Diagnosis of European Woodwasp Injury
Trees with European woodwasp infestation show a range of symptoms. Green needles will wilt and change color (from the initial dark green to a yellow and finally to red) within six months of infestation in a pine. Trees may have resin “pitch-outs” (thin beads or dribbles of resin) at points where the adult female drills into the tree to lay eggs (Figure 6). However, such symptoms may be produced by several native species and should not be considered evidence of European woodwasp infestation without adult specimens. As they emerge from a tree adults produce a round exit hole, but this is a shared feature of all woodwasps.
Figure 6. “Pitch-outs” produced by European woodwasp females during oviposition. Photo courtesy of Dennis Haugen
Regional Woodwasps of Similar Appearance to the European Woodwasp
At least eleven species of siricid woodwasps are present in Colorado. The most commonly encountered species is the pigeon tremex (Tremex columba) that develops within declining maples and other hardwood shade trees. All other species in the state are associated with conifers, as is the European woodwasp. Siricid woodwasps also show great variation in size. Size variations ranging from 1/4 to 1 inch in body length excluding the ovipositor have been recorded within some species. As such size is not a very useful tool to discriminate between the different siricid species. While there can be substantial variation in color within some species, colors and patterns on certain areas of the body (antennal markings, leg markings) are useful in helping to differentiate some of the woodwasp species. The most easily identifiable of the woodwasps is the pigeon tremex. In addition to differences in host (hardwoods vs. conifers) it is a generally brown color, a feature that allows it to be distinguished easily from the European woodwasp. Colorado State Extension Fact Sheet 5.604 provides additional images of this insect along with its most prominent natural enemy, the giant ichneumon wasp. The link to this sheet is http://www.ext.colostate.edu/PUBS/INSECT/05604.html. Seven of the woodwasps found in Colorado that are associated with conifers (pines, Douglas-fir, etc.) should be fairly easy to distinguish from the European woodwasp: Urocerus albicornis. Urocerus albicornis resembles the European woodwasp in body shape and length. They can be separated from the European woodwasp by checking antennae color. Females of U. Albicornis have antennae that are white except at the base and tips while the antennae of the European woodwasp are entirely black. Urocerus californicus. Urocerus californicus may be separated from the European woodwasp by checking antennae color. Females of U. californicus have antennae that are entirely yellow in contrast to the entirely black antennae of the European woodwasp. Figure 7. Pigeon tremex (female).
Figure 8. Urocerus californicus (female). Photo courtesy of the Ken Gray collection