Figure 108. Egg gallery of roundheaded pine beetle. Note that galleries are vertical, but more snake-like in appearance than mountain pine beetle egg galleries.
Symptoms/Signs: Reddish brown boring dust is present in bark crevices and
numerous pitch tubes are observed on the bark at entrance holes.
In heavily attacked decadent trees, pitch tubes are often missing
or very small. Later, the foliage fades from green to yellow or
bright red, and eventually a dull brown. Woodpecker activity on
the trunk is also a good indication that bark beetles have attacked
the tree.
Biology: Adult roundheaded bark beetles
attack and colonize susceptible trees in October and November. Females
initiate the attack producing an aggregation pheromone drawing large
numbers of beetles to the tree. The beetles chew through the bark
and excavate a chamber in the moist tissue beneath the bark. Males
enter the chamber and mating occurs. Female beetles then excavate
horizontal tunnels in the inner bark region for 25 to 50 mm and
then longitudinally with the grain an average distance of 300 mm.
Eggs are laid individually in niches on alternate sides of the egg
galleries, which are packed with frass. The larvae mine across the
grain in the inner bark until in the third instar and then bore
into the outer bark to complete development.
Figure 109. Pitch tubes caused by roundheaded pine beetle are typically larger and more cream colored than those formed by western pine beetle
Effects: Roundheaded pine beetles attack, colonize, and kill trees
in the southwestern United States and Mexico. Periodic outbreaks
have killed large numbers of ponderosa pine in southern New Mexico
and southeastern Arizona. In 1950, 16,000 pole and sawtimber-sized
trees were infested on 2,500 acres near Cloudcroft and 400,000 pole-sized
ponderosa pines were killed on 150,000 acres from Mayhill to Ruidoso
in 1971. Similar outbreaks occurred during the 1990s in the Sacramento
Mountains in southern New Mexico and the Pinaleño Mountains
in southeast Arizona.
Similar Insects: The roundheaded pine beetle
is similar to other Dendroctonus beetles, Ips
beetles, and other members of the subfamily Scolytidae. Dendroctonus
beetles are distinguished from each other mainly by their unique
egg galleries and, in the case of the Douglas-fir beetle and spruce
beetles by the host species they attack. Dendroctonus beetles are
distinguished from Ips beetles by their rounded posterior ends and
galleries, which are packed with frass. In contrast, the posterior
ends of Ips beetles are slightly concave with and have several to
many small spines and the runways (egg galleries) are free of frass.
Figure 110. Ponderosa pine mortality caused by roundheaded pine beetle in the Pinaleño Mountains, Arizona.Figure 111. Aerial view of ponderosa pine mortality caused by roundheaded pine beetle in the Pinaleño Mountains, Arizona.