Subterranean insects are those insects that attack plants below the surface of the soil. Although the gall is entirely plant tissue, the insect controls and directs the form and shape it takes as it grows. The insect then finds shelter and abundant food inside this plant growth. Gall insects sting plants and cause them to produce a structure of deformed tissue. Control measures for internal feeding insects are most effective if aimed at adults or the immature stages prior to their entrance into the plant.Ī number of internal feeders are small enough to find comfortable quarters and an abundance of food between the upper and lower epidermis of a leaf. In nearly all of them, the insect lives inside the plant during only a part of its life and emerging sooner or later as an adult. Each group, except the third, contains some of the foremost insect pests of the world. The chief groups of internal feeders are indicated by their common group names: borers worms or weevils in fruits, nuts or seeds leaf miners and gall insects. A large hole in a fruit, seed, nut, twig or trunk generally indicates where the insect has come out, and not the point where it entered. In either case, the hole by which they enter is almost always minute and often invisible. They gain entrance to plants either in the egg stage when the female thrust into the tissues with sharp ovipositors and deposit the eggs there, or by eating their way in after they hatch from the eggs. Many insects feed within plant tissue during a part or all of their destructive stages. Aphids, scale insects, squash bugs, leafhoppers and plant bugs are examples of piercing-sucking insects. The hole made in this way is so small that it cannot be seen with the unaided eye, but the withdrawal of the sap results in either minute white, brown or red spotting on leaves, fruits and/or twigs leaf curling deformed fruit or a general wilting, browning and dying of the entire plant. This results in a very different but nonetheless severe injury. These insects have a slender and sharp pointed part of the mouthpart which is thrust into the plant and through which sap is sucked. In this case, only internal and liquid portions of the plant are swallowed, while the insect feeds externally on the plant.
Injury by Piercing-Sucking InsectsĪnother important method which insects use to feed on plants is piercing the epidermis (skin) and sucking sap from cells. Cabbageworms, armyworms, grasshoppers, the Colorado potato beetle and the fall webworm are common examples of insects that cause chewing injury.
Perhaps the best way to gain an idea of the prevalence of this type of insect damage is to try to find leaves of plants with no sign of insect chewing injury.
It is easy to see examples of this injury. One method is by chewing off external plant parts. Insects take their food in a variety of ways. Insects injure plants by chewing leaves, stems and roots, sucking juices, egg laying or transmitting diseases. Image courtesy of North Dakota State University Insect Injury Figure VI-2 depicts the developmental stages of insects with incomplete life cycles.įigure VI-2. Insects with an incomplete life cycle can be controlled at any stage, but are easier to control in the nymphal stage just after they hatch from the eggs.
Nymphs either do not have wings or have wings that cannot be used for flight. Adults have fully developed wings and can fly great distances. They stay in the nymphal stage for several weeks, while growing and molting into larger insects until they reach adulthood. Regardless, insects with an incomplete life cycle are unique in that they hatch from eggs into tiny nymphs that resemble the adult stage. Some, such as the grasshopper, chew on leaves and stems. Many insects in this category have piercing, sucking mouthparts and suck juice from plants. Insects with incomplete life cycles include grasshoppers and true bugs (stink bug and squash bugs). Insects with a complete life cycle almost always have a chewing mouthpart. The adult stage, moths and butterflies, feed on nectar or may not feed at all. Moths and butterflies also have a complete life cycle similar to beetles except that the damaging stage is the larvae or worm stage which usually feeds on the stems, leaves or fruits.
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