What's on the menu? A predator gut content assay for identifying active predation from scavenging

Scavenging commonly occurs among predaceous arthropods. As such, if a predator preferentially consumes carrion it has little value as a biological control agent. Determining the frequency of carrion feeding versus active predation is important toward understanding predator effectiveness as a control agent. However, due to small size, cryptic behavior, and nocturnal activity, observing scavenging or active predation in nature is difficult. Here, we describe a predator gut content assay that can differentiate scavenging events from active predation events. We marked a cadaver cohort of sweetpotato whitefly, Bemisia tabaci with chicken immunoglobulin G protein and a living cohort with rabbit IgG protein. Individuals of Hippodamia convergens and Collops vittatus were then offered 10 marked whiteflies for 30 minutes. Retention of the protein mark in the predators’ guts was tested at 0, 3, 6, 12, 24, and 48 hours after feeding using protein-specific enzyme-linked immunosorbent assays (ELISAs). Each protein-specific ELISA was able to detect the presence of the target protein for up to 48 hours after consumption. Simultaneously, we directly observed H. convergens and C. vittatus and quantified their prey handling time and preference for living and carrion prey items. No difference in consumption rates between the prey types were observed in the feeding choice tests; however, differences in behavior were identified (e.g. handling time, probing) between the prey treatments. Next, we plan to use this methodology in prey manipulated field cages to identify the degree of active predation and scavenging exhibited by the entire cotton predator assemblage.