BARK BEETLES

Background showing appearance of tree under attack. A, Entrance holes in bark (natural size). B, Inside of bark showing frass-filled tunnels and life stages; a, egg in niche; b, young larva; c, mature larva; d, pupa; e, adult in nuptial chamber; f is the entrance hole. (All of B is considerably magnified.)

BARK BEETLES

Ips engraver and turpentine beetles are occasional pests of pines and other coniferous trees grown in the vicinity of dwellings, summer-home sites, and in recreational areas in various parts of the country. These bark beetles are usually found only in trees weakened by drought, mechanical injury, severed roots, sunscald, or like condition. sunscald is caused by excessive exposure to the sun following sudden removal of many of the surrounding trees. The beetles seldom attack and kill healthy trees, but may do so when they are present in large numbers. If only a few turpentine beetles are present in a tree, it may survive through its ability to secrete sufficient resin to drown the adult beetles or their young in their tunnels. Such wounds heal over later. If engraver or turpentine beetles attack and make holes in the bark entirely around the trunk of a tree, the tree is killed.

Turpentine beetles emerge from infested trees in the spring, fly to green, uninfested ones and bore holes in the bark on the lower part of the trunk. The female beetles deposit their eggs in groups in the inner bark. The eggs hatch in a few days and the larvae feed side by side on the soft inner bark, leaving a cavity behind them. In about 8 weeks the larvae are full-grown, and a month later the adult beetles emerge. Soon after the beetles bore into the bark, large globules of resin flow from the holes and harden on the bark surface.

In the Bay region of California, Monterey pines are frequently infested by the red turpentine beetle. It also occurs over much of the rest of the country. The most prevalent species in the South is known as the black turpentine beetle. The number of generations varies from two or more a year, to one every 2 years, depending upon the locality and climate.

The adult Ips engraver beetles are smaller than turpentine beetles and attack the entire trunks of trees. Sometimes they attack the upper parts of trees that are infested lower down with turpentine beetles. Tunnels made for egg-laying by Ips are elongate and generally in the direction of the grain of the wood. When the eggs hatch, the larvae make galleries at right angles to the tunnels. The tunnels and galleries give the inner bark and outer surface of the wood an engraved appearance.

Control: Small infestations of turpentine beetles only three or four attacks in a large-size tree can be disregarded. But if five or more attacks occur per square foot of bark, the tree may be killed. To save it, remove the resinous masses and flood each tunnel with a 2 percent chlordane emulsion or with ethylene dichloride. Or one can inject into each tunnel about a teaspoonful of carbon disulfide, which is highly inflammable and dangerous to inhale. Household insect sprays in which 2 tablespoonfuls of naphthalene flakes per half pint of spray are dissolved are also effective.

Danger from bark beetles is great in droughty periods. Weakened trees should be watched closely for signs of beetle activity. A spray containing 0.5 percent of the gamma isomer of benzene hexachloride prepared from either lindane or benzene hexachloride emulsion or wettable powder, applied to the trunk, may help to prevent further attack for 2 to 3 months. The bark should be sprayed until it begins to drip.

Trees which are heavily attacked by engraver beetles and from which comes brownish boring dust should be felled and the bark removed to destroy the brood before it emerges as adult beetles. This should be done while the foliage is green or pale yellow. Usually the beetles have already left trees whose foliage is brown or red.