Landscape context affects aphid parasitism by Lysiphlebus testaceipes (Hymenoptera: Aphidiinae) in wheat fields

Authors: Elliott, Norman - Norm; BREWER, MICHAEL - Texas A&M University; GILES, KRISTOPHER - Oklahoma State University

Submitted to: Environmental Entomology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2018
Publication Date: 8/1/2018
Citation: Elliott, N.C., Brewer, M.J., Giles, K.L. 2018. Landscape context affects aphid parasitism by Lysiphlebus testaceipes (Hymenoptera: Aphidiinae) in wheat fields. Environmental Entomology. 47(4):803-811. https://doi.org/10.1093/ee/nvy035.
DOI: https://doi.org/10.1093/ee/nvy035

Interpretive Summary: Winter wheat is Oklahoma's most widely grown crop, and is planted during September and October, grows from fall through spring, and is harvested in June. Winter wheat fields are typically interspersed in a mosaic of habitats in other uses, and we hypothesized that the spatial and temporal configuration of landscape elements, which contribute to agroecosystem diversity also influences biological control of common aphid pests. The parasitoid Lysiphlebus testaceipes Cresson is highly effective at reducing aphid populations in wheat in Oklahoma, and though a great deal is known about the biology and ecology of L. testaceipes, there are gaps in knowledge that limit predicting when and where it will be effective at controlling aphid infestations in wheat. Our objective was to determine the influence of landscape structure on parasitism of cereal aphids by L. testaceipes in wheat fields early in the growing season when aphid and parasitoid colonization occurs and later in the growing season when aphid and parasitoid populations are established in wheat fields. Parasitism of aphids in wheat fields was affected by the composition, shape, and distribution of habitats in the landscape surrounding the field. This was true in both autumn and spring. Overall, the results indicate that L. testaceipes utilizes multiple habitats throughout the year depending on their availability and acceptability, and frequently disperses among habitats. Colonization of wheat fields by L. testaceipes in autumn appears to be enhanced by proximity to fields of summer crops and semi-natural habitats other than grasslands. The significance of the research lies in documenting the importance of landscape structure in influencing the effectiveness of L. testaceipes as a biological control agent and indicates that land management strategies can alter the level of biological control of cereal aphids achieved in wheat fields.

Technical Abstract: Winter wheat is Oklahoma's most widely grown crop, and is planted during September and October, grows from fall through spring, and is harvested in June. Winter wheat fields are typically interspersed in a mosaic of habitats in other uses, and we hypothesized that the spatial and temporal configuration of landscape elements, which contribute to agroecosystem diversity also influence biological control of common aphid pests. The parasitoid Lysiphlebus testaceipes Cresson is highly effective at reducing aphid populations in wheat in Oklahoma, and though a great deal is known about the biology and ecology of L. testaceipes, there are gaps in knowledge that limit predicting when and where it will be effective at controlling aphid infestations in wheat. Our objective was to determine the influence of landscape structure on parasitism of cereal aphids by L. testaceipes in wheat fields early in the growing season when aphid and parasitoid colonization occurs and later in the growing season when aphid and parasitoid populations are established in wheat fields. Seventy-one fields were studied over the three growing seasons. Significant correlations between parasitism by L. testaceipes and landscape variables existed for patch density, fractal dimension, Shannon's patch diversity index, percent wheat, percent summer crops, and percent wooded land. Correlations between parasitism and landscape variables were generally greatest at a 3.2 km radius surrounding the wheat field. Subsequent regression models for L. testaceipes parasitism in wheat fields in autumn and spring showed that landscape variables influenced parasitism. Overall, results indicate that L. testaceipes utilizes multiple habitats throughout the year depending on their availability and acceptability, and frequently disperses among habitats. Colonization of wheat fields by L. testaceipes in autumn appears to be enhanced by proximity to fields of summer crops and semi-natural habitats other than grasslands.