Part 5

On warm sunny days in late October and early November, the adult sawflies emerge from their cocoons in the litter, mate, and the females lay eggs. The female is equipped with a saw-like ovipositor with which she cuts a slit at the edge of a needle and inserts a small, white, oval egg. Several eggs are usually laid at evenly spaced intervals in each needle, but in only one needle per fascicle. From 30 to 100 eggs are deposited in this manner by each female. The eggs hatch the following April and the young larvae feed gregariously on the old needles. Larval development is usually completed by the time the new needles come out, giving heavily defoliated trees a tufted appearance. Mature larvae crawl to the ground and spin cocoons in the litter or surface soil. They remain as prepupae until late September when pupation occurs.

Heavy defoliation for two or more years can weaken trees and make them more susceptible to other insects and diseases, particularly when associated with drought. In commercial stands the growth loss caused by several years of 50% defoliation by this insect can amount to ⅓ of the expected growth.

Several parasites, predators, and a virus attack the Virginia pine sawfly, but weather conditions seem to be primarily responsible for the drastic fluctuations in sawfly populations. Several chemicals have proven effective in preventing damage to ornamentals.

REDHEADED PINE SAWFLY, Neodiprion lecontei (Fitch)

The redheaded pine sawfly did not become an important pest until extensive planting of pine in pure plantations began in the 1920’s. Since then, outbreaks in young natural pine stands and plantations have been common in the South, the north-central states, and eastern states. Feeding is primarily restricted to the two- and three-needled pines under fifteen feet in height. Shortleaf, loblolly, longleaf, and slash are the species most commonly attacked in the southern states.

In the fall, sawfly larvae drop to the ground, spin cocoons in the duff or topsoil, and overwinter as prepupae in a small, brown cocoon. With the coming of spring, pupation occurs and adult emergence follows in about two weeks. Some prepupae may remain in a resting stage for more than one season before emerging. Each female lays about 120 eggs. She cuts a small slit in the edge of a needle and deposits a single egg inside each slit. Eggs laid by a single female are generally clustered on the needles of a single twig. Eggs hatch in three to five weeks, depending on temperature and locality. Larvae feed gregariously on the host for 25 to 30 days. When fully grown, larvae drop to the ground and spin their cocoons. In the South there are at least two generations per year with a maximum of five being recorded. Colonies of different ages may co-exist in the late fall or early winter.

Outbreaks occur periodically and tend to subside after a few years of heavy defoliation. Numerous parasitic and predatory insects play an important role in causing the decline of infestations, as do adverse weather conditions during the larval stage. When deemed necessary, chemical treatment is an effective control.

TEXAS LEAF-CUTTING ANT, Atta texana (Buckley)

Damage caused by the Texas leaf-cutting ant, or town ant, is confined in the United States to southeast Texas and west-central Louisiana. The ant causes damage to a variety of green plants throughout the year and causes serious damage to pine seedlings during the winter when other green plants are scarce. During this period, stands of young seedlings may be completely defoliated and the stems girdled. The ant carries bits of needles, buds, and bark back to its nest to serve as the medium on which it cultivates a fungus. The fungus is the ant’s only known food.

Ant colonies are characterized by numerous crescent-shaped mounds five to fourteen inches high, and by a series of well defined foraging trails cleared of vegetation. The mounds may be confined to a relatively small area or extend over an acre or more. Each mound serves as the entrance to a football-sized, hemispherical-shaped nest which the ants construct at depths up to 20 feet below the surface. The nests are interconnected by a series of narrow tunnels, and connected to lateral foraging tunnels which may surface a hundred yards or more from the colony. Leaf-cutting ants, like many other social insects, are segregated into castes. The queen dominates the colony and is responsible for its reproduction. Large worker ants, or soldiers, provide protection from intrusion by other insects, while the smaller workers collect the leaves and tend the fungus gardens.

Various chemicals such as fumigants, contact poisons, and baits have been used to control the leaf-cutting ants with varying success. No natural control has yet been found.

SOUTHERN PINE BEETLE, Dendroctonus frontalis (Zimm.)

Probably no other insect is of more concern to managers of southern pine forests than the southern pine beetle. Loblolly and shortleaf pine seem to be preferred hosts, but all of the southern pines may be attacked wherever they occur in North and Central America.

Adult beetles are about the size of a grain of rice, stout and reddish-brown in color. While they commonly attack lightning-struck or weakened trees, they can also quickly build up to high populations capable of successfully attacking healthy trees during periods favorable to their development. Adult beetles bore directly through the bark, mate, and the females begin to excavate S-shaped egg galleries in the inner bark. Eggs are deposited in niches on either side of these galleries and hatch into small legless grubs within four to nine days. The grubs mine for a short distance before boring into the outer bark where they pupate. There are from three to seven generations per year depending on locality and weather. Drought seems to be associated with major outbreaks of this insect.

Control includes rapid salvage and utilization of infested trees and piling and burning of infested material. Outbreaks usually subside with the advent of unfavorable weather and improved host vigor.

IPS ENGRAVER BEETLES, Ips spp.

With the possible exception of the southern pine beetle, no other insects cause as much mortality to southern pine forests as do the three species of Ips engravers. Usually they attack severely weakened trees, lightning-struck trees, or fresh slash left by logging operations. During drought periods they can successfully attack otherwise healthy pines.

Attacked trees are quickly girdled by the adults as they construct their egg galleries in the inner bark. Death is usually hastened by the introduction of blue-stain fungi which blocks the flow of sap. Small reddish pitch tubes are frequently the first sign of attack, but they are usually absent in trees suffering from drought. Peeling back the bark of an infested tree will reveal typical Y- or H-shaped egg galleries with short larval galleries extending perpendicular to them on either side. Ips beetles are easily recognized by their “scooped out” posteriors which are surrounded by varying numbers of tooth-like projections. It takes only 18-25 days to complete one generation, allowing populations of these beetles to increase very rapidly during favorable conditions.

At present the best control is the speedy removal and utilization of actively infested trees, making sure that the bark and slabs are destroyed.

BLACK TURPENTINE BEETLE, Dendroctonus terebrans (Oliv.)

The black turpentine beetle is found from New Hampshire south to Florida, and from West Virginia to east Texas. It is a particularly serious pest in the Gulf States where recent outbreaks have killed large acreages of timber. Attacks have been observed on all pines native to the Southeast, and also on red spruce.

This is the largest of the southern bark beetles, varying in length from ⅕ to ⅓ of an inch, or about the size of a raisin. They are reddish-brown to black in color. The beetle attacks fresh stumps and living trees by boring through the bark and constructing galleries on the face of the sapwood where eggs are laid. Fifty to 200 eggs are laid in a group. They hatch into white larvae which feed on the inner bark. The beetle may girdle trees when several broods occur at approximately the same height, killing the trees. From 70 to 90 percent of the trees attacked by the beetle die.

After the larvae complete their development, they pupate. Adult beetles emerge and infest more pine trees. The entire life cycle takes from 2½ to 4 months, depending on temperature. In the insect’s southern range there usually are two generations and part of a third each year. In its northern range, the third generation does not develop; consequently the beetle is not a serious pest there.

Weather is probably the most influential factor in regulating the numbers of this insect. During outbreaks the removal or chemical treatment of infested trees helps to keep losses to a minimum.

AMBROSIA BEETLE, Platypus flavicornis (F.)

Ambrosia beetles are represented in the South by several species of the genus Platypus of which only P. flavicornis (F.) is known to attack dead or dying southern pines. P. flavicornis (F.) will secondarily invade other conifers and on some occasions may be found in hardwood trees. It is so abundant in the South that few dying pines, stumps, or logs escape attack. The beetle is found from Texas east to Florida and north to New Jersey.

The adult is a reddish-brown elongate beetle approximately one-fourth inch in length. The male of the species has a pair of blunt tooth-like structures on the third abdominal segment. Several males are usually found in the presence of a single female. This species requires moist wood which is favorable to the growth of fungi upon which they feed. The adults bore into sapwood or heartwood of logs and lumber, making pin-sized holes which are stained by the ambrosia fungus. The female lays eggs in small clusters in the tunnel and the developing larvae excavate tiny cells extending from the tunnel parallel to the grain of wood. There may be several generations a year.

Ambrosia beetle damage to green sawlogs and lumber may result in considerable degrade and strength reduction. The best control is rapid utilization of dead or dying trees. Lumber should be seasoned as soon as possible to reduce or eliminate losses.