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40 Years Young – The Discovery and Life of Bacillus Thuringiensis Israelensis

In 1972, an award was created to recognize individuals who contributed in an outstanding manner toward scientific knowledge and public leadership that preserves and enhances the environment. In 2003, the prestigious Tyler Award for Environmental Achievement went to Dr. Yoel Margalith for the discovery of an unassuming soil bacterium that has saved millions from mosquito- and blackfly-borne diseases.

The bacterium is Bacillus thuringiensis subsp. israelensis, commonly referred to as Bti.

2016 marked 40 years since the discovery of one of nature’s most powerful interventions. It’s time for a look back through the discovery and successes of the life-saving bacterium.


Dr. Margalith, also known as “Mr. Mosquito,” is well-known for his wide range of work in the public health field. His crowning achievement began in the Negev Desert in 1976 when he observed dying Culex pipiens larvae in a temporary pond. From samples of that pond bed, Margalith isolated Bti which he found to be lethal to most species of mosquitoes and black flies. What distinguished Bti from other materials being used to combat vector-borne illnesses was its lack of negative impact on its surroundings or non-target species and built-in resistance management capability.


One of the first successful Bti interventions was introduced in the 1980s when many river-bordering villages of West Africa were experiencing outbreaks of Onchocerciasis, a disease brought on by infection from the filarial worm Onchocerca volvulus and the blackflies that vector it. The disease was referred to as “River Blindness” due to the fact that, when left untreated, the worm’s offspring migrate to the ocular region of the host causing itching, weakness, muscle pain, rashes, lesions, and ultimately blindness. Between a combination of Bti – to control the blackfly vector – and an effective antiparasitic known as MECTIZAN® to help those already infected, interventionists were able to eradicate River Blindness.


Bti owes its effectiveness to controlling vector populations at the source. A powerful biological control that produces protein toxins specific to dipteran larvae, Bti causes the insect to stop feeding within one hour. Activity is reduced within two hours and paralysis occurs within six hours after ingestion. Bti is desirable because it has no adverse effects on non-target insects nor the surrounding environment.

Due to its multiple modes of action, the resistance management is so effective that in the 40 years since the discovery of Bti, there has not been a single case of Bti resistance reported in the field. With insecticide resistance to other interventions being a major concern, Bti looks to be an effective larvicide well into the future and is already having a strong impact on vector-borne diseases such as malaria, chikungunya, dengue, West Nile virus, Onchocerciasis, and Zika virus, among others.


Today, Bti is being applied directly to drinking water in developing countries to protect the population from vector-borne diseases. The World Health Organization approved the safety of the direct Bti application to water that is going to be consumed.

While it is impossible to fully quantify the magnitude of Bti’s contributions to public health, it is estimated that the bacterium is responsible for saving millions of lives around the world since it was first registered in 1980. According to Steven T. Su, Ph.D., M.D., Scientific Director for the West Valley Mosquito and Vector Control District, “When it comes to vector control, Bti is the number-one material at our disposal. It has contributed tremendously to the public health community without having a negative impact on the environment.” Dr. Su asserts that there is nothing comparable to Bti in its combined efficacy, inherent resistance management, and lack of impact on non-target species. He believes that, looking ahead, Bti will be strongly utilized in combination with other pesticides that are currently experiencing issues with resistance due to its inherent resistance qualities.

To see how biological larvicides containing Bti are used today in developing countries as a response to the Zika Virus, visit to view a short, comprehensive video on application methods and its effectiveness.

To commemorate this achievement in public health, a statue was erected in front of the World Health Organization (WHO) headquarters in Geneva depicting a young boy leading a blind man suffering the effects of River Blindness.

MECTIZAN® is a registered trademark of Merck & Co., Inc