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Small sap sucking diaspid scale insects can encrust the leaves and stems of glasshouse orchids and some other glasshouse plants.
Diaspid scales (Diaspis boisduvalii)
Diaspid scale insects are small sap sucking bugs that can infest glasshouse orchids and some other glasshouse plants. There are many types of scale insects that may be encountered by gardeners.
There are several species of diaspid scale in Britain that have a similar appearance and lifecycle. Adult female diaspid scales are covered by flat rounded whitish brown shell, about 2mm in diameter, and occur on the leaves and stems of host plants. The narrow elongate adult males are usually covered with a fluffy white wax; they generally cluster together at the base of the leaves. No honeydew is produced. Reproduction occurs throughout the year.
Heavy infestations can weaken plants and the scales and white wax produced by the males can be unsightly.
Diaspid scale insects can be difficult to control, replacing severely infested plants should be considered.
Physically squashing or removing scales may control light infestations.
A small black ladybird Chilocorus nigritus, which predates on all stages of diaspid scales is sometimes available from some suppliers of biological control (Adobe Acrobat pdf document).
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
Diaspid scales feed by sucking sap from the leaves and stems of orchids and other glasshouse plants. Scales are named for the waxy shell-like casing which covers most of their body. When mature, the females lay their eggs under the protection of this shell. The eggs hatch into small active nymphs, known as crawlers, which wander over the plant surface until they find a suitable place to feed. They then become immobile and begin to produce their characteristic scale covering.
Infestations of scale insects are spread by the crawler stage, which may travel quite long distances before stopping to feed, and which can be spread by wind currents. Diaspid scales reproduce throughout the year on glasshouse plants.
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