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Miscanthus x giganteus (Miscanthus) grass shelterbelts can deliver multiple ecosystem services on New Zealand commercial dairy farms. However, there has been little investigation into how these shelterbelts contribute to insect pest management. Here, on a Canterbury dairy farm, we investigated what generalist surface-dwelling invertebrate natural enemies of insect pests inhabit three separate Miscanthus shelterbelts compared to three unmanipulated field margin plots. The potential contribution of these natural enemy assemblages to future biological control was also investigated. To measure this, live moth egg baits with associated pitfall trapping were deployed in autumn, winter and spring of 2015. Miscanthus and the field margin plots were found to have similar potential natural enemy richness but differed in their community composition. The potential predation rate of pests in Miscanthus was 85% higher than in the field margin. Infrared video and Sanger sequencing confirmed that the harvestman Phalangium opilio and the slug Deroceras reticulatum consumed the egg baits in Miscanthus. Conversely, no bait-consuming invertebrates were identified in the field margin. These preliminary results indicate potential natural enemies inhabit Miscanthus and may consume insect pest eggs on the soil-surface. However, to achieve anyinsect pest suppression, further habitat manipulation would be required. [ABSTRACT FROM AUTHOR]

The availability of nonhost resource subsidies affects the ability of parasitoids to overcome egg and time limitation and maximize lifetime reproductive success. We combined field and laboratory experiments to examine the effects of floral resource subsidies on the reproductive fitness of aphid parasitoids. Under controlled laboratory conditions, sugar resources significantly increased longevity and potential fecundity (egg load) in the endoparasitoids Aphidius rhopalosiphi and Diaeretiella rapae (Hymenoptera: Aphidiidae). Laboratory microcosm experiments showed that increased potential fecundity translated into significantly higher realized fecundity (i.e., rates of aphid parasitism) by A. rhopalosiphi receiving resource subsidies. Mechanisms of enhanced realized fecundity also operated under natural field conditions. Replicated field experiments on cultivated wheat, with host density controlled by experimental placement of aphids, showed that, in general, proximity to floral resource patches significantly increased rates of parasitism. Parasitism rates declined exponentially with increasing distance from floral patches, reaching zero beyond 14 m. Increased potential fecundity reduces the chances of parasitoids becoming egg-limited, whereas increased longevity reduces the chances of parasitoids becoming time-limited during host oviposition. Although the plasticity of egg load and longevity observed under varying conditions of resource availability is probably more relevant to parasitoid evolution, the individual fitness benefits from ephemeral resource patches are certainly important in the ecological enhancement of biological control agents. Key words: aphid; Aphidiidae; Aphidius rhopalosiphi; egg limitation; egg load; fecundity; fitness; flower-feeding; lifetime reproductive success; parasitoid; resource subsidies; time limitation.