THREE IMPORTANT BEETLES
Pine Bark Beetles account for more damage to southern timber than any other types of insect. The following important information concerns all pine bark beetles. The individual insects will be discussed in detail following this section.
The BLACK TURPENTINE BEETLE (BTB) the IPS ENGRAVER BEETLES (IEB), and the SOUTHERN PINE BEETLE (SPB), although the names differ, have many similarities. Specific information on each species follows, but an accurate name for all three is simply PINE BARK BEETLES. This reflects their habit of tunneling and feeding within the soft inner bark of pine trees. In Florida, the most important pine bark beetles are the IEB, followed by the BTB; significant losses to the SPB occur infrequently in Florida. A substantial portion of the 3 billion cubic feet lost in the South is due to pine bark beetles.
Biology and Habits
Generally, adult bark beetles are first attracted to weakened or stressed trees, however, during outbreaks seemingly healthy trees are susceptible to beetle infestation.
Death of a pine tree results from the pine bark beetles boring through the outer bark and into the inner bark and outermost sapwood. It is not uncommon for two or more pine bark beetle types or species to infest a tree simultaneously. The female beetles construct long EGG GALLERIES, depositing eggs along the sides of the tunnels. After emerging from the eggs, the LARVAE tunnel in the same tissues as the adult beetles. The tunneling of the larvae and adults severs the tree's nutrient transport systems. Equally damaging to the tree is the plugging of the water transport system by bluestain fungi, which are introduced into the tree by the adult bark beetles. When they have finished feeding the larvae PUPATE within the bark in small cells or chambers. Following pupation, the new adult bark beetles emerge from the tree to begin the cycle again in another susceptible tree.
There can be up to 10 generations per year for the smaller IEB species, but only 2 ½ -3 generations per year of the much larger BTB. Variation will occur from year to year due to changes in temperature, moisture, and nutrition.
Management of Pine Bark Beetles
In many instances pine bark beetles are designated as secondary pests, much like a cleanup crew for weak and suppressed trees. Typical materials utilized by pine bark beetles are fresh logs, logging debris, windthrown trees, and trees damaged or killed by natural or man-caused means. Living pine trees in a weakened condition are especially susceptible to pine bark beetle infestation. This condition may have arisen from a temporary or permanent weakening caused by drought, age, competition disease, annosom root rot, fire, hail, lightning, logging injury, or other insects.
IEB and BTB attacks on standing trees are usually of short duration due to a limited supply of acceptable host material (stressed trees) occurring in one area. Rarely are healthy trees killed in large numbers.
Vigorously growing trees with a high oleoresin exudation pressure and a copious resin supply are more resistant to bark beetle attack. A mechanical resistance results from the high resin pressure because attacking beetles are simply pitched out or forced out from the inner bark. Chemical resistance is imparted by the toxic vapors of fresh resin. An important component of the pitch-out mechanism is a ready access to water. Adequate soil moisture is important in maintaining high resin pressure in pine trees.
Forest management practices or homeowner yard-care which emphasize the reduction or minimization of tree stress while encouraging vigorous growth reduce the susceptibility of the stand or individual tree to bark beetle infestation. NOTE: There is the danger of pine trees growing too well. (See pitch canker).
Two important and related factors in the resistance of pine to bark beetle attack are (1) a healthy root system with sufficient moisture and air supplies, and (2) sufficient resin pressure in the stem and branches to resist the first beetles.
Pine bark beetle attacks in urban areas are associated most frequently with root injury, especially through the alteration of soil and water levels. Mechanical root injury is evident at all building sites and results from construction of curbs, driveways, sidewalks, patios, foundations, drainages, and utility trenches. The following are some suggestions for maintaining a tree's resin pressure when such damages occur:
- Maintain soil moisture with irrigation
- Prune back or thin tree crowns to restore root to shoot balance. Prune preferably during the coldest months of the year to lessen beetle activity.
- Conduct early removal of high-risk trees where more than half of a root system is or will be destroyed by construction.
Soil fill is often found to be fatal to pines, causing a lack of oxygen for respiring roots. As little as 5-10 cm of heavy clays, 10-15 cm of clay loams, or 15-20 cm of sandy loams spread over root systems is generally associated with pine bark beetle infestations. The use of gravel, bricks, tiles, or commercially available aeration systems should be considered if soil fill is planned for landscaping.
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