How to recognise it
Colonies (containing young and adult mealy bugs) develop on leaves, stems, buds, flowers, fruits and other above ground parts of the plants. Each adult is greyish/white and looks like a tiny woodlouse, measuring only around 3mm in length. Adults produce fine waxy threads for protection, which often completely cover the insects.
Each female lays 100 to 150 eggs in each batch, covering it with protective woolly wax. Eggs hatch within a few days (particularly in higher temperatures) and the young nymphs can move around the plants for a few hours before settling to feed.
They feed for long periods during which they are immobile and then move on to different sites. In high temperatures and humidities (around 26-30˚C) it can complete its lifecycle (from egg to adult) within 22 days. Generally the mealy bugs will mature in summer, leading to the highest population figures in autumn and early winter. Breeding continues throughout the year (so long as temperatures remain high enough). Adults are cocooned and emerge as winged males in large numbers at a time.
Why it’s a problem
It spoils the appearance of glasshouse crops (especially orchids, coleus species cacti and solanum species) and weakens the plant by feeding off the plant’s phloem through the bug’s stylet (tubular mouthpart). Dense infestations can produce sufficient honeydew to attract sooty mould and may cause leaf drop.
Where you are likely to find it
In glasshouses. While adults do have wings it is generally introduced with new plants and only spreads between plants which are touching.
They are occasionally found outdoors in particularly hot, dry weather.
The following plants are particularly susceptible (although pretty much any plant can be affected): vines, currants, sprouting potatoes, abutilons, anthuriums, asparagus ferns, begonias, cacti, ceanothus, chrysanthemums, codiaeums, crassulas, dracaenas, eucharis, ferns, ficus, fuchsias, gardenias, hippeastrums, hoyas, jasmines, laburnums, musas, oleanders, pelargoniums, saintpaulias, solenostemons (coleus) and palms.
How to deter it
Carefully check newly introduced plants for nymphs and scales. If in any doubt, new plants should be quarantined for a month or so and treated if any signs of mealy bug infestation appear.
How to get rid of it
Infestations can be manually removed by pruning, washing with a high powered spray and removal by hand with a paint brush (which could be dipped in methylated spirits or one of the insecticides outlined below). Brushing is the only manual option for cacti. This should remove the main colonies and make subsequent biological or chemical control treatments more effective.
The biological control Cryptolaemus montrouzieri (a tropical ladybird) is effective in high light intensities and temperatures above 20˚C.
Their thick, wooly cuticle can be resistant to chemical treatment, but fatty acid based insecticides (which block the insect’s breathing apparatus) can be effective. Systemic chemical control can also be used; acetamiprid, imidacloprid, thiacloprid or thiamethoxam.
Is it good for anything?!
Other useful information
These are tropical and sup tropical species which have been accidentally introduced into glasshouses in Britain and Northern Europe.