Mass‐flowering crops increase richness of cavity‐nesting bees and wasps in modern agro‐ecosystems

Abstract

Considerable uncertainties exist on how increased biofuel cropping affects biodiversity. Regarding oilseed rape, the most common biofuel crop in the EU, positive responses of flower-visiting insects to plentiful nectar and pollen seem apparent. However, previous investigations on this insect guild revealed conflicting results, potentially because they focused on different taxonomic groups representing a narrow range of ecological traits and considered only short time periods. Here, using trap nests in landscapes with independent gradients in area of oilseed rape and seminatural habitats, we assessed the whole community of cavity-nesting bees and wasps, including early-and late-emerging species. Our study's temporal resolution allowed determination of flowering and postflowering effects of oilseed rape on these species' richness, abundance, and mortality. Species richness of cavitynesting bees and wasps significantly increased with oilseed rape, although nesting activity was considerably higher after mass flowering. In addition to increasing richness independently of oilseed rape, the amount of seminatural habitat in the landscape was the sole positive driver of insect abundance once the community's dominant species was accounted for as a covariate. Thus, growth of the co-occurring species' community is not stimulated by the resource pulse provided by oilseed rape early in the year, but by persistent resources provided by seminatural habitats after mass flowering. Early individuals of bivoltine species' first generations accumulated in seminatural habitats when these habitats were scarce, but became increasingly diluted when habitat availability increased. Once established, later foraging females generally benefited from the resource availability of seminatural habitats when initializing the second generation. We conclude that mass-flowering crops, despite covering only a short interval of the community's main activity phase, benefit bee and wasp species richness. However, seminatural habitats are crucial in maintaining viable communities of flower-visiting insects at the landscape scale, mitigating potential negative effects of high land-use intensities in modern agro-ecosystems.

Managing trap‐nesting bees as crop pollinators: Spatiotemporal effects of floral resources and antagonists

“…As Osmia bicornis is often a dominant trap‐nesting species (e.g. Diekötter et al., ), we performed the same analysis considering whether season variations in nest colonization differed between O. bicornis populations and non‐ O. bicornis species, separately. In these cases, field boundary ID was also included in the model as a random factor.…”

To integrate or to segregate food crop and energy crop cultivation at the landscape scale? Perspectives on biodiversity conservation in agriculture in Europe

“…Oilseed rape, as a mass flowering crop, can provide food resources for pollinating insects but only during a limited period of the year [69]. A sustainable benefit for pollinators can only be achieved when a continuous flower supply is ensured through supplementary habitats in the landscape [29].…”

“…These studies included the spatial and temporal aspects of bioenergy-driven land-use change and/or adaptations of the whole farming system (e.g. [25][26][27][28][29][30]). …”

Large-scale monitoring of effects of clothianidin-dressed oilseed rape seeds on pollinating insects in Northern Germany: effects on red mason bees (Osmia bicornis)

“…Mass-flowering OSR fields were found to have a strong positive influence on the abundance of generalist solitary bees (Holzschuh et al 2013) and bees of the genus Osmia have been shown to be efficient pollinators of OSR (Jauker et al 2012a). Furthermore, several studies indicated that high amounts of OSR at the landscape scale have positive effects on solitary bees nesting in semi-natural habitats (Jauker et al 2012b; Diekötter et al 2014). However, foraging in agriculturally managed fields also enhances the risk of pollinating insects to be exposed to PPPs, which might potentially harmful.…”