| Life Cycle: | The adult greenhouse whitefly is 1-2 mm long. As its name suggests it is white and has wings. It is primarily a greenhouse pest as it cannot overwinter in Canada; however, as long as there is vegetation for feeding it can survive in greenhouses. The female whitefly will lay as many as 300 eggs on the underside of new leaves. The eggs are microscopic and tend to be laid in a circular pattern. They hatch in 5-10 days and pass through four instars. The skins from each instar moulting can be found underneath leaves. Temperature has a significant impact on the lifecycle of the greenhouse whitefly. At 30C the whitefly will complete its lifecycle in 18 days, while at 18C it would take 35 days. |
| Host: | The greenhouse whitefly is attracted to tomato and cucumber transplants in greenhouses as well as bean crops in the field. It is also a serious threat to ornamentals such as poinsettia, begonias and hibiscus. Weeds are also potential hosts and can be the original source of infestations. |
| Bio Region: | Throughout North America, but in Canada primarily as a greenhouse pest. |
| Damage: | Greenhouse whiteflies damage plants by sucking the juices from them. They do so by inserting their stylet through the leaf tissue into the phloem of the host. The whitefly tends to feed on newer leaves. They also spread diseases such as the pseudo yellows virus. The greenhouse whitefly regurgitates a large amount of a sticky subtance referred to as honeydew. This promotes the formation of a black sooty mould. The mould shades the leaf surface, which prevents photosynthesis and weakens the plant. |
| Management: | Management of greenhouse whiteflies is achieved mainly through prevention. Greenhouse operators should inspect all plants entering the greenhouse for whitefly and all other greenhouse pests. Isolation rooms if available should be used. Whiteflies are particularly difficult to control because all three developmental stages of the insect can be found on a plant at any given time. Interventions that only affect one developmental stage will have only a short-term effect. Vacuuming is effective. Yellow sticky traps can also play a role in monitoring and keeping populations in check. Yellow traps should be placed at ventilation entrances to the greenhouse. On plants they should be placed so as to be level with the top leaves. As with other greenhouse pests that have weed hosts, a no-vegetation buffer of up to 30 feet should be maintained around greenhouses. |
| Controls: | Encarsia formosa is a parasitic wasp that is commercially available and is particularly effective at controlling greenhouse whitefly. Greenhouse operators with controlled atmosphere capabilities can reduce oxygen or increase carbon dioxide levels within the greenhouse and achieve near 100% mortality rates in adult whiteflies in just a few hours; larvae and eggs require up to eight hours of reduced oxygen content. Dormant oils can be used to kill eggs laid in woody ornamentals. Insecticidal soaps can also be used although repeat applications are often necessary and beneficial insects populations could be harmed. |
