In the mid-1980s, the red turpentine beetle was inadvertently introduced into China from North America along with its symbiotic blue-stain fungi. For the first decade or so after its introduction it went essentially unnoticed, although there are museum specimens dating from that period in Chinese collections. More recently, the beetle/fungus combination became a very serious pest in China, killing millions of Chinese pines, leading to speculation that a new fungal associate may have arisen that enhanced aggressiveness of the beetle/fungus complex. Intensive surveys of the red turpentine beetle fungal associates were conducted both in North America and in China, to determine the geographic source and the possible role of the fungi in the invasive success of the symbiotic complex in China. Using microsatellites, we discovered a novel fungal genotype in China that is far more virulent toward host pines than the North American genotypes. These novel genotypes induce host trees to produce and release much higher levels of 3-carene, which is the primary host attractant of the red turpentine beetle vector. The result is a positive feedback mechanism that may have enhanced the invasive success of the beetle/fungus combination. There are concerns that this novel fungal genotype may find its way back to North America, with unpredictable consequences for native forests.