In Ontario, a team of Canadian Forest Service pathologists have identified the presence of white rot decay in pines. This disease is caused by a fungus injected into trees by the Sirex woodwasp. The fungus and a phytotoxic mucus produced by the insect weaken the host tree and provide conditions favourable to larval development. The insect and the fungus thus have a symbiotic relationship: the fungus uses the insect as a means of transportation and, in turn, it is indispensable to the insect’s larval development in the wood.

Although the insect vector is native to Eurasia and North Africa, it has spread in recent decades, particularly in the Southern Hemisphere (New Zealand, Australia, South America and South Africa). The first report of its presence in North America dates back to the summer of 2005, when it was found in the state of New York. The following autumn, the insect was discovered in southern Ontario.

In their natural habitat, the fungus and the insect live in equilibrium with their parasites and host trees. However, their introduction into the Southern Hemisphere and later into North America has led to major outbreaks in forest tree plantations. More advanced genetic tests would make it possible to better determine the geographic origin of the insect-fungus complex. This knowledge is essential for developing biological control agents.