Agricultural management reduces emergence of pollen beetle parasitoids

Natural enemies such as predatory arthropods and parasitoids have the potential to suppress pest species and provide the ecosystem service biological control. When predicting the potential of biological control in agriculture it is important to give evidence on how agricultural management influence the abundance and functions of the natural enemies. In this study we examined whether managements practices as insecticide application and different tillage regimes, can influence biological control of a herbivorous pest on oilseed rape (Brassica napus L.). The endoparasitoids Phradis interstitialis Thomson and Tersilochus heterocerus Thomson were studied as they are important for the biological control of the pollen beetle (Meligethes aeneus F.) which is a common pest on oilseed rape in Europe. The number of emerging female parasitoids was quantified by capturing the parasitoids in emergence tents from fields where the oilseed rape plants were grown the previous year. The number of emerging P. interstitialis and T. heterocerus were significantly reduced in insecticide treated fields, but the tillage regimes had no effect on the number of emerging females of either parasitoid species. We conclude that when predicting the biological control potential by pollen beetle parasitoids in agricultural landscapes it is important to consider insecticide treatment of former oilseed rape fields as that can influence population densities at the landscape scale the following year.