Environment: South African invaders spell death for the floral symbol of Spain's sunny south

The face of Spain is being transformed as a South African butterfly eats its away through the essential feature of every Mediterranean balcony and patio. Elizabeth Nash reports on the eradication of the geranium.

So farewell then, that riotous blast of colour as essential to the image of southern Spain as sultry senoritas in polkadot flounces. The decline of the geranium, renowned for its indestructibility, is preoccupying a nation of balcony-lovers as they watch their favourite pot plants wither and die.

The geranium is being destroyed by a plague of South African butterflies and the southern Mediterranean is set to become a geranium-free zone. The culprit is Cacyreus marshalii, known as the Geranium Bronze, a common cohabitee with the flower in its South African habitat but a murderous predator in Europe since it was inadvertently introduced into Mallorca in 1989.

The butterfly lays its eggs on a plant and when the grubs hatch they burrow into the stems and buds and munch the plant from within. Protected from pesticides, they destroy a pot of blossoms within weeks.

Only the far northern Cantabrian coast remains untouched by the butterflies, which have spread to Portugal, southern France, Italy and the Netherlands.

"The butterfly was introduced by someone importing an infested cutting, because this is not a migratory species. It's now impossible to stop the plague," says the Catalan botanical scientist Albert Masso, who has been studying the matter for six years.

In Spain 500 greenhouses produce 10 million geraniums for sale in a business worth pounds 13m a year. The agricultural pressure group Vida Sana (Healthy Life) says commercial pressures caused the problem. "Intensive cultivation in the greenhouse at a temperature of 30 degrees speeds up the butterfly's life-cycle from its normal 82 days to 33 days. This produces twice as many generations of butterflies in the year, even during the winter," a spokeswoman said.

Nonsense, says Dr Masso."The problem comes when the plants are put in gardens or balconies. The majority of geraniums start off healthy and are attacked later, because the Geranium Bronze has no natural predators in Europe." Strong insecticides applied every two weeks, keep the plague at bay, he says. But Vida Sana says pesticides tackle only the symptoms, not the cause of the problem.

Dr Masso agrees that pesticides are only a short-term solution. "We cannot combat this plague effectively. It might leave some corners untouched, but it will continue. I am pessimistic."

We must, therefore, reconsider the virtues of the petunia.