Biological parameters and prey consumption by zigzag beetle Menochilus sexamaculatus Fab. against Rhopalosiphum maidis Fitch, Aphis gossypii Glov. and Therioaphis trifolii Monell

In the present laboratory studies of some biological parameters and prey consumption of zigzag beetle Menochilus sexmaculatus F. (Coleoptera coccinellidae) with three species of aphids as prey were conducted at the Department of Entomology, Sindh Agriculture University Tandojam during 2005. The result showed that egg incubation period of M. sexmaculatus was 7.5, 7.1 and 7.2 days when reared on R. maidis, A. gossypii and T. trifolii Menell aphids respectively. Mean fecundity of the beetle female was 642, 530, 600, eggs when fed on R. maidis, A. gossypii and T. trifolii respectively. Egg hatchability percentage of the predatory beetle was 65.42 with R. maidis, 64.33 with A. gossypii and 70.69 with T. trifolii. The grubs passed through four instars to reach pupal stage. Feeding of different host aphids did not significantly influence the duration of various life stages of M. sexmaculatus where duration of first, second, third and fourth instars ranged between 6.5-7.0, 4.5-5.5, 3.9-6.5 and 6.5-8.5 days, respectively. Duration of pupal period ranged between 3.1 and 5.5 days. The pre-oviposition, oviposition and post oviposition periods were 3.1-3.7, 23.4-27.7 and 3.5-4.5 days respectively. Adult life span ranged as 30.0-35.0 days. All the immature instars where found voracious feeders of all the tested aphid species. However, the third and fourth instars consumed more prey/day than first and second instars. The fourth instar beetle grubs consumed more R. maidis. The adults consumed more T. trifolii than the other aphid species. Mean daily prey consumption by the beetle during the 1st, 2nd, 3rd and 4th instar and the adult stage ranged between 6.20-12.00, 20.00-27.00, 30.5-55.00, 43.27-45.27 and 72.00-82.5 prey respectively. Mean total number of prey consumed during entire adult life was 80.08 R. maidis, 69.95 A. gossypii and 68.96 T. trifolii.