Ambrosia Beetle

Ambrosia Beetles

Most of the ambrosia travelers are harmless, but a few species have reproduced wildly in their newly colonized lands and gained a reputation as some of the most damaging tree pests. Two examples are the redbay ambrosia beetle (Xyleborus glabratus) and the polyphagous shot hole borer (Euwallacea aff. fornicatus).

The redbay ambrosia beetle has devastated lauraceous trees such as avocados throughout the American Southeast by inoculating them with its pathogenic symbiont fungus Raffaela lauricola. The shot hole borer has wreaked havoc on the other side of the continent in California, Oregon, & Washington. Euwallacea aff. fornicatus has destroyed trees in cities, orchards, and forests. Its fungus is not particularly pathogenic, but the beetles mass-colonize branches of trees until they eventually break off.

Habitat

Douglas fir, hemlock, and spruce trees and logged trees.

Food

The ambrosia beetle grows it’s own food in it’s host tree. The ambrosia or fungai spores are carried into the gallery system by the adult beetles. The spores germinate, grow, and then are harvested for food. 

Biology

Ambrosia beetles mainly overwinter within the log, stump, or tree. Adult beetles take flight in the spring when daytime temperatures exceed 60 degrees for several hours, usually in May and June. During this time they locate a suitable log or tree to infest. During the initial boring activity they produce a chemical attractant called the aggregation pheromone. The attractant draws in many more flying beetles and the log or tree is rapidly colonized. The mating takes place on the bark surface near the entrance hole. The pair work together extending the gallery and keeping it clear of boring dust and excrement. Young beetles occur within 6-10 weeks after egg deposition. 

Threat

Death of healthy trees, loss profit in wood timber products. In a log or tree, the borrowing beetle’s tunnels are generally confined to the sapwood, but may penetrate deeper in western hemlock and certain other conifers. The term ambrosia refers to the fungus the insect carries with it into the host logs/tree. The growth of the fungus in the wood produces the blackish stain surrounding the beetle tunnels. This results in a reduction in graded values of the logs and timber products.

Detection

Piles of white boring dust indicate ambrosia beetle attacks. Also, the beetle does not eat the wood, so it pushes out the sawdust. This creates a “worm like” appearance when it exits the tree.

Prevention

A key factor for avoiding ambrosia beetle damage is the rapid removal and processing of logs. Another management tool is the use of aggregation pheromone lures for trapping ambrosia beetles.