Impact of the neozoic ladybird Harmonia axyridis on the coccinellid community in Bohemia

Abstract

Since 2007, when Asian harlequin ladybird Harmonia axyridis (Pallas) has become a part of coccinellid entomofauna in Bohemian hop gardens, the spectrum of aphidophagous coccinelids has changed considerably. Whereas, in the period before its invasion native species Coccinella septempunctata L., Adalia bipunctata L. and Propylea quatuordecimpunctata L. used to be the dominant predators of damson hop aphid (Phorodon humuli Schrank), Harmonia axyridis has been the most frequent ladybird species in Zatec (Saaz) hop growing region nowadays. Population densities of adults of aphidophagous ladybirds in the middle of the eighties (1985), shortly before the invasion of the above-mentioned Asian species (2004) and in the recent years (2011 and 2015) are compared. Whereas four years ago harlequin ladybird represented just 10% of the total Coccinellidae, in 2015 it forms nearly half of coccinellid adults observed in hop gardens in NW Bohemia. It is followed by tiny species P. quatuordecimpunctata and A. bipunctata, which consist together more than one third, whereas in the middle of the eighties they generally formed two thirds of the coccinellid populations. On the other hand adults of C. septempunctata have become less abundant. It may be caused by aggressiveness of H. axyridis, whose larvae were observed to feed on eggs and young larvae of C. septempunctata. To prevent attacks from larvae of H. axyridis, females of C. septempunctata appear on hop plants and begin to lay eggs earlier as illustrated by the presence of the third and the fourth instars larvae in the time when larvae of H. axyridis reach much smaller size and are not competitive enough. Decline in population densities of native species of ladybirds on response to arrival of the Asian invasive species, their responses and potential efficiency of aphidophagous coccinelids, including H. axyridis, on damson hop aphid will need to be observed in the future so as us to know more about this issue.