Wanted dead or alive: scavenging versus predation by three insect predators

Authors: MANSFIELD, SARAH - Lincoln University - New Zealand; Hagler, James

Submitted to: FOOD WEBS
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/11/2016
Publication Date: 11/28/2016
Publication URL: https://handle.nal.usda.gov/10113/5695343
Citation: Mansfield, S., Hagler, J.R. 2016. Wanted dead or alive: scavenging versus predation by three insect predators. FOOD WEBS. 9:12-17.

Interpretive Summary: Knowledge of the impact that predators have on insect populations is crucial for understanding food webs in agroecosystems. Many insect predators may engage in scavenging. If a given predator has a proclivity for dead prey instead of live prey, then the level of biological control rendered by that predator may be reduced. An ARS scientist at Maricopa, AZ in collaboration with a scientist at The University of Sydney, NSW, Australia placed unique protein markers on live and dead pest prey and exposed them simultaneously to three different predators on caged cotton plants. Results revealed that scavenging was more prevalent than predation for all three predator species. In addition, observations suggested that two of the predators were feeding on another predator in addition to the pest prey items. The protein marking procedure combined with direct observation proved useful for distinguishing scavenging from predation, which is not possible when using conventional methods that detect predation through chemical analysis of the predators.

Technical Abstract: Many generalist insect predators may engage in facultative scavenging. If an apparent predator frequently consumes dead prey instead of live prey then the biological control services provided by that predator may be overestimated. The use of unique protein markers on live and dead prey of the same species followed by gut content analysis of the predators is an effective method to distinguish between scavenging and predation events. The frequency of predation and scavenging on third instar Lygus hesperus prey by Collops vittatus, Hippodamia convergens and Chrysoperla carnea was measured using rabbit IgG and chicken IgG markers. Predators and rabbit IgG-marked dead (cadaver) and chicken IgG-marked live L. hesperus were placed on or adjacent to cotton plants enclosed in small cages for six hours. The plants were then searched for both predators and uneaten prey and examined for the presence of the two proteins by IgG-specific enzyme linked immunosorbent assays (ELISA). The gut analyses revealed that scavenging was more prevalent than predation and all three predators were facultative scavengers. In addition, direct visual observations of the predators in the cages and the number of Chrysoperla carnea that went missing during the study suggested that C. vittatus and/or H. convergens were engaging in intraguild predation on C. carnea. The immunomarking procedure used here when combined with a standard caging procedure proved useful for distinguishing scavenging from predation events, which is not possible when using conventional prey-specific ELISA and PCR assays.