Quantitative assessment of aphid parasitoids and predators in central Oklahoma wheat fields during five growing seasons

Authors: Elliott, Norman - Norm; GILES, KRISTOPHER - Oklahoma State University; BAUM, KRISTEN - Oklahoma State University; ELZAY, SARAH - Oklahoma State University

Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/28/2021
Publication Date: 12/17/2021
Citation: Elliott, N.C., Giles, K.L., Baum, K.A., Elzay, S.D. 2021. Quantitative assessment of aphid parasitoids and predators in central Oklahoma wheat fields during five growing seasons. Southwestern Entomologist. 46(4):833-842. https://doi.org/10.3958/059.046.0404.
DOI: https://doi.org/10.3958/059.046.0404

Interpretive Summary: Winter wheat is Oklahoma is the most widely grown crop and is typically planted in autumn and harvested in June. Wheat in Oklahoma is often infested by insect pests the most important of which are the greenbug and bird cherry-oat aphid, two species of cereal aphids. In this study we collected aphid natural enemies and aphids in numerous wheat fields in early November and again in the middle of March of five wheat growing seasons. During the five wheat growing seasons adult Lysiphlebus testaceipes and Aphelinus nigritus were the most consistent and abundant parasitoids in wheat fields with L. testaceipes being present and abundant in each of the five growing seasons. Aphelinus nigritus was present in four of the five growing seasons but was less abundant than L. testaceipes. Among arthropod predators larval lady beetles were recovered and abundancr in each growing season. Spiders were present and abundant in the five growing seasons. Several other predator taxa were encountered in samples including Chrysopidae, Hemerobiidae, Nabidae, and Syrphidae. Abundance of most species increased from November to March. Abundance of seven out of the fifteen natural enemy species or taxa sampled were positively correlated to aphid abundance suggesting that these natural enemies exhibited a numerical response to aphid populations. In spite of the many unknowns regarding the nature of interspecies interactions among natural enemies in wheat it is likely that the combined contributions of several natural enemy taxa determine levels of biological control achieved in wheat fields in central Oklahoma. This reseasch demonstrated that several natural enemies are active in wheat fields in Oklahoma that may contribute to aphid biological control and be ammenable to management through natural enemy conservation strategies.

Technical Abstract: Winter wheat (Triticum aestivum L.) is the most widely grown crop in Oklahoma and typically is planted in autumn and harvested in June. Wheat in Oklahoma is often infested by insect pests, the most important of which are the cereal aphids - greenbug, Schizaphis graminum (Rondani), and bird cherry-oat aphid, Rhopalosiphum padi (L.). We sampled a total of 69 wheat fields in central Oklahoma during five wheat-growing seasons. The number of wheat fields sampled ranged from seven in the 2016-2017 growing season to 24 fields in the 2009-2010 growing season. We used a D-vac suction sampler to collect aphids and their natural enemies in wheat fields in early November and again in the middle of March. During the five wheat-growing seasons, adult Lysiphlebus testaceipes (Cresson) and Aphelinus nigritus (Howard) were the most consistent and abundant parasitoids, with L. testaceipes present in each of the five growing seasons. The mean number of adult L. testaceipes per D-vac sample ranged from 1.38 in 2018-2019 to 64.3 adults per sample in the 2008-2009 growing season. Aphelinus nigritus was present in four of the five growing seasons and ranged from 0.86 to 7.82 adults per sample among the four growing seasons. Among arthropod predators, larval coccinellids were found in each growing season and ranged from 2.23 to 15.38 individuals per sample. Spiders were present in the five growing seasons and ranged from 1.63 to 19.0 per sample. Several other predator taxa in samples included Chrysopidae, Hemerobiidae, Nabidae, and Syrphidae. Abundance of most species increased from November to March. Abundance of most natural enemy species (or taxa) was positively correlated to aphid abundance, suggesting natural enemies had an aggregative and/or reproductive numerical response to aphid populations.