Occurrence and impact of Agrilus spp. and associated egg parasitoids in hazel groves of Northwest Italy

In several hazel ( C orylus avellana L.) groves in the area of L anghe ( P iedmont, N orthwest I taly), many hazel branches suddenly withered, and in some cases, the whole tree died, with heavy economic losses for the farmers. Symptoms of jewel beetle attacks were detected on the trees. Eight A grilus species were caught by traps from 2007 to 2009 in the surveyed hazel groves; among them, only four species have been known to develop on hazel. On the traps, A grilus olivicolor K iesenwetter was the most abundant species, while almost only A grilus viridis (L.) was sampled by plant beating from 2008 to 2010. Moreover, almost all adults emerged from field‐collected hazel wood belonged to this latter species that proved to be the main responsible for the severe attacks on the hazel trees. Agrilus viridis adults emerged from late M ay to late J une, and generally lived until the end of A ugust, while egg masses were observed from late M ay to late J uly. The egg parasitoid O obius zahaikevitshi T rjapitzin was found in all of the investigated groves; adults emerged already from the first egg masses collected on hazel trees in late M ay‐early June. O . zahaikevitshi was able to largely reduce A . viridis populations, with a parasitism rate of more than 50% in some groves. Recent attacks of A . viridis were related to a long period of drought; however, appropriate agronomic practices to minimize the effects of water stress and to conserve natural enemies, such as O . zahaikevitshi , could be more effective to protect hazel groves against boring beetle attacks.