Overwintering, phenology and fecundity of Harmonia axyridis in comparison with native coccinellid species in Italy

Classical biological control is generally understood as an environmentally safe practice of insect pest management. However, questions have been raised about possible negative effects for native species. As part of a risk assessment study a semi-field trial was carried out in northern Italy in order to compare the overwintering of the native species Propylea quatuordecimpunctata (L.) and Adalia bipunctata (L.) (Coleoptera: Coccinellidae) with the exotic Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae). All the experiments were carried out from April 1998 to April 2001. Harmonia axyridis was able to overwinter successfully in northern Italy. Fecundity, oviposition rate, longevity and rate of increase of overwintering females were calculated and the phenology of the three species was studied. Harmonia axyridis overwintering mortality (31.9%) was lower in comparison with mortality of native species (68.9% for P. quatuordecimpunctata and 61.3% for A. bipunctata). As a consequence, post-overwintering rate of increase of the exotic species was higher. Longevity of overwintered females was similar among the species. Mean fecundity of H. axyridis (783.8 eggs per female) was slightly higher than A. bipunctata (720.2 eggs per female), and much higher than P. quatuordecimpunctata (193.7 eggs per female). H. axyridis and A. bipunctata completed four generations and P. quatuordecimpunctata three generations in a year. The results show that H. axyridis appears to posses a high potential for establishment in Italy.