Despite their names, Whiteflies are bugs, not flies; found in the order Hemiptera. Within Hemiptera, you'll also find Scale Insects and Aphids. Because they're closely related, they form the Suborder Sternorrhyncha. Many species of whitefly are regarded as serious plant pests. They're most problematic in agriculture and horticulture, occurring frequently indoors and in glasshouses. There are roughly 1,500 species of whitefly in the group. Some species will only be found feeding on one kind of plant, whereas others may feed on plants across several plant families.
Whiteflies produce honeydew which encourages sooty moulds to develop on the plant.
Whiteflies have many natural enemies to help control their numbers.
Adults: The adults look like are tiny white-winged flies, that only measure around 2mm in length and will fly up on mass when an affected plant is disturbed. It may seem like they're covered in white, waxy dust. Nymphs: The young nymphs are flat and scale-like, light green in colour, and are immobile. The latter will grow until it forms a protective casing (cocoon/puparium). It hatches as a fully developed, winged-insect. Eggs: Whitefly eggs are laid by the adult fly onto the underside of the leaf and are tiny white to cream or sometimes yellow; they're often arranged in a circle.
Tiny white-winged insects fly off the plant when disturbed. Sticky honeydew can be found on the upper-surface of the leaf, which may be colouring grey from sooty mould development. Leaves can begin to turn yellow. Some species are capable of spreading diseases between plants. Whitefly eggs are typically laid in circles, beneath the leaves. Plants may lose vigour/ become weakened.
Whitefly infestations tend to be more problematic indoors, for example, in a glasshouse setting. Planting rhubarb in greenhouses is thought to deter whitefly. Whitefly eggs can be found underneath the leaves of plants, so these areas should be inspected regularly. Remove Whitefly eggs with a cloth and soapy water or rubbing alcohol. Any spacing between plants should be kept clear of weeds and debris. The use of netting can sometimes improve protection. For lighter infestations, plants can be gently hosed down to remove whitefly and eggs. Ant traps placed near affected plants will aid controlling any secondary infestations. Whitefly is drawn to the colour yellow. You can use yellow cards or sticky traps to attract whitefly and monitor the infestation level. Insecticidal soaps and neem oil can give some control over whitefly, and it's less harmful to the environment when compared with pesticides. Bottle labels should be read carefully. Oils can react badly with high temperatures and burn the surfaces of plants. More organic treatments may require more frequent applications to plants. Beneficial garden creatures such as beetles, wasps, lacewings and spiders will eat whiteflies. These can be attracted into the garden using a few simple tricks, such as incorporating insect hotels or by letting parts of the garden grow a little wild. All you need to do is provide enough food (pests) and cover, and the beneficial creatures soon follow!
There are pesticides available for home gardeners. Please note that whiteflies can quickly develop tolerance to the toxins found in sprays. Systemic insecticides can sometimes eliminate whitefly, be sure to get good coverage beneath the leaves (where the younger whitefly hide). Please read bottle instructions carefully, taking care not to spray any plants in flower. Some pesticides can be extremely toxic to wildlife and should be applied with extreme caution.
Attracted to plants grown undercover.
Using companion planting of Tagetes species may be beneficial to reduce Whitefly attack. Yearly crop rotation is advisable.