Southern Pine Beetle
Author: S.M. Salom, Department of Entomology; Virginia Tech
Contact: Eric Day, Manager, Insect Identification Laboratory
ENTOMOLOGY PUBLICATION 444-243, August 1996
Southern Pine Beetle
Southern Pine Beetle Internet Control Center
Distribution and Hosts
The southern pine beetle (SPB) occurs in the southern and
southeastern United States, extending as far west as Arizona and
as far south as Central America. The northern range extends from
southern New Jersey and Pennsylvania, west to southern Missouri,
south to east Texas, and east into Florida. Generally, this
insect occurs wherever shortleaf and loblolly pines are grown.
The beetle has been reported to attack and kill all pine species
in its range. In the southeastern states, loblolly and shortleaf
pine are preferred, yet Virginia, pitch, table-mountain,
longleaf, and slash pines are often successfully attacked.
Description of Damage
Southern pine beetles are the most destructive forest insect pest
in the southeastern U.S. They mass-attack the trunks of mature
or overmature pine trees. The beetles bore through the bark and
develop "s-shaped" galleries in the phloem tissue where the eggs
are laid and brood develop. They also introduce a blue-stain
fungus into the sapwood that eventually inhibits water flow in
the tree. The colonization by the beetles and the fungus
combined results in tree death only days after mass-attack. It
may take weeks or even months (if attacks are in late fall) for
the foliage to fade from green to red. Pitch tubes are often
present at the entrance holes made by the beetles. In addition,
reddish-yellowish boring dust may also be present in bark
crevices or around the base of the tree. The tree attempts to
pitch out the beetles and is sometimes successful. Beetle
populations will remain at endemic levels for years until
populations build up to epidemic levels for a two or three year
period. These cycles occur about every 10 years. Often
infestations that show up in the spring do not continue and will
die out. However, when populations are high, infestations can
expand almost like wildfire within pure pine stands, killing
thousands of trees and covering hundreds of acres.
For trees that are killed, loggers try to salvage the wood as
quickly as possible to minimize the amount of degrade. The blue-
stain fungus is apparent in the sapwood, reducing the price at
which sawtimber is sold.
Identification
Adults are 2 - 4 mm in length and brownish-black in color. They
are cylindrical and somewhat stout to elongated in shape. The
head is broad and prominent with a distinct longitudinal median
groove bordered by a narrow elevation of tubercles (protrusions)
on each side. The pronotum (shield behind the head) is slightly
narrow at front, broadest at the middle, and about as long as
wide. The wings are as wide as and over twice as long as the
pronotum. Immature adults not ready to emerge from trees are
light brown in color.
Females lay eggs on alternate sides of "s-shaped" galleries in
the phloem tissue. The eggs are opaque, pearly white, and shiny,
measuring about 1.5 mm long by 1 mm wide. They are slightly
oblong to oval in shape. The larva is a wrinkled, legless grub
with three thoracic and 10 abdominal segments. They are
yellowish white, and 2 mm long upon emergence from the egg,
developing up to 5 - 7 mm long prior to pupation. The pupa is
also yellowish-white. It has the form of the adult, but the wing
pads and legs are folded beneath with the abdominal segments
exposed. The pupae range in size from 3 - 4 mm in length.
Larvae migrate from the phloem tissue into the bark as they
develop. Pupae and callow adults occur near the outer bark in
preparation for emergence.
Life History
The duration from egg to adult stages ranges from 26 to 54 days,
depending upon the season. The beetles may have as few as three
generations in Virginia and as many as seven generations in
Texas. The beetles overwinter inside trees at all stages. In
the spring when the dogwoods bloom, adults begin to fly. Females
land on host trees, 2 - 9 m off the ground, bore through the
bark, and if successful, produce a pheromone that attracts males
and females together to attack the tree en mass. Females begin
building egg galleries. Mating takes place in the gallery
followed by female egg laying. Adults can re-emerge from
galleries and attack new trees.
Often within an infestation fresh attacked trees serve as a
center of attraction. Usually as the infestation grows, adjacent
trees succumb to attack, resulting in a group of trees producing
pheromones. Therefore, infestations often move in one or more
directions.
Control
Prevention is the best form of control. Forest stands should be
thinned two to three times during the rotation. Thinned stands
keep trees healthy and vigorous. Overmature stands are most
susceptible to attack. Therefore, harvesting trees at rotation
age should be followed.
It is very important to aerial survey for SPB activity in the
spring and periodically in the summer. This must be followed up
by immediate ground checking. Quick action to protect a stand of
trees is essential in trying to suppress the infestation.
Active infestations can be halted using several cultural tactics.
One is to salvage all old and new attacks, plus a buffer strip of
unattacked trees in the direction the infestation was spreading.
Size of buffer strips should range between 6 to 35 meters,
depending on the number of fresh attacked trees present. Another
option, for pre-commercial sized timber or hard to get to areas
is to cut the timber down and leave it at the site. These trees
should be felled toward the center of the infestation. The brood
in the felled trees will not survive very well under the bark due
to solar heating at the forest floor.
Knowledge of the complex chemical communication system used by
this bark beetle species has stimulated scientists to develop a
suppression tactic based on disrupting the flight of adult
beetles. While the tactic is not yet operational, it will
provide an important alternative in the near future.
Insecticides are available for application; however, they are
only feasible for situations where the owner is interested in
protecting individual trees. Please consult the Pest Management
Guide for Horticultural and Forest Crops, Virginia Cooperative
Extension Publication 456-017.
Further Reading
Drooz, A.T. Insects of Eastern Forests. 1985. U.S.D.A. Forest
Serv ice. Miscellaneous Publication No. 1426. 608 pp.
Flamm, R.O., R.N. Coulson, and T.L. Payne. 1989. The southern
pine beetle. pp. 531-553. In A.A. Berryman (ed.). Dynamics of
Forest Insect Populations. Plenum Publ. Co.
Thatcher, R.C. and P.J. Barry. 1982. Southern pine beetle.
U.S.D.A. Forest Service Forest Insect & Disease Leaflet 49.
Thatcher, R.C., J.L. Searcy, J.E. Coster, and G.D. Hertel. 1980.
The southern pine beetle. U.S.D.A. Forest Service Technical
Bulletin 1631.