Comparison of reproductive numerical response of two coccinellid predators, Scymnus levaillanti Mulsant and Cycloneda sanguinea L. (Coleoptera: Coccinellidae)

The reproductive numerical response of Scymnus levaillanti Muls. and Cycloneda sanguinea L. (Coleoptera: Coccinellidae) in relation to prey consumption was compared in the laboratory at various temperatures. These two species present different aphidophagous strategies: S. levaillanti is a small tropical species, laying small single egg, while C. sanguinea from cooler climates is a large species laying large eggs in egg batches. There are highly significant positive linear correlations between the number of eggs laid and the number of aphids consumed by both coccinellid species. C. sanguinea required more aphids to start laying the eggs than S. levaillanti. The smaller species, S. levaillanti, began to oviposit at much lower aphid densities than did the larger species, C. sanguinea. At low densities of aphids, therefore, S. levaillanti could be the dominant species due to the lower minimum threshold for egg production and the greater sensitivity of the adults to low aphid populations; whereas, C. sanguinea could be the dominant species at high densities of aphids due to its greater fecundity. The reproductive numerical response of S. levaillanti confined to a narrow range of cotton aphid densities due to its satiation at low aphid densities (80 aphids per 64 cm super(2)) can account for its poor efficiency as a biological control agent. On the other hand, C. sanguinea required more aphids to be satiated (480 aphids/64 cm super(2)) than S. levaillanti, which can provide a better result for control of the aphids.