Diversity of beetles in oilseed rape in Changins (VD)

In order to understand the diversity of insects colonizing oilseed rape, a survey focusing on beetles was conducted in a plot of winter rape in Agroscope Changins (Prangins VD). Beetles were captured with yellow water bowls over the whole cultivation period from August 2017 to June 2018. In total, 11,856 individuals were caught from exactly 104 beetle species. This large species richness exceeds by far, what could be expected in a crop surrounded by a priori poorly favorable environment for biodiversity (suburban zone and field crops). 14 species or 98 % of the beetle individuals are well-known oilseed rape pests. With 8’686 individuals (73.3 %), the pollen beetle (Meligethes aeneus) was by far the most abundant. 25 phyto-pyllophagous and 3 granivorous species are related to other cultivated or wild plant families. 13 other species feed on pollen as adults, but they are not restricted to oilseed rape. The final 49 species are either predators (21), omnivores (18) or coprophagous, mycophagous, saprophagous or do not feed at all as adults (10). The carabid Bembidion latinum (vulnerable) and the white-spotted rose beetle Oxythyrea funesta (potentially threatened) figure on the Swiss Red List. With Cantharis annularis, C. pulicaria and Cteniopus sulphureus three other rare species were identified. The observation of Psilothrix viridicoerulea is the first mention for the canton of Vaud. Many other invertebrate species find refuge and food in oilseed rape and some can play an important role in the control of pests (e.g. parasitoid wasps). It is therefore important to protect this crop with a sustainable pest management strategy that allows for an economically sufficient yield without threatening biodiversity.

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