Problem Solver Guides for Gardeners: Insects Mouthparts

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	FIGURE 1. Chewing mouthparts (tobacco hornworm feeding on Datura leaf).


	FIGURE 2. Piercing/sucking mouthparts (brown stinkbug feeding on tomato fruit).


	"FIGURE 2. Siphoning mouthparts (butterfly feeding on nectar).


	FIGURE 4. Rasping mouthparts (thrips damage on rose petals).

If you're a home gardener then you may wonder what's so important about understanding (or even having some appreciation of) insect mouthparts?

There is a due measure of irony in discussing insect mouthparts when there are several variations among entomologists in their spelling of the term “mouthparts.” So, should be spelling be "mouthparts" or "mouth parts" or "mouth-parts" (i.e., one word, two words or a hyphenated word)? We elected to use the spelling as "mouthparts" as utilized by Dr. Bastiaan M. Drees (Professor & Extension Entomologist, The Texas A&M University System) and Dr. John A. Jackman (Professor & Extension Entomologist, The Texas A&M University System) in their book entitled A Field Guide to Common Texas Insects (Gulf Publishing: Field Guide Series; ISBN 0-87719-263-4).

Regardless to the how you elect to spell the term under discussion, there should be no misunderstanding regarding the importance of a basic understanding of insect mouthparts. Recognizing the basic types of plant damage that results from the feeding of a particular insect or group of insects is important for applying effective insect pest management strategies. In addition, some insecticides are more effective against insects with certain types of mouthparts.

Classifications of insect mouthparts are based on the manner insects feed on plants. Some entomologists utilize broad categorizations (lumpers) in describing mouthparts while other entomologists split the basic categories into more narrowly defined categories.

Be mindful that the mouthparts of given species of insect can be different during the various life cycle stages. For example, the caterpillar stage of butterflies and moths has chewing mouthparts while the mouthparts of adult butterflies are siphoning.

This article will focus on four commonly encountered types of mouthparts: chewing, piercing-sucking, siphoning, and rasping.

Insects with Chewing Mouthparts

Chewing insects feed by biting, ripping or tearing plant tissue. They may damage all or part of the plant including roots, stems, leaves, buds and open flowers. Chewing insect pests on plants include caterpillars, beetles, grasshoppers, leaf-cutter bees, etc.

Chewing insects produce varied plant damage including:

• Irregular holes in foliage or stems.
• missing leaves
• leaves with "windowpanes", i.e., showing bared veins (caused by leaf skeletonizing insects)
• discolored areas on the surface or margins of leaves or petals
• severed stems, leaves or buds or wilting of stems or canes (limb girdling)
• wilting of plants (from root damage by white grubs or other root feeders)
• Beneficial insects can often keep pace with pest populations.• Aids in maintaining a more natural balance in our ecosystem.
• circular to semicircular holes in leaves (e.g., leaf-cutting bees)
• caterpillars use their chewing mouthparts to consume several times their own weight in plant tissue over the course of their development. Much fibrous tissue passes through the caterpillar gut undigested and forms a major component of the large fecal pellets caterpillars leave behind. These pellets are a characteristic sign of caterpillar damage.

Many insects feed on a liquid diet (i.e., plant fluids) for which chewing mouthparts are not effective. Many of these insects have a beak, referred to as a proboscis, that is modified to suck up liquids in a manner similar to humans sucking through a straw. The proboscis has a groove down its front inside which contains several very slender, sharp, and needle-like stylets that can pierce plant tissue to extract plant fluids. (Although we’re discussing insect pests on plants here, residents along the Gulf Coast are well-acquainted with mosquitoes which have very efficient sucking/piercing mouthparts!)

Sucking insect pests on plants with sucking/piercing mouthparts include aphids, leafhoppers, scale insects, whiteflies, etc.

Insects with Sucking/Piercing Mouthparts produce varied plant damage including
    • Sucking/piercing insects produce varied plant damage including:
    • Discoloration (yellow or brown), mottled or necrotic (dead) spots on leaves or petals
    • Wilted appearance of plant or plant parts
    • Curled, malformed leaves and petals
    • Many of insects pests that feed through in this manner defecate a sticky liquid (known as honeydew) that often builds up on the upperside of leaves or fruit, leaving a shiny residue that may support the growth of a black or gray sooty mold.

Insects with rasping/sucking mouthparts actually rasps or scrapes the surface of plant tissue (such as leaves or petals) and sucks up the fluids that ooze from the damaged area of tissue.

Examples of pests with rasping-sucking mouthparts include thrips and mites. Thrips prefer to feed on succulent plant tissues. They may feed on fully expanded foliage, open flowers, and even pollen grains. Light-colored flowers (white, yellow or other pale colors) are often preferred. Affected tissue dies, turns brown and tears easily, a situation especially noticeable on the edges of pastel-colored rose petals. Leaves that are attacked become bleached and dry. Skin of damaged fruit appears sanded and the underlying tissues may be off-flavored, hard and/or dry.

General note on Insect Mouthparts: Mouthparts can be different during the various life cycle states, i.e., larval stage caterpillars are chewing insects, and the adult stage butterflies are siphoning.

Problem Solver Guides for Gardeners is an EarthKind^TM-program coordinated through Extension Horticulture at Texas A&M University. Earth Kind uses research-proven techniques to provide maximum gardening and landscape enjoyment while preserving and protecting our environment.