Impact of the arrival of Harmonia axyridis on adults of Coccinella septempunctata and Coleomegilla maculata (Coleoptera : Coccinellidae)

The impact of the arrival of the exotic coccinellid Harmonia axyridis on the biological control and dispersion of apple mites and aphids, and on the vertical distribution of the established coccinellids Coccinella septempunctata and Coleomegilla maculata have been studied. Assemblages of adults of the three coccinellid species were tested on apple saplings and on apple trees against Aphis citricola and Tetranychus urticae. The presence or substitution of adults of H. axyridis for adults of C. maculata or C septempunctata did not reduce the predation impact on mite or aphid prey. H. axyridis was a more efficient predator of mites than was C septempunctata and generated lower prey dispersal from host plants. Substitutions of adults of H. axyridis for those of C maculata, and in some cases of C septempunctata, resulted in greater reduction in number of aphids. On apple trees, the three coccinellid species occurred at different heights. Neither C maculata nor C. septempunctata modified their vertical distribution on apple tree over a 24 hour period in response to the presence of H. axyridis.