A handful of beetle species attack and kill pine trees, including the southern pine beetle (Dendroctonus frontalis Zimmermann) and the mountain pine beetle (Dendroctonus ponderosae). Although the beetles may vary, infested pine trees share similar symptoms.
Adult beetles burrow into the pine's bark to lay eggs. The tree produces sap as a response, and the oozing sap hardens into popcorn-shaped nodules called pitch tubes. Fresh pitch tubes are soft and pale or rose-white. The nodules harden as they age, eventually turning brittle and yellow. An infested tree may show multiple pitch tubes or, in drought-stricken areas, none at all.
Larvae feed underneath the bark. Red-tinged dust from the burrowing larvae powders the tree and the adjacent ground, and the bark begins to loosen and flake. The larvae leave serpentine paths underneath the bark and, as they mature, produce exit holes. The pine tree's inner wood often has a blue fungus.
Newly infested trees remain green, but the needles begin to yellow within three to four weeks. In some cases, the needles may remain green through the winter and only show damage in spring. The pine tree's entire crown fades, yellows and eventually turns a red-brown as the pine dies.
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