In a nutshell: Major greenhouse pest in temperate regions; wide range of host plants; sap suckers—excrete sticky “honeydew”, cause leaves to wilt and fall; adults group together in the upper leaves; survive swell at low temperatures.
What are greenhouse whiteflies?
The greenhouse whiteflies (Trialeurodes vaporariorum) are a major pest of ornamentals and vegetables worldwide. Although they originate from tropical America, they have a high mortality rate at high temperatures. The lower temperatures of a temperate environment favour it, but it can't overwinter.
What kinds of plants do they attack?
First noted as a problem in tomatoes over 100 years ago, this whitefly now occurs on hundreds of other plant species, including eggplant, beans, cucumber, peppers, roses, gerbera and poinsettia.
What do they look like?
Greenhouse whitefly females are around 1.1 mm in length and the males are slightly smaller, around 0.9 mm. Adults of both sexes have wings set flat against the back that extend past the tail end of the insect’s body. The wings are transparent in newly emerged adults, but within a few hours they become covered with a white, waxy powder, as does the body.
Female whiteflies lay their eggs on the underside of young leaves, near the top of the plant. They’re often deposited in a ring, with the female turning on the spot as she lays them. The eggs are white, oval shaped and about 0.25 mm in size. They may or may not be covered in waxy powder from the female’s wings. Two to three days after being laid, the eggs turn dark brown or black.
During the first larval stage, the whitefly is about 0.3 mm long, oval shaped and has well-developed legs and antennae. After they hatch, they spend several hours looking for a good place on the leaf to feed. Once they’ve found a nice spot, they stay there for the rest of their larval development. In the second and third stages, the larvae get progressively bigger. They’re flattened on the leaf and have legs and antennae reduced so much that they’re no longer visible. The insects are also virtually transparent at these stages and very difficult to detect.
Finally, greenhouse whiteflies entering the pupal stage change form to become a white, oval case about 0.7 mm in size encircled by a ring of waxy threads. The adult emerges from the pupa through a T-shaped slit.
How do I know if my plants are under attack?
Greenhouse whiteflies are sap suckers. Similarly to aphids, whitefly larvae consume large amounts of sap. They excrete the excess as a "honeydew" on the leaves.
This honeydew encourages the growth of black fungal moulds on the plant and its fruit. The mould reduces photosynthesis and moisture regulation in the leaves and, in serious cases, can rot fruit.
Adult whiteflies are found in the tops of plants, on the underside of the topmost leaves. They will fly up when disturbed, then settle back on the leaves. They prefer to lay their eggs on these young upper leaves, and the lower leaves, the older the larvae found there.
If the whitefly population is large, the plant won't grow well, and in full sunlight the leaves can wilt and fall off. This in turn can affect fruit development, lower the plant's yield, and ruin the appearance of ornamentals.
The greenhouse whitefly also transmits several different viruses among vegetables and fruits.
How to get rid of Greenhouse whitefly
Koppert offers different solutions for biological pest control of Greenhouse whitefly.