Effects of wildflower strips and an adjacent forest on aphids and their natural enemies in a pea field

Landscape diversification is a key element for the development of sustainable agriculture.
This study explores whether the implementation of habitats for pest natural enemies enhances
conservation biological control in an adjacent field. In the present study conducted in Gembloux
(Belgium) in 2016, the effect of two different habitats (wildflower strips and a forest) and aphid
abundance on the density of aphid natural enemies, mummified aphids and parasitism on pea
plants was assessed through visual observations. The effect of the habitats on aphids was also
evaluated. The habitats but not aphid density significantly affected hoverfly larvae, which were
more abundant adjacent to wildflower strips than to the forest. The contrary was observed for
ladybeetle adults, which were positively related with aphids but not affected by the adjacent habitats. The abundance of mummies and the parasitism rate were significantly affected by both the habitats and aphid density. They were both significantly enhanced adjacent to wildflower strips compared to the forest, but the total parasitism rate was low (<1%), questioning whether parasitoids could significantly control aphids on the pea crop. As for the aphids, their abundance was not significantly affected by the adjacent habitats. These results are discussed with respect to the potential of these habitats to provide overwintering sites and food resources for natural enemies, and thereby enhance conservation biological control.