Hymenopteran Parasitoids of Aphid Pests within Australian Grain Production Landscapes

SIMPLE SUMMARY: In grain crops, aphids are important pests, but they can be suppressed by parasitoid wasps that use them as hosts for their developing offspring. These wasps occur naturally in the environment and can be utilized in the control of these pests. We investigated how the number and species of pest aphids within the grain crops varied over the season, how their associated parasitoid wasp species and numbers varied over time, and how these organisms interacted at crop edges. In our study, aphid numbers remained low early in the season, and increased as the crop growth progressed. Wheat field edges can act as reservoirs for the aphids and wasps; however, this was not the case for canola field edges, likely due to the different plant hosts available. One wasp dominated this study throughout the canola fields, although it was only found in low numbers at field edges and in wheat fields. Within these areas, another wasp dominated. These findings can assist in the management of grain aphid pests. ABSTRACT: In grain crops, aphids are important pests, but they can be suppressed by hymenopteran parasitoids. A challenge in incorporating parasitoids into Integrated Pest Management (IPM) programs, however, is that parasitoid numbers can be low during periods within the season when aphids are most damaging. Understanding the population dynamics of key aphid species and their parasitoids is central to ameliorating this problem. To examine the composition and seasonal trends of both aphid and parasitoid populations in south-eastern Australia, samples were taken throughout the winter growing seasons of 2017 and 2018 in 28 fields of wheat and canola. Myzus persicae (Sulzer) was the most abundant aphid species, particularly within canola crops. Across all fields, aphid populations remained relatively low during the early stages of crop growth and increased as the season progressed. Seasonal patterns were consistent across sites, due to climate, crop growth stage, and interactions between these factors. For canola, field edges did not appear to act as reservoirs for either aphids or parasitoids, as there was little overlap in the community composition of either, but for wheat there was much similarity. This is likely due to the presence of similar host plants within field edges and the neighbouring crop, enabling the same aphid species to persist within both areas. Diaeretiella rapae (M’Intosh) was the most common parasitoid across our study, particularly in canola, yet was present only in low abundance at field edges. The most common parasitoid in wheat fields was Aphidius matricariae (Haliday), with field edges likely acting as a reservoir for this species. Secondary parasitoid numbers were consistently low across our study. Differences in parasitoid species composition are discussed in relation to crop type, inter-field variation, and aphid host. The results highlight potential focal management areas and parasitoids that could help control aphid pests within grain crops.