Red turpentine beetle, Dendroctonus valens
The red turpentine beetle is a native insect distributed throughout much of North and Central America, including most regions of the United States except for the southeast. This insect is considered a pest of secondary importance in its native range and is most often associated with pines (Pinus spp.), specifically ponderosa pine (Pinus ponderosa), Monterey pine (Pinus radiata), and sugar pine (Pinus lambertiana). Other conifers susceptible to attack include Douglas-fir (Pseudotsuga spp.), larch (Larix spp.), and true fir (Abies spp.). In the western US, this beetle has killed pole-size ponderosa pines under drought-stress after thinning and soil ripping in the spring of the same year.
There are several ways to identify red turpentine beetle, including insect morphology and the appearance of injuries on infested trees (see injury section below). At 0.6-0.95 cm (1/4-3/8 inch) long, the red turpentine beetle is relatively large when compared with other Dendroctonus spp. inhabiting north America. Adults of red turpentine beetle are cylindrical and have a distinct red brown color with elbowed, clubbed antennae. After emerging from the puparium, young beetles have yellow bodies, while older beetles are dark red to brown in color. When handled, adult males often produce an audible chirping sound.
The opaque, white eggs are oblong and less than 1.6 mm (1/16 inch) in length. When mature, the creamy white larvae are roughly the size of adults. They are legless grubs with a red or brown head capsule and a sclerotized brown spot with minute spines, which is a distinguishing feature of this species. The pupae are creamy white and have certain structures indicative of a developing adult beetle, such as legs, wings, eyes, and antennae.
- The red turpentine beetle is native to the United States and tends to prefer attacking pines, especially ponderosa pine. More recently, this beetle has also been reported in Colorado blue spruce.
- Healthy trees can withstand attack by red turpentine beetle. However, under high beetle populations, periods of drought-stress combined with fire damage or certain landscaping practices can increase the likelihood of mortality after an attack.
- The red turpentine beetle can be detected with Lindgren funnel traps baited with pheromones. The presence of pitch tubes on the tree trunk also indicates that an infestation is present, however pitch tubes may be present on trees infested with other bark-boring beetles. When the bark is removed from dead wood of a ponderosa pine, the presence of galleries with frass is an indication that the galleries were excavated by red turpentine beetle.
- Preventing damage due to fire, mechanical wounding, or root disease will help maintain adequate tree health. Preventative sprays that cover the entire trunk can help protect susceptible trees against red turpentine beetle.
Adult of red turpentine beetle. Note the red-brown coloration, which is a feature of older adults. After emerging from the puparium, young adults are lighter in color. Image credit: Joseph Berger, Bugwood.org
Lateral view of a red turpentine beetle. Image credit: Erich G. Vallery, USDA Forest Service – SRS-4552, Bugwood.org
Frontal view of a red turpentine beetle. Note the clubbed antennae. Image credit: Erich G. Vallery, USDA Forest Service – SRS-4552, Bugwood.org
Larva of red turpentine beetle. Note the absent legs, brown head capsule, and sclerotized patch with spine-like projections at the tip of the abdomen. Image credit: Donald Owen, California Department of Forestry and Fire Protection, Bugwood.org
A large, fan-shaped gallery with larvae of the red turpentine beetle. Image credit: Ladd Livingston, Idaho Department of Lands, Bugwood.org
Red brown pitch tubes are present on this tree trunk due to attack by the red turpentine beetle. Attack by the red turpentine beetle can produce pitch tubes with different colors. Image credit: Bob Oakes, USDA Forest Service, Bugwood.org
Life history and habits
The red turpentine beetle can overwinter as larvae or adults, after which the beetles emerge from dying trees or recently cut tree stumps and can fly over 10 miles in search of suitable host trees for reproduction. Typically, the red turpentine beetle attacks trees with a minimum diameter of 20 cm (8 inches) in forests, parks, or landscapes. The red turpentine beetle is a generalist that interacts with other wood-boring beetles and microorganisms, and tree mortality is often attributed to the activity of other, more aggressive wood-boring species. Initially, eggs of red turpentine beetle are laid on the tree trunk, but the egg-laying zone can gradually extend up to eight feet above the ground, to the root collar, and areas below the ground.
When a female finds a suitable host, she begins boring through the bark and spongy phloem and is soon joined by a male beetle. After mating, egg galleries are typically established in a linear arrangement and oriented longitudinally along the grain of the trunk and roots, but sometimes there can be branching or lobed egg galleries. Within galleries, eggs are laid in groups that can contain up to 100 eggs. Under heavy infestations, multiple egg galleries can merge, and individual galleries may be difficult to distinguish. After laying eggs, adults will either exit the galleries in search of new egg-laying sites or continue feeding within galleries until they die. The eggs hatch in one to three weeks, depending on temperature. In Colorado, there is likely at least one or fewer generations each year, depending on elevation. In southern areas of the US, there can be multiple generations produced each year at lower elevations, which is partially due to the ability of individual females to establish multiple broods in a single tree.
Larvae mine away from the egg gallery in a side-by-side feeding behavior. They tend to feed in groups, and as the larvae mature, their feeding gradually becomes more extensive and results in additional fan-shaped galleries with irregular margins. When fully mature, larvae construct individual pupation cells by scooping out wood fragments between the bark and wood. Newly emerged adults can remain in the gallery for up to several months until they bore exit holes and begin flying to new hosts in warmer weather.
Trees are most susceptible to mortality after they have been previously infested with bark beetles, scorched by wildfire, wounded by construction machinery, or suffered from soil grade changes or compaction. In addition, red turpentine beetle can introduce blue stain fungi to host trees, which have been identified as important microbial pathogens in the decline of living pines. Newly formed pitch tubes are sticky, soft and are either white, pink, or red brown to dark brown, depending on the amount of bark or oxidized phloem fragments. On pines, the tubes can have a diameter of up to 5.1 cm (2 inches). Eventually the tubes harden and can remain on trees for several years. The presence of pitch tubes on pines is little cause for concern and indicates that the tree is healthy and defending itself by producing resin. However, failure to form pitch tubes indicates that the tree is more susceptible to infestation. Infestations that produce non-resinous boring dust indicate that the tree’s defenses are failing, or that the tree is already dead.
It is worth noting that spruce and fir produce much less resin than pines, and often the pitch tubes will be small or absent. Rather, small pitch pellets or boring dust may be observed on the ground beneath the affected site on the trunk. In addition, while fading of crowns from green to yellow or red can lead to the discovery of a red turpentine beetle infestation, this fading is typically the direct result of infestation by other bark-boring beetles.
Lindgren funnel traps can be baited with pheromones to help attract and capture various bark beetles. It is worth noting that, while these traps can reliably bait and capture adults during flight, they also attract beetles to the area which can lead to tree attacks. Given this, traps should be placed at least 18 m (20 yards) from susceptible trees. In some instances, 8- or 12-unit Lindgren funnel traps can help reduce beetle populations in a given area. Traps should be checked a minimum of once a week or every two days if possible.
To determine the severity of the threat posed by red turpentine beetle, injuries should be assessed while also considering the condition of nearby trees. Healthy trees can often withstand attacks. However, under high beetle populations, pines that are young and pole-sized may be killed during periods of drought-stress when combined with fire damage and landscape practices such as thinning, pruning, chipping, and soil ripping. The presence of non-resinous boring dust indicates that the tree may already be dead.
To determine whether an infested tree is dead, small portions of bark can be removed and galleries examined for the presence of feeding larvae, live adults, and eggs. The galleries will be well-developed with many living life stages in dead trees and short with copious resin and some dead adults in healthy trees.
Maintaining healthy trees is an effective approach to preventing attacks by red turpentine beetle. This includes protecting the trunk and roots and avoiding the placement of freshly cut or chipped pine material next to standing trees. Consider removing or treating fresh stumps, slow-dying trees, exposed roots of live trees, and trees with compact soil. In construction zones, care should be taken to maintain the health and integrity of nearby trees and their environment. In forests, thinning can help reduce the possibility of mortality by increasing the spacing between trees.
Under periods of drought-stress and high beetle populations, preventative insecticide treatments can provide short-term protection of individual trees. Often, a single treatment before flights of red turpentine beetle is sufficient to protect susceptible trees. It is recommended that preventative insecticide treatments be applied directly to the tree trunk with a high-pressure sprayer. Complete coverage is necessary, as areas of the trunk not covered with the insecticide are still susceptible to attack. Insecticides that have been used with success include formulations of carbaryl, chlorpyrifos, or permethrin. It is important that formulations be labeled specifically for management of bark beetles, and that treatments are only applied to healthy trees or trees that can recover from an infestation.
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