CHEWING INSECTS

General Description

The two major groups of insects that cause damage to plants via their chewing mouthparts include the caterpillars and beetles. Other chewing insects that are sometimes damaging to plants include grasshoppers, katydids and their relatives.

Caterpillars are the immature or larval stage of moths and butterflies. Their bodies are usually cylindrical in shape and either slender or robust. However, some are oval and others are flattened. They may be striped, marked with various color patterns or solid in color. They also may be naked, extremely hairy, or possess tufts of hair. Most mature larvae are 3/4 - 1 1/2 inches long, but some are much smaller and some may be more than 4 inches long. Caterpillars have three pairs of jointed, true legs on the thorax and usually four pairs of soft, fleshy projections (prolegs) on the abdomen, with a fifth pair at the extreme rear of the abdomen. The prolegs have tiny hooked spines (crochets) to aid in holding on to leaves and other plant parts.

Many species of beetles frequently cause injury to woody ornamentals. Both the adult stage and the larval stages are injurious and both have chewing mouthparts. Some beetles, such as lady beetles, are extremely beneficial in both the larval and adult form. Adult beetles vary in size tremendously. Some are less than 1/8 inch long while others are more than 2 inches in length. They may be any color or combination of colors. However, the most common colors are black or brown. The larvae of beetles vary greatly in feeding habits, body shape, size and color. Some species feed on leaves while other species feed on roots. Some are elongate with relatively long legs and may be brightly colored while others, usually grubs, are robust, C-shaped and white with a brown head. Mature beetle larvae vary from 1/8 inch to over 2 inches in length.

Grasshoppers are 3/4 to almost 3 inches in length, gray or brownish and some have brightly colored hind wings. The lubber grasshopper is the largest grasshopper in Florida. Adults often exceed 2 1/2 inches. They have very short wings, are clumsy and incapable of flight. There are two color forms of the adult lubber grasshopper. Some are yellow with red, brown and black markings and others are almost black. The nymphs are black with red markings.

Important Species

There are over 11,000 species of moths and butterflies in the United States and Canada. Over 95 percent of the economically important species are the larvae of moths. Very few butterfly larvae are damaging to woody plants. Adult moths and butterflies feed on nectar, pollen, etc. and are not harmful to plants. Some of the more important species are:
Azalea caterpillarDantana major
BagwormThyridopteryx ephemeraefarmis
Fall webwormsHyphantia cunea
Forest tent caterpillarMalacosoma disstria
Nantucket pine tip mothRhyacionia frustrana
Redbud leaffolderFascista cercerisella
No common nameGlyphidocera juniperella
No common nameEpisimus tyrius

There are over 30,000 species of beetles in the U. S. and Canada and most feed on plants. Only a few are discussed here.

No common nameAltica foliacea
Flea beetlesColaspis spp.
Whitefringed beetlesNaupactus spp.

In addition, the Schistocerca grasshopper complex and the eastern lubber grasshopper are the most damaging grasshoppers in Florida for ornamental plants.

There are several "stinging" caterpillars that feed on ornamentals. The most common are the puss caterpillar, io moth caterpillar, hag caterpillar, buck moth caterpillar, flannel moth caterpillar, saddleback caterpillar, and the spiny oak-slug caterpillar. They do not possess stingers, but have spines which are connected to poison glands. Some people experience severe reactions to the poison released by the spines and require medical attention. Others experience little more than an itching or burning sensation. For first aid: Place scotch tape over affected area and strip off repeatedly to remove spines. Apply ice packs to reduce stinging sensation, and followed by a paste of baking soda and water. If an individual has a history of hay fever, asthma or allergy, or if allergic reactions develop, a physician should be contacted immediately.

Biology

The life cycle of moths and butterflies is divided into four distinct stages: (1) the egg; (2) the caterpillar or larva; (3) the pupa or resting stage; and (4) the adult. Although there is considerable variation in the group, the life cycle is quite similar for the different species. In general, adult females lay several hundred eggs, singularly or in clusters. The eggs hatch in two days to two weeks. The larvae begin feeding immediately after hatching. After feeding for several days, the caterpillars molt and in the process increase greatly in size. The period between each molt is referred to as a larval instar. Caterpillars pass through five to seven larval instars before they enter the pupal stage. Many moth larvae construct small earthen cells below the surface of the soil in which they change to the pupa stage, while others construct silken cocoons. Two to three weeks are spent in the pupal stage, where they transform to adult moths. After the adult emerges from the soil or cocoon, mating takes place and the female is ready to lay eggs. Under optimum conditions, three to six weeks are required for most moths to develop from egg to adult.

Like moths, beetles go through a complete body change or metamorphosis (egg, larva or grub, pupa and adult).

Host Plants

Virtually all woody plants are subject to attack from one or more species of moths, beetles, beetle larvae or grasshoppers and their relatives (katydids and crickets).

Damage

Caterpillars begin feeding immediately after hatching. Initial infestations of newly hatched caterpillars are difficult to detect because they feed on the tissues of the lower leaf surface. After feeding for several days, leaf skeletonization begins to appear. Mature larvae chew holes or irregular areas in the leaves or flowers.

Adult beetles usually feed on foliage or flowers while the larvae or grubs feed on foliage, roots or bore through stems. Like caterpillars, some species restrict their feeding to a single plant, while others are general feeders. Usually they chew holes in the leaves along the leaf margins. Sometimes they cause scars on the leaf by chewing only through the upper epidermis. Many species of beetles feed during the night hours. The damage is noticed the following day, but there are no insects present because they tend to hide under mulch or other debris on the soil surface during the daylight hours.

Sampling

Observe for caterpillars, beetles or other chewing pests or for leaf skeletonization or holes in the leaves during the regular scouting of the nursery.

Biological Control

There are many predators and parasites that attack caterpillar and beetle larvae. Purchase and release of beneficials is usually not practical. Instead, preserve those that occur naturally by applying pesticides only when scouting indicates an application is needed and using those pesticides that are least detrimental to beneficial organisms.

Chemical Control

For the most current insecticide recommendations to control these pests, please contact the local county office of the Cooperative Extension Service. If you have access to the World Wide Web you can consult the University of Florida's Insect Management Guide at:

http://edis.ifas.ufl.edu/TOPIC_GUIDE_Insect_Management_Guide

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