Image of an Oak Splendor Beetle, a type of Metallic Beetle
- Adults are attractive, slender, sub cylindrical insects, 9-12 mm long
- Metallic green in color
- Posterior third of the elytra have two distinct white marks on their interior edge
- Mature larvae are legless grubs, 25-43 mm long when mature and creamy white in color
- First thoracic segment is wider than the other body segments
- Two hornlike projections are found on the last abdominal segment
- Adults are strong fliers on warm, sunny days and could travel several kilometers in search of suitable host material
- Could be transported in wood products moving via international trade
Metallic Beetles, such as the Oak Splendor Beetles, may have one generation a year, but a two-year cycle is more common. In northern Germany, the larvae hibernate over two winters. Adult flight occurs from May to July. After maturation and feeding on foliage in the crowns of oaks, females deposit clusters of 5-6 eggs in bark crevasses usually in the south facing side of large oaks.
Larvae feed in the cambium layer in longitudinal, winding, “zig-zag” galleries and overwinter inside the bark. They undergo five instars. When feeding is completed, an individual larva may excavate a gallery up to 155 cm long. Older larvae produce galleries in irregular, twisting, transverse directions. This can lead to partial or complete girdling of trees. Larval activity can result in twig and branch dieback, thin crowns and epicormic branching. Heavily infested trees or trees attacked for several successive years will die.
The pupae develop in the bark, in chambers 10.4-14.4 mm long and 3.0-4.5 mm wide. Adults remain under the bark for about two weeks in late spring-early summer and construct D-shaped exit holes through which they emerge. Typically, infestations are progressive and require two to three years to kill a tree. In heavily infested trees, the entire main stem contains galleries and the trees are girdled and killed in a single season.
In their native range, Metallic Beetles have been regarded as a secondary invader of stressed and weakened trees. They are frequently found in trees that have been stressed by insect defoliation, frost damage or warm, dry summers. These insects have recently been associated with a European oak decline throughout its nature.
Extensive mortality of oak forests due to a complex of factors including the Metallic Beetle, known as oak decline, can alter the species composition of forests. As a secondary insect, the Metallic Beetle is one of a large group of insects instrumental in the decomposition of dead trees. To date, at least six exotic species of Metallic Beetle have become established in the U.S. Between 1985 and 2000, 38 confirmed interceptions of Metallic Beetle were made at U.S. ports of entry. Twenty-eight of these interceptions were from dunnage, 4 from crating, 4 from grape leaves, 1 from a cutting and one was at large in a ship’s hold.
Portions of this article courtesy of: EXFOR Database