Typically covered in a white waxy material, mealybugs are

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.

• Glasshouse mealybugs are found mainly on greenhouse plants and houseplants, especially cacti and succulents, African violets, bougainvillea, citrus plants, fuchsia, grape vines, hoya, orchids (especially Phalaenopsis), oleander, passion flower, peach and tomato
• Some other mealybug species can attack outdoor plants, such as ceanothus, laburnum, New Zealand flax (Phormium mealybug) and redcurrant
• Glasshouse mealybugs thrive in warm conditions and are rarely found on outdoor plants. Glasshouse mealybugs are active all year round on houseplants and in greenhouses
• Some species of glasshouse mealybug feed on plant roots, most of these are Rhizoecus species and are also confined to glasshouse and house plants. One species of root mealybug the golden root mealybug, will survive on roots out of doors

You may see the following symptoms:

• Glasshouse mealybug is usually first noticed as a fluffy white wax produced in the leaf axils or other sheltered places on the plant. The insects or their orange-pink eggs can be found underneath this substance
• Black sooty mould is a sign of sap sucking insects. Large numbers of mealybugs may result in an accumulation of honeydew. This makes plants sticky and encourages the growth of sooty moulds, giving leaf and stem surfaces a blackened appearance
• Large populations can reduce plant vigour and stunt growth and may cause premature leaf fall
• Root mealybugs (Rhizoecus species) are also covered in a white waxy substance and found on plant roots. The golden root mealybug is yellow in colour

If you encounter this insect on indoor plants then please consult our page on indoor plants: sap feeders for indoor specific advice.
 
Female mealybugs do not fly or crawl far, so they are usually brought in on an affected plant. Inspect new plants carefully before putting them in a greenhouse or conservatory and, where possible, keep them in quarantine (isolated from other plants) for at least a month before adding new acquisitions to an existing collection.

• Plants can tolerate some levels of mealybug, although populations can quickly build if left unchecked
• Dead leaves and pruning’s should be removed from greenhouses and around houseplants as these may have mealybugs or eggs on them
• It can be simpler to dispose of heavily affected plants rather than try to eliminate mealybugs
• A ladybird, Cryptolaemus montrouzieri, can be released into greenhouses to manage mealybug populations. Note that the ladybird's larvae look like large mealybugs! Both the adult ladybirds and their larvae are able to find and eat mealybugs and their eggs in confined spaces on the plants. Parasitic wasps (Leptomastix spp., Leptomastidea spp. and Anagrus spp.) are also sometimes available for use against these insects. The parasitic wasps can give control of mealybug populations where population levels are fairly low. The ladybird and parasitic wasps need relatively high temperatures and so are only likely to be successful during May to September. They are available by mail order from suppliers of biological controls.

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Biological control suppliers (pdf document)

Several species of mealybug occur in greenhouses or on houseplants. These include Pseudococcus calceolariae (Glasshouse mealybug), P. longispinus (Long tailed mealybug) and Planococcus citri (citrus mealybug) and Rhizoecus species (root mealybugs).

The adult females have flattened oval-shaped soft bodies up to 4 mm in length; they are sometimes pink in colour but appear whitish due to the white, waxy powder that covers their bodies. Waxy filaments project from the edges of their bodies. Some species are all female; others have small winged males, but the latter are infrequently seen.

Female mealybugs lay eggs under a white, waxy coating. Mealybug nymphs resemble the adult insects and can complete their development in about a month in mid-summer. Breeding continues throughout the year in greenhouses, but takes place at a slower rate in winter.