Intraguild responses of aphid predators on apple to the invasion of an exotic species, Harmonia axyridis

The effects of the invasion of an exotic predator, Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae), were investigated using three experiments on the ecology of aphid predators on apple. One experiment, 1992, was collected prior to the H. axyridis invasion, and two others, 1996 to 1997 and 1999 to 2000, were collected after the invasion. Except for one year, 1999, H. axyridis was the dominant coccinellid, replacing the formerly dominant Coccinella septempunctata L. (Coleoptera: Coccinellidae), another exotic species. The dominance of H. axyridis was greater among larvae than among adults. There was no apparent effect of the H. axyridis invasion on abundance of the predator, Aphidoletes aphidimyza (Rondani) (Diptera: Cecidomyiidae) and a possible positive effect on the abundance of chrysopids (Neuroptera: Chrysopidae). Principal component analysis indicated that although individual species were affected, the overall effect of H. axyridis invasion on the predator guild as a whole was negligible. The data indicate that the interaction between the two exotic species, H. axyridis and C. septempunctata, may be allowing native coccinellids to become more abundant on apple than when C. septempunctata was the dominant coccinellid.