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

Tatyana A. Rand, Debra K. Waters, Robert B. Srygley, David H. Branson
Agriculture, ecosystems & environment 2020 v.301 pp. 106981
Bracon, Cephus cinctus, Triticum aestivum, agroecosystems, atmospheric precipitation, biological control agents, climatic factors, factor analysis, field experimentation, grain yield, growing season, host-parasite relationships, insect infestations, insect pests, natural enemies, parasitic wasps, parasitism, phytophagous insects, plant pests, plant-insect relations, tritrophic interactions, wheat
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. We carried out field experiments to examine how precipitation, attack by parasitoid wasps (Bracon cephi (Gahan))(Hymenoptera: Braconidae) and their potential interaction affect the performance of a major pest of wheat, Cephus cinctus Norton (Hymenoptera: Cephidae), and its impact on wheat yield. We independently manipulated insects (no insects, +C. cinctus, or +C. cinctus and B. cephi) and precipitation (-50% to -70%, ambient, +70%) in a factorial design in each of two growing seasons. 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 addition relative to reduction in the second year, both insects had strong and significant impacts on crop yield. These effects 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 that examine climate influences within a tri-trophic context are critical to predicting how pest insects will ultimately impact crop production under changing climatic conditions.