5. Natural oils such as neem, citronelle, eucalyptus, or garlic have mosquito repelling properties and can be used in various ways, either applied directly on the body in the form of cream, ointment or spray, or heated (e.g. as in electric 'mats' or in aromatherapy) or burnt (e.g. in candle form, or directly in a fire) to create mosquito-repelling va-pours in a room. If used in candle form, several candles must be placed within a few feet of where people are sitting. It is important to know that while neem and citronelle oils are effective in repelling mosquitoes, the application of unmixed oils on direct unprotected skin should be done with caution. There are several methods of extracting oil from plants; one method uses solvents. Sometimes, traces of these solvents may still be found in the oil. Some people may develop allergic reactions to the oil or to the solvent used in the extraction process. On no account should these oils be taken orally, unless they are specified for that pu

Date:   6/16/2006 6:15:11 PM ( 18 y ago)

Mosquitoes and chikungunya.
Posted on Friday, May 26 @ 06:08:57 GMT by MauRIsUN

Health
The mosquito species that transmits the Chikungunya virus is the Aedes albopictus, commonly known as the Asian tiger mosquito or forest mosquito.


It is generally more aggressive than other mosquito species, and often outcompetes them. The adult mosquito is small (about 5 mm) and has a rapid bite that allows it to escape most attempts by people to swat it. There being no vaccine or preventive drug for chikungunya at present, the best way to avoid the infection is to control the mosquito population in the region and prevent mosquito bites.
Click to enlarge


The incidence and risk of a chikungunya epidemic in Mauritius justified the extensive application of insecticides, through fogging and spraying of synthetic insecticides such as temephos and pyrethroids over the past several months. However, with the apparent decrease in the number of new chikungunya cases, and the expectation that the mosquito population will decrease in winter, it is time to consider using a more environmentally-friendly strategy for mosquito control. This can be done by reducing the present level of use of synthetic insecticides and supplementing with more eco-friendly measures (an approach known as IPM i.e. Integrated Pest Management). A few such environmentally-friendly methods that can be used along with synthetic insecticides are listed below.
1. A particular species of bacteria, called Bacillus thuringiensis israelensis (Bti), kills mosquito larvae. This bacteria, commonly known as Bti, is safe to humans, fish and other aquatic organisms, household pets, and to the environment in general, and therefore can be applied directly to any water body without any danger. The Bti toxin released by the bacterium attacks the digestive system of the mosquito larvae and kills them. Bti is marketed in the form of granules or donut-shaped balls, under different trade names, e.g. Bactimos. The granules or balls just need to be added to the water body where mosquitoes breed. The balls break down in water and release the toxin over a period of about 1 month, while granules are quicker but need to be reapplied more frequently. Granules are more suitable for small areas on a domestic scale, while the balls can be used on larger water bodies, ponds, lakes, streams, etc.
2. Methoprene is another chemical that can be used to control mosquitoes. It is not an insecticide; it acts by disrupting the development of mosquito larvae and thus prevents them from transforming into adult mosquitoes. Methoprene is not harmful to humans, fish, other aquatic animals, birds, or household pets. Methoprene is marketed in the form of granules, under different trade names, e.g. Altosid. It can inhibit mosquito development for up to a month.
3. Dragonfly larvae live in water and eat mosquito larvae found in the water, while adult dragonflies catch adult mosquitoes as they fly and eat them. Hence dragonflies can be used as an additional mosquito control measure (this is known as 'Biological Control'), which can supplement the other methods used.
4. Similarly certain fish, e.g. Gambusia sp., Poecilia spp., eat mosquito larvae and pupae, and can be released in rivers, streams, lakes for this purpose. There are also a few species of very tiny invertebrate organisms (cyclo-poid copepods) that eat mosquito larvae and pupae and can be added to water tanks and cisterns.
5. Natural oils such as neem, citronelle, eucalyptus, or garlic have mosquito repelling properties and can be used in various ways, either applied directly on the body in the form of cream, ointment or spray, or heated (e.g. as in electric 'mats' or in aromatherapy) or burnt (e.g. in candle form, or directly in a fire) to create mosquito-repelling va-pours in a room. If used in candle form, several candles must be placed within a few feet of where people are sitting.
It is important to know that while neem and citronelle oils are effective in repelling mosquitoes, the application of unmixed oils on direct unprotected skin should be done with caution. There are several methods of extracting oil from plants; one method uses solvents. Sometimes, traces of these solvents may still be found in the oil. Some people may develop allergic reactions to the oil or to the solvent used in the extraction process. On no account should these oils be taken orally, unless they are specified for that purpose.
6. Extracts, oil or formulations of neem, citronelle, eucalyptus, geranium or garlic, applied in low concentrations to water bodies, kill mosquito larvae and pupae, and can help to reduce mosquito populations. If applied in recommended concentrations, these extracts are not harmful to humans or to the environment. These studies are ongoing at the Faculty of Agriculture, University of Mauritius.
7. Fresh neem leaves can be ground in water and left covered overnight in a dark place to extract the maximum amount of the bioactive ingredient. The mixture can be diluted and added to any water body, such as a pond or accumulated stagnant water. This kills mosquito larvae and pupae. Eucalyptus, geranium and garlic extracts can also be made and applied in exactly the same way. Garlic was found to be much less effective than the others. The concentration of the extracts to be applied will depend on the size of the water body and volume of water present.
8. Neem oil can be used similarly. However, since oil and water do not mix, small amount of liquid soap or detergent will need to be added to the oil to make an emulsion before it is applied to the water body.
9. In case of puddles, accumulated rain water, or other such small water bodies, a small amount of neem, citronelle, eucalyptus or other light oils can be directly poured on the water to make a thin film on the surface. This will prevent the larvae from getting atmospheric air and will cause them to suffocate. However, this is not recommended for ponds, rivers, streams, where the volume of water is much too large.
10. Commercial formulations of neem are also available. Although they are meant mainly for control of agricultural pests, investigations at the Faculty of Agriculture, University of Mauritius, have shown that they can also be used for mosquito control. They can be sprayed on the surface of the water body and also on vegetation where female mosquitoes are likely to lay eggs.
11. The plant extracts or oils mentioned above can also be sprayed on the inner or outer walls of buildings, on vegetation, to the base of tree trunks, etc., where adult mosquitoes are expected to rest and/or lay eggs.
12. Neem leaves and twigs placed on burning coals (e.g. in an old-fashioned 'resseau') in a room liberate a very effective insecticidal smoke, which can keep mosquitoes away for up to 48 hours. The process can then be repeated.
13. Bunches of fresh neem or geranium leaves placed around a room can repel adult mosquitoes from the room. The leaves should be replaced with fresh ones every 2 days. The old neem leaves can be burnt to produce insecticidal smoke as explained above.
- Sunita Facknath, BSc, MSc, F.R.E.S., Char. Biol., M.I.Biol. Entomologist Senior Lecturer, Faculty of Agriculture, University of Mauritius

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