Mosquito Control in Tobago
The problem of mosquitoes and the means to control them is a reality that now confronts the Tobago population. This issue of mosquito control is quite serious because of the implications for the health of the population, both in terms of the threat from the Aedes aegypti mosquito and also from some the control measures now being applied.
The Aides Egypti mosquito is a vector for dengue fever. When a female mosquito feeds on the blood of an infected person it absorbs the virus that causes dengue. If that same mosquito ‘bites’ an uninfected person it injects the virus into that individual’s blood. This can lead to this second individual developing dengue fever.
At present, Tobago and most of the other Caribbean islands are faced with high risks of dengue fever epidemics. This is due to two major factors. The first is that there are a significant number of persons who are carrying the dengue fever viruses. The second is the high populations of Aedes aegypti mosquitoes.
In addition to spreading dengue fever, mosquitoes can also transmit yellow fever and malaria. Mosquitoes also cause anemia and contribute to skin infections. It is therefore critical that proper measures be applied to keep the level of mosquitoes as low as possible.
MOSQUITOES BREEDING HABITS
To successfully control the Aedes aegypti mosquito, one must first determine the factors that are contributing to its successful breeding. The female mosquito is known to deposit its eggs in relatively clean, stagnant water. The larvae and pupae also inhabit the water in which the eggs were deposited. It is reasonable to suggest therefore, that for Tobago to have such high mosquito indices, the mosquitoes are having access to water that serves as breeding grounds. Research done in Trinidad by D.A Focks and D.D Chadee and published in the American Journal of Tropical Medicine and Hygiene A. 56. (1997) 159, has identified outdoor drums, water storage tanks, buckets, laundry tubs, discarded tires drink bottles and cans as the most common breeding areas for the Aides Egypti mosquito. Outdoor drums, tubs, buckets and small containers were found to account for over 90% of all Aedes aegypti pupae. It is reasonable to assume that these research results can be applied to the Tobago situation based on similarities in climate and culture.
Three types of approaches can be utilized in seeking to control the Aedes aegypti mosquito. The first is the elimination of access to stored water in which the female mosquitoes can lay eggs. Chadee and Focks in their research report have estimated that environmental sanitation efforts aimed at eliminating tires, bottles, tins, etc. would reduce mosquito densities by 43%. They have also estimated that eliminating water stored in drums and buckets have the potential for achieving a further 38% reduction is the Aedes aegypti population.
The second approach to mosquito control is the use of chemicals to kill the different stages of the mosquito life cycle. Oil can be applied to water, causing the larvae and pupae to suffocate. The extensive use of oil will cause pollution of surface water. Insecticide targeted at the adult mosquitoes can also be applied. One such insecticide used in Tobago is Malathion. This is a broad-spectrum insecticide used to kill a wide variety of insects.
In Tobago, the health department applies Malathion mainly through fogging. There are drawbacks to the use of Malathion. This chemical is toxic. It is an organophosphate compound. Organophosphates were first developed during World War 1 for use as chemical weapons to kill soldiers (gas warfare). Research has found out that Malathion causes genetic damage to mammalian cells. These mutations can lead to cancer and weakened immune systems.
The use of Malathion in Tobago is believed to be having serious negative impacts on the populations of beneficial insects. Malathion is highly toxic to honeybees. Beekeepers are complaining of the loss of bees and the resultant decline in honey production. Decreases in the populations of butterflies and ladybugs have also been observed. A question that is being increasingly asked is “Where have all the butterflies gone?”
Malathion is also toxic to snails, worms, crustaceans, fish, birds, toads and frogs. Studies done in Nigeria have found that Malathion inhibits nitrification in soil for up to 30 days, thus reducing soil fertility. Due to such widespread effects being associated with the use of Malathion, this chemical should be utilized with extreme caution.
In the application of Malathion by fogging, diesel is used as the dispersal agent (thermal application). The diesel fumes that are produced constitute an environmental hazard. The pollutants in diesel fumes include carbon monoxide, carbon particulates and nitrous oxides. If any industry was to release these types of fumes, one can be sure that the relevant agencies would act quickly to have this nuisance stopped.
The third approach to controlling the Aedes aegypti is biological control. This is the use of one type living organism to control another. An example is the use of ladybugs and wasps to control the mealybug. At present, the main biological agent being used for mosquito control in Tobago is a bacterium called Bacillus thuringiensis. This bacterium kills the larvae of mosquitoes and is applied to water in the form of granules. The major disadvantages in using Bacillus thuringiensis are that it is expensive and its effectiveness in the field is short-lived (30-45 days).RECOMMENDATIONS
1. An island wide effort to remove discarded tires, bottles, tins, etc. should be organized since research has indicated that the elimination of these types of containers can reduce the population of Aedes aegypti mosquitoes by more than 40%. This effort should be accompanied by stringent enforcement of the Litter Act. There is a definite link between illegal dumping/littering and the high mosquito population.
2. A programme aimed at mosquito proofing water storage tanks and drums should be implemented immediately. This may require legislative support and enforcement.
3. The use of Malathion should be restricted and possibly eliminated due to its serious environmental impacts.
4. Local production of Bacillus thuringiensis should be initiated to reduce the cost of this biological agent. A new, low-tech method to produce Bacillus thuringiensis has been developed in Peru utilizing coconut water as the fermentation medium.
5. The use of other low-cost, low tech and low toxic methods of mosquito control such as garlic preparations and citron should be researched and applied if found to be viable.
6. Householders should mosquito proof their homes to prevent the entry of mosquitoes and also avoid infection with dengue fever.