beetles (such as Xyleborus) feed on fungal "gardens" cultivated on woody tissue within the tree. Ambrosia beetles carry the fungal spores in either their gut or special structures, called mycangia, and infect the trees as they attack them. Once a beetle chooses a tree, they release spores of this fungus along tunnels within the tree. These spores grow and eventually produce fruiting structures to be consumed by the beetles. This can allow for ambrosia beetles to indirectly feed from more tree species due to the reliance on the fungi for food and the fungi's ability to overcome some of the plant's chemical defenses. While the majority of ambrosia beetles infect dead trees, several species will infect trees considered healthy or under stress. Biochemistry The bark beetle's pheromones, including kairomones, can attract other insects. The pheromones distinguished as kairomones are hormones, pheromones, or allomones of bark beetles, which in turn are used as a locator by insects that are attracted by it, such as flies, which may intend to harm the bark beetle itself. These chemicals interact with pine trees as the bark beetle's host, based on the behavioral, physiological, and biochemical effects of monoterpenes. Monoterpenes are a chemical fragrance that plays a significant role in tree-insect interactions, specifically within pine trees. It is an aggregation pheromone that attracts insects to the plant/ tree host, including the bark beetle. Monoterpenes has also been known to prevent fungal growth and are also toxic to bark beetles at high vapor concentrations. This latter process demonstrates a defense of pines using monoterpenes against the bark beetle. Taxonomy There are around 6,000 described species of bark beetles in 246 genera, placed into 26 distinct tribes. As pests Bark beetles are most commonly recognized by their impact on the lumber industry. Massive outbreaks of mountain pine beetles in western North America after about 2005 have killed millions of acres of forest from New Mexico to British Columbia. Bark beetles enter trees by boring holes in the bark of the tree, sometimes using the lenticels, or the pores plants use for gas exchange, to pass through the bark of the tree. As the larvae consume the inner tissues of the tree, they often consume enough of the phloem to girdle the tree, cutting off the spread of water and nutrients. Ambrosia beetles are also known to aid in the spread of pathogens, such as diseases that can