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.

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Southwestern Entomologist


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