Typically covered in a white waxy material mealybugs are sap sucking true bugs (Hemiptera) closely related to scale insects https://www.rhs.org.uk/biodiversity/scale-insects  and often considered to be unarmored scale insects.  Most species are found in moist warm climates and those that occur in the UK are typically found in glasshouses and other protected environments.

Glasshouse mealybugs are common insects that tend to live together in clusters in inaccessible parts of plants, such as leaf axils, leaf sheaths, between twining stems and under loose bark. There are also some mealybug species found on plant roots. Mealybugs suck sap from plants and then excrete the excess sugars as a substance called honeydew. This lands on the leaves and stems were it is often colonised by sooty moulds, giving the surfaces a blackened appearance.

• 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

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.

Check susceptible plants frequently so action can be taken before a damaging population has developed. When choosing control options you can minimise harm to non-target animals by using the methods in the non-pesticide section below. Pesticide treatments are likely to kill natural enemies and are only likely to be successful if the entire plant can be reached.

Non-pesticide

• Dead leaves and pruning’s should be removed from the greenhouse 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
• Plant can tolerate some levels of mealybug, although populations can quickly build if left unchecked

Pesticides

The RHS recommends that you don't use pesticides. Most pesticides (including organic types) reduce biodiversity, including natural enemies, impact soil health and have wider adverse environmental effects.
 
Where you cannot tolerate mealybugs, manage them using the information above as your first course of action.
 
Pesticide treatments are likely to kill natural enemies and so reduce the likelihood of natural control and can lead to resurgence of the target animal.
 
If you do decide to use pesticides, the shorter persistence products (that are usually certified for organic growing) are likely to be less damaging to non-target wildlife.
 
The pesticides listed are legally available in the UK. This information is provided to avoid misuse of legal products and the use of unauthorised and untested products, which potentially has more serious consequences for the environment and wildlife than when products are used legally.
 
Always follow the instructions on the products. For edible plants, make sure the food plant is listed on the label and follow instructions on maximum number of applications, spray interval and harvest interval.
 
Homemade products are not recommended as they are unregulated and usually untested.
Be aware that products such as Neem oil are not registered for use in the UK and we cannot advise on their use.
 
Plants in flower must not be sprayed due to the danger to bees and other pollinating insects.

• Organic sprays, such as natural pyrethrum (e.g. Bug Clear Ultra 2, Neudorff Bug Free Bug and Larvae Killer) or plant oils (e.g. Vitax Plant Guard Pest & Disease Control, Bug Clear Fruit & Veg, Vitax Rose Guard) have a largely physical mode of action and can give control of mealybugs.These are broad spectrum so will kill a wide range of insects. These pesticides have a very short persistence and so may require reapplication to keep mealybugs numbers in check. Plant oil and fatty acid products are less likely to affect larger insects such as ladybird adults
• Plant invigorators combine nutrients to stimulate plant growth with surfactants or fatty acids that have a physical mode of action against mealybugs (e.g. Ecofective Bug Control, Growing Success Bug Stop, RoseClear 3 in 1 Action and SB Plant Invigorator). These products contain some synthetic ingredients and so are not considered organic
• More persistent contact-action insecticides include the synthetic pyrethroids lambda-cyhalothrin (e.g. Resolva Bug Killer), deltamethrin (e.g. Provanto Ultimate Fruit & Vegetable Bug Killer, Provanto Sprayday Greenfly Killer) and cypermethrin (e.g. Py Bug Killer). Permethrin is available as a smoke formulation for use in glasshouses (e.g. DeadFast Greenhouse Smoke Fumigator)These products have long lasting action against insects including those that are beneficial
• Pesticides, with both systemic (absorbed and transported through plant tissues) and contact action, are available. These include Flupyradifurone (Provanto Smart Bug Killer) for  use on ornamentals and selected edibles and the neonicotinoid insecticide acetamiprid (e.g. Bug Clear Ultra). These pesticides are widely considered to be the most environmentally damaging, remain active for a long time and will kill beneficial invertebrates
• Further information about the use of pesticides available for management of mealybugs is available on the pesticides for gardeners leaflet

Downloads

Pesticides for gardeners (pdf document)
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 4mm 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.