Nonconsumptive effects of parasitoids and predators in stored products: the impact of Theocolax elegans and other field‐collected predators on the foraging of lesser grain borer and rice weevil

To date, prior research on the biological control of stored products has focused on the direct consumptive effects of parasitoids and predators. However, in other systems, trait-mediated indirect interactions or nonconsumptive effects have been shown to be as or more important in maintaining the suppression of pest populations. Thus, in this study, our aim was to evaluate the effect of the parasitoid, Theocolax elegans, the predator community around food facilities, and their associated chemical cues on the foraging behavior of Sitophilus oryzae and Rhyzopertha dominica. We evaluated consumptive predation of a variety of insect and arachnid predators on S. oryzae as well as effects on the foraging behavior of S. oryzae and R. dominica in a series of movement assays after exposure to adult T. elegans, headspace extracts from T. elegans or gryllids, and a facsimile gryllid model to determine potential nonconsumptive effects. We found the headspace from T. elegans colonies to be distinct from other treatments. The strength of nonconsumptive effects appeared to be greater after exposure to T. elegans adults compared to other predators or extracts. The presence of T. elegans in a block led to a 48-58% reduction in distance moved and 40-56% reduction in instantaneous velocity for the control and wheat treatments by S. oryzae and R. dominica compared to when wasps were absent. Rhyzopertha dominica exhibited 73% reduced frequency of entering the zone with wheat when adult T. elegans was present. We conclude that nonconsumptive effects may result in alterations in behavior by stored product insects, but these effects may vary by the coevolutionary relationship between the natural enemy and pest. Published 2025. This article is a U.S. Government work and is in the public domain in the USA.