Sap is a fluid that circulates through a plant's vascular system, in a similar way to blood moving through our veins. Phloem sap carries the sugars produced in the leaves by photosynthesis down to roots and other storage organs, as well as carrying minerals and hormones. Xylem sap is watery and transports nutrients absorbed by the roots upwards to the rest of the plant. Some plants leak sap from wounds or pruning cuts, and this is known as bleeding.

sap

Scale insects are sap sucking true bugs belonging to several families in the Hemiptera. Typically the adults are immobile having a flattened or raised appearance, with no visible legs. They often look like a ‘scale’ on a leaf or stem, many species produce a white wax often covering egg masses. There are more than 100 species found in Britain, 26 of which have been introduced. More than 25 species can be found in gardens or on houseplants.

Hemispherical scale rarely causes direct damage to plants. Apart from the presence of the insects the main symptom is the presence of honeydew on which sooty mould can grow.

It can appear similar to other diaspid scales.

If you encounter this insect on indoor plants then please consult our page on indoor plants: sap feeders for indoor specific advice.

• Where possible tolerate populations of scale insects. Well-tended healthy plants are able to tolerate light populations of these insects and so they do not necessarily require management
• Encourage predators, some parasitoid wasps that affect this scale can be found indoors
• The nematode Steinernema feltiae can be purchased to as a biological control of hemispherical scale and is available from some Biological control suppliers. Nematode controls have the potential to infect non-target animals. They should therefore be used with care and only when there is a specific problem to treat
• Consider replacing severely affected plants 

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Biological control suppliers (pdf document)

Hemispherical scale insects feed by sucking sap from the leaves and stems of various 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.

All hemispherical scales are female and reproduction is continuous throughout the year and entirely parthenogenetic. 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.

It is the crawler stage of this scale insect that are mobile, they may travel quite long distances before stopping to feed, and can be spread by wind currents.