Patch Assessment for Oviposition by a Predator: the Effect of Prey Density and Prey Oviposition Period

Abstract

Density dependent numerical response is considered advantageous for biocontrol agents. Although density dependent behaviors have been examined in aphidophagous ladybirds, they haven’t been studied for coccidophagous ladybirds. The relationship of prey density and prey oviposition stage on the aggregating behavior and oviposition of the coccidophagous predator Nephus includens (Coleoptera: Coccinellidae) was empirically investigated. In a semi-field experiment potted citrus trees were artificially infested with Planococcus citri (Hemiptera: Pseudococcidae) prey in order to obtain two densities, one mealybug and ten mealybugs per tree. Released N. includens adults were found to aggregate at citrus trees with high prey density. In a subsequent laboratory experiment four prey densities of P. citri were used ranging from 1 to 8 adult mealybugs at 3 ovipositional stages, a) at the young gravid female stage, b) at mid oviposition (half of egg load oviposited) and c) at the end of the ovipositional period (full egg load oviposited). Nephus includens females increased their oviposition rate as prey density increased and as prey oviposition progressed. It is hypothesized that this behavior of the predator might be advantageous for offspring survival and the efficacy of N. includens as a biological control agent against mealybugs.