The pine-wood nematode was introduced into Japan, probably from North America, shortly after World War II. Nematodes are carried to pine trees in the tracheae (breathing tubes) of adult longhorned beetles (Cerambycidae), similar to the one shown in this slide. Beetles feed on the elongating shoots of pines and the nematodes enter the resin duct system through the feeding scars. Following infection, the tree goes into rapid decline and then becomes susceptible to attack by cerambycid larvae. Remember that roundhead borers can only feed in dead or dying trees. Adult beetles lay their eggs on the dying pines and the larvae develop in the phloem and wood, killing the tree (Slide).

The system formed by the nematode-cerambycid-pine interaction is dominated by a destructive +feedback process (see textbook): more beetles infect more trees, which give rise to more beetles, which infect more trees, and so on. Eventually the forest is completely destroyed and, unless there are some resistant individuals, Japanese pines could become extinct. Unfortunately, Japanese pines do not seem to have much resistance to this nematode (Slide).

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