Evaluating the use of common grasses by the wheat stem sawfly and its native parasitoids in rangeland and Conservation Reserve Program grasslands

Authors: Rand, Tatyana; Kula, Robert; Gaskin, John

Submitted to: Journal of Economic Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/26/2024
Publication Date: 3/23/2024
Citation: Rand, T.A., Kula, R.R., Gaskin, J.F. 2024. Evaluating the use of common grasses by the wheat stem sawfly and its native parasitoids in rangeland and Conservation Reserve Program grasslands. Journal of Economic Entomology. 117(3):858-864. https://doi.org/10.1093/jee/toae046.
DOI: https://doi.org/10.1093/jee/toae046

Interpretive Summary: The wheat stem sawfly is a major pest of wheat across the northern Great Plains. It attacks numerous wild grasses and cultivated small grains in crop and grassland habitats, where it is in turn attacked by two native biocontrol parasitoids. Determining levels of pest infestation and parasitism by biological control agents in different grass species across the full spectrum of available hosts is important in assessing the extent to which grasslands, or specific grass species, may be reservoirs of pests or biocontrol agents moving into wheat. We quantified infestation and parasitism levels in over 25,000 stems collected from 17 grass species and wheat spanning 35 sites in central Montana, USA, over two years. Infestation levels in five grass species, primarily wheatgrasses, were high (38-65%) and similar to the levels observed in wheat. In contrast, the majority of grass species (12 of 17) had low levels of infestation (<10%) suggesting that most grasses are not important sources of wheat stem sawfly. Levels of attack of the wheat stem sawfly by parasitoids were on average three times higher than those in wheat suggesting that these grasses could provide important conservation habitat for parasitoids. Future work examining the relative performance of pests and parasitoids in these grasses will be important in gauging their relative value as plant materials to bolster parasitoid conservation in seeded grassland habitats.

Technical Abstract: The wheat stem sawfly, Cephus cinctus Norton (Hymenoptera: Cephidae), is a major pest of wheat (Triticum aestivum L., Poales:Poaceae) across the northern Great Plains of North America. Cephus cinctus has a wide host range attacking numerous wild grasses and cultivated cereals in crop and grassland habitats, where it is in turn attacked by two native braconid parasitoids. Quantitative assessments of C. cinctus infestation and parasitism levels in different grass species across the full spectrum of available hosts is important in assessing the extent to which grasslands, or specific component grass species, may be reservoirs of pests or parasitoids moving into wheat. We quantified infestation and parasitism levels in over 25,000 stems collected from 17 grass species and wheat spanning 35 sites in central Montana, USA, over two years. Infestation levels in five grass species, primarily wheatgrasses, were high (38-65%) and similar to the levels observed in wheat. In contrast, the majority of grass species (12 of 17) had significantly lower levels of infestation (<10%) suggesting that most grasses are not important reservoirs of C. cinctus. Parasitism levels in highly infested wheatgrasses were on average three times higher than those in cultivated wheat suggesting that these grasses could provide important conservation habitat for parasitoids. Future work examining the relative performance of pests and parasitoids in these grasses will be important in gauging their relative value as plant materials to bolster parasitoid conservation in seeded grassland habitats.