Insect of the Week: the Emerald Ash Borer

Adapted from pages 434-435 of Garden Insects of North America

The larvae of the emerald ash borer develop under the bark of trees, creating zigzag tunnels through the cambium. Cumulative injuries cause a progressive dieback that initially involves upper limbs but ultimately moves into the trunks. Typically trees are killed within 5 years after they are first colonized.

The first North American detection of emerald ash borer was in 2002 in Detroit. By 2016 this insect was found in most states east of the Mississippi, two Canadian provinces, and two western states (Colorado, Texas). The rapid spread of this insect over wide areas has been largely through the human-assisted movement of infested ash firewood. Once introduced into a location, local dispersal occurs from the flight of adults during late spring and early summer. Adults are metallic green beetles, approximately 1/2 inch long. The larvae are flatheaded borers that make meandering tunnels through the cambium, under the bark. Adults emerge from trees through D-shaped exit holes in the bark.

An emerald ash borer with wings open (Agrilus planipennis).                            Photo credit: David Shetlar.

Winter is spent as a larva within tunnels under the bark and pupation occurs in mid-spring. Adults can be expected to begin to emerge in late May, about the time black locust (Robinia) is in full bloom. Initially they feed on the foliage and, about 2 weeks later, after mating, females begin to lay eggs on the surface of trunks and branches. About 100 eggs may be laid on the trunk or larger limbs, usually at points of rough bark and in cracks of the bark, with most egg laying completed by early July. 

Eggs hatch about 2 weeks after being laid, and the larvae bore into the plant where they feed on the sapwood. As they feed and develop the larvae extend their mines under the bark, the size of the tunnels gradually widening as the insect grows. Fine sawdust frass packs these galleries. Larval feeding continues until the larva is mature or until weather becomes too cold for development. Growth is resumed in spring when they complete their development. Normally, one generation is produced annually. Development may be slowed in more vigorous trees in early stages of infestation and in cooler areas some larvae that develop from eggs laid late in the season have been observed to require a second season to mature.

Garden Insects of North America: The Ultimate Guide to Backyard Bugs
Second Edition
By Whitney Cranshaw & David Shetlar

This second edition of Garden Insects of North America solidifies its place as the most comprehensive guide to the common insects, mites, and other “bugs” found in the backyards and gardens of the United States and Canada. Featuring 3,300 full-color photos and concise, detailed text, this fully revised book covers the hundreds of species of insects and mites associated with fruits and vegetables, shade trees and shrubs, flowers and ornamental plants, and turfgrass—from aphids and bumble bees to leafhoppers and mealybugs to woollybears and yellowjacket wasps—and much more. This new edition also provides a greatly expanded treatment of common pollinators and flower visitors, the natural enemies of garden pests, and the earthworms, insects, and other arthropods that help with decomposing plant matter in the garden.

Designed to help you easily identify what you find in the garden, the book is organized by where insects are most likely to be seen—on leaves, shoots, flowers, roots, or soil. Photos are included throughout the book, next to detailed descriptions of the insects and their associated plants.

An indispensable guide to the natural microcosm in our backyards, Garden Insects of North America continues to be the definitive resource for amateur gardeners, insect lovers, and professional entomologists.

  • Revised and expanded edition covers most of the insects, mites, and other “bugs” one may find in yards or gardens in the United States and Canada—all in one handy volume
  • Features more than 3,300 full-color photos, more than twice the illustrations of the first edition
  • Concise, informative text organized to help you easily identify insects and the plant injuries that they may cause
This post is part of a series, explore additional posts here<< Insect of the Week: the Green LacewingInsect of the Week: the May/June beetle >>