Ambrosia beetles come from two weevil subfamilies (Scolytinae and Platypodinae) and, like all weevils, they are species-rich. Among the high impact pest species list published by Aukema et al. 2010 (article here), there is only one ambrosia beetle species listed: the Redbay Ambrosia Beetle (Xyleborus glabratus).
There are, however, 26 invasive ambrosia beetle species in the US. All ambrosia beetles share one thing: they have a mutualistic symbiosis with a fungus (polyphyletic, but generally referred to as “ambrosia fungus”), the spores of which they carry at the bases of their mandibles in structures called “mycangia.”
When they burrow into a tree, they disperse the fungal spores along the inside of the wood. The fungus grows and digests the tough wood, and the ambrosia beetles feed on the fungus. (It is a tidy little symbiosis.)
The high economic impact of the Redbay Ambrosia Beetle comes from the fact that the fungus it disperses (Raffaelea lauricola) is itself a pathogen that causes Laurel wilt in members of the plant family Lauraceae (including, for example, the avocado).
The range of the Redbay Ambrosia Beetle is limited at this time to Florida, Georgia, and South Carolina, but ambrosia beetles can be found throughout North America.