Pest 411 Wax scale insects

Wax scale insects

Look for white, waxy, oyster-like globs on twigs

by Shimat V. Joseph, Department of Entomology, University of Georgia

United States National Collection of Scale Insects Photographs, USDA Agricultural Research Service, Bugwood.org Fig. 1. Females of Indian wax scale.

Scale insects are very common pests of landscape trees and shrubs yet are often overlooked when scouting. They can, however, be responsible for chlorosis, branch dieback, or ultimately the death of the plant.

Wax scales are grouped into soft scales as they produce soft, cottony, powdery, or waxy substances that cannot be separated from the scale body. Indian wax scale (Ceroplastes ceriferus) (Fig. 1) and Florida wax scale (Ceroplastes floridensis) (Fig. 2) are the common wax scale insect species that occur in Georgia. The Indian wax scale is prevalent in the eastern U.S. from Florida to Maryland, whereas the Florida wax scale is found from New York to Florida and up to New Mexico in the west.

General description and biology

Females of wax scale insects are brownish-purple or reddish-brown with a white or pinkish-white wax covering the body. Males are not present. Adult females are about 1/4 inch long. The wax produced by females is often sticky. The females lay pale-purple, ovoidshaped eggs under female scales (Fig. 3). Females of the Indian wax scale lay from 1,200 to 2,000 eggs. The eggs are laid during late winter and early spring. The eggs hatch into the first nymphal stage, often referred to as crawlers. Egg hatch occurs beginning mid to late May to early June in Georgia. Crawlers are the only mobile stage of the wax scale insect. The crawlers are pinkish-red or red and flat, and they have functional legs. Once the crawlers settle on the stem, they molt into the second instars by inserting their piercing and sucking tube-like mouthparts. Once the mouthparts are inserted into plant tissue, they lose their legs and hardly move from that spot. The second instars subsequently molt into third instars. Both the second and third instars secrete waxy material, covering their body. The second instars have a tiny star-shaped

Joseph LaForest, University of Georgia, Bugwood.org Chazz Hesselein, Alabama Cooperative Ext. System, Bugwood.org

Fig. 2. Adults & nymphal stages of Florida wax scale. Fig. 3. Eggs of Florida wax scale.

appearance (Fig. 2), whereas the third instars resemble a cameo pin and, thus, are referred to as cameo stage (Fig. 4). The nymphs continuously mature through the summer months. The third instars molt into adult females. They are covered with a gummy, white wax that looks like a thick, dunce cap (Figs. 1 and 5). There is one generation per year in Georgia, especially central to North Georgia. Multiple generations of wax scale insects are possible in the southern parts of Georgia. Adult females overwinter on the bark.

Damage

Nymphs and females feed on sugars by inserting the piercing and sucking mouthparts into the phloem vessels of the plant. If the infestation is severe, they suck up a large amount of nutrients vital to the growth and development of the plant, which can cause leaf discoloration, heavy leaf drop, and ultimately branch dieback. These affected plants may die in certain situations. Severely infested host plants often appear black (Fig. 6) as the wax scale insects excrete excessive amounts of honeydew (the sugary substance they don’t need), where a black sooty mold fungus grows. The sooty mold infection completely changes the appearance of the host plant with a black coating.

United States National Collection of Scale Insects Photographs, USDA Agricultural Research Service, Bugwood.org Fig. 4. Third instar of Indian wax scale.

Host plants

Although wax scales feed on many shrubs and trees (such as hemlock, azalea, blueberry, camellia, citrus, fig, eugenia, gumbo-limbo, yaupon, jasmine, mulberry, pear, persimmon, plum, sabodilla, and turkscap),

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John Ruter, University of Georgia, Bugwood.org Fig. 5. Florida wax scale infestation on holly.

John Ruter, University of Georgia, Bugwood.org Fig. 6. Sooty mold infection after Florida wax scale infestation on holly. they prefer Japanese holly, Chinese holly, euonymus, boxwood, firethorn, spirea, barberry, and flowering quince.

Monitoring

Beginning in May, examine female wax scales on leaves and twigs at one to two-week intervals to determine when the eggs hatch. Crawlers begin to emerge in early summer in Georgia. The increased activity of foraging bees, wasps, hornets, and ants on dense shrubs may indicate heavy honeydew production and severe wax scale infestation. Look on twigs and small branches for all wax scale insect stages.

Management

Before installing hosts in the landscape, scout for the presence of any wax scale insects on them. If the wax scale insect infestation is found on twigs, remove heavily infested twigs or branches to reduce the eventual size of wax scale insects on the plant. Wax scale insects can be physically removed by handpicking if the infestation is light. Avoid planting susceptible hosts, such as ‘Burford’ holly. A study (Hodges et al. 2000) showed that certain species of hollies, such as Ilex buergeri, Ilex crenata, Ilex glabra, Ilex myrtifolia, Ilex verticillata, and Ilex vomitoria have demonstrated a degree of resistance to wax scales.

The thick layer of wax on the nymphs (except crawlers) and females protect them from exposure to applied insecticides. The thickness of the wax is greater for females than for nymphs. Crawlers have no wax covering and are the most susceptible stage of the wax scale insect.

A thorough spray of contact insecticides, such as horticultural oil, or insecticidal soap, or synthetic insecticide (e.g., pyrethroids, such as permethrin, bifenthrin, etc.) is necessary, especially when the crawlers are present on the twig for effective control. Contact insecticides can harm beneficial insects, such as predators and parasitoids, which can cause problems with resurging secondary pests otherwise regarded as minor pests. Systemic insecticides (e.g., neonicotinoids, such as acetamiprid, thiamethoxam, dinotefuran, etc.) can be soil drenched or injected and can effectively reduce densities of developing nymphs and females. The dead wax scales may not naturally fall off the twigs, and it may be challenging to determine whether the applied insecticide killed the wax scale insects. Squish the wax scale insect. If no liquid oozes out from the insect, that indicates the wax scale insects are dead. Systemic insecticides are generally compatible with biological control agents, such as predators, but they could harm the pollinators, such as foraging bees seeking pollen and nectar from the plant. Insect growth regulators, such as pyriproxyfen, novaluron, and buprofezin, etc., are also effective control options. They reduce the egg hatch or viability and normal development of the nymphs. It is critical to read the insecticide label, including the precautionary statements, before the insecticide is used for wax scale insect control. The insecticide label is the law.