Predation and avoidance behavior of the pea aphid Acyrthosiphon pisum confronted with native and invasive lady beetles in Europe

Invasive species are a major driver of global biodiversity loss. However, we often lack a mechanistic understanding why some non-native species become invasive. Missing coevolutionary history between invasive predators and native prey can lead to a lack of predator avoidance by native prey and consequently higher consumption rates by invasive predators. We compared predation rates of four native European lady beetle species and the invasive lady beetle species Harmonia axyridis Pallas (Coleoptera: Coccinellidae), using the native pea aphid Acyrthosiphon pisum Harris (Hemiptera: Aphididae) for prey. Here, we also quantified initial dropping of A. pisum from host plants. In an additional plant-choice experiment, we tested for aphid avoidance of plants bearing lady beetle cues. Differences in predation were determined by predator body size. Initial dropping of aphids did not differ between the invasive lady beetle species H. axyridis and the remaining native lady beetle species. However, A. pisum showed no avoidance behavior towards H. axyridis cues, but to cues of the most voracious native species. Thus, relatively large body size and missing chemical cue avoidance by aphids can benefit the invasive H. axyridis.