Non-host habitat at local and landscape scales promotes overwintering success of a specialist insect pest

Abstract

Incorporating non-crop habitats around cropping fields is often promoted to enhance biodiversity and deter crop pests. However, few studies have investigated how these habitats influence the overwintering success of pest populations. In this study, we investigate how a specialist insect pest, the asparagus beetle (Crioceris asparagi, Coleoptera: Chrysomelidae), uses local and landscape resources for overwintering. We surveyed beetles in 2019–2020 at 11 asparagus farms in Michigan, USA, and conducted experiments to compare overwintering survival of adult beetles in five substrates commonly found in asparagus agroecosystems. We compared the overwintering number of beetles across three habitat types: asparagus field, weedy margin, and woodlot. Overwintering asparagus beetle abundance was highest within sites with deciduous leaves and decomposing asparagus stalks. We found a negative relationship between the abundance of dead trees in adjacent woodlots and adult beetle abundance. We then expanded beyond the woodlots with a landscape analysis conducted at multiple spatial scales. Landscape analysis indicated that deciduous forest within 1250 m of sites increased beetle abundance in focal asparagus fields, while asparagus production at spatial scales greater than 1500 m suppressed their populations. Our findings indicate that certain specialist pests, like asparagus beetles, depend on host resources for overwintering, but non-host habitat from the surrounding landscape is also important to their success. Practically, removal of host and non-host debris (leaf litter) from asparagus fields may lead to decreased survival and lower pest pressures. In addition, crop-dominated landscapes may not require in-field habitat management of overwintering substrates to the same extent as more diverse landscapes with higher proportions of non-host habitat (deciduous forest). Ultimately, we argue that the net positive and negative impact of increasing non-host habitat at the landscape level should be considered when developing integrated pest management strategies for specialists at the local scale.