The potential of harlequin ladybird beetle Harmonia axyridis as a predator of the giant willow aphid Tuberolachnus salignus: voracity, life history and prey preference

The giant willow aphid, Tuberolachnus salignus is an invasive insect in New Zealand for which control measures are being sought due to its detrimental effects on willow cultivation and apiculture. We evaluated the biocontrol potential of the harlequin ladybird beetle, Harmoniaaxyridis, by measuring voracity and feeding preference of larvae and adults in laboratory trials. Results show that H. axyridis consumes T. salignus, with females being more voracious than males and larvae. However, H. axyridis fed T. salignus took longer to develop, gained less weight and had lower survival compared with those fed eggs of the Mediterranean flour moth, Ephestiakuehniella. In a choice test, larval and adult H. axyridis preferred the green peach aphid, Myzuspersicae, as prey item, rejecting T. salignus. We suggest that H. axyridis is likely to use T. salignus only as a facultative prey, and therefore cannot be prioritised as a potential biocontrol agent.