Mealybugs mainly attack plants or crops grown in greenhouses or conservatories.  They are often observed on cacti and succulents but do attack many other plants.  Nymphs and aduts feed on plant sap, reducing growth and secreting excess sugar called honeydew.  Sooty moulds often form on this.  Infested plants often drop their flowers and leaves. Mealybugs are soft bodied and grey to white in appearance.  Some species are pink.  The larval stage is covered in a white wax, which looks like "cotton wool".  The most common and effective biological control is with the predatory beetle; Cryptolaemus montrouzieri,which is a ladybird like beetle originating from Australia.

Both the larvae and the adults of this beetle feed on mealy bug. The young Cryptolaemus larvae can reach 13mm in length, and resemble the mealy bug in appearance as they are white with mealy like points sticking from them. The adults and young larvae feed on mealybug eggs and nymphs and the older larvae feed on the whole lifecycle of the mealybug. Mealybug Killer Product Guide [pdf]

Just Mealybug Killer is supplied as either larvae or adult Cryptolaemus montrouzieri. For small plants or quicker establishment, apply the larvae. For taller plants and larger infestations of mealy bug, apply adults. Just Mealybug Killer is only suitable for use in glasshouses or conservatories as Cryptolaemus require a minimum temperature of 16ºC  (61ºF) and development is much quicker at higher temperatures.  Apply between April and September when Cryptolaemus reproduce effectively.

Mealybug can also be controlled with Just Savona, an insecticidal soap, which is useful for heavy infestations or treatments during the winter period.

There is also a root mealybug, which feeds on roots, this can be treated with the compost dwelling predatory mite, hypoaspis.