Background: Two long sewerage canals in the city of Kolkata, India were heavily infested with larvae, pupae and egg rafts of the mosquito Culex quinquefasciatus. Although the burden of bancroftian filariasis and other diseases transmitted by C. quinquefasciatus in the city is practically zero, the night-biting mosquitoes are a great nuisance to residents living alongside the canals. It is known that mosquitoes survive poorly in water agitated by wave and wind action.
Method: The health department of Kolkata Municipal Corporation undertook, from November 2010 to April 2012, a programme of plying speedboats along the canals to prevent C. quinquefasciatus breeding. At the same time, along stretches of canal too shallow to permit the use of speedboats and where the canal banks are inaccessible to spraymen, the edges were treated with larvicidal spray, Temephos 50% EC (emulsifiable concentrate), using small rowing boats as transport.
Result: The densities of egg rafts and immature and adult insects declined dramatically when the speedboats were deployed and remained low for the duration of the project. For Feburary, the peak month for C. quinquefasciatus breeding, densities for egg rafts, larvae, pupae and adults, respectively, declined from 800, 2942, 1457 and 662 to 3, 75, 15 and 27. The cost was comparable to that of using larvicidal spray where this required the use of rowing boats.
Conclusion: Speedboat-generated waves are effective in preventing the breeding of mosquitoes in otherwise mosquitogenic canals. Where use of boats is an option and use of insecticides is unfeasible or undesirable, the plying of speedboats is a potentially ecofriendly approach to mosquito control.