Found! Ambrosia Beetles Identified in Ontario

Ambrosia beetles have been identified in Ontario apple orchards. This pest first hit our radar last year after hearing about the damage these beetles were causing in orchards in New York. Reports of borers attacking healthy trees have arisen in the state with dying trees and oozing sap being identified in multiple orchards. We identified these beetles this past season in an Ontario orchard. There have also been suspected infestations in other orchards in different areas of the province. Although ambrosia beetles have been present in apple growing regions for years they have only recently begun to be a pest in apple orchards.

Ambrosia beetles are a group of insects which includes the granulate ambrosia beetle (GAB), Xylosandrus crassiusculus, and the black stem borer (BSB), Xylosandrus germanus. Most of these beetles were introduced to North America and have since been expanding their ranges. The BSB is currently raising concern in the Northeastern US. We identified GAB this year in Ontario orchards, which is still a concern and a serious pest of nursery and fruit trees in the US.

Ambrosia beetles, such as the BSB and the GAB, are approximately 2 mm long and will bore 1.5 mm wide tunnels through the bark and into the heartwood of trees. While related bark beetles will tunnel through the bark and form shallow galleries running parallel to the wood grain, ambrosia beetles tunnel straight into the bark, leaving a series of shotholes in the wood (Figure 1).

Figure 1. Brood chamber where eggs are laid

Figure 1. Brood chamber where eggs are laid. Photo credit: L. Hyche, Auburn University

Branches and stems of affected trees may wilt and die, and larger branches can become riddled with galleries, creating weakened branches subject to breakage. Look for small tubes of sawdust coming out of large branches or trunks to identify ambrosia beetle tunneling. Heartwood infested by ambrosia beetle is usually stained brown along gallery walls. Direct damage from females boring into the heartwood is not the only damage; the females introduce and cultivate an ambrosia fungus for the developing larvae to feed on. This fungus signals to the tree that it is under attack. In response to this attack, trees will wall off their vascular systems, resulting in the decline and death of the tree. Additionally, there is a concern that these beetles could be a vector for pathogens. Affected trees have had sap or fire blight ooze issuing from beetle entry holes, leading researchers to consider the possibility that these borers are also spreading disease.

Studies suggest ambrosia beetles move into orchards from surrounding wooded areas. While these beetles typically attack stressed trees, they have been known to attack apparently healthy trees as well. Flooding, drought, and extreme winter temperatures can all result in physiological stresses that can attract ambrosia beetles. Stressed trees produce different types of volatiles, including ethanol, which attracts these beetles. Ethanol can therefore be an effective tool to monitor for this beetle. Using ethanol-baited bottle traps has been successful at trapping the insects and monitoring population trends.

There are limited options available for the control of ambrosia beetles. Maintaining tree vigour, using latex paint on trunks, and removal of infested trees and branches can reduce infestations. Trap logs can also be used, by placing fresh cut pieces of hardwood logs along the orchard edges. These logs must be removed and destroyed before any new adults emerge.

Correctly identifying these beetles is very difficult, as they are very similar to other beetles present in Ontario apple orchards (Figure 2). We do not know the extent of this insect's presence in Ontario orchards. Ambrosia beetles have the potential to cause serious damage to apple trees as well as other fruit trees, therefore general awareness is important. If you think you are seeing ambrosia beetle damage in your orchard, please contact us.

Figure 2. Black stem borer.

Figure 2. Black stem borer. Photo credit: Pennsylvania Dept. of Cons. & Natural Resources

References:

  • Agnello, A., D. Breth, E. Tee, K. Cox, & H.R. Warren. 2015. Ambrosia Beetle- An Emergent Apple Pest. New York Fruit Quarterly. 23(1): 25-28.
  • Reding, M.E., C.M. Ranger, J.B. Oliver and P.B. Schultz. 2013. Monitoring attack and flight activity of Xylosandrus spp. (Coleoptera: Curculionidae: Scolytinae): The influence of temperature on activity. J. Econ. Entomol. 106(4): 1780-1787.

For more information:
Toll Free: 1-877-424-1300
E-mail: ag.info.omafra@ontario.ca