Influences of the seminatural and natural matrix surrounding crop fields on aphid presence and aphid predator abundance within a complex landscape

The biological control of pest insects in farmlands is an important ecosystem service provided by natural enemies, a tenet that is frequently supported by natural ecosystems; however, natural ecosystems can sometimes serve as a source of pests and can maintain them as an ecosystem disservice. We examined the effects of the surrounding seminatural and natural matrix on aphid presence and aphid predator abundance in buckwheat fields. We specifically aimed to detect whether the seminatural and natural matrix causes a trade-off between pest and natural enemy abundances. We established buckwheat study fields in a region of central Japan, the landscape of which is quite complex. Our results showed that aphid presence was not affected by either the abundance of ladybirds and lacewings or the area of the surrounding seminatural and natural matrix. We also found that the abundance of ladybirds, but not of lacewings, was significantly affected by the area of the seminatural and natural matrix. These findings suggest that in a complex landscape, as the area of seminatural and natural lands increases, some assemblages of natural enemies could also increase, but their biological control services would have little effect or would be compensated for by larger pest migration, leading to no net difference in pest damage.