Flower fields and pesticide use interactively shape pollen beetle infestation and parasitism in oilseed rape fields.

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Pollen beetles (Brassicogethes spp.) are the main pest of oilseed rape (OSR, Brassica napus) in Europe and responsible for massive yield losses. Upcoming pesticide resistances highlight the need for other means of crop protection, such as natural pest control. Sown flower fields aim to counteract the decrease of insect biodiversity in agricultural landscapes by providing breeding and foraging sites to ecosystem service providers such as parasitoids. However, the optimal age and size of flower fields to increase natural pest control is still unclear.
We conducted experiments on 31 OSR fields located along a gradient of landscape-scale semi-natural habitat (SNH). OSR fields were located adjacent to flower fields which differed in age, continuity and size, or adjacent to crop fields or calcareous grasslands. In the OSR fields, pesticide free areas were established to examine interactive effects of pesticide use and flower field characteristics. The a...