Cooperative Extension Service 
Institute of Food and Agricultural Sciences
Hendry County Extension    P. O. Box 68    LaBelle, Florida 33975-0068    Phone (863) 674-4092

Hendry County Horticulture News

 Pine Bark Beetles - Aggressive and Destructive

There are five species of pine bark beetle species, which commonly infest pines in the southern United States. In recent years outbreaks have increased in frequency and severity owing to the increased acreage, density and maturity of planted pine in the state.  The southern pine beetle (Dendroctonus frontalis) is the most studied of the southern forest insects. The southern pine bark beetle may be found throughout the state wherever there are loblolly pines,  i.e., northern and central Florida. According to John Foltz, Forest Entomologist at the University of Florida, there are only a few planted loblloy pines in Hendry County and Dendroctonus frontalis has never been found here. There is currently a souther pine bark beetle outbreak in Hernando County which coincides with the southern edge of the natural range of loblolly pine.

There are five different species of bark beetles which can infest pine trees. To identify the species present, it is necessary to remove some bark and look at the size and shape of the beetles and their associated egg galleries. The southern pine beetle is the smaller of the two beetles with rounded rear ends. It is about 1/8 inch long, about half the size of a grain of rice, while the larger black turpentine beetle is about 1/4 to 3/8 inch long.  The other three, know as Ips beetles all have scooped-out rear ends with small spines around the margin.

Research on pine beetles beetles affecting slash pines at Myakka River State Park in Sarasota County,  indicates that the Ips pine bark beetle, Ips calligraphus is probably the predominant beetle infesting drought-stressed pines in our area. The black turpentine beetle, Dendroctonus terebrans, may also be present in the base and roots of  trees.

Southern pine beetles make winding, intersecting egg galleries packed with boring dust. Black turpentine beetles start with a short horizontal gallery and then turn and tunnel downward toward the ground. Galleries of the Ips beetles are distinguished by one to four clean galleries radiating out from a central chamber beginning at the site of entry.

The scientific name of the insect Dendroctonus means "tree killer," which,  as many homeowners have found, is quite accurate.   Pine bark beetles reproduce rapidly and mass attacks by thousands of beetles can easily kill vigorous pines.  The southern pine beetle at times is an exception to the general rule that bark beetles are generally scavengers of dead or severely weakened trees. When populations are high, this species will mass attack and kill trees that otherwise would live for many additional years. Because this species can develop from egg to reproducing adult in as little as four weeks, there is relatively little time to detect an infested tree and keep the brood from dispersing to colonize new trees.

A tree is doomed once bark beetles colonize and destroy its inner bark. Without this phloem tissue, the carbohydrates  produced in the needles cannot nourish the living cells in the roots. Without living roots to provide water and nutrients to the crown, the needles dry out and die. The blue stain fungus carried by beetles often hastens needle death by growing into the sapwood and plugging the water-conducting cells.

Some signs of  pine bark beetle attack include the following: popcorn-like pitch tubes on the trunk of loblolly pines, brown pitch-runs on slash and longleaf pines, small approximately 1 mm diameter holes in bark, pine needles changing from dark green to light green, to yellow, to red, and then falling to the ground and woodpeckers debarking stems of green pines.

Infestations often start on stressed and injured trees in older-aged dense stands, so cultural practices that promote healthy trees will reduce the frequency and severity of infestations. When beetles are present, avoid pruning and other activities which cause sap to flow - releasing compounds know as terpenes that might attract dispersing beetles.

The goal in minimizing southern pine bark beetle damage lies in  managing populations such that the number of attacking beetles is unlikely to exceed a tree's ability to resist colonization. In addition to avoiding tree injury and pruning and other activities that produce terpenes and attract beetles and the promotion of tree vigor, it is essential to quickly detect and treat infested trees.

There are a number of control options.  Sometimes a cluster of infested trees can be cut and sold to a wood processor where the bark is quickly removed and burned while the wood is processed for pulp or lumber.  Individual infested trees can be cut down and burned or buried or cut into manageable sections and sprayed with an approved insecticide to prevent the beetles from migrating to healthy trees.

If nearby trees are infested, homeowners may wish to have a pest control service apply insecticide to their un-infested trees. Two currently registered insecticides are 1% Dursban, which provides two to four months of protection and 0.5% lindane which provides three to six months of protection. The insecticide should be applied on dry bark, to the point of runoff.  Note: Due to recent EPA action,  Dursban will no longer be available to homeowners after January, 2001.

Insecticidal treatments have several draw backs to consider in addition to potential adverse environmental impacts. It is difficult and expensive to properly treat mature pines which may be 50 -60 or more feet tall.  It is almost impossible to know when beetles may attack a particular tree, especially in suburban settings, where a number of different properties under various levels of management may occur.  For this reason community-based solutions are often most effective.

This includes a community wide effort to quickly detect and treat southern pine beetle hot spots. Promoting tree vigor and reducing tree stress and injury through proper care and management and reducing forest susceptibility by increasing the spacing between pines and by planting resistant hardwoods.

Better understanding of  these damaging pest should help reduce homeowners reduce the loss of valuable trees in their landscape   Good luck and good gardening.

Gene McAvoy is the horticulture agent with the Hendry County Extension Service.  Direct your horticulture questions to PO Box 68, LaBelle, FL 33975,  e-mail - or phone 863-674-4092 or  863-983-1598.  You are also welcome to visit the Hendry County Extension Office at 225 Pratt Blvd., LaBelle.   Office hours are from 8:00 - 5:00.

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