Abstract
In intensively cropped agricultural landscapes, the vegetation in edges and hedges (henceforth “field margins”) represents an important semi-natural habitat providing fundamental resources for insect pollinators. We surveyed the pollinating insects associated with two mass-flowering crops, apple and oilseed rape, and compared the insect fauna of the main crop with that in the field margins in the grass-dominated agricultural landscapes of Ireland. Different insect groups responded differently to the presence of the flowering crop, with honey and bumble bees more abundant in crops than margins during crop flowering, but more hover flies and butterflies in margins throughout. The composition of the insect assemblage also shifted over time due to taxon-specific changes in abundance. For example, solitary bees were most abundant early in the season, whereas hover flies peaked, and butterflies declined, in mid-summer. The temporal shift in insect community structure was associated with parallel changes in the field margin flora, and, although we found no relationship between insect abundance and abundance of field margin flowers, Bombus abundance and total insect abundance were positively correlated with floral diversity. After the crop flowering period, floral abundance and diversity was maintained via margin plants, but by late summer, floral resources declined. Our results confirm the importance of field margins for insect pollinators of entomophilous crops set within grass-dominated landscapes, even during the crop flowering period, and provide additional support for agri-environment schemes that protect and/or improve field margin biodiversity. The results also demonstrate that although shifts in insect and plant communities may be linked phenologically there may not always be simple relationships between insect and floral abundance and richness.
Highlights
Flower-visiting insects such as honey bees, bumble bees, solitary bees, hover flies and butterflies provide an ecosystem service by pollinating a wide range of wild and cultivated plants (Ollerton et al 2011)
Apis mellifera and solitary bees showed no significant differences in abundance between the crop centre and the field margins (Tab. 1A; Fig. 2), whereas butterflies and syrphids were more abundant in the field margins than in the crop centre, especially in oilseed rape (OSR)
In the context of our study set in the grassbased Irish agricultural landscape, these results demonstrate that pollinating insects are relatively abundant in field margins even when these margins enclose an in-flower mass-flowering crop, and highlight that this pattern is highly taxon specific
Summary
Flower-visiting insects such as honey bees, bumble bees, solitary bees, hover flies and butterflies provide an ecosystem service by pollinating a wide range of wild and cultivated plants (Ollerton et al 2011). Outside of the flowering period of mass-flowering crops, both managed and naturally-occurring pollinating insects can face ‘hunger gaps’ when the quantity and quality of pollen and nectar available does not meet requirements (Timberlake et al 2019). In this scenario, hedgerows and naturally-occurring wild
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