Unique species on the Galápagos Islands are under threat from mosquitoes introduced by tourist planes and boats, according to research published today.

The southern house mosquito, Culex quinquefasciatus, capable of carrying West Nile fever and avian malaria, is being transported from mainland Ecuador and breeding with existing populations on the islands, prompting fears of disease outbreaks.

The Galápagos giant tortoise and marine iguana, which are unique to the archipelago, may now be at risk, say scientists from the University of Leeds and the Zoological Society of London (ZSL), who carried out the research in conjunction with the Galápagos national park and Charles Darwin Foundation.

Endemic birds, including the waved albatross, red-footed booby and flightless cormorant, may also be vulnerable.

Dr Simon Goodman, from Leeds University, said that while fumigation measures had been introduced on planes, their success had yet to be evaluated. He said that to prevent the mosquito spreading both cargo and tourists boats should also be regularly treated with insecticide and boat lights changed to ones less likely to attract flying insects.

The Galápagos – an archipelago of volcanic islands in the Pacific ocean – are particularly well-known for their huge number of endemic species, and the number of visitors to the island chain has increased from 40,000 in 1990 to more than 170,000 last year.

Tourism is a major source of income for the Galápagos and Ecuador. In 2007 there were 2,194 flights to the islands, and an estimated 363,000 passenger days on boats.

"Few tourists realise the irony that their trip to the Galápagos may actually increase the risk of an ecological disaster," said Goodman.

Arnaud Bataille, a Leeds-ZSL PhD student, said: "Our research consisted of looking for insects in aircraft holds and genetic analysis of the mosquito populations. The former allows us to quantify the arrival rates of mosquitoes on aeroplanes, and the latter allows us to estimate how many survive and spread around the islands once in Galápagos.

"On average the number of mosquitoes per aeroplane is low, but many aircraft arrive each day from the mainland in order to service the tourist industry, and the mosquitoes seem able to survive and breed once they leave the plane."

The introduction of the southern house mosquito to Hawaii in the 19th century devastated the islands' endemic birds.

Goodman added: "That we haven't already seen serious disease impacts in Galápagos is probably just a matter of luck. The Ecuadorian government recently introduced a requirement for all aircraft flying to Galápagos to have insecticide treatment, but the effectiveness hasn't yet been evaulated, and similiar measures still need to be introduced for ships.

"With tourism growing so rapidly, the future of Galápagos hangs on the ability of the Ecuadorian government to maintain stringent biosecurity protection for the islands."

Earlier this year, on the 200th anniversary of the birth of Charles Darwin – who developed his theory of evolution after visiting the islands – the Darwin Foundation warned that an ecological disaster might only be a decade away.

The influx of visitors has caused a sharp spike in alien species, which now seriously threaten the fragile ecosystem of the island chain. In 1900 just 112 alien species were recorded, compared with 1,321 in 2007.

While programmes are already in place to remove pests such as feral goats, pigs, cats and dogs, insects such as mosquitoes and the fire ants that have also been imported to the island are more difficult to eradicate.

Andrew Cunningham, a senior scientist at ZSL said: "Our research has shown that everything is in place for a similiar disaster to occur in Galápagos as occurred in Hawaii."