Asian long-horned beetle
The Asian long-horned beetle is one of those exotic species that can be serious forest game-changers. It’s in North American but not yet in Michigan. Anyone interested in forests should keep an eye out for this insect.
There are few native regional beetles as large as the Asian long-horned beetle (ALB). Both sexes are over an inch long, with females as long as 1.5 inches. Bodies are black with numerous white blotches. Antennae have alternating light and dark segments, about as long as the body in females and longer in males.
Cottonwood borers are a similar size and general coloration, but the lighter markings are more connected and patterned. The very common spotted sawyer and pine sawyer beetles are sometimes thought to be ALB, but their markings are quite different and they’re smaller. The spotted sawyer is mostly black and the pine sawyer a mottled gray or brown.
Breeding populations were first confirmed in New York in 1996. Infestations have since been found in Chicago, Massachusetts, Toronto, New Jersey, and southern Ohio. In some locations, ALB has not been found after eradication efforts.
Michigan State University Extension recommends if anyone should believe they’ve seen an ALB, it should be reported. Reports can be made on the MISIN website or through the Michigan Department of Agriculture and Rural Development (MDARD). People can also contact their county conservation district, most of which are informed about the ALB and other exotic species threats.
However, by the time adult beetles are flying around, an infestation is probably fairly well advanced. All the more reason to report! Peak time for beetle dispersal is July and August. Although, considering most of the beetle life cycle is spent in the wood of a tree it is difficult to detect.
The effects of ALB might be sooner noted by tree crown diebacks. However, many things can cause dieback, especially in a residential environment. However, dieback of maple trees should warrant a bit of investigation, as maples are the preferred host of ALB. Leaking sap may appear on the trunks and large branches. “Sawdust” or frass might be seen on the ground, from where adults have chewed their way out of the wood.
Two other ALB clues include the presence of oviposition sites and adult exit holes.
Females excavate a shallow area on the bark to lay an egg, in late summer or early fall. Sometimes, careful observers can spot these sites, especially with binoculars. Fresh oviposition sites are easier to see than older ones.
The adult exit holes are large, about a half-inch in diameter and reach more than an inch into the tree. Actually, they’re a bit similar to sugar maple tapping holes. The ALB attacks the upper part of the tree first, making observation more difficult.
When infestations are confirmed, treatment can be rather drastic, a mix of removal and chemical injections. Research teams attempt to map the extent of the infestation, which is difficult. Following the mapping, maple trees within a quarter-mile or so, are treated and maybe cut down. Smaller infestations are easier to contain and cause less visual impact. Larger infestations can be persistent and involve extensive tree removal. And, of course, don’t move firewood around!
Ongoing research is attempting to find a biological control, considering many taxa, as well as look at better identification techniques and more about ALB dispersal and host preferences. Potential annual damage from ALB reaches in the many billions of dollars.
Most new infestations are found by non-professionals who are curious about tree health and stay informed about tree threats, such as the ALB. In Michigan, the “Eyes on the Forest” project is designed to help citizens learn about and find new infestations of particularly harmful exotic species.