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Unlucky Bamboo hides Asian Tiger Mosquito An aggressive species of tropical mosquito has been recently discovered in the Netherlands, associated with imported bamboo in glasshouses. In August 2005, growers in one of Europe’s largest areas of glasshouse cultivation, between Amsterdam and Rotterdam, complained of biting mosquitoes. Willem Takken and co-workers of Wageningen University, Netherlands, investigated the reports, and found the Asian tiger mosquito (Aedes albopictus) to be present. The species is native to South East Asia where it is commonly found. Giving a painful bite, it is also an important vector of several arboviral diseases including Dengue fever, as well as dog heartworm. This discovery in the Netherlands is the most northerly record for this mosquito in Europe. After installing adult mosquito monitoring devices at several locations, Takken found sites belonging to 3 horticultural companies to be positive for Asian tiger mosquitoes: all companies had been importing “lucky bamboo” (Dracaena sanderiana). Adult mosquitoes were found outside close to glasshouses until September, and were sighted inside until early November. In addition to the local threat, there is also concern that some bamboo may have been re-exported to other destinations in Europe. Lucky bamboo is exported from China around the world as an ornamental plant. The bamboo is transported by sea in large containers where it stands in 5-10cm of water. The tiger mosquito typically breeds in small bodies of water, and these containers of bamboo provide an ideal site for the female mosquitoes to lay their eggs. On arrival, the adult mosquitoes can escape into their new habitat. This association of tiger mosquitoes and lucky bamboo is a relatively new phenomenon, with importation of mosquitoes in lucky bamboo shipments first being found in California during 2001. As a result, the USA and Canada have now banned the import of lucky bamboo in standing water. However the tiger mosquito initially acquired notoriety as an unwelcome stowaway in used car tyres being transported around the world for recycling or re-use. The water that collects in such tyres is an ideal breeding site, and the eggs can survive for months should the water dry up. The tiger mosquito was accidentally introduced by the car tyre trade into the USA during the 1970’s, and by 1999 it was found in around 25 states in the USA, all east of the Rocky Mountains. In Europe the species was first found associated with used tyres in Albania, again back in the 1970’s. Although the glasshouses in the Netherlands provide an ideal habitat for the tiger mosquito, due to the controlled temperature, humidity, and long day-length, the mosquito has also become successfully established outdoors in many areas of Europe. From the first foothold in Albania (1988), it is now widespread around the northern coast of the Mediterranean. It is common in Italy, and has spread west to Nice and Marseille in France. Populations are also well-entrenched in Spain from Barcelona to Seville. In recent years isolated outbreaks of the tiger mosquito have also been found in Paris, Le Havre and Antwerp, associated with used tyres, but these pockets now appear to have been eradicated. The Asian tiger mosquito ranks among the top 100 of the “World’s Worst Invasive Species,” a database compiled by the World Conservation Union. Tiger mosquito populations are very hard to eradicate once established. In Spain and Italy for example, the authorities are now focussing on reducing local biting nuisance, rather than attempting complete eradication. Despite the proven role of this mosquito as a vector of a range of arboviruses in SE Asia, in Europe the main problems are limited to biting nuisance. In Italy, the tiger mosquito’s day-time human biting behaviour and its abundance in urban areas, is believed to be having a significant effect on the tourist industry. The tiger mosquito is also a concern for the UK, since the mosquito may be able to survive in the British climate. The -5°C isotherm appears to be the limit to its northerly spread, but that leaves much of the UK potentially suitable. With the UK trading in both used car tyres and lucky bamboo, and lacking comprehensive mosquito monitoring at ports, it could well be the next destination for this global mosquito. Meanwhile the population of tiger mosquitoes identified by Takken in the Netherlands will continue to be monitored, at least until June 2006. So far, the numbers of mosquitoes found in the glasshouses have been low, and they do not appear to have become established outside. However Takken is curious to see whether any mosquitoes survive the Dutch winter. Given that the eggs of this mosquito readily survive long periods of relatively low temperatures providing it does not freeze, glasshouses would appear to be ideal conditions for this insect. This example should act as a warning to countries that do not have established populations of Asian tiger mosquitoes. Monitoring ports and importation routes is essential to prevent invasion of the mosquito. After all, not only is prevention better than cure, but once Asian tiger mosquitoes are established “cure” might not be possible. Written by Nick Boase Professor Willem Takken (contributor)
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