Bark Beetles
Twig Beetles
Pityophthorus spp.,
Pityogenes spp., Pityoborus secundus

Hosts: Pines and other conifers.

Figure 132. Figure 132. Pitch tubes of twig beetles on piñon are typically very small (<1/8 inch).

Symptoms/Signs:  Trees attacked and colonized by twig beetles exhibit fading needles on twigs and branches, and twig and branch dieback throughout the crown. Tan sawdust is produced around the attack sites. On smaller twigs and branches, most of the cambium is mined beneath the bark. Small, star-shaped egg galleries generally occur under the bark of the larger branches and small trunks.

Biology:  Adult twig beetles are about 3 mm long and dark brown. Most species have a rounded rear end, but a few have a pair of short spines. The larvae are fat, white, C-shaped grubs with light brown head capsules and feed under the bark. Most species have 2 to 4 generations per year, depending on local conditions.

Effects:  Typically attacks and kills small twigs and branches of drought stressed or otherwise weakened pines and other conifers. Although twig beetles are generally considered of secondary importance, under favorable conditions they may develop in sufficiently high numbers and attack and kill small trees. Pityogenes carinulatus killed thousands of young ponderosa pine in 1967 in New Mexico as a result of populations increasing in thinning and logging slash. Twig beetles infested high numbers of young piñon in 2002, 2003, and 2004 across New Mexico and Arizona.

Similar Insects and Diseases:  See Ips discussion. Most twig beetles have elytral declivity and egg galleries that are somewhat similar to Ips; however, twig beetles are smaller in size and are typically found in branches and very small diameter trees.

References:  9, 24

Figure 133. Figure 133. Damage to ends of piñon branches caused by twig beetles. Very small pitch tubes may be present on twigs.
Figure 134. Figure 134. Mortality of piñon regeneration killed by twig beetles near Los Alamos, NM.