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Glasshouse mealybugs are common sap-feeding insects that infest a wide range of houseplants and greenhouse plants. Mealybugs can weaken plants and excrete a sticky substance (honeydew) on foliage, which allows the growth of sooty moulds.
Mealybugs. Image: RHS, Horticultural Science
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 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.
You may see the following symptoms:
A ladybird, Cryptolaemus montrouzieri, can be released into greenhouses to control mealybugs. 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 susceptible to most insecticides and should therefore be used as an alternative, rather than in addition to pesticide control. They are available by mail order from suppliers of biological controls.
Due partly to the waxy covering mealybugs are difficult to control with insecticides, affected plants should be sprayed thoroughly. In many cases it may be impossible to eliminate mealybugs.
Pesticides for gardeners (Adobe Acrobat pdf document outlining pesticides available to gardeners)
Biological control suppliers (Adobe Acrobat pdf)
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.
Chemical labels explained
Chemicals: using a sprayer
Chemicals: using safely and effectively
Chemicals: storing and disposing safely
Glasshouse red spider mite
Golden root mealybug
Protect your garden
RHS statement on pesticides in horticulture
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