Agrilus mali Matsumara (Coleoptera: Buprestidae), a new invasive pest of wild apple in western China: DNA barcoding and life cycle

Agrilus mali Matsumara (Coleoptera: Buprestidae) is a wood-boring beetle distributed to eastern China that occasionally injures apple species. However, this wood-boring beetle is new to the wild apple forests (Malus sieversii) of the Tianshan Mountains (western China) and has caused extensive tree mortality. The development of a biological control program for these wild apple forests is a high priority that requires exploration of the life cycle, DNA barcoding and taxonomic status of A.mali. In this study, to determine the diversity of invasive beetles, a fragment of the mitochondrial cytochrome oxidase gene was analyzed. Based on the results, beetles from Gongliu and Xinyuan counties of Xinjiang were identical but differed from those in the apple nursery of Gongliu by a single-nucleotide substitution. We summarize the taxonomic status, relationships, and genetic distances of A.mali among other Agrilus species using the Tajima-Nei model in maximum likelihood phylogeny. Analysis revealed that A.mali was closely related to Agrilus mendax and both belong to the Sinuatiagrulus subgenus. The life cycle of A.mali was investigated based on a monthly regular inspection in the wild apple forests of Tianshan. Similar to congeneric species, hosts are injured by larvae of A.mali feeding on phloem tissue, resulting in serpentine galleries constructed between bark and xylem that prevent nutrient transport and leading to tree mortality. Future studies will focus on plant physiological responses to the invasive beetles and include surveys of natural enemies for a potential classical biological control program.