Effects of landscape composition on wheat stem sawfly (Hymenoptera: Cephidae) and its associated Braconid parasitoids

Authors: PEIRCE, ERIKA - COLORADO STATE UNIVERSITY; Rand, Tatyana; COCKRELL, DARREN - COLORADO STATE UNIVERSITY; ODE, PAUL - COLORADO STATE UNIVERSITY; PEAIRS, FRANK - COLORADO STATE UNIVERSITY

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/6/2021
Publication Date: 1/6/2021
Citation: Peirce, E.S., Rand, T.A., Cockrell, D.M., Ode, P.J., Peairs, F.B. 2021. Effects of landscape composition on wheat stem sawfly (Hymenoptera: Cephidae) and its associated Braconid parasitoids. Journal of Economic Entomology. 114(1):72-81. https://doi.org/10.1093/jee/toaa287.
DOI: https://doi.org/10.1093/jee/toaa287

Interpretive Summary: Several agroecological and integrated pest management strategies focus on landscape management to increase complexity and foster biodiversity. However, landscape complexity does not always enhance biological control and in some cases may lead to increased pest populations. Understanding how pest and natural enemy populations respond to landscape structure can lead to more informed management practices. Using several different experimental approaches, we examined the prevalence of Bracon spp. parasitoids of the wheat stem sawfly, a major pest of wheat in winter wheat and assessed the degree of non-crop host plant utilization and responses to landscape composition of the pest and its parasitoids. Surprisingly, we found no instances of Bracon parasitism in our three-year statewide winter wheat survey. However, we found small populations of Bracon spp. in non-crop landscapes throughout eastern and western Colorado. The native grass, Pascopyrum smithii, had the highest infestation and instances of parasitism of the host grasses examined. Our models suggests that an increase in wheat cover at the local level results in the greatest increase in the chance that Bracon spp. will attack sawfly. In contrast, a decrease in non-crop herbaceous (grass dominated) cover at a landscape scale was the best predictor of increase in wheat stem sawfly infestation. These results suggest an increase in herbaceous landcover could increase non-crop populations of Bracon spp. leading to a spill over into cultivated winter wheat in Colorado.

Technical Abstract: Several agroecological and integrated pest management strategies focus on landscape management to increase complexity and foster biodiversity. However, landscape complexity does not always enhance biological control and in some cases may lead to increased pest populations. Understanding how pest and natural enemy populations respond to landscape structure can lead to more informed management practices. Using several different experimental approaches, we examined the prevalence of Bracon spp. parasitoids of the wheat stem sawfly, a major pest of wheat in winter wheat and assessed the degree of non-crop host plant utilization and responses to landscape composition of the pest and its parasitoids. Surprisingly, we found no instances of Bracon parasitism in our three-year statewide winter wheat survey. However, we found small populations of Bracon spp. in non-crop landscapes throughout eastern and western Colorado. The native grass, Pascopyrum smithii, had the highest infestation and instances of parasitism of the host grasses examined. Our models suggests that an increase in wheat cover at the local level results in the greatest increase in the chance that Bracon spp. will attack sawfly. In contrast, a decrease in non-crop herbaceous (grass dominated) cover at a landscape scale was the best predictor of increase in wheat stem sawfly infestation. These results suggest an increase in herbaceous landcover could increase non-crop populations of Bracon spp. leading to a spill over into cultivated winter wheat in Colorado.