Abstract
The aim of this study was to investigate the effects of Elado®-dressed winter oilseed rape (OSR, 10 g clothianidin & 2 g beta-cyfluthrin/kg seed) on the development, reproduction and behaviour of large earth bumble bees (Bombus terrestris) as part of a large-scale monitoring field study in Northern Germany, where OSR is usually cultivated at 25–33 % of the arable land. Both reference and test sites comprised 65 km2 in which no other crops attractive to pollinating insects were present. Six study locations were selected per site and 10 bumble bee hives were placed at each location. At each site, three locations were directly adjacent to OSR fields and three locations were situated 400 m distant from the nearest OSR field. The development of colonies was monitored from the beginning of OSR flowering in April until June 2014. Pollen from returning foragers was analysed for its composition. An average of 44 % of OSR pollen was found in pollen loads of bumble bees indicating that OSR was a major resource for the colonies. At the end of OSR flowering, hives were transferred to a nature reserve until the end of the study. Colony development in terms of hive weight and the number of workers showed a typical course with no statistically significant differences between the sites. Reproductive output was comparatively high and not negatively affected by the exposure to treated OSR. In summary, Elado®-dressed OSR did not cause any detrimental effects on the development or reproduction of bumble bee colonies.
Highlights
Pollination is one of the most essential ecosystem services provided by nature to wild plant species, and for a number of arable crops (Klein et al 2007)
The mean amount of OSR pollen varied between 16 % and 32 % in the first sampling (DAP 6, Fig. 4)
Pollen samples taken during the second sampling (DAP 16) showed an OSR pollen content of 51 % to 95 % indicating that OSR was the most important pollen source at this time
Summary
Pollination is one of the most essential ecosystem services provided by nature to wild plant species, and for a number of arable crops (Klein et al 2007). While commercially bred colonies are available for the use in agriculture (Velthuis and Doorn 2006), their use is often restricted to greenhouses so that field crops rely on naturally occurring bumble bee colonies. Declines in populations of bumble bees have been reported worldwide (e.g., Kosior et al 2007; Williams and Osborne 2009; Colla et al 2012; Kerr et al 2015). Multiple stressors may affect bumble bees, e.g., parasites, lack of floral resources and plant protection products (PPPs) (Goulson et al 2015). In agricultural landscapes, massflowering crops such as OSR serve as a valuable nectar and pollen source for bumble bees (Westphal et al 2006 2009), but, on the other hand, agricultural practices such as the use of PPPs may pose a risk to pollinating insects
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