Native ladybird decline caused by the invasive harlequin ladybird Harmonia axyridis: evidence from a long-term field study

Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is regarded as an invasive non-native species in Europe, where it has been spreading rapidly since the early years of the 21st century. This study examines changes in ladybird communities at four sites (two lime tree sites, one pine tree site and one nettle site) in East Anglia, England, over an 11-year period (2006-2016) following invasion by H.axyridis. Overall, H.axyridis represented 41.5% of all ladybirds sampled [varying from a low of 0.2% (1 of 520 ladybirds at three sites) in 2006 to a high of 70.7% (724 of 1024 at four sites) in 2015] and was over three times more abundant than the second commonest species, Coccinella septempunctata L. The proportion of native ladybirds declined from 99.8% (520 of 521 ladybirds at three sites) in 2006 to 30.7% (383 of 1248 at four sites) in 2016, but H.axyridis dominated only at the lime tree sites and not at the pine or nettle sites. There was a significant negative relationship between H.axyridis and Adalia bipunctata (L.) (Coleoptera: Coccinellidae) adults at the lime tree sites, but not between H.axyridis and adults of any of the other main ladybird species sampled. Adalia bipunctata adults and Adalia spp. larvae were the only native ladybirds that significantly declined. Our study shows a clear change in the ladybird community on lime trees over an 11-year period in which H.axyridis invaded England. Intraguild predation is hypothesised to be an important driver of the changes observed.