Perennial wildflower strips to enhance natural enemies of insect pests in Belgium

Increasing plant diversity at the local scale is expected to enhance conservation biological control of insect pests. To test this hypothesis, we sowed perennial wildflower strips within a wheat field and found that hoverflies (Diptera: Syrphidae) were more abundant and aphids (Hemiptera: Aphididae) were reduced in wheat in between wildflower strips compared to adjacent monocultures. However, wildflower strips did not affect the other natural enemies, i.e. ladybeetles (Coleoptera: Coccinellidae), lacewings (Neuroptera: Chrysopidae) and Hymenopteran parasitoids. We then compared the abundance and diversity of these natural enemies in five flower mixtures that were different in their functional diversity based on seven plant traits. No significant effect of functional diversity was found. We hypothesised that the presence of some attractive flower species in the mixtures affected the spread of insects in the field. Finally through an RDA analysis, we identified that visual traits (colour, ultra-violet reflectance) and the shape of the corolla are the flower traits that significantly affect the abundance, in wildflower strips, of the wasps that parasitize oilseed rape beetles. This research highlight that perennial wildflower strips can enhance conservation biological control but understanding the interactions between insects and flower traits in fields is needed to compose flower mixtures that support a diversity of natural enemies.