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Research Project: Bacterial Endosymbiont Effects on Biology of Cereal Aphids and Key Natural Enemies in Cereal Agroecosystems

Location: Peanut and Small Grains Research

Project Number: 3070-22000-017-008-S
Project Type: Non-Assistance Cooperative Agreement

Start Date: Sep 1, 2020
End Date: Sep 1, 2025

Objective:
The objectives of this project are to: (1) determine the presence and impact of endosymbionts in aphids in sorghum and non-cultivated hosts using OCR analysis; (2) assess the effects of endosymbionts on parasitism rates of aphids and reproductive success by naturally occurring parasitoids; and (3) assess the effects of endosymbionts on competitive relationships among parasitoid species and fitness.

Approach:
Critical information on factors that influence aphid population suppression is needed to develop and deliver more informed integrated management programs in wheat and sorghum. The primary cereal aphid pests in winter wheat are the greenbug (Schizaphis graminum) and birdcherry-oat aphid (Rhopalosiphum padi; BCOA) and both can reduce forage and grain yields when populations are above thresholds. The sugarcane aphid (Melanaphis sacchari) is a recent invasive species which has been devastating to sorghum production in the region, but the greenbug and other aphids also infest this summer crop. From Texas, Oklahoma and into Kansas native parasitoids have been shown to play an important role in regulating cereal aphid populations, often preventing the need for curative insecticide applications. Bacterial symbionts, primarily Hamiltonella defensa, common in local aphid populations in other parts of the world and the U.S., have been shown to render aphids resistant or even immune to parasitoid attack. These symbionts prevent development of immature parasitoids within aphids and ultimately have been shown to cause reductions in local parasitoid populations. We hypothesize that these symbionts are present in cereal aphid populations throughout the U.S. Southern Plains and may be the cause of low levels of parasitism sometimes observed, however no one has documented their spatial and temporal occurrence or how parasitoids and their pest control services are impacted. Eliminating endosymbionts from local aphid populations is not possible, but knowledge of their presence and impact is critical for informed pest management decisions. In the absence of these symbionts, producers can rely as they already do on parasitoid pest control services, but if symbionts are present and they prevent pest control, insecticide use is likely justifiable and should be recommended to preserve forage or yields.