Slow release pesticide hits resistant bugs
25 June 2009
Ned Stafford/Hamburg, Germany
Italian chemical company Endura has signed a licensing agreement with UK and Australian research institutes allowing it to commercialise a new crop protection method that involves time-delayed release of micro-encapsulated insecticides.
The crop protection method involves applying a mixture that includes enzyme inhibitors, dubbed synergists, to disable enzymes used by insects to build up resistance to pesticides. The synergists are combined with insecticides in micro capsules, meaning the insecticides are released five hours later after the synergists have had time to disable the insect enzymes.
The new crop protection method is the result of nearly 10 years of research involving scientists at Rothamsted Research in the UK and New South Wales Department of Primary Industries (NSWDPI) in Australia, according to Graham Moores, an insect biochemist at Rothamsted and co-leader of the project.
Moores told Chemistry World that one of the first problems faced by the team was finding the proper synergist, as most are too toxic for agricultural uses. He and other co-leader Robin Gunning, of NSWDPI, chose piperonyl butoxide (PBO), a naturally occurring synergist that inhibits esterases and oxidases (cytochrome P450s), the two main metabolic systems that confer insecticide resistance. Endura is the largest PBO producer in the world and holds the patent on a synthetic manufacturing process.
Moores says that in initial tests, the PBO and insecticide mixture was not effective, as resistant insects were able to break down the insecticide before PBO had a chance to act. In a subsequent test, the team first sprayed PBO on crops and then five hours later applied insecticide. 'This worked very well,' Moores said. However, such a two-step process would be too expensive and time consuming for large farm plots, he said. So they decided to try delay release of insecticide through encapsulation.
Formulation of the future?
Tests have been successfully conducted in the UK on peach potato aphids and on tobacco white flies and boll worms in Australia, Moores says. But in addition to being used for protecting cotton, potatoes and sugar beets, he says of the method: 'It can be used on any crop against any insect.' He says the method also allows use of smaller quantities of pesticides than traditional methods.
Valerio Borzatta, R&D director at Endura, says Endura played the key role in developing the time-delay technology in collaboration with an Italian firm and institutes. Endura has developed two different methods for delaying release of insecticides, he says. The first combines an insecticide with cyclodextrins, with the insecticide lodging in cavities or pillars of cyclodextrins for delayed release, with PBO outside. The mixture resembles a white powder that is added to water at the farm field for spraying.
The second method encapsulates insecticides and PBO using polyurea, he says. The microcapsules are about 10 micrometres in diameter and suspended along with free-standing PBO in water.
Cosimo Franco, Endura managing director, told Chemistry World that Endura, which has exclusive global rights to market the technology, does not plan to market the technology directly. Instead the firm will seek a small number of commercial agricultural partners in various regions around the world to handle promotion and marketing.
But Allan Felsot, professor of entomology & environmental toxicology at Washington State University in Richland, Washington, told Chemistry World that he does not believe using PBO or other synergists to reactivate pesticides is a technology for future crop protection. 'It's basically a backward-looking technology,' says Felsot, who has served on several agricultural task groups of International Union of Pure and Applied Chemistry. 'The best way to fight resistance is altering compounds with different modes of action - and to quit spraying so much in the first place.'
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