INSECTS IN WOOD PRODUCTS

THOMAS E. SNYDER.

Insects attack the forest tree in all stages of its life, from seed to maturity. The log that is cut from the tree also is vulnerable in all its stages to attack by other kinds of wood-boring insects while it is still in the woods, while it is green or seasoned lumber at the mill, or is being stored, or, indeed, after it has been put to use in a house, barn, or a manufactured item.

The insects that bore into lumber cause losses of many kinds and degrees. Sometimes much of the wood is riddled by holes. Sometimes it is entirely pulverized so as to be completely unusable. Sometimes only the quality of the wood is lowered by the holes so that the grade is reduced. Certain stain fungi, carried by bark beetles and borers, discolor the logs and lumber; they do not affect performance, but the wood becomes unsuitable for outside and decorative purposes. After the lumber, pole, or other wood product is in use, insect damage is even more serious, because then the loss includes the costs of production, seasoning, storage, and replacement.

TWO TYPES OF INSECTS are primarily responsible. One requires wet wood; the other dry wood. Sometimes the injury is one caused by the adult beetles which fly to the log or lumber and bore directly into the wood. At other times the damage is caused by the young hatching from eggs laid under the bark or in the wood.

Adult ambrosia beetles so-called because they require green or moist wood within which they raise fungi for food rapidly penetrate green logs and lumber. The males may assist the females in forming new colonies, and the fungus is raised for the young to eat. They have the beginning of a social life, but do not develop different forms or castes as do the true social insects, the termites, ants, and bees. The holes, not more than one-sixteenth of an inch in diameter, are made by the adult beetles. They riddle the wood, and near them the wood is stained black. Serious losses to tight cooperage or barrel stock and balsa wood for marine life rafts and a lowering in grade of valuable lumber for veneer to be used in houses, boats, or airplanes result from their boring and staining.

Larger holes more than one-fourth of an inch in diameter are caused by the young of large beetles. These young are called sawyers because their borings in green logs result in piles of sawdust, as if the wood had been sawed by man. Their gnawing can be heard, and their activity is so conspicuous that it is hard to convince a tree owner that it was not this insect that killed his pines. Actually, it was the small, grain-sized bark beetles, often associated with a stain fungus, that girdled the inner bark and shut off the food and moisture supply of the tree and caused its death, thus preparing it for the larger borers.

Some types of insects need dry wood for their food. Among them are many kinds, sizes, and shapes of powder-post beetles, which pulverize wood and have other odd habits. One kind specializes in boring into wine and whiskey barrels. Another drills into and around lead-sheathed cables, unmindful of the short circuits that result when moisture penetrates the insulation. Some years ago one kind, like a weevil, damaged the trusses in the roof of the White House. An odd lot, indeed.

An extremely destructive kind is the Lyctus powder-post beetles, small, winged beetles that lay their elongate eggs in the pores of the sapwood of certain large-pored hardwoods but do not attack the heartwood. They go after dry or seasoned sapwood of such hardwoods as hickory, ash, oak, and walnut lumber; manufactured products like tool handles, gun stocks, tent stakes, wooden artillery wheels, wagon spokes, oars, and other products stored for long periods; and, sometimes, furniture, woodwork, flooring, and timber in homes. The young reduce the wood fibers to a powder from which all strength is gone. The presence of these insects is usually betrayed by small piles of fine powder expelled from the burrows by the young. These beetles relish items like dry ax handles because they find the wood rich in starch and quite suitable for raising their families.

But the ones that give householders the most gray hairs and sleepless nights are termites, the most destructive of all. In the United States they are of two main types. The subterranean kind, which is the worse, requires much moisture and attacks wood indirectly from the moist soil. The dry-wood termites directly attack dry wood. They are injurious only in southern California and Florida and normally do not occur in the Northern States. Termites damage buildings of all types, various kinds of stored materials, poles, posts, derricks, mine props, and many another. By their boring, also, they riddle or corrode with their moist excrement many materials that they cannot eat. Often, however, termites can be easily and cheaply controlled.

PRECAUTIONARY AIFASURES in handling the green wood and lumber can eliminate much of the damage by the insects that prefer them. The measures are rapid moving, seasoning, sorting, and periodic inspection.

The logs should be handled quickly, with a minimum of delay between felling the log and stacking the lumber for drying. Drying the lumber, in the air or in a kiln, will stop the insects from boring. Any damage that has been done to the wood usually will not affect its strength. It is termed "sound wormy grade."

As for the beetles that prefer seasoned wood: Because only the sapwood is susceptible to them, sapwood and part sapwood should be sorted and piled separately from the heartwood. The stacks of sapwood then should be dated so that the oldest or longest seasoned wood can be used first. The drier the wood, the more appetizing it is to the powder-post beetles.

Further protection can be gained by periodic inspections of the stock so that infested material can be removed for burning or treatment. This is a live-worm defect, and the insects will continue to bore until the product is destroyed or they are controlled.

SOME WOODS have chemicals in their cells that protect them from insects, and heartwood is more resistant than sapwood. So, because insects are ready to pounce even after the wood is safely through storage and has been put to use, it is sensible to select carefully the species and grades that fit exactly the purpose at hand.

Whenever possible, one should use the heartwood of the more naturally durable or insect-resistant and rot-resistant woods instead of the perishable woods. Resistant woods like foundation-grade redwood, the southern tidewater red cypress, and the mahogany contain alcohols, alkaloids, gums, resins, or bitter essences that makes them distasteful to boring insects. Some kinds of wood that are not subject to attack by certain wood borers but are adapted for the same use should be substituted for susceptible kinds. For example, yellow pine or Douglas-fir can be used instead of oak for storage pallets to prevent losses by Lyctus powder-post beetles.

The relative termite resistance of certain native and exotic particularly tropical American untreated timbers has been determined by long-time service tests conducted in the United States and in the Canal Zone.

Among those commercially available in the United States are close-grained heartwood foundation-grade California redwood, southern tidewater red cypress, and very pitchy southern longleaf pine. The information from the long-time service tests also permits the recommendation of naturally resistant woods for use in building or bridge construction where chemically impregnated timber is not locally available, especially in the various tropical regions of the world. Greenheart, manbarklak, and guayacan of the Americas, teak and sal of India, molave and ipil of the Philippines, and cypress-pine, brush-box, and turpentine wood of New South Wales are a few of the woods found to be termite-resistant.