Tessellated Scale, Ecualymnatus tessellatus (Signoret) (Insecta: Hemiptera: Coccidae)

Introduction

The tessellated scale, Eucalymnatus tessellatus (Signoret), is a soft scale (Hemiptera: Coccoidea) that is believed to be native to South America. This species may be a pest in greenhouses, commercial nurseries, and in the south Florida landscape (Dekle 1973). Palms, crepe-jasmine, and mango are some of the common south Florida hosts in the landscape for this pest.

Distribution

This scale is widely distributed and has been found in Africa; Australia; North, Central, and South America; the Caribbean; Asia; and Europe.

Tessellated scale has been found throughout Florida, and is frequently found on palm species.

Field Characteristics

The adult female body is often slightly asymmetrical, oval or pear shaped, measuring 0.098–0.196 inches (2–5 mm) long, and 0.078–0.118 inches (2–3 mm) wide. It looks flat when viewed from the side. It is reddish to dark brown in color. It has polygonal, sclerotized plates on the dorsum (top surface) with a raised ridge on the median area. It does not have a wax cover or ovisac. No males are known to occur. Legs are well developed compared to most soft scale insects (Hamon and Williams 1984, Miller et. al. 2007).

Life Cycle

One or two generations occur per year in a natural setting, but more frequent, overlapping generations may occur within greenhouse environments. They are parthenogenic (i.e. reproduce asexually without mating) and ovoviviparous, meaning that the eggs hatch within the female body, and the female gives birth to live young scale crawlers, or in some cases lays eggs that hatch quickly. This species has a relatively low reproduction rate among scale insects, producing less than two dozen young per female (Vesey-Fitzgerald 1940). They are usually found on leaves and stems (Hamon and Williams 1984).

Hosts

Tessellated scale has a very wide host range that includes monocot and dicot plant species such as ornamentals and fruit trees.

Tessellated scale is particularly common on palm species (family Arecaeae) and it specifically attacks the following:

Areca, yellow-cane-palm, Areca spp.

Arenga spp.

fishtail palms, Caryota spp.

Kentia palm, Howeia forsterana

coconut palm, Cocos nucifera

Lantanier jaune, Latania verschaffeltii

Chinese fan palm, Livistona chinensis

Attap palm, Nypa fruticans

Canary Island date palm, Phoenix canariensis

date palm, Phoenix dactylifera

miniature date palm, Phoenix roebelinii

lady palm, Rhapis spp.

Washington palm, Washingtonia spp.

In addition to palm species, some other hosts of tessellated scale include species in the following plant families:

Acanthaceae—Sanchezia spp.

Anacardiaceae—Mangifera indica (mango)

Apocynaceae—Nerium oleander, Plumeria rubra

Aquifoliaceae—Ilex cassine (Dahoon holly)

Araceae—Anthurium spp.

Caricaceae—Carica papaya (papaya)

Curcubitaceae

Lauraceae—Cinnamomum, Laurus, Litsea, and Persea spp.

Moraceae—Ficus spp.

Myrtaceae—Eucalyptus, Eugenia, and Myrtus spp.; Psidium guajava (guava)

Oleaceae—Jasminum

Pittosporaceae—Pittosporum spp.

Rubiaceae—Coffea and Gardenia spp.

Rutaceae—Citrus spp.

Sapindaceae - Euphoria longana (longan), Litchi chinensis (litchi).

A complete host reference list is available at ScaleNet: A Database of Scale Insects of the World.

General Plant Damage

Heavy infestations can weaken or even kill a host plant. In commercial nurseries, infestations may become of economic importance when not controlled. For example, in a dense planting of 'Malayan Dwarf' coconut palms in Miami, a serious infestation of E. tessellatus with up to 200 mature female scale insects per pinna has been observed. This planting had been sprayed repeatedly with insecticides to control palm aphid, Cerataphis brasiliensis (Hempel) without much success, and it is thought that the treatments may have interfered with natural enemies of both aphids and tessellate scale. Most of the foliage of these palms was coated with a thick crust of sooty mold, which was undoubtedly supported by the honeydew of both the palm aphids and the tessellated scale (Howard et al. 2001).

Management

Metaphycus stanleyi (Hymenoptera: Encryptidae) is a common natural enemy of this scale. A fungus, Verticillim lecanii (Zimmerman) Viegas, has been reported attacking E. tessellatus in the Seychelles (Vesey-FitzGerald 1940). This is a cosmopolitan fungus that attacks many kinds of insects and that has been developed as a biocide.

General management of scale insects begins with detection and identification of the pest. Scale insects can be very small or resemble disease organisms or even plant structures, making detection difficult. Regular monitoring will allow detection of these pests before damage is obvious and will also allow improved control. All plant parts, including the underside of leaves and stems, need to be searched. Inspection of plants prior to introducing them into the landscape, nursery, or collection is very important in reducing new infestations of scales.

Management of scale insects can be difficult to control because of the waxy covering they produce which provides protection from many of the insecticides. Pruning or washing infested plant parts can be helpful in reduction scale populations, particularly in cases of small infestations. A brisk wash spray of water can also be helpful in removing scales from plants and reducing the population. Scale insects are commonly attacked by predators, parasites, and diseases which can help manage scale populations particularly for long term control. It is important to recognize the presence of beneficial insects and to take steps to conserve them in the environment so they are available to control the pest insects.

It is often necessary to manage scale insects with insecticides so it is important to select appropriate insecticides, timing, and application methods to reduce negative impact on the natural enemies but still get maximum control. Contact insecticides commonly provide quick knockdown of the pest but require good coverage and typically repeat applications. The stage most susceptible to contact insecticides is the crawler stage. Horticultural oil and insecticidal soaps also can provide good control, but must be treated like a contact insecticide that requires thorough coverage and repeat applications. Systemic insecticides can provide excellent options for scale control and can provide some flexibility in application timing and methods. These insecticides move up through the plant and provide an excellent way to expose scale insects to the insecticide when they feed on the plant. It is important to not overuse or misuse insecticides, which can lead to numerous problems including insecticide resistance. To avoid insecticide resistance it is critical to rotate among insecticide groups.

Tessellated scale is common on palms, but usually occurs in very sparse populations such as a few individuals on a frond or even on an entire palm. Damaging populations are most apt to be brought about by interference in natural control, as in the above example. Also, this scale insect could occur in dense populations if introduced into a new region without its natural enemies.

Florida Insect Management Guide for Scales and Mealybugs on Ornamental Plants

Florida Insect Management Guide for Fruit

Selected References

Buss EA,Turner JC. (June 2006). Scale insects and mealybugs on ornamental plants. Gainesville: University of Florida Institute of Food and Agricultural Sciences. https://edis.ifas.ufl.edu/mg005 (January 2016).

Dekle GW. 1973. Tessellated scale, Eucalymnatus tessellatus (Signoret). Florida Department of Agriculture, Division of Plant Industry, Entomology Circular 138: 1-2.

Hamon AB, Williams ML. 1984. Arthropods of Florida and Neighboring Land Areas: The Soft Scale Insects of Florida (Homoptera:Coccoidea:Coccidae). Florida Department of Agriculture and Consumer Services, Division of Plant Industry.

Howard FW, Moore D, Giblin-Davis RM, Abad R. 2001. Insects on Palms. CABI Publications, Wallingford, UK. 400 pp.

Miller DR, Rung A, Venable GL, Gill RJ. (August 2007). Scale Insects: Identification tools, images, and diagnostic information for species of quarantine significance. Systematic Entomology Laboratory USDA-ARS. (1 June 2009).

Vesey-FitzGerald D. 1940. The control of Coccidae on coconut in the Seychelles. Bulletin of Entomological Research 31: 253-286.