A spray made from crab shells and silver nanoparticles may curb the spread of malaria-carrying mosquitoes, say scientists who tested the environment friendly solution successfully in India.

“The solution can be employed at low dosages to strongly reduce populations of the malaria vector, the Anopheles sundaicus mosquito without detrimental effects on the predation of natural mosquito enemies, such as goldfishes,” said Jiang-Shiou Hwang of the National Taiwan Ocean University.

Researchers, including those from Bharathiar University in Tamil Nadu, took chitosan or chitin, a non-toxic natural substance that has been used in wound healing and in manufacturing biodegradable food package coating.

Chitin is found in animal tissues, such as the exoskeletons of arthropods, bird beaks and insect eggs, researchers said.
It can easily be chemically changed, is quite strong and, because of its abundance in nature, is cost-effective to use.

Researchers first crushed and oven-dried the exoskeletons of a number crabs before extracting chitin and other minerals.

The subsequent creamy-white filtrate was then mixed with silver nitrate to obtain a brown-yellow solution of silver nanoparticles.

The solution was sprayed over six water reservoirs at the National Institute of Communicable Disease Centre in Coimbatore.

Researchers found that even in small concentrates it killed mosquito larvae and pupa quite effectively.

“This research highlighted that chitosan-fabricated silver nanoparticles are easy to produce, stable over time,” Hwang said.

“It had the greatest effect during the early stages of the mosquito larvae's development,” researchers said.
The solution was also tested in conjunction with freshwater goldfish that fed on mosquito larvae.

The nanoparticle solution did not have any effect on the fish, indicating that it is an environmentally friendly and non-toxic product.

It also inhibited the growth of disease-causing bacterial species such as Bacillus subtilis, Escherichia coli, Klebsiella pneumoniae and Proteus vulgaris, researchers said.

“This research highlighted that chitosan-fabricated silver nanoparticles are easy to produce, stable over time,” said Jiang-Shiou Hwang of the National Taiwan Ocean University.

“Hence it can be employed at low dosages to strongly reduce populations of the malaria vector, the Anopheles sundaicus mosquito without detrimental effects on the predation of natural mosquito enemies, such as goldfishes,” Hwang said.

The study was published in the journal Hydrobiologia.