Tri-trophic interactions are resilient to large shifts in precipitation levels in a wheat agroecosystem

Authors: Rand, Tatyana; Waters, Debra; Srygley, Robert; Branson, David - Dave

Submitted to: Agriculture, Ecosystems and Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/25/2020
Publication Date: 6/11/2020
Publication URL: https://handle.nal.usda.gov/10113/6985418
Citation: Rand, T.A., Waters, D.K., Srygley, R.B., Branson, D.H. 2020. Tri-trophic interactions are resilient to large shifts in precipitation levels in a wheat agroecosystem. Agriculture, Ecosystems and Environment. 301:1-10. https://doi.org/10.1016/j.agee.2020.106981.
DOI: https://doi.org/10.1016/j.agee.2020.106981

Interpretive Summary: Changing climate conditions can fundamentally alter the interactions between species (e.g., herbivory and predation) with important implications for agriculture. The impacts of shifts in precipitation on trophic interactions have been understudied relative to other climate drivers, yet understanding such impacts will be critical to development and implementation of effective and resilient pest management strategies. We carried out manipulative field experiments to examine how precipitation, attack by parasitoid wasps and their potential interactions affect the performance of the wheat stem sawfly, a major pest of wheat, and its impact on wheat yield. We independently manipulated insects (no insects, + wheat stem sawfly, or + wheat stem sawfly and parasitoids) and precipitation (-70%, ambient, +70%) in a factorial design over two years. Crop-herbivore-parasitoid interactions were remarkably robust to our precipitation manipulations with no significant changes in sawfly infestation, survival or levels of parasitism observed in the first (wetter) year of the study. Despite slight declines in pest infestation and percent parasitism under precipitation reductions relative to addition in the second year, both insects had strong and significant impacts on crop yield and these were consistent across precipitation manipulations. The results suggest that natural enemy benefits to crop production in this system can be substantial, and are likely to be robust across a relatively wide range of rainfall levels. While rare, studies such as this, which examine climate influences within a tri-trophic context, will be critical to predicting how pest insects will ultimately impact crop production under changing climatic conditions.

Technical Abstract: Changing climatic conditions can fundamentally alter the interactions between species with important implications for agriculture. The impacts of shifts in precipitation on trophic interactions have been understudied relative to other climate drivers, yet understanding such impacts will be critical to development and implementation of effective and resilient pest management strategies. We carried out manipulative field experiments to examine how precipitation, attack by parasitoid wasps (Bracon cephi (Gahan) (Hymenoptera: Braconidae) and their potential interactions affect the performance of a major pest of wheat Cephus cinctus Norton (Hymenoptera: Cephidae), and its impact on wheat (Triticum aestivum L. (Poaceae) yield. We independently manipulated insects (no insects, + C. cinctus, or +C. cinctus and B. cephi) and precipitation (-70%, ambient, +70%) in a factorial design over two years. Crop-herbivore-parasitoid interactions were remarkably robust to our precipitation manipulations with no significant changes in C. cinctus infestation, survival or levels of parasitism observed in the first (wetter) year of the study. Despite slight declines in pest infestation and percent parasitism under precipitation reductions relative to addition in the second year, both insects had strong and significant impacts on crop yield and these were consistent across precipitation manipulations, as evidenced by the lack of a significant interaction between insect and precipitation treatments. The results suggest that natural enemy benefits to crop production in this system can be substantial, and are likely to be robust across a relatively wide range of precipitation levels. While rare, studies such as this, which examine climate influences within a tri-trophic context, will be critical to predicting how pest insects will ultimately impact crop production under changing climatic conditions.