Laboratory observations on exploitation rate of spotted beetle, Coccinella septempunctata Linn. against mustard aphid, alfa alfa aphid and corn leaf aphid

Observation exploitation rate of spotted beetle Coccinella septempunctata Linn. against mustard, alfa alfa and corn leaf aphid studies were conducted in Laboratory, Department of Entomology, Sindh Agriculture University, Tandojam. The mean incubation period of C. septempunctata eggs laid by females reared on mustard, alfa alfa and corn leaf aphid was 6.9, 7.0 and 7.3 days respectively with non- significant chi-square value (0.038) at 0.05 level. The mean number of eggs per female was 624, 607 and 633 reared on mustard, alfa alfa corn leaf aphid and these values are highly significant at 0.05 level (X2=4.97). The hatch percent of eggs of C. septempunctata was 65.3, 69.5 and 64.32 which are non-significant at 0.05 level (X2=0.51.) The grubs passed through four instars reach the pupal stage. Feeding of different host aphids did not significant influence (X2 test, at 0. 05 level.) the duration of various life stages of C. septempunctata. The duration values in days for first, second, third and fourth instar ranged between 5.5- 6.4, 4.2-5.3, 4.1-7.9 and 6.5-9.2, respectively. Pupa period ranged between 3.0 and 4.5. Pre-oviposition, oviposition and post oviposition periods were 3.2-3.9, 22.5-25.4 and 3.5-4.6 days, respectively. Adult life span was 32.00-36.00 days. All the instars were found voracious feeding of all the aphid species tested. Exploitation rate in terms of aphids eaten per day values based on X2 test were highly significant at 0.05 level among host aphids within third and fourth instar and non- significant within first and second instar. Fourth instar septempunctata grubs devoured more alfa alfa aphid, followed by corn leaf aphid and mustard aphid. Adults devoured more corn leaf aphids followed by mustard aphid and Alfa alfa aphid. Values for aphid exploitation rate per day for first, second, third, fourth instar and adult beetle were 6.4- 9.95, 22.5-26.30, 32.00-50.50, 45.25-135.6 and 75-92 respectively. This shows that exploitation rate increased with advance stages specially fourth instar grub had the highest predation rate. The exploitation rate of adult C. septemunctata on all aphid species tested increased with the age with maximum exploitation rate on 11th day for corn leaf aphid (feeding rate 117.0), 9th day for mustard aphid (109.0) and 14th day for alfa alfa aphids (98.6). The exploitation rate decreased after maximum in case of each host- aphid species. The mean exploitation rate through adult life was 72.49, 72.51 and 82.66 for mustard aphid, alfa alfa aphid and corn leaf aphid respectively.