Demographic parameters of the predaceous ladybird, hippodamia variegata (Goeze), on the aphid species, aphis craccivora (koch), reared on four host plants

Abstract

The reproductive and demographic attributes of the aphidophagous ladybird, Hippodamia variegata (Goeze) (Coleoptera: Coccinellidae), when fed on the aphid species, Aphis craccivora (Koch), reared on four host plants, viz. Dolichos lablab L., Vigna unguiculata L. Walp, Cajanus cajan (L.) Millsp., and Ranunculus sceleratus L., were investigated in the laboratory to find host suitability for the production of the ladybird. Results indicated that there was a significant effect of host plant on both reproductive and demographic parameters of the predator. The host plant suitability was in the rank order D. lablab = V. unguiculata > C. cajan > R. sceleratus. This ladybird started reproducing very early and laid a high number of eggs for a longer period of time when the adults were fed on aphids raised on D. lablab and V. unguiculata. Both the fecundity and percent egg hatching increased significantly in the case of the abovementioned two host plants. Similar host plant effects were found on demographic parameters of H. variegata, with significantly high values of net reproductive rate (rm ), short generation ( Tc ), and doubling times (D.T.) on D. lablab and V. unguiculata. Age-specific fecundity of H. variegata at all host plant treatments was triangular in function with an initial increase in ovipositional rate with age, followed by attainment of peak and gradual decline till egg laying ceases. These peaks were higher on the host plant treatments, D. lablab and V. unguiculata. Sub-optimal values of both reproductive and demographic parameters were found on the host plant, R. sceleratus. Thus, it could be concluded that both D. lablab and V. unguiculata were the suitable host plants to raise aphid, A. craccivora, for the augmentative rearing of the ladybird, H. variegata.