Interspecific exploitative competition between Harmonia axyridis and other coccinellids is stronger than intraspecific competition

Abstract

The invasion of Harmonia axyridis has had negative consequences on coccinellid assemblages, with a decline in abundance and diversity, but the coexistence of invasive and resident species may depend on the strength of intra- and interspecific exploitative competitive interactions. These antagonistic interactions have been scarcely studied in coccinellids. Through a laboratory study we assessed aphid consumption, weight gain and reproduction when the invasive Harmonia axyridis, the alien Hippodamia variegata and the native Eriopis chilensis were alone, in conspecific and heterospecific groups, at low and high aphid densities. Under intraspecific competition, coccinellids were more voracious than when they were alone, particularly H. axyridis and H. variegata at high aphid density; H. axyridis and H. variegata gained more weight than E. chilensis, and H. axyridis barely reproduced at low aphid densities, even when alone, while in the other two species reproduction wa