significant positive correlation (r=0.92, 0.91), and relative humidity and rainfall had significant negative correlation (r= -0.92,-0.93) with the population of C. septempunctata. The first instar larva of ladybird beetle, C.septempunctata consumed on an average 23.30±1.10; while second, third and fourth instar larva consumed on an average 34.60±1.91, 102.50±11.49 and 194.20±8.61 aphids, respectively. The total number of aphids consumed during whole larval period averaged 354.60±15.00 aphids. On an average, a male consumed 2409.50 aphids in 25 days with an average of 96.38±3.42; whereas, a female consumed 2936.90 aphids in 25 days with an average of 117.48±4.63 aphids per day.