Efficient transmission of an introduced pathogen via an ancient insect-fungus association.

In Cupressus sempervirens the association between seed insects and tree pathogens has resulted in optimal exploitation of the cones. A fungus- infected cone can be inhabited by the nymphs of a true seed bug (Orsillus maculatus), the adults of which may carry a heavy spore load at emergence. Cones are infected when eggs are laid within the cone, most frequently via the emergence holes of a seed wasp (Megastigmus wachtli). This symbiotic association evolved with the nonaggressive fungus Pestalotiopsis funerea within the natural range of the cypress. When the aggressive cypress canker disease (Seiridium cardinale) was introduced into Europe, it was transmitted by O. maculatus to cones usually colonized by Pestalotiopsis funerea, with disastrous consequences for the regeneration and survival of C. sempervirens in the entire Mediterranean area.