An insecticide cocktail that packs more punch

March 12th, 2008 - 12:05 pm ICT by admin  

Washington, March 12 (IANS) A cocktail of a plant protein and a common insecticide may be more lethal to pests than either ingredient used alone, according to a new study. The study, by researchers at Penn State University, found that the double whammy also inhibits the growth rate of insects and reduces their chance of developing resistance.

“We found a synergistic effect, where the two insecticides together decreased the growth rate of caterpillars more than either one did alone,” said Dawn Luthe, who led the study, which appears in the current issue of PLoS ONE.

“The insect mortality rate was also much greater than the sum of mortality rates when only one insecticide was used.”

One of those insecticides, Bt, is commonly used around the world. When insects feed on plants genetically modified to produce Bt, the toxin binds to chemical receptors lining the insects’ mid gut. This disrupts the receptor’s function, eventually killing the insects.

But researchers say some insects always survive the ordeal and over time subsequent populations could develop resistance to the toxin. Luthe and her colleagues Srinidhi Mohan and Peter W. K. Ma, of Mississippi State University and W. Paul Williams of US Department of Agriculture studied a unique plant-based insecticide known as Mir1-CP.

Their goal is to see if Mir1-CP, when used in tandem with other biological pesticides, such as the Bt toxin, can prevent pests from developing resistance and make the toxin more effective.

“This protein, which we developed from certain strains of corn from Antigua, breaks down other proteins and peptides in the insects’ gut,” said Luthe.

Unlike Bt, Mir1-CP breaks down proteins in a protective membrane covering the mid-gut. This membrane acts as a barrier that protects the caterpillar from toxins in the diet, and cycles nutrients to the mid-gut. “It is the caterpillar’s first line of defence against toxins and chemicals in its diet,” said Luthe.

They found that when used alone, a concentration of Bt at five parts per billion killed four percent of all corn earworms and five percent of tobacco budworms. Mir1-CP, when used at a concentration of 60 parts per billion, killed eight percent of the corn earworms and 3 percent of the tobacco budworms.

But when researchers added the two insecticides together, the mixture killed 61 percent of corn earworms and 57 percent of tobacco budworms, which is more than 10 times better than either by itself.

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