Early season parasitism of cereal aphids in wheat fields and field borders

Authors: Elliott, Norman - Norm; GILES, KRISTOPHER - Oklahoma State University; BREWER, MICHAEL - Oklahoma State University; JESSIE, CASI - Oregon State University

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/14/2019
Publication Date: 3/1/2019
Citation: Elliott, N.C., Giles, K.L., Brewer, M.J., Jessie, C.N. 2019. Early season parasitism of cereal aphids in wheat fields and field borders. Southwestern Entomologist. 44(1):11-19. https://doi.org/10.3958/059.044.0102.
DOI: https://doi.org/10.3958/059.044.0102

Interpretive Summary: Winter wheat is Oklahoma's most widely grown crop and is typically planted in early autumn and harvested in June. Wheat in Oklahoma is often infested by insect pests, the most important of which are cereal aphids. Our objective was to determine the relationship between parasitism rates of cereal aphids in wheat field borders to parasitism rates in the wheat field itself just prior to wheat planting and soon after planting when wheat plants are just emerging from the soil. Three parasitoid species were parasitized cereal aphids in borders and wheat fields during the two-year study. We found that while the same parasitoid species forage for aphid hosts in field borders as forage for cereal aphids in wheat fields, parasitism levels in borders do not reflect levels in the adjacent field. This suggests that cereal aphid parasitoid activity levels in wheat field borders have minimal relationship to activity levels and, hence cereal aphid parasitism, in the adjacent wheat field. The significance of this research is that biological control of cereal aphids in wheat fields is not dependent on the structure of wheat field borders, but as our previous research has shown, is dependent on landscape structure at broader spatial scales.

Technical Abstract: Winter wheat is Oklahoma's most widely grown crop and is typically planted in early autumn and harvested in June. Wheat is often infested by insect pests, the most important of which are cereal aphids. Our objective was to determine the relationship between parasitism rates of cereal aphids in wheat field borders to parasitism rates in the wheat field itself. We utilized sentinel plants deployed in borders of wheat fields and also in the wheat fields to measure parasitoid activity (number of aphids parasitized). We also measured aphid abundance in borders and fields by D-vac suction sampling. Three parasitoid species were reared from cereal aphids on sentinel plants deployed in borders and wheat fields during the two-year study. Overall, Lysiphlebus testaceipes (Cresson) was the most abundant species followed by Aphelinus nigritus Howard and then Diaeretiella rapae (M'Intosh). There was no significant correlation between the number of parasites emerging from sentinel plants in field boundaries prior to wheat planting to the number emerging from sentinel plants stationed in the field border post-wheat plant emergence. Nor was there a correlation for any species in the number of individuals emerging from sentinel plants stationed in field borders after wheat plant emergence to the number emerging from sentinel plants stationed in the adjacent wheat field at the same time. Within a habitat there were significant correlations among species in the number of parasitoids emerging from sentinel plants. While the same parasitoid species forage for aphid hosts in field borders as forage for cereal aphids in wheat fields, parasitism levels in borders do not reflect levels in the adjacent field. This suggests that cereal aphid parasitoid activity levels in wheat field borders have minimal relationship to activity levels and, hence cereal aphid parasitism, in the adjacent wheat field.