Evidence of intraguild predation on a key member of the cotton predator complex

Authors: Hagler, James; Blackmer, Felisa

Submitted to: FOOD WEBS
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2015
Publication Date: 9/15/2015
Publication URL: http://handle.nal.usda.gov/10113/61606
Citation: Hagler, J.R., Blackmer, F. 2015. Evidence of intraguild predation on a key member of the cotton predator complex. FOOD WEBS. 4:8-13.

Interpretive Summary: It is well known that arthropod predators are important regulators of pest populations in agricultural systems. Although the quantitative relationships between populations of pests and their predators can be difficult to describe, even less is known about how the population of one predator may impact the population of another predator. Because predator population levels are typically much lower than pest population levels, predator-predator interactions are exceedingly difficult to observe directly. In response to this challenge, methods to detect chemical signatures (DNA) of a specific prey species in the stomach of its predator can be developed. We used such a chemical test to demonstrate that more than 10% of arthropod predators collected from cotton had preyed on a common predator, the green lacewing (Chrysoperla carnea). Results also indicated that insect predators were nearly twice as likely to prey on lacewings as were spiders. Finally, predation on lacewings was detected more often when predators were collected in nets than when they were collected by searching the plants visually. Results indicate that better understanding of predator-predator interactions is needed to accurately assess their collective impacts on pests, and that the influence of sampling method must be considered in the interpretation of chemically-detected predation data.

Technical Abstract: Understanding trophic level interactions of arthropods is vital for identifying the biological control services provided by the predator complex. A polymerase chain reaction (PCR) assay was developed to examine the gut contents of the cotton predator community for the presence of the DNA of green lacewing, Chrysoperla carnea (Stephens), a fellow member of the predator community. A total of 1,440 predators were captured using both a sweep net and whole plant sampling method. The gut content analyses revealed that over 10% of the predator population contained C. carnea DNA in their gut. Of these, prey DNA was detected almost twice as frequently in predaceous insects as spiders. Also, predation events were detected more frequently for those predators captured in the sweep nets. This raises concerns regarding the method used to capture predators for studies requiring molecular analysis of gut contents.