The Southern Pine Beetle in Florida

by

John L. Foltz and James R. Meeker

Contents


Introduction

Aerial view of large infestation

The Southern Pine Beetle (SPB), Dendroctonus frontalis, is the most aggressive and destructive of the 5 bark beetles species commonly infesting pines in the southern United States. In recent years outbreaks in northern Florida have increased in frequency and severity owing to the increased acreage, density and maturity of loblolly pine, the beetle's most important host. This document provides a brief overview of SPB biology, behavior, dynamics, and control. It will help citizens across the state to identify and monitor beetle populations in dying pines and, when appropriate, initiate community-wide suppression activities. As demonstrated in the Gainesville area in 1994-1995, quick detection and prompt treatment of all infested trees will substantially reduce the duration and severity of SPB outbreaks. If you suspect SPB activity, contact your local office of the Florida Division of Forestry or the University of Florida Cooperative Extension Service.


Biology and Behavior

SPB adultSPB galleries

The adult SPB is a reddish-brown to black cylindrical beetle about 3 mm (1/8 inch) long. Females initiate the attacks on trees and emit a pheromone that attracts males and additional females. Within a few days thousands of beetles may colonize the tree and overwhelm its defenses. Excess beetles often land on and colonize nearby trees. Females tunnel through the inner bark, periodically constructing a niche and laying an egg. Males follow females and fill the gallery behind them with boring dust. After about a week of egg laying, parent beetles emerge to infest additional trees. Larvae feed on inner bark for about 2 weeks, then pupate in the outer bark. New adults begin emerging just 4 weeks after initial attack, about the same time the pine needles are turning from yellow-green to red. These beetles may several miles before attacking a new tree.
 


Detection and Identification

Infested pinesSPB pitch tubes

SPB infestations usually occur in spots that gradually or rapidly enlarge with time. Red-crowned trees and surrounding green-needled pines should be examined for signs of infestation. Popcorn-like pitch tubes, running pitch, boring dust, and numerous holes through the bark are signs of bark beetle infestation. A southern pine beetle infestation is distinguished from those of other beetles by the winding and overlapping galleries constructed under the bark by females as they lay eggs. Ips beetles, in contrast, construct galleries that appear I-, Y-, or H-shaped because 2 to 4 egg galleries extend up and down from the "nuptial chamber" constructed by male beetles. Black turpentine beetles make short, mostly vertical galleries before laying a large clutch of eggs. All five species often occur on the same infested tree, so examine the trunk at several heights to avoid overlooking an SPB infestation.


Natural Enemies

Redbellied clerid

SPB-infested trees may harbor over 150 species of insects vying to utilize the resources of the rapidly changing habitat. Some compete with the SPB for utilization of the fresh phloem tissue, some feed on the less nutritious xylem, some feed on microorganisms introduced into this environment, and some feed upon the waste products and cadavers of the community. Added to these are a number of parasites and predators, many of which feed on any insect of suitable size. Although all these competitors, parasites, and predators certainly contribute to SPB mortality, they are ineffective at rapidly suppressing SPB outbreaks.


Identifying Outbreak Conditions

The SPB, like most bark beetles, may be present for many years as an innocuous scavenger of dead and dying pine trees. Occasionally, however, conditions are appropriate so that populations explode to levels where thousands of beetles will infest and kill healthy trees. Criteria for assessing population status include the distance between beetle spots (clusters of beetle-infested trees), spot size, spot growth, and the abundance of the SPB relative to other species of bark beetles. No suppression is required when small, inactive spots are separated by great distances and the SPB accounts for only a small percentage of the bark beetles present. Signs of outbreak conditions include an increasing number of spots, more infested trees per spot, spots continuing to enlarge beyond the initial cluster of infested trees, and the SPB being the dominant species infesting the main stem. During outbreaks, quick detection and rapid treatment of small spots will greatly reduce tree mortality and SPB-caused disruption of management plans.


Control

Removing infested treesSpraying infested trunk

Because of the dispersal and aggregation abilities of this insect, it is important that all infested trees over a large area be treated during outbreaks. If possible, remove newly infested trees and destroy or treat the infested bark before beetles mature and emerge to disperse and attack surrounding trees. Once beetles have emerged from a tree, removal is unnecessary except to protect life and property from falling branches and stems. The preferred control in most circumstances is to send infested trees to pulp and sawmills where the bark is removed and burned. Where such mechanical control is not feasible, then trees should be felled and the SPB-infested bark sprayed with an approved insecticide (described below). Bucking the trunk into short sections that can be rolled and adding a dye to the insecticide solution assist in providing thorough coverage to kill emerging beetles.
 


Prevention

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. During outbreaks, avoid pruning and other activities which produce terpenes that attract dispersing beetles. If nearby trees are infested, homeowners may wish to have a pest control service apply insecticide to their uninfested trees. Currently Onyx™, a bark-adhering formulation of bifenthrin, is the only insecticide demonstrated to be as effective as the formerly used lindane and chlorpyrifos. The insecticide should be applied on dry bark, to the point of runoff, from at least the base of the crown down to the ground line. If Ips beetles are abundant and aggressive, then the upper stem and larger branches should also be treated. When carefully and properly applied, insecticides dry in a few hours and pose little danger to birds, squirrels, and humans.


Selected References


Additional Online Information


Authors and Credits

Prepared by Credits -- The images above were extracted from "Forest Insects and Their Damage," a two-volume set of Kodak Photo CDs produced by the Southern Forest Insect Work Conference. For further information check out the SFIWC web site.


Send comments and suggestions to John Foltz.
Prepared 24 Nov 1997. Last modified 17 May 2004.
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