How Insects Injure Plants: Mouth Parts
- Chewing - (grasshoppers, caterpillars, beetles & grubs) - bites/holes.
- Piercing/Sucking - (aphids, scale, mealybugs, whitefly) causing stunting, discoloration.
- Rasping/Slurping - (mites and thrips) - scrape epidermal layer, lap out chlorophyll - symptoms are called chlorosis (yellowing), stippling (dot effect).
- Miners (flies, moths) - eggs laid between layers of the leaf, larvae hatch and feed as they travel, pupate inside leaf, emerge as adult. (Serpentine or blotch paths)
Terms
- Honeydew - a sweet secretion produced by sucking insects that falls on leaves below. On this secretion grows:
- Sooty mold - a black fungus which does not harm the plant, it is growing only on the honeydew and can be washed off.
Note: Some ants feed on honeydew, you are often alerted to a pest problem by the presence of many ants on the plant.
Examples of Common Insect Pests
APHID (Homoptera) sap-suckers: piercing/sucking mouthparts
Description: Soft bodied, pear shaped, cornicles on rear, in clusters, can be different colors.
Life Cycle: Incomplete; from eggs or live birth, winged forms when crowded population.
Symptoms: Stunted and deformed new growth where population concentrates.
Signs: Pest, shed skins, honeydew/sooty mold, see ants harvesting honeydew.
Hosts: Tender new growth of most plants (Raintrees, Seagrape, Citrus, Pyracantha, Jaboticaba, etc.)
Management: Biological - Many natural predators, parasites and fungi naturally exist.
Physical - Wash them off with a garden hose.
Chemicals, soaps
MEALYBUG (Homoptera) piercing/sucking mouthparts
Description: Soft-bodied sucking insects, close relatives of scale insects. Covered with powdery white or gray threads of wax.
Life Cycle: Incomplete: egg to adult in one month.
Symptoms: Stunted and deformed new growth, chlorotic patches, weakened plants.
Signs: See pests esp, on new growth and in leaf axils, honeydew/sooty mold.
Hosts: Most ornamentals (Fukien tea, Nashia, Malpighia, Sago Palms, Grewia caffra, etc.)
Management: Horticultural oil spray (alone or combined with pesticide), soaps, systemics
SCALE (Homoptera) piercing/sucking mouthparts
Description: Many shapes, sizes and colors. (Tea scale, Oleander scale, Cottony-cushion scale.)
Life Cycle: Incomplete. Scale eggs hatch into male and female crawlers, nymphs with legs. These crawl briefly before becoming stationary and growing hard shells. Males pupate beneath their shells and emerge as winged adults. They mate with stationary females, then die.
Symptoms: Stunted, sickly plants, yellow chlorotic spots on upper leaf surface.
Signs: Scales on underside of leaves, pick off to see if alive, soft scales usually on twigs or petioles, Honeydew/sooty mold.
Hosts: Ornamentals, palms (Podocarpus, Sago Palm, Acacia)
Management: Successful control can be determined by sliding your thumbnail across a group of scales. If they are dry, hollow and flake off readily, they are dead. Live ones stick more firmly and are juicy when squashed.
Cultural - prune out
Chemical systemics, suffocate with oils or soaps (alone or in combination with pesticide). Be sure to spray leaf undersides.
WHITEFLY (Homoptera) piercing/sucking mouthparts
Description: Tiny, snow-white insects that resemble moths if viewed under a magnifying glass.
Without magnification, they look more like flying dandruff. (They are not moths: whiteflies are related to scale insects.)
Life Cycle: Incomplete. Adult female whiteflies lay eggs on the undersides of leaves. These hatch into nymphs, which crawl briefly and then settle down, scalelike, to suck plant juices. After a short pupal stage, adults emerge to feed and mate.
Symptoms: Leaf yellowing or mottling.
Signs: Flying "dandruff", black sooty mold.
Hosts: Ornamentals, citrus.
Management: Horticultural oils and soaps. Pesticides easily eliminate whitefly adults and crawling nymphs. However, eggs, feeding nymphs and pupae defy insecticides. You must spray four times at 4 to 6 day intervals to control nymphs as they hatch. Be sure to spray leaf undersides, where whiteflies congregate. Cygon or Di-Syston for systemic control.
BARK BEETLES and TREE BORERS (Coleoptera) - chewing mouthparts
Description: Beetles and their larva (borers).
Life Cycle: Complete - Adult beetles mate and then lay eggs in tunnels under tree bark. The eggs hatch into larvae, which make galleries as they feed. The fully grown larvae form pupae, which emerge as adult beetles.
Symptoms: Foliage or branch declines. The tunneling of the larvae and adults severs the tree's nutrient transport system; equally damaging is the plugging of the water transport system by fungi which are introduced by the adults.
Signs: shot-gun holes, sawdust, pitch or sap on tree stem branches, beetles.
Hosts: Conifers, Cypress, Ficus, Black Olive, Maple, Orange Jasmine, etc.
Management: drench bark surfaces with Lindane or Dursban. Spray anytime from March to early July every 4-6 weeks. Destroy infested branches.
SPIDER MITES: (Arachnida) not insects, closely related to spiders and ticks
Description: tiny - need magnification to see them. 2 body parts, 8 legs.
Life Cycle: under Florida conditions, mites complete their life cycle in 7 to 10 days at 80 degrees, so spray again in 5 or 6 days
Symptoms: Tiny chlorotic spots (stippling), general yellowing, leaf drop.
Signs: Webs in crotches of branches or petioles, on older leaves and underside, see eggs, nymphs, adults, shed skins. Hold a clean, white sheet of paper under the sick plant leaf. Briskly thump the leaf several times. You should see several minute specks on the paper. With a pen, draw a tight circle around each speck. Now, wait. If the specks move out of the circles, then they are alive.
Hosts: Junipers, fruit trees, citrus, Pyracantha, Buttonwood, etc.
Management: Chemicals systemics, contacts, Kelthane, (Soaps and oils) *Horticultural oils
on woody plants (read label carefully to be certain your plant is listed). Dormant oil on deciduous trees to kill mite eggs, during growing season, oil sprays destroy mites at varying states. Because oil works by suffocating mites, it will only be effective if you spray all plant surfaces.
FLEA BEETLES: (Coleoptera) chewing mouthparts.
Description: 1/16 inch long, enlarged flea-like hind legs. They jump like fleas, though not related. Some are striped, but most are either black, brown or green. Larvae are small slender and white with a black band.
Life Cycle: Complete.
Symptoms: Adults chew numerous small round holes in leaves of most vegetable crops as well as many flowers and weeds. Leaves appear to have been peppered with fine shot. When feeding damage is heavy and there are many holes, leaves may wilt and turn brown; the host plant may become stunted and may even die. The larvae feed on roots or tubers.
Signs: Adult beetles. Begin control as soon as you first see damage in the spring.
Hosts: Serissa, vegetables.
Management: Chemical
LEAFMINER (Diptera)
Description: Flattened larvae of Diptera (flies).
Life Cycle: Complete. Eggs laid between the layers of the leaf, larvae hatch and tunnel while they feed, pupate outside the leaf, emerge as adults.
Symptoms: mines - either winding (Serpentine) or blister (Blotch).
Signs: Sometimes pupal cases, larva as leaf tiers
Hosts: Citrus, Severinia buxifolia (Orange Boxwood), Schefflera, Azalea, Lantana, Bougainvillea, Ilex.
Management: Physical (remove fallen leaves, hand-pick leaves with mines). Chemical, systemics.