Biolarvicide obtained from sugarcane bagasse kills larvae of Aedes aegypti

Product interrupts development cycle of mosquito that transmits dengue, zika and chikungunya.

By Elton Alisson  |  Agência FAPESP – Researchers at the University of São Paulo’s Lorena School of Engineering (EEL-USP) in Brazil have developed a sugarcane bagasse-based biolarvicide capable of eliminating larvae of Aedes aegypti, the mosquito that transmits dengue, zika and chikungunya, by making it hard for them to breathe and destroying the cuticle that covers their bodies (exoskeleton).

The biolarvicide production process, which has been patented, is one of the outcomes of the FAPESP-funded project “Biosurfactants as versatile molecules” and of Paulo Franco’s PhD research at EEL-USP.

“We found that the product can kill larvae of A. aegypti within 24 hours after being diluted in water and destroy them within 48 hours,” said Silvio Silvério da Silva, a professor at EEL-USP and principal investigator for the project, in an interview with Agência FAPESP.

According to Silva, who is Franco’s PhD supervisor in industrial biotechnology, the product is a surfactant – a substance that reduces surface tension (elasticity) in liquids and emulsifies compounds with different polarities (electronegativity), i.e., polar and non-polar compounds.

Surfactants are widely used in manufacturing, especially in cleaning products such as detergents because of their capacity to emulsify (combine) substances that do not normally mix, such as oil and water. However, most of the surfactants marketed today are derived from petroleum and are extremely harmful to the environment, especially in aquatic ecosystems, Silva explained.

“Studies have shown that excessive amounts of surfactant in rivers lead to a build-up of foam, a decrease in oxygen dissolved in the water, and less light permeability,” he said. “In addition, surfactants interfere in biological processes like the nitrogen cycle, and their degradation can increase concentrations of xenobiotic compounds, which are lethal to most organisms.” Xenobiotic compounds are chemicals that are foreign to the biosphere.

Silva and Franco set out to develop a surfactant from a renewable source and with no or very little toxicity. They succeeded in obtaining a product from sugarcane bagasse with the same properties as a synthetic surfactant produced by purely chemical processes.

“We were able to develop what we call a ‘green’ surfactant, or second-generation biosurfactant, from yeast that produces the substance during fermentation of the sugar present in sugarcane bagasse hemicellulose hydrolysate,” Silva said.

Trials with Aedes aegypti

Like synthetic surfactants, their biosurfactant also reduced surface tension in liquids and emulsified substances with different polarities, so it occurred to them to try it out as a weapon against A. aegypti.

Trials were conducted in partnership with Cláudio Von Zuben and Jonas Contiero, professors at the Rio Claro campus of São Paulo State University (UNESP), and Vinicius Luiz da Silva, a PhD student at the same institution.

The results of the trials showed that the biosurfactant caused the death of A. aegypti larvae by blocking their respiratory siphon. This region consists of non-polar molecules, with humidity controlled and protected by the exoskeleton. The researchers found that it was susceptible to interaction with water and that larvae exposed to the biosurfactant suffered asphyxia.

More specifically, the biosurfactant’s presence in water where mosquitoes laid eggs altered or impaired their larvae’s hydrostatic balance, forcing them to expend so much energy that they eventually drowned.

“The larvae were unable to breathe and died from asphyxia within 24 hours after coming into contact with the biosurfactant,” Silva said.

The researchers were also surprised to find that the larvae’s exoskeletons disintegrated within 48 hours after initial contact with the biosurfactant. They believe this could be because, chemically speaking, the biosurfactant is amphiphilic, meaning part is soluble in water and part in fat. The chemical structure of its molecules, like those of synthetic surfactants, has a polar region that is water-soluble and a non-polar region that is not water-soluble but is soluble in lipids and organic solvents. As a result, the biosurfactant can interact with, and in some cases dissolve, both polar and non-polar substances. In this respect, it resembles a detergent, in which surfactants blend with water and fatty particles to remove the particles from kitchen utensils, for example.

“Now, we want to find out whether this same process occurs in the cuticular hydrocarbons of A. aegypti larvae,” Silva said.

According to the scientific literature, he explained, the hydrocarbons in the larva’s cuticle are non-polar compounds that are not very water-soluble. “We plan to conduct experiments as part of the project to find out whether these cuticular hydrocarbons interact with the biosurfactant,” he said.

Other diseases

The researchers tested the product in liquid form to determine the ideal dose for application in breeding grounds of A. aegypti. They will now develop it in powder form, test the physicochemical properties of the formulation and verify the best application method.

“We plan to perform new tests to develop the product in solid form and try out different doses to see which is best, as well as to investigate the optimal formulation, which may be solid or liquid,” Silva said. “We also want to analyze the physicochemical properties of the biosurfactant in powder form and see how often it should be applied. All this is required if the product is to be manufactured on an industrial scale.”

The researchers also plan to develop other biosurfactants for use in combating other neglected tropical diseases, such as leishmaniasis and schistosomiasis.