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Wasps spell sticky end for unwelcome resident

18 July 2006

Scientists have found a natural predator, a minute parasitic wasp, to help fight an invasion of whiteflies in the Canary Islands.

The whiteflies,Lecanoideus , leave nasty deposits on benches, cars and laundry and the deposits have even caused asthmatic attacks in some locals as it blows in the wind.

Fluffy waxy secretions
Fluffy material on leaves and trees caused by whiteflies © Jon Martin

Fluffy material on leaves and trees caused by whiteflies © Jon Martin

Young whiteflies secrete a fluffy, waxy material covering shrubs and trees. Scientists are unsure of this material's function but it may provide a favourable environment for the young whiteflies to grow in.

Adult whiteflies produce large amounts of excreted sap rich in sugars known as honeydew. This combines with the waxy fluff to make a sticky mess that coats pavements, benches and drying laundry. If it isn't washed off promptly an unsightly black 'sooty mould' grows in the nutritious substance.

Accidentally introduced
Woolly larvae of the whitefly on coconut leaves © Jon Martin

Woolly larvae of the whitefly on coconut leaves © Jon Martin

Whiteflies were accidentally introduced to Tenerife and La Gomera, for example by boats importing items such as food. The insects thrived in the warm climate and because they face no natural predators or cold winters on the islands they have established enormous populations. Natural predators of whiteflies are usually insects, such as ladybirds, lacewings and tiny internal parasites.

Investigation begins
Whitefly egg trails © Jon Martin

Whitefly egg trails © Jon Martin

A whitefly specimen was sent to Jon Martin, insect expert at the Natural History Museum, for identification. The culprit was an undocumented species so Jon searched through the Museum's collection of unidentified insects.

Jon came across a few examples of the immature stages of this same whitefly species, each with a hole chewed by an emerging wasp parasitoid. A parasitoid is an organism that kills its host as it develops, whereas parasites rarely kill their host.

These unidentified whitefly specimens had come from a town called Coca in Ecuador, South America. So Jon set off to Coca with colleagues from the Canary Islands and Ecuador in search of the wasp parasitoid that caused the tell-tale holes in the Museum's whitefly material.

Search for a parasitoid
The natural predator for the whitefly pest, a wasp parasitoid. © Estrella Hernadez-Suarez

Scientists found this natural predator for the whitefly pest, a wasp parasitoid. © Estrella Hernadez-Suarez

Luckily, they found several colonies of the whiteflies, with accompanying parasitoids, in the same location in Coca.

'We parked under a coconut palm and we were suddenly hit by the realisation that it was covered in our target species,' said Jon. 'The following day we returned with a large cold-box in which to keep the cut leaves ready for transit to Europe, but it was a true Eureka moment when we realised that our quarry was right there, in town.'

They took live specimens to the Canaries and are growing many tiny parasitoid wasps under quarantine conditions.

When the wasps are released they should control the whitefly numbers by killing a large proportion of them. Fortunately these wasps target only a narrow range of insects as hosts so will not affect other wildlife on the islands.

If the wasps bring down the population numbers this will be an excellent demonstration of natural biological control . The Canary residents wait patiently for a successful outcome.