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GCB Bioenergy (2014) 6, 219–226, doi: 10.1111/gcbb.12080

Mass-flowering crops increase richness of cavity-nesting
bees and wasps in modern agro-ecosystems
€ T E R * , F R A N Z I S K A P E T E R * † , B I R G I T J A U K E R * , V O L K M A R W O L T E R S * and
*Department of Animal Ecology, Justus Liebig University, Heinrich-Buff-Ring 26-32, Giessen, D-35392, Germany,
†Deptartment of Conservation Ecology, Faculty of Biology, Philipps University, Karl-von-Frisch-Str. 8, Marburg, D-35032,

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.
Keywords: agricultural landscapes, bioenergy, biofuel, canola, ecosystem service, environmental change, functional traits, oilseed rape, pollination, resource pulse

Received 27 March 2013; revised version received 27 March 2013 and accepted 28 March 2013

The rapid expansion of biomass and biofuel production
in agricultural systems will result in major land-use
changes at large spatial scales (Koh, 2007). In the EU,
oilseed rape is the most common oleaginous crop for
biofuel production (FAO, 2008) and the production area
has more than doubled within the past 20 years (Fig. 1).
However, significant uncertainties exist about the effects
of this extensive increase in biomass and biofuel cropping on biodiversity, especially at the regional scale (Eggers et al., 2009; Dauber et al., 2010). Here, to reduce
these uncertainties, we studied the diversity effects of
Correspondence: Tim Diek€
otter, tel. + 49-(0)641-9935701, fax + 49(0)641-9935709, e-mail: tim.diekoetter@uni-giessen.de

© 2013 Blackwell Publishing Ltd

the mass flowering of oilseed rape on the community of
trap-nesting bees and wasps in modern agro-ecosystems.
Considering the bounty of nectar and pollen that
mass-flowering crops supply, it seems plausible to
expect positive responses of flower-visiting insects to
oilseed rape at the landscape scale. Increased abundances of short-tongued social bumblebees with increasing area of oilseed rape early in the year seem to
confirm this assumption. This numerical increase in
worker bees, however, fails to translate into improved
sexual reproduction later in the year when food
resources are usually scarce in modern agro-ecosystems
(Westphal et al., 2003, 2009). Moreover, long-tongued
bumblebees were negatively affected by an increasing
area of oilseed rape. Once mass flowering had ceased,