Montana Field Guide

See Animal and Plant Health Inspection Service Story Map on Emerald Ash Borer.

The following is from Parsons (2008). Adult beetles are typically bright metallic green dorsally with the elytra being duller and darker green. Variable amounts of brassy, coppery, or reddish reflections may be present, especially on the pronotum and ventral surfaces. Emerald Ash Borer is somewhat larger in size and more brightly metallic green than most other species in the genus Agrilus that are present in North America with total lengths less than 10-13 mm. This is the only North American species in this genus that has a bright red dorsal surface of the abdomen when viewed with the wings and elytra spread. A small blunt, slightly notched, spine is present at the tip of the abdomen and the antennae are serrate or toothed after the fourth segment.

Barker et al. (2023) present a spatialized model of phenology and climatic suitability for EAB for use in the Degree-Days, Risk, and Phenological event mapping (DDRP) platform, which is an open-source decision support tool to help detect, monitor, and manage invasive threats. Overall, the model exhibited strong performance, particularly in predicting adult phenological events.

Adults are the most easily identified, and are small beetles 8.5 mm in length. The wing-covers (elytra) are metallic green. If exposed, the abdomen is a metallic red to purple color. These two characteristics can be used to separate this species from other beetles similar in color. The exit holes of the larvae are a characteristic “D” shape (Yu 1992).

In its introduced range the species is associated with native and introduced ash trees (Fraxinus spp.). It is a serious threat to Green Ash trees in North America, which is also the only native ash tree found in Montana.

In its introduced range within North America, the Emerald Ash Borer may take 1-2 years to complete its life cycle. Adults begin to emerge in May or June with peak emergence in mid-June to early July. Adults live between 3 and 6 weeks during which they seek mates on suitable host trees. Females produce an average of 40-70 eggs but may produce up to 200. These are deposited in cracks or crevices on the host tree. Approximately 2 weeks later these eggs hatch and larvae burrow into the vascular tissue of the tree. Larvae continue to feed through the fall and overwinter in chambers within the bark or outer sapwood. The cycle is completed the following spring when these larvae pupate and emerge as adults. Some larvae extend this life cycle and spend an additional summer feeding before emerging the next spring (as reviewed in Herms and McCullough 2014).

See Compilation of Emerald Ash Borer Resources.

Larvae are capable of surviving cold temperatures to approximately -30 Centigrade (-22 Fahrenheit) (Crosthwaite et al. 2011), and suitable habitat across much of Montana is probably limited more by the presence of host species than climate. In Montana the Department of Natural Resources and Conservation published a plan in 2015 detailing actions take to prepare for the introduction of this pest species and the response if an introduction is found (Montana Department of Natural Resources and Conservation 2015).

Emerald Ash Borer infestations can be managed in several ways. Preventing the spread of the pest through quarantine of ash nursery stock, firewood, and other wood products capable of harboring eggs and larvae may reduce long-distance spread. Previously the Animal Plant Health Inspection Service (APHIS) regulated movement of items that were likely to spread the species by quarantining areas where it was found. In a rule published in the Federal Register on the 15th of December 2020, APHIS changed its approach to managing EAB and dropped domestic quarantine regulations to focus on less invasive and more effective strategies.

Management of established Emerald Ash Borer populations with insecticides has been attempted, but it proved ineffective beyond the local scale and did not prevent the spread of the pest outside of the areas it was initially detected (Herms and McCullough 2014). Biological control of EAB has been attempted since 2007 and is now the primary management tool for control of this species across its introduced range. Three parasitoids native to China were released in the US: Tetrastichus planipennisi, Spathius agrili and Oobius agrili, with limited success in controlling spread. Since this initial introduction, O. agrili and T. planipennisi show evidence of reproduction in the wild and these parasites may protect young ash trees and help facilitate regeneration (Duan et al. 2018).

For further information on the EAB see Animal and Plant Health Inspection Service Story Map on Emerald Ash Borer.

Information on impacts, detection, protection, and spread prevention efforts specific to Montana are available in a fact sheet published by the Montana State University Extension Service. These data are also summarized by the Emerald Ash Borer Information Network and the South Dakota Department of Agriculture's Emerald Ash Borer web page.

For information and resources on plant pests and diseases see the USDA's Animal and Plant Health Inspection Service's Plant Pests and Diseases Profiles