The neem tree (Azadirachta indica), whose seed and leaf extracts are known to kill more than 60 types of insects, has recently been the subject of several interesting studies. Researchers at Virginia Polytechnic Institute and State University effectively control the Colorado Potato Beetle (CPB) in eastern Virginia using extracts from seed kernels of the tree. Meanwhile, in Louisiana, USDA researchers have found that leaves from the India native may block fungi from producing aflatoxins in stored grains. Another study in Israel conducted on pest and predacious mites indicates that neem extracts are considerably more toxic to the pest than to the predator.

Neem Leaves and Aflatoxin

While growing up in India, Deepak Bhatnagar says his parents used to put leaves of the neem tree inside containers of wheat to keep insects out of the wheat they stored in their own homes. Dr. Bhatnagar, a USDA scientist in Louisiana, has found that leaves may also block fungi from producing a food toxin.

Greenhouse studies will be getting under way later this year to confirm what he says are the first laboratory experiments showing that neem leaves stop fungi from producing aflatoxin. In the hot, dry conditions of the field, or in improper storage environments where the fungi Aspergillus flavus and A. parasiticus thrive, this toxin can form on peanuts, corn and other crops.

In laboratory tests at the agency's Southern Regional Research Center in New Orleans, Bhatnagar ground up or boiled neem leaves in a solution of potassium phosphate or in water. He applied solutions of between 5 percent and 50 percent neem in water or potassium phosphate to fungi growing in standard sugar or mineral solutions. Aflatoxin measurements were taken four days later. Results demonstrated that the solutions of between 10 percent and 50 percent did not kill the fungi, but did block more than 98 percent of the aflatoxin that normally would have been produced.

Bhatnagar says that the results are 'promising but preliminary.' In order to confirm the lab findings, he plans to conduct greenhouse studies with cotton. Neem solution will be injected into cotton bolls, which will then be infected with fungus and monitored to see if the earlier results are replicated.

The mechanism that enables neem to block aflatoxin production is not known for certain, but lab studies indicate that it occurs early in the organism's growth. Neem extract appears to interfere with the formation of substances called polyketides, which the fungi convert into other chemicals that eventually form aflatoxin. Enzymes which the fungi use in production of the aflatoxin were present during experiments, but key chemicals needed to synthesize the toxin were absent. Workers in the field might want to test neem solutions in storage of grains and pulses.

Neem Leaves Show Promise for Controlling Aflatoxin, USDA NEWS Release, April 11, 1988.


Deepak Bhatnagar
Food and Feed Safety Research
Southern Regional Research Center
Agricultural Research Service, USDA
New Orleans, LA 70179 (504) 286-4388