New biopesticide conquers mosquito larvae

AN ENVIRONMENTALLY safe,biotechnological toxin that killsmosquito larvae has been producedby the Centre for Biotechnology(CBT) at Anna University in TamilNadu. Named Biocide-S because it isproduced from the Bacillus sphaericus bacterium, the pesticide has beensuccessfully field-tested in a yearlong project at Kochi in Kerala. TheMadras municipal corporation is alsocarrying out a six-month pilot projectin the city.

Biocide-S is expected to hit themarket soon. The Tuticorin AlkaliChemicals and Fertilisers Ltd, a sisterconcern of Southern PetrochemicalIndustries Corp, has bought thescaled-up technology from CBT, butwill first test it semi-commercially byproducing about 100 tonnes perannum before'full-scale launch of itsRs 5-crore project.

Biocide-S kills mosquito larvae. ExplainedG Suresh of CBT, "Whenthe biocide formulationis sprayed on stagnantwater bodies like drains,wells and tanks, it isabsorbed by the quito larvae which arefilter-feeders (they filterin soluble matter fromthe water). The Bacillussphaericus, which isJan Mar May July Oct 1991 Jan Mar May July Octretained in the larva'slarvicidal protein (theprotein that kills the larvae) released causespores in the gut of thelarva, leading to gutparalysis and death."

In the 1991 Kochiproject, biocide was9prayed in a trial area of8 sq km once a fortnight.At another test site halfa-kilometre away, a chemical pesticide calledBeytex was sprayed, TheCentre for Research inMedical Entomology (CRME) inMadurai, which evaluated the project, reported that though the fall inbreeding in both areas was almostidentical in March, by October thetrial area drop in breeding was morethan in the chemically tested site. Anopinion poll conducted as part of theevaluation also showed that 85.4 percent of the people living in the areareported a significant fall inmosquito numbers in the trial area.
More capableAnother bacterium, Bacillusthuringiensis (type israelensis) wasalso found capable of producing larvicidal toxins, but CBT opted forBacillus sphaericus "as the other bacterium showed evidence of cytolyticaction (breaking up of cells, including red blood cells) in mammals andwe did not want to take a chancewithout knowing the adverseeffects," said Suresh.

The gene in Bacillus sphaericusthat produces the larvicidal toxinwas first discovered in 1984 byKunthala Jayaraman and an associate. Four years later, Jayaraman, whohad by then joined CBT, discovered asecond gene that produces anothertoxic protein. Said Jayaraman, "Thediscovery of two genes gave us confidence that there was less chance ofmosquitoes developing resistance-toour product."

However, identification of thegenes was not enough. Large-scaleproduction required upgrading oftechnology. A large part of the fundscame from the Swiss DeyelopmentCorp. CBT opted for a sopbe'anbased medium thdt could producelarge quantities at comparatively lowcosts. While the first 10 litres werepr-oduced in the CBT laboratory,mass production of upto 3,000 litreswas successfully carried out atZurich in Switzerland. Tests atthe Hindustan Antibiotics Ltdplant in Pune followed, with technology upscaled to produce 23,000litres.

CBT is now working on transferring the toxin-producing genes inBacillus sphaericus to anotherbacterium, Escherichia coli.This technique has been successfulin the laboratory and is expectedto reduce costs even further whencommercial production becomespossible.