CAN Bti DO THAT? (A review on biological pest management of Dengue in Sri Lanka.)

CAN Bti DO THAT?

(A review on biological pest management of Dengue in Sri Lanka.)

Dengue epidemic causes a huge public outcry all over the country, as it kills over 158 lives up to this July since beginning of year 2010. During past few days, you have heard many tragedies regarding to this fatal dengue fever.Dengue prevention is a very common headline in the society, when an epidemic has arisen. Although many strategies were used for dengue prevention, still the epidemic is out of control. Meanwhile the controversial Bti bacteria came into the stage emerging as a consolatory break to this fatal epidemic. Can Bti really control this situation? Let’s discuss on this matter.

As the death count increases due to the dengue fever, the allegations are directed towards the Health authorities for their failure of controlling the situation. As a result of this, Health Ministry invited two Cuban scientists for a paid official visit in order to obtain their expertise on this matter, from where the dengue epidemic is said to have been eliminated. After investigating the problem, Cuban scientists recommended a bacterium known as Bacillus thurengiensis israelensis (Bti) which is capable of destroying the larval population of the vector Aedes aegypti when the bacterium inoculated to the breeding sites of mosquitoes. Importation of Bti bacterium from Cuba is still under discussions but it is said that at the middle of this August (2010), first portion of the bacterium will be arrived to Sri Lanka. Meanwhile a Sri Lankan scientist, Dr. Radika Samarasinghe, a Senior Researcher at the Industrial Technology Centre (ITI), has also been able to produce the Bti bacterium in Sri Lanka and which also said to be used in near future as a product under the trademark of Bio Power Lanka (Pvt.) Ltd.

Since dengue is a viral disease, it can not be eradicated using chemotherapeutic methods. The one and only way to eradicate the disease is by controlling the vector population. According to insect management strategies, elimination of an insect population is out of rules. In order to minimize the loss caused by insects, rather than elimination, managing insects at very low population level is performed. Insect species including mosquitoes are highly adaptive organisms to various environments as they can develop various mechanisms for their survival against the controlling strategies used by human within few generations. That is why their elimination is quite difficult.

Bti is an aerobic spore-forming bacterium commonly found in the environment. During sporulation, this bacterium can produce a crystalline protein which acts as an insecticide. Bti is not a contact poison like some other insecticides available in the market but at the mid gut of the alimentary canal of the insect, Bti releases its toxic effect; hence it is a stomach poison for insects. The crystalline protein produced by Bti dissolves in the mid gut of insect and results protoxins which bind with the receptors of the mid gut epithelial cells. Then they generate pores in the epithelial cell membrane disturbing the cellular osmotic balance which results the death of the insect.

There are about 34 subspecies of Bacillus thurengiensis species and all of them are tend to be toxic to larvae of butterflies and moths. Few subspecies like Bacillus thurengiensis kurstaki, Bacillus thurengiensis israelensis (Bti) and Bacillus thurengiensis tenebrionis are toxic to mosquitoes and beetles. In USA the subspecies Bacillus thurengiensis israelensis is widely used to control mosquitoes. According to the news sources, Bacillus thurengiensis israelensis is the bacterial species which is planned to be introduced as the biological insecticide for mosquitoes in near future. The crystalline protein produced by Bacillus thurengiensis israelensis has no prior records about the negative effects on non target organisms and environment. Unlike many of other insecticides available in the market, this toxin has no hazardous effect on humans, wild or domestic animals and this toxin remains in the environment for a short time thus it has a minimum effect on the environment.

But the most considerable point is that, with the mere introduction of Bti, is it possible to suppress this dengue epidemic?

• Bti is a foreign bacterium. It may take a considerable time for the establishment in this environment. So the expected result from Bti may not be obtained immediately.

• A sudden introduction of Bti in large scale may affect the balance of this environment, although Bti is known as a harmless alternative for humans, wild or domestic animals.

• It is obvious that the pest management of an insect vector species like mosquitoes which are capable of breeding in places where water is available cannot be achieved only by spraying of a chemical or a bacterium. Even though 80% of the population is destroyed the remaining 20% can make a rapid multiplication of insect number, if the breeding sites are already available for them. So it is a necessity to launch an integrated pest controlling strategy with the cooperation of the government sector, the private sector and especially with the citizens. According to my point of view, the real problem is related to this integration. Elimination of the breeding sites of mosquitoes is one of the most important strategies that the integrated pest controlling program should contain. And also Bti toxin can be used as a supplement for that program.

In other words, we as a society should be united to maintain a clean environment by destroying breeding places of mosquitoes and giving our maximum cooperation to the authorities who are dealing with this problem. All other countries that have overcome the diseases vectored by insects achieved that target through the maintenance of a clean environment by doing public awareness campaigns and the active involvement of citizens. Government has declared one week, 16th August to 22nd August 2010, as the Dengue prevention national week. Think again, this kind of a declaration is not necessary, if you are sensitive enough about this tragedy.

Active involvement of citizens of this country will play a major role in order to make this dengue prevention venture a success.

Until then, no more deaths dengue, please!!!

References –

• An article published on web space by Dr P.M. Wijeratne, Senior Entomologist,Department of Agriculture.

• http://www.news.lk/index.php?option=com_content&task=view&id=10966&Itemid=52

• http://www.sundayobserver.lk/2009/07/26/fea20.asp

• http://www.colombopage.com/archive_10B/Jul21_1279724896KA.php (2010/07/22)