Numerical response of ladybird beetles (Col., Coccinellidae) to aphid prey(Hom., Aphididae) in a field bean in north-east India

Two predaceous species of Coccinellidae, Menochilus sexmaculatus and Coccin ella transversalis, occurred abundantly in bean crops infested with the aph id, Aphis craccivora Koch in north-east India. The number of eggs and adult s of the two coccinellids increased in response to the increase in the popu lation of aphid prey. Reproductive numerical responses were found to be syn chronous to prey density whereas aggregative numerical responses appeared a synchronous in the later part of the aphid cycle on beans. Menochilus sexma culatus oviposited smaller clusters of eggs at lower density of aphids than C. transversalis which laid larger clusters and showed greater numerical r esponse at higher densities of aphids. Within a species cluster the size of the eggs seems to be directly related to aphid density. The two coccinelli d species of this study seem to be efficient predators of A. craccivora in terms of their reproductive and aggregative numerical responses.