WHITEFLIES ON HOUSEPLANTS
(Homoptera: Aleyrodidae)

Whiteflies - Adult and nymph ©1999 Zunke & Eisenback*

Whiteflies are minute insects of the order Homoptera. They are more closely related to aphids and scales than to true flies, which belong to the order Diptera. In Ontario whitefly infestations tend to be a more serious problem on greenhouse-grown flowers and vegetables than on crops grown out-of-doors.

The greenhouse whitefly (Trialeurodes vaporariorum) is the most common species at our latitude. Tomatoes, cucumbers, squash, lettuce and beans as well as fushia, hibiscus, coleus, hollyhock, impatiens, Jerusalem cherry, poinsettia, and roses are especially attractive to this species. Whiteflies are sucking insects feeding on the sap of their various host plants. Infested leaves turn pale green, then yellow and may eventually drop off. Whiteflies are vectors of some viral diseases and also secrete honeydew, which serves as a substrate for sooty moulds.

The adult greenhouse whitefly is about 1 mm long, with four powdery white wings. The adults readily fly, and, on heavily infested plants, are easily recognized if the plant is disturbed. The eggs, initially light yellow but turning grey as incubation proceeds, are laid on the underside of leaves. Upon hatching, the first-instar larva, or crawler, is mobile and actively searches for a feeding site where it will insert its stylet and transform into a sedentary scale for the remaining immature instars. The adults emerge 3 to 5 weeks after egg laying and will live and feed for about 4 weeks. Whiteflies cannot overwinter outdoors in Ontario; they survive the winter in greenhouses and on houseplants.

CONTROLS

Whiteflies are particularly difficult to control. Indoors and in greenhouses, whiteflies become established following the introduction of infested plant material. Thoroughly inspect, paying a particular attention to the underside of leaves, all newly purchased and outdoor plants before bringing them indoors or into the greenhouse, making sure they are free of whiteflies. Reject or treat infested plants. Isolating while regularly inspecting new plants is also recommended. Whiteflies can rapidly spread from a single plant. Adult whiteflies can be vacuumed up or caught on yellow sticky traps placed in proximity of infested plants. A parasite of whiteflies, Encarsia formosa, is an effective a biological control agent in greenhouse operations but is of limited use for household purposes.

The eggs and pupae (scale stage) are quite tolerant of most insecticides. To complicate matters, all stages of whiteflies can occur on the same plant. A single application of a particular insecticide only affects the susceptible stages present at the time of treatment or shortly thereafter. The surviving stages will continue the cycle. Several applications at weekly intervals may be necessary. Insecticides, having low toxicity and available in garden centres are registered in Ontario for the control of whiteflies on houseplants. Control is usually not warranted outdoors.

FOLLOW LABEL DIRECTIONS TO ENSURE THE SAFE USE AND EFFICACY OF EACH PESTICIDE PRODUCT.

Image source: *© 1999 J.D. Eisenbach & Zunke, EntoPix, A Journal of Entomological Images, Vol. 1.

H.W. Goble/M. Sabourin

PDCF-103 (Revised 2003/11/07)