Agrilus mali Matsumura (Coleoptera: Buprestidae) density and damage in wild apple Malus sieversii (Rosales: Rosaceae) forests in Central Eurasia under four different management strategies

In 1993, the apple buprestid, Agrilus mali Matsumura (Coleoptera: Buprestidae) native to northeast Asia, invaded the Yili River valley, Xinjiang Uyghur Autonomous Region, China. It is now widespread across 95% of wild apple forests (Malus sieversii (Ledeb.) Roem) in the region. This invasive species poses a major threat to wild apple populations serving as the key germplasm refuge for the ancestor of domestic apples across 6 countries in Central Eurasia. We first described the symptoms and damage caused by A. mali to wild apple trees, and then assessed the abundance of A. mali and tree damage under four different management strategies in three consecutive years (2016-2018): release of commercial biocontrol agents, aerial spraying of insecticide, aerial spraying/pruning, and establishment of fenced areas aiming to preserve understory vegetation and enhance natural pest control. The apple buprestid feeds on inner bark and preferentially damages the small branches (1-4 cm in diameter) located in the canopy 4-6 m above ground. The average fruit production declined from 90 kg to 10 kg per tree after the pest invasion. Pest abundance, as measured by counting damage scars, declined in sprayed areas. Fenced areas had higher pest abundance (damage). Fruit production in biological control and spraying/pruning areas increased slightly, while tree damage ranking declined over the years. Our results suggest that a combination of biological control and spraying/pruning may contribute to pest management of A. mali and resilience of wild apple forests in Central Eurasia.