common name: boisduval scale
scientific name: Diaspis boisduvalii Signoret (Insecta: Hemiptera: Diaspididae)

Introduction - Distribution - Description - Life Cycle - Hosts - Damage - Management - Selected References

Introduction

The boisduval scale, Diaspis boisduvalii Signoret, is an economically important pest of orchids, and was reported as the most important insect pest of orchids in Florida (Dekle 1965). Miller and Davidson (2005) list boisduval scale as one of the 43 most serious worldwide armored scale pests.

adult females

Distribution

The boisduval scale occurs throughout the tropics, and as a greenhouse pest in more temperate climates (Dekle 1965, Miller and Davidson 2005).

Description

Females are white to light yellow, approximately 0.05-0.09 inches (1.2-2.25 mm) in diameter, circular or oval in shape, and covered with a centrally located, white-transparent, flat circular or oval shed skin. When the scale cover is removed, a single, horn-like projection on either side of the body, near the head and thorax may be visible (Dekle 1965, Howard et al. 2001, Miller and Davidson 2005).

adult female

adult females

adult female - with exuviae removed

Males are oval to elongate in shape, with a white cover and marginal shed skin. Males measure approximately 0.04 inches (1mm) in length.

cluster of males

Life Cycle

Each adult female may produce up to 200 eggs and live as long as seven months. Eggs hatch within five to seven days and become crawlers. Egg color depends upon maturity, and ranges from clear to yellow, and finally orange. The development from egg to the adult stage averages 33 days for males and 50 days for females (Miller and Davidson 2005).

male, female and crawler stages

Hosts

This species has been recorded in over 15 families and 65 genera in Florida alone, but is most commonly found on orchids and palms.

Within the palm hosts (family Arecaceae) the following genera are susceptible (Howard et al. 2001, Miller and Davidson 2005):

Recorded orchid hosts (Orchidaceae) include the following genera:

Other recorded host plant families include:

A full listing of recorded hosts for boisduval scale is available at: ScaleNet: A Database of Scale Insects of the World.

Damage

Boisduval scales are normally found on the leaves and stems of palms. For orchids, this scale tends to prefer the leaf midrib and the portion of the petiole that is covered by the sheath. Boisduval scale is also capable of infesting orchid pseudobulbs and all aerial portions of the plant, including bark and fruit (Miller and Davidson 2005).

leaf damage

Management

Various cultural, biological, and chemical control options may be effective for management. Nutritional problems may enhance a host's susceptibility.

Cultural control. Exclusion is the first measure to be taken to avoid boisduval scale infestation. Carefully examine all plants and propagative materials before purchasing them. However, buyer beware, it is easy to miss scales located underneath leaf sheaths and not all life stages are visible to the unaided eye. New plants should be isolated from collections and nursery stock for at least two weeks to ensure they are pest free. Spacing plants so that their leaves do not touch can help avoid biosduval crawlers moving from infested plants onto clean neighboring plants (Beardsley and Gonzalez 1975). The crawlers can also move from infested to clean plants through strong wind currents in greenhouses and rooms. If it is possible, isolate infested plants to avoid biosduval scale spread and begin a treatment regiment.

Biological control. Coccidencyrtus sp. (Hymenoptera: Encyrtidae) have been reported as parasites of boisduval scale (Miller and Davidson 2005, Tenbrink and Hara 1992).

adult parasite

Chemical control. Horticultural oils are often very effective for controlling scale insects, but product labels should be carefully followed. For example, dormant oils applied to the actively growing stage of a plant may result in a burning effect on the plant material. Because crawlers tend to establish themselves on the upper and lower leaf surfaces, near the base of the plant, and in leaf sheaths, thorough spray coverage is important.

For small collections, using 70% isopropyl alcohol and a gentle cloth or cotton swab to wipe away the scales can provide effective control. However, some soft-leaved orchids may be damaged by isopropyl.

The American Orchid Society has a helpful, online video demonstrating how to treat scales with alcohol (AOS Video Library 2008).

If a chemical application is used, remember that timing the application to target the immature or crawler life stage may be critical for appropriate control. As biosduval scale is an armored scale, the waxy covering may still be present even after it has been effectively killed.

Florida Insect Management Guide for ornamentals
American Orchid Society management recommendations

Selected References

Authors: Adriana Espinosa, Heidi Bowman, and Amanda Hodges, SPDN, University of Florida; Greg Hodges, Florida Department of Agriculture & Consumer Services, Division of Plant Industry
Photographs: Florida Department of Agriculture and Consumer Services, Division of Plant Industry; Lyle J. Buss and Heidi M. Bowman, University of Florida
Project Coordinator: Thomas R. Fasulo, University of Florida
Publication Number: EENY-467
Publication Date: November 2009
Copyright 2009

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Department of Entomology and Nematology
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