Linda Benedict, Bogren, Richard C. | 3/31/2005 2:25:16 AM
Cotton farmers may soon have a new way to evaluate the effectiveness of one class of insecticides, thanks to a new LSU AgCenter procedure that received a U.S. patent.
The patent was issued Nov. 21, 2000, to the LSU AgCenter and to the inventors James Ottea, entomologist, and Guomin Shan, one of Ottea’s former students, now at the University of California. The patent involves a way to determine if insects are developing resistance to pyrethroids.
Ottea said there are two major types of resistance—metabolic resistance, when the insects develop something akin to an immunity to only one form (or structurally related forms) of the chemical, and target-site resistance, when the entire chemical class of the insecticide no longer is fully effective in controlling the insect population.
“The countermeasure you choose when insects are resistant depends on the type of resistance they have,” he said.
If the problem is metabolic resistance, Ottea said the answer often is a matter of switching to another pyrethroid compound that the insects cannot metabolize. If the problem is target-site resistance, however, the grower must change to a different class of chemicals.
The advantage of pyrethroids is they are less costly than alternative insecticides, Ottea said. But because insects have developed resistance, pyrethroids have been replaced by new compounds.
Ottea and Shan identified both metabolic and target-site resistance in tobacco budworms in cotton and used the information to develop a diagnostic kit growers can use to determine which type of resistance is in a population of insects. The kit includes two vials into which farmers put insects gathered from their fields. The first vial contains a standard pyrethroid and the second, a modified pyrethroid.
“We’ve put the essence of a panel of biochemical tests that took us a week to do in the lab into this one test,” Ottea said. “It’s easy to interpret—the insects die or they don’t.”
(This article was pulished in the winter 2001 issues of the Louisiana Agriculture Magazine)
The LSU AgCenter and the LSU College of Agriculture