Life history and mortality factors of Agrilus mali Matsumura (Coleoptera: Buprestidae) in wild apples in Northwestern China.
Wild apple Malus sieversii (Ledeb.) M. Roem. (Rosales: Rosaceae), the ancestor of cultivated apples, is widely distributed in Central Asia and is recognized as an important germplasm bank. Recently, the invasive pest Agrilus mali Matsumura (Coleoptera: Buprestidae), originally distributed in eastern Asia, has damaged endemic apple forests in the Yili River valley, Xinjiang, China, and has spread rapidly, infesting more than 80% of wild apple trees in this region. We investigated the life-history traits and native natural enemies in the recently invaded range during 2016 and 2017. Agrilus mali has a univoltine life cycle and overwinters as young larvae in galleries in the cambium. Adults emerged from early June to mid-August and their density peaked in mid-July. Several native natural enemies were identified from Agrilus mali larvae, including Atanycolus denigrator (L.) (Hymenoptera: Braconidae), the mite Pyemotes moseri Yu et Liang (Acari: Pyemotidae) and fungal entomopathogens. Combined, these natural enemies were responsible for mortality rates ranging from 20% to 80% during the summer and autumn. The most abundant and important natural enemy was A. denigrator, which was responsible for up to 15% mortality of A. mali. The results of the present study suggest that augmentation and conservation of A. denigrator and P. moseri should be considered with respect to biological control against this devastating pest.