Insects' biological clocks could pave way for more effective pest control

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Washington, Aug 13 (ANI): The circadian rhythms or biological "clocks" in some insects can make them far more susceptible to pesticides at some times of the day instead of others, reveal researchers at Oregon State University.

The scientists said that with further research, they can tap into this genetic characteristic, identify the times that a target insect is most vulnerable to a specific pesticide, and use that information to increase the effectiveness, reduce costs and decrease the amounts of pesticide necessary for insect control.

The researchers said that such approaches may also be highly useful in programs of "integrated pest management," which aim to minimize pesticide use, prevent development of resistance to pesticides, and use a broad range of physical or chemical control measures to enhance the long-term effectiveness of an insect control program in crop agriculture.

"We found that it took triple the dose of one pesticide to have the same lethal effect on fruit flies at the time of day their defenses were strongest, compared to when they were weakest. A different pesticide took twice the dose. This makes it pretty clear that the time of day of an exposure to a pesticide can make a huge difference in its effectiveness," said Louisa Hooven, a postdoctoral fellow in the OSU Department of Zoology and lead author on the study.

In the study, circadian rhythms appear to coordinate "xenobiotic metabolizing" genes, or the genes responsible for breaking down and detoxifying various poisons, such as pesticides.

Besides it is also possible that circadian clocks may also affect absorption, distribution, excretion, and molecular targets of toxicity.

"This rhythmic defense mechanism may have evolved in order to disarm the noxious compounds that plants produce to avoid being eaten by an insect," said a co-author of the study.

The study found that insect defenses against two commonly used pesticides, propoxur and fipronil, were strongest during mid-day, and weakest around dawn, dusk or the middle of the night.

The effectiveness of two other pesticides studied - deltamethrin and malathion - did not seem to be so strongly associated with time of day, at least with fruit flies.

"For this approach to be useful in agriculture or other places pesticides are used, we will need to test specific insects against specific pesticides, and we will probably find differences in time of maximum effectiveness for various pest-pesticide configurations. In some cases we may be able to greatly improve the effectiveness of pesticides or allow the use of reduced doses," said the co-author.

Although many pesticides have a residual effect, the researchers said, the timing of the first exposure could be critical.

The OSU researchers said that the new findings are also another example of how circadian rhythms are important in other detoxification systems in biology.

They said that in human medicine, a field called "chronopharmacology" is already developing, based on the observation that some medications are far more effective if administered at one time of the day instead of another.

"Our study strongly suggest that time of day should be included in insect control strategies and human risk assessment of chemical exposures, including pesticides. In some cases, the clock, together with the dose, may make the poison," said the researchers.

The findings were recently published in PLoS ONE, a professional journal. (ANI)

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