Home Is Where Your Trees Are

Insects

Insects occur among trees as naturally as leaves and, in Nature's code, just as rightfully. By no means all of them are harmful. Some insects are positively benign and should be recognized as such before you take spray gun in hand. All the bees help the plant world as pollen carriers. All the larger wasps and hornets are strictly insectivorous and only one - a giant from Europe which occasionally strips twigs for nesting material - has any bad habits other than stinging savagely in self-defense. The spiders prey on all manner of flies, bugs, and grubs without themselves ever harming plant life. (The tiny "red spider" that infests cedars, boxwood, and other plants is really a mite.) The daddy longlegs or harvestrnan is, despite his alarming physique, the meekest of spiders. Ladybugs, shiny red or brown with dainty spots, are almost entirely non-vegetarian. They consume amazing quantities of aphids and scales. When our American orange-growers found this out they sent to Australia for more and hungrier ladybugs.

A most ferocious-looking insect in size and posture is the mantis. His first name is spelt "praying," for the way he holds up his forelegs, or "preying," for his predations of other insects. The Japanese keep mantes on long silken leashes near their beds to devour mosquitoes. There is in the United States a mantis industry, run by people who collect the gall-like egg-masses off shrubs and weeds and sell them to horticulturists for hatching where needed. The big, black sexton beetle or undertaker, with huge frontal nippers, is another denizen of everyone's grounds that is horrendous to behold - but its diet is strictly carrion. The insects injurious to trees fall into four main categories: Gnawers (borers, beetles, weevils), Chewers (worms, caterpillars, beetles), Suckers (aphids, scales), and Stingers (mites, minute wasps).

Gnawers. The larvae of many species which later become beetles or moths start life as vermiform borers, like the three-inch pink and brown grub of the leopard moth, largest of the lot. Unless the parents of such invaders have the habit of feeding on foliage (which few do) before laying their eggs (which are difficult to destroy), no spray can check them unless it is shot directly into their bores from a DDT or carbon disulfide pressure can, and the holes plugged. Often their entrances are invisible, being started as tiny perforations where the eggs hatch in bark crevices. Fortunately, most destructive borers advertise their presence by putting out frass (sawdust) or, in the cases of peach and pine borers, by masses of gum which ooze out behind them. When thus detected, boring grubs can be crushed in their tunnels by a wire probe, or fetched out with a crochet needle or straightened fishhook. The gnawing beetles trace labyrinthine patterns through inner bark and cambium, but most of them emerge to breed and are then vulnerable to stomach or contact poisons. Weevils are specialized beetles which, both as larvae and adults, feed on tissues usually shallow and tender enough for penetrant poisons to reach. Various ants gnaw wood, but only after it has begun to decay. Winged termites and long, black carpenter ants are the worst offenders because they eat on past the dead wood into live and are so voracious they can weaken trees, and even houses, structurally. Ants swarming up and down the outside of a tree are not cause for alarm. They are doubtless only tending their flocks of aphid on the leaves aloft, which you can dispatch with one spraying. Certain ants "milk" aphids just as we do cows, and even move them about to fresh pastures. The ant-aphid symbiosis (life partnership) is most damaging to the roots of corn and strawberries, not to trees.

Chewers are the most obvious of plant pests since they feed on leaves, where their inroads are quickly visible. Most such creatures bite through the whole leaf and hence can be poisoned by chemicals laid down, with some sticker like soap or a household detergent, on either surface. But some skeletonize the leaf by chewing only from the underside, where the spray sticks least well. And some go an insidious step further and chew between the leaf surfaces, eating the inner tissues. These last are called "miners" and their work eviscerates leaves to near transparency. It takes a potent dual-purpose poison - stomach and contact - to get through to them.

Suckers are insects whose feeding organs are probes which they thrust into tree tissues to extract the juices. No poisons spread in wait for them will enter their systems. Their bodies must be hit with chemicals that kill on contact. Aphids or plant life are vulnerable to such treatment, being soft-bodied, but many of the scale insects have hard shells as adults and can be shriveled by contact poisons only in their unarmored crawler stage. Knowing their life cycles is necessary to control the scales called terrapin, oyster shell, lecanium, and San Jose. In general, the scales' vulnerable moment comes in early spring, which adds importance to so-called "dormant" spraying, the year's first.

Stingers are flies, mites, mini-wasps, and some aphids which puncture leaves and twigs with their ovipositors, to insert eggs which form galls as they develop. Witches'-broom has been described. Some other galls caused by stingers are of various shapes and sizes on oaks, bladder gall on maples, flower galls on ash, cockscomb gall on elms, club gall on dogwood, Sitka gall on blue spruce, cone gall on other spruces.