Invasion of the Wasps

Photo by Kent Loeffler

There is yet another invasive pest to beware of, says Cornell Extension Associate Dr. E. R. Hoebeke. Last September, he happened across the woodwasp Sirex noctilio (Fabricius) while searching screening traps in Fulton County, New York, set by the New York State Cooperative Agricultural Pest Survey to capture bark beetles. This woodwasp poses a major threat to all pine tree species throughout North America if it becomes established in our woodlands.

Hoebeke’s surprising find is the first female specimen discovered in the U.S. Male woodwasps were first found at our borders in 1985. Since then, the U.S. Department of Agriculture Animal and Plant Health Inspection Service inspectors have intercepted 103 S. noctilio wasps at U.S. ports. Native to Europe, Asia, and northern Africa, the pest travels in the wooden crates or packing material used during shipping of tile and marble from Spain and Italy.

In countries such as New Zealand, Australia, South America, and South Africa, the insect is responsible for damage to 80 percent of the pine trees in some areas. The possible infestation of the species in the U.S. spells trouble for pine trees coast to coast. The stately loblolly pines (Pinus taeda) in Georgia and the Monterey pines (Pinus radiata) of California are the most likely targets, as these species have been damaged in other countries. Also recorded in conifers such as spruce, fir, and larch, woodwasps are potentially dangerous in the forests of the eastern U.S.

Alone, the female wasp would only do minimal damage to a tree by boring into its bark to lay eggs. The pathogenic fungus Amylostereum areolatum, which is associated with the wasp, is the actual killer. Female woodwasps drill holes in the tree’s bark and insert poisonous mucus and the fungus. When a tree is attacked with fungus, its usual response is to send sugar from the leaves to the infection site to form a toxin that kills the fungus. The mucus prevents that response, allowing the fungus to infect the tree, causing it to dry out and die, sometimes within a few months.

As a female bores into the tree, she determines if it is suitable for her eggs. If it is, she will lay her eggs as she injects the fungus. The fungus serves as food for the larvae, offering a more easily digested form of cellulose. Larvae will tunnel toward the heartwood of the tree and then make a u-turn back toward the sapwood, where they bore out into the world.

If more woodwasps are found in our forests, there are possible solutions. Other countries are successfully using biological controls to deal with the pest, although the control organisms do not increase their range along with the insect. Primarily, countries are relying on the nematode Deladenus siricidicola, which achieves up to a 90 percent parasitism rate and renders females unable to reproduce. South Africa also uses two types of parasitic wasps, Ibalia leucospoides and Megarhyssa nortoni. Fortunately, many species of the Siricidea nematode are native to North America and could be used as biological control if necessary.

Currently, federal and state regulatory agencies are running detection and delimiting surveys, beginning in New York, to search for further infestations of the insect. If more woodwasps are found, a fast response will be needed.

Keeping watch on invasive species is a daunting task – but one that if not done could have drastic impacts on the life of our forests. With hemlocks suffering from an infestation of the hemlock woolly adelgid and sugar maples vulnerable to the Asian longhorned beetle, can we afford to lose another tree in our forests to non-native species? For more information on this and other invasive species, contact the National Invasive Species Council at


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