The home gardener need not be a graduate entomologist to acquire knowledge of the appearance, shape, feeding habits, and plant preferences of a considerable number of insects and of the kinds of plant damage that they inflict.
It is also wise to remember that the insect may inflict damage not only by its feeding but often is additionally a carrier of a fungus disease, a blight, virus, or specific spores, bearing the disease from one plant to another as it feeds along the way. In this case it is like a rodent or common house fly as known factors in transporting diseases of humans.
All insects are not necessarily harmful. Some are absolutely necessary for the pollination of flowers to set fruit or seed. Such insects are bees, some wasps, and forms of moths. In general they may readily be recognized and set apart from those that inflict damage. Another group of helpful insects are those which cat or lay their eggs on other insects, thus becoming natural enemies of and a check to the harmful members of the insect world. Among these helpful ones are many species of spiders, wasps, and the praying mantis.
Sucking and chewing insects
Insect enemies may be divided into two classes-those with beaklike mouth parts that suck vital plant juices, and those which chew parts of plant tissues, eating and swallowing portions of leaves and flowers, tunneling into stems, and feeding on roots.
Contact insecticides and stomach poisons
Sucking insects, such as scale insects, aphids, plant bugs, mealybugs and leafhoppers, extracting their food from within the plant, are not killed by insecticides known as stomach poisons and must be destroyed by contact insecticides which, on touching them, burn, poison through their breathing parts, suffocate them, or affect their nervous systems. Chewing insects, such as caterpillars and leaf eating beetles, which eat and swallow plant parts, are killed by stomach poisons, although certain species also are killed by contact insecticides.
The various poisons recommended to combat garden pests should be handled and used with great care. Read directions on containers and keep in mind the fact that the materials may be potential hazards to other forms of life.
Again, some insects attack only specific crops and related plants, while others feed generally on all types of vegetation. Among the foremost of the general feeders are the following:
Cutworms-Caterpillars. Seldom seen because they hide all day in topsoil or under clods of earth, emerge at night and chew on small plants near the ground line. They are highly destructive to plants growing in seedbeds or just transplanted. One cutworm is capable of killing several plants in a single night. Cutworms are smooth, plump, gray or brown worms, 1 to 2 inches long at maturity. One of the best counter measures is a poisoned bait mixed at the following ratio and scattered about the infested ground: a quart of dry wheat bran mixed with 2 teaspoonsful of Paris green and moistened with a pint of water. This will serve an area 50 feet square. Scatter it thinly late in the afternoon so it will be moist when the pests come out for their nightly feast. This method may be augmented effectively simply by going into the garden with a flashlight and picking off the cutworms by hand. This would not be feasible in a large commercial garden, but in the average home plot it is highly practical, since those which are missed by hand still may find the bait.
Armyworms-Caterpillar relatives of cutworms, so-called because they travel in armies when they forage. They can strip the foliage of all sorts of plants rapidly and destructively. Like their kin they hide by day, feed by night. They are about 1 1/2 inches long, dark green with white stripes.
Yellow Wooly Bear. The widely present, hairy caterpillar. It carves a plant to raggedness, eating buds, flowers, leaves, and stems. A preventive measure is to destroy the cocoons in which they winter over, whenever you can find them. These cocoons, constructed of the insects woolly coat and silk, may be found, as many as 20 or 30 of them together, under such shelters as dead leaves and earth clods.
Cabbage Looper. Although this caterpillar prefers cabbage, it attacks a wide range of ornamental plants, gnawing holes in leaves and buds. It is pale green when hatched and grows to about 1/2 inch in length, with a white stripe along each side of its green body. It has an odd looping motion in its crawl. Keep the number of pests down by cleaning and burning all crop remnants and weeds around the garden.
Hornworms. Large caterpillars that grow to a length of 3 or 4 inches, with a short fleshy hornlile projection atop the last body segment. Both the tobacco hornworm and tomato hornworm are pale green with whitish stripes on each side but the latter bears a V-shaped mark on each segment. Another bornworm, the white-lined sphinx, varies from green to black in color with small broken lines on the back, and the bead and horn of orange or yellow. Hornworms feed usually on foliage. Do not kill bornworms bearing white objects on their backs, these are the cocoons of parasites that kill bornworms.
Greenhouse Leaf Tier. One of a group of caterpillars that fold, roll, and tic leaves and terminal growths together, feeding on the in sides of these leaves and also eating buds and flowers. The tier is about 3/4 inch long, of yellowish green. If only a few plants are involved, break off and destroy the affected parts.
Poisonous Caterpillars. The treatment for this group is the same in all cases. If there are only a few caterpillars, pick them off by hand but be sure to wear gloves to protect your hands against their stinging spines. As a preventive measure keep the ground around the plants clear of refuse in the fall and, if you must protect the plants, use a clean mulch. Among the poisonous caterpillars are the stinging rose caterpillar, the saddleback caterpillars, the hag moth, the crinkled flannel moth, and the puss caterpillar. The stinging rose caterpillar is sluglike. Usually achieving full growth in September, it is about 3/4 inch long, vividly marked with red, white, and violet stripes and has seven pairs of spine-bearing processes. It feeds from the underside of rose leaves. The saddle-back caterpillar, about an inch long at full growth, is brown at each end, green at the middle, with a small purple saddle in the center. Among the plants it attacks are canna, holly, rose, lily, and dahlia. The hag moth is about 3/4 inch long and brown with curved, twisted plume-like processes extending from each side. It feeds on foliage of shrubs and trees. The crinkled flannel moth is about an inch long, flashy, and covered with silky brown hairs forming a crest along the back. It is a northern insect and usually feeds on apple, birch, cherry, oak, locust, raspberry, bayberry, and sweetfern. The puss caterpillar, about an inch long, is wide and flat, covered with long reddish yellow hairs and similar to the flannel moth in appearance. It is a general feeder.
Cucumber Beetles. The spotted cucumber beetle attacks a wide variety of garden flowers, feeding on leaves and buds, but chiefly chewing holes into flower petals. After many of its favorite food flowers have matured, it turns to the late season growers, such as dahlias and asters, and damages them severely. It is a yellowish green bug about 1/2 inch long with black spots on its wing covers. The striped cucumber beetle, about the same size, is light yellow with stripes on its wing covers. In the flower garden it feeds largely on roses and asters, eating holes in the petals and leaves. Destroy the beetles at the first sign of plant injury for they probably will be recurrent. In late summer protect prize plants with a cheesecloth covering.
Blister Beetles. These chewing insects, feeding on leaves and flowers, travel in hordes and destroy all plants in their path. They are soft-bodied, about 3/4 inch long, and are found in various colors entirely black, brown or yellow with black spots or stripes, gray with black spots, or dark gray. The black blister beetle is the most general form. Control is difficult because they are too active to be covered readily with contact insecticides. You may pick off these insects if there are only a few on your plants, but be sure to wear gloves because contact with them may blister tender skin. The best practice is to knock them into a bottle of water and kerosene. Protect prize plants with cheesecloth covering.
Flea Beetles. These insects create a hole-like appearance in leaves, which they chew from the underside. They are tiny, scarcely a quarter-inch long, steely dark in color. They prey especially on young seedlings. Cover seedlings and prize plants with cheesecloth as a protection.
Aphids. Also known as plant lice, they suck juices. The plants, although they usually are not killed by such attacks, suffer injury to their vigorous growth, leaves curling, buds hardening, flowers developing in distorted shapes. They excrete a sticky, sweet liquid known as honeydew, which draws large numbers of ants and other insects for feeding and gives a lacquered finish to the objects on which it is deposited. Aphids usually are found on new growth, at the base of buds, on the nether side of a leaf. They are minute, scarcely 1/8 inch long, grayish white or greenish black in color, with bodies shaped like a top and 3 pairs of long legs. Attack the insects as soon as they appear.
Leafhoppers. These sucking insects are pale green or brown, about 1/8 inch long and slender. In addition to sucking vital juices they cause leaves to curl or white; the rose leafhopper kills tender tips; the potato leafhopper inflicts hopperburn, or the drying of leaf edges, on dahlias and other plants; and the aster leafhopper transmits the aster yellows virus from diseased plants. As a preventive measure, burn out all weed patches early in the spring.
Grasshoppers and Crickets. These familiar insects eat flowers, leaves, and tender growth throughout the season. As a prevention, spade the earth deeply, burying many of the eggs and thus keeping them from hatching the next spring.
Ants. No completely effective measure is known to control all species in all conditions; consequently several suggestions are offered. When you can find the nests in the soil of yard or garden, fumigate the anthills powder.
Red Spiders or Spider Mites. These tiny relatives of the spider, hardly visible to the naked eye, suck juices from leaves and other tender tissue, causing foliage to turn pale or brown. They swarm on the undersides of leaves and some species spin a webbing. The common red spider winters over in litter and in buds and crowns of various plants. A good preventive measure is to clean up the garden, burning litter and infested plants.
White Grubs. White grubs are the immature forms of the socalled June bug. They live in the soil and sometimes feed on roots or other underground plant parts. They frequently kill grass by their subsurface root feeding.
Termites. When the soil is heavily infested with termites and the dead wood or dead vegetable matter on which they usually feed becomes scarce, they attack living plants, especially woody sorts, working up into the roots and burrowing into the stems. Wounds near the ground surface and dead or dying roots also are points of entry. They are soft-bodied white insects about 1/4 inch long, sometimes called white ants but not related to ants. A preventive measure is the removal of dead plants, wood, and vegetable matter from the soil in the garden and around infested plants, spade deeply to disturb termite tunnels, and use commercial fertilizer when they are in the soil; manure and compost provide a. hearty food supply for them.
Wirevorms. The larvae are smooth, wiry and shiny, about an inch long and ranging in color from light yellow to brown. Wireworms feed on bulbous or tuberous roots and fleshy underground plant parts. In small plantings they may be spaded up and killed. Well-fertilized plants, growing with increased vigor, withstand wireworm injury.
Snails and Slugs. These night feeders, gnawing large holes in leaves, are particularly harmful in shady, damp places. Slugs are slimy insects of black, brown, or gray, some 6 inches long, that look like snails without shells. Dust infested areas with airslacked lime, and clear away boards, rocks, and other litter under which these creatures hide.
Earthworms. There are widely varying points of view as to the value of earthworms in soil. One school definitely extols their service, contending that they aid in aerating the soil by their burrowing, thus permitting oxygen to enter and poisonous gases to escape. This school also maintains that the worm breaks down coarse vegetable matter into digestible or soluble organic substances that become available to the plants, and finally that the excrement and regurgitation of the soil from the burrowing worm is rich in nitrogenous substance which is of vital assistance to plants. These contentions are practically all correct. Tiny mounds of dirt are frequently seen on the soil, indicating worm activity; many persons make it a business to gather this worm soil and sell it as the rich nitrogenous soil it is. Worms are even farmed and merchandised for the purpose of implanting them in the soil as "workers for fertility." Department of Agriculture research workers, however, have experimented to determine the value of the worm in soil and their general conclusion is that it is somewhat exaggerated, that soils are fertile whether worms are present or absent, that the natural soil fauna are the real workers, and that worms consume more of the fertility than they contribute. Worms are at the very least highly selective as to the soil in which to live and thrive. It must be loose, aerated, and not waterlogged or they will be drowned. Their presence in the soil is a good indicator of its qualities, but many persons claim that they do serious harm since they are ravenous consumers of the valuable humus in the soil. Often a potted flower with no visible sign of sickness, no insect evidence, no discoloration, no spots, will fade. Despite careful attention it will make no progress. Removal of the plant from the pot will reveal a worm or two that escaped into the screened soil used originally to pot the plant. They were so small at that time that they went through the mesh of the screen. In the pot they grew fat on the natural fertility of the soil at the expense of the plant. Remove the worms, repot in new soil, and the plant will attain health and vigor.
Sowbugs (Pillbugs). These pests are dark gray ovals about 1/2 inch long. Some forms, at any disturbance, roll themselves into round, flat discs in the shape of pills. They feed on tender plant parts and roots, and live in dark shelters, As beneath decayed boards or in decayed manure or similar spots where decomposition is in process.
Millipedes. These so-called "thousand legged worms" are hard shelled, brown or gray, and live under boards, rocks, or other debris. They hide during the day and come out to bore into bulbs, roots, tubers, and fleshy plant parts and sometimes even eat planted seeds. They live mainly in damp soil rich in decaying organic material.