Spillover of tachinids and hoverflies from different field margins

Abstract

The introduction and conservation of field margins have been proposed as an intervention to counteract the decline in farmland biodiversity. However, how these margins can affect the movement of species and individuals (i.e. spillover) of natural enemies between field margins and crop is still unclear. In this work, we investigated the spillover of two different groups of natural enemies: tachinids (Diptera: Tachinidae) and aphidophagous hoverflies (Diptera: Syrphidae). For comparison we also investigated the response of non-aphidophagous hoverflies. We examined the spillover from two types of field margin (grass margin vs. hedgerow+grass margin) to adjacent maize fields located in landscapes with different proportion of arable land. The spillover of natural enemies was affected by the field margins, but the response varied between insect groups. The spillover of tachinids was higher from the grass margin than from hedgerows, suggesting that the spillover of this group may be related to the low contrast between the vegetation structure of the margin and the crop. In contrast to tachinids, the abundance of aphidophagous hoverflies was higher toward the center of the crop field, independently of the type of field margin. The spillover of non-aphidophagous hoverflies was not affected by the type of field margin. These species were only affected by the landscape composition as their species richness and abundance were higher in landscapes with low amounts of arable land. Measures focusing on the creation and management of field margins need to consider the local contrast between field margins and crops in relation to the life-history traits of different taxa.