Bark Beetles of the Southern California Forests

Bark Beetle Life History

Western Pine Beetle

The Western Pine Beetle occurs in forests throughout the western half of North America and northern portions of Mexico from below 1,000 feet (300 m) to above 8,000 feet (2,400 m) in elevation. This beetle attacks Coulter and Ponderosa pines, but primarily targets Coulterpines in Southern California. Western Pine Beetles can produce up to 4 generations per year in the warm climate of southern California. Western Pine Beetles invade new host trees greater than 6 inches (15 cm) in diameter. The attacks typically take place mid way up the trunk. Females who have successfully invaded a tree emit aggregating pheromones to attract males and females to the tree. Mated females lay approximately 60 eggs in individual niches along the sides of egg galleries. The eggs hatch in 7 to 14 days, revealing white larva. The larva bore galleries to access phloem, their first source of food. Eventually the larva bore into the inner bark to feed and pupate. The new adults feed on middle and outer bark. The entire life cycle, from egg to adult, can take a little as 2 months. The adults emerge to attack a new host throughout the warmer months. These attack periods can last up to three weeks. The host tree is typically dead within a year of the initial infestation. (more)

Mountain Pine Beetle

The Mountain Pine Beetle is found in forests throughout the western half of North America from sea level to 11,000 feet (3.353 m) in elevation. This beetle targets 4 major tree species, White, Sugar, Lodgepole, and Ponderosa pines, but inflicts the most damage on Ponderosa and Sugar pines in Southern California. Mountain Pine Beetles typically produce a single generation per year, but in the warmer climate of California this species may produce 2 generations in a single year. Female Mountain Pine Beetles are first to invade mature host trees below 15 feet on the trunk and emit aggregating pheromones to attract males and females. The mated females lay eggs in galleries 4 to 48 inches long during late spring to early fall. After 10 to14 days the eggs hatch, revealing white larvae with brown heads. The larvae overwinter under the bark of the tree until the following spring orsummer, approximately 10 months (fewer in California). During this time the larvae bore galleries at right angles to the egg gallery to access and feed on phloem. During the early summer months the larva bore oval chambers into the inner bark where they become pupae. The pupae then emerge as adults, usually by July. The adult Mountain Pine Beetle feeds on the inner bark of the host tree. As adults converge within the bark they form exit holes and leave the tree. The host trees are generally killed by a single generation of Mountain Pine Beetles. (more)

Jeffrey Pine Beetle

The Jeffrey Pine Beetle occurs in the west coast from the border of southwestern Oregon to northern Mexico and is host specific to Jeffrey pine. Jeffrey Pine Beetles complete a single generation in 1 year in cooler climates, and up to 2 generations in Southern California. Jeffrey Pine Beetles invade new host trees typically 10 inches or greater in diameter but will occasionally attack trees as small as 4 inches in diameter. Mated females lay eggs singly in characteristic J shaped galleries packed with boring dust. The eggs hatch after 1 to 3 weeks, revealing white larvae with yellow heads. The length of the larval stage varies, depending upon the time of year. Larvae may complete their development during the warmer months or may over winter in the bark of the tree. When mature, the larvae pupate and emerge as adults in about 10 days. The adults tunnel out through the bark and invade new Jeffrey pines from June to as late as early October. Jeffrey pines are slow to die. The beetles had usually abandoned the tree by the time in begins to fade. (more)

Red Turpentine Beetle

The Red Turpentine beetle is found throughout the forested areas of North America and Mexico, with the exception of the Atlantic and Gulf coast states. This beetle is known to attack a variety of conifer species but is most problematic to Sugar and Ponderosa pines in the West. Red Turpentine beetles complete 1 generation per two years in cold climates and as many as 3 generations per year in warmer climates. Females invade a new host tree and emit aggregating pheromones to attract males and females to the tree. A mated female bores egg galleries between the inner bark and sapwood where she lays eggs in an elongate mass. She will lay from a few to 100 or more eggs in one or more groups along the length of the gallery. The eggs hatch in 1 to 3 weeks during the summer. The larvae, white with a brown head and hind end, feed in the inner bark tissue, feeding side by side. When mature, the larvae form chambers and pupate. The pupa emerges as an adult in about a week. The adults will spend a few days to several months within the tree before exiting to invade a new host in the spring. Outbreaks of the Red Turpentine Beetle are not as common as outbreaks of other species of bark beetles. (more)
San Bernardino County Museum