Survey of ambrosia beetles (Scolytinae) in Ontario apple orchards

Ambrosia beetles (Scolytinae) can be successful colonizers of planted fruit orchards, often preferring dead or dying trees. However, some species may attack healthy trees causing significant economic impact. Ambrosia beetles are successful because they are fungus-farmers, have a wide host range and arrhenotokous reproduction. In Ontario, Canada, apple growers are experiencing recent, significant tree losses in young, high-density plantings; however, the community of ambrosia beetles in apple agroecosystems has not been determined nor has their role in causing or exacerbating tree decline and death. Using ethanol-baited traps at 9 orchards in 2019 and 6 in 2021, we collected primarily Xylosandrus germanus (black stem borer), but also significant numbers of the more recently invasive Anisandrus maiche. Population peaks in May and July/August consistent with two generations per year occurred, but A. maiche was more abundant in the summer and into the fall. Xyleborinus saxesenii (fruit tree pinhole borer) was the third most common species at most sites. Native species were captured, but they were never abundant. Xylosandrus crassiusculus was found at a couple sites in 2021. In 2022, dead and dying apple trees with evidence of ambrosia beetle attach were collected from orchards and held in bins under control conditions until beetles emerged. Data collection is in-progress. Overall, ambrosia beetle captures varied widely among orchards, and in many orchards edge-placed traps captured up to 5X as many beetles as traps placed in the orchard, both suggesting that site specific factors are important determinants of beetle communities.