Invasive non-native species can drive community change through key functional behaviours, such as predation. Parasites and pathogens are common within communities and have been shown to mediate invasive species impacts in addition to holding the potential as biological control agents, yet their inclusion in quantification studies remains lacking. We quantified predatory behaviour of native (Coccinella septempunctata and Adalia bipunctata) and invasive non-native (Harmonia axyridis) Coccinellidae to gain insight as to the potential impacts of the non-native species. Predators were also subject to a pathogen (Beauveria bassiana) infection treatment to ascertain how behaviours might change under either biological control conditions or the sub-optimal health of the predator. We defined efficient predatory behaviour as either increased prey attack rates, reduced time spent handling prey or a higher predatory functional response. Comparisons were then made between both between species, treatments and with respect to both predator adult and larval life-stages.
Results/Conclusions
Invasive H. axyridis were significantly more efficient predators than both native species. Adult A. bipunctata were significantly less efficient predators than both H. axyridis and C. septempunctata, with a significantly lower overall functional response and reduced attack rates. Pathogenic infection reduced predatory efficiency of both A. bipunctata and H. axyridis adults, while the relative predation efficiencies of species remained consistent between infection treatments. Conversely, infected adult C. septempunctata and larval H. axyridis and A. bipunctata showed increased variation in their behaviours with individuals both increasing and decreasing their consumption rates in comparison to uninfected conspecifics. We propose that these results aid us in understanding the documented impacts of H. axyridis, notably the decline of UK and European A. bipunctata populations following the arrival of H. axyridis while C. septempunctata populations remained stable. Furthermore, we provide evidence that B. bassiana infection can negatively impact H. axyridis by reducing the predatory ability of the species to levels consistent to that of native C. septempunctata. The rate of species invasions is expected to continue with efforts to quantify and understand such ecological events becoming increasingly important.