Leaf pubescence mediates intraguild predation between predatory mites

Plant morphological traits such as leaf pubescence may affect herbivores and their natural enemies at the individual, population and community levels. Leaf pubescence has been repeatedly shown to mediate predator-herbivore interactions whereas the influence of leaf pubescence on predator-predator interactions such as intraguild predation (IGP) has seldom been investigated. Using a three-pronged approach we assessed the influence of leaf pubescence on the predatory mites Kampimodromus aberrans and Euseius finlandicus. Both predators occur on broad-leaved trees in Europe. Euseius finlandicus is mostly found on trees with glabrous leaves whereas K. aberrans mainly occurs on trees with pubescent leaves. We hypothesized that leaf pubescence mediates IGP between K. aberrans and E. finlandicus and thereby determines their dominance and proportional abundance. A field survey on apple revealed that the abundance of K. aberrans and E. finlandicus is negatively correlated, with the former predominating on cultivars with strongly pubescent leaves and the latter predominating on cultivars with little pubescent or glabrous leaves. Microhabitat choice tests showed that K. aberrans preferentially resides on pubescent leaves whereas E. finlandicus preferentially resides on glabrous leaves. The effects of leaf pubescence on survival and development of immature IG predators and IG prey were reversed for K. aberrans and E. finlandicus. In the presence of the IG predator E. finlandicus, immature K. aberrans had higher survival probabilities on pubescent leaves than on glabrous ones. In contrast, the survival chances of immature E. finlandicus were higher on glabrous leaves than on pubescent ones when the IG predator K. aberrans was present. Artificial leaf pubescence enhanced IG prey capture by immature K. aberrans and prolonged their longevity but impaired IG prey capture by immature E. finlandicus and shortened their longevity. We conclude that leaf pubescence mediates IGP strength and symmetry and discuss the implications to natural and biological control.