Insects' Biological Clocks can be Used Against Them

A team of researchers from the Oregon State University in the U.S. found that insect's biological clocks can be used to make them more susceptible to pesticides at specific times of the day. Louisa Hooven and colleagues, in a paper published by PLoS ONE, detail how circadian rhythms coordinate xenobiotic metabolizing genes, or genes responsible for breaking down toxic substances such as pesticides. The researchers examined daily profiles of enzyme activity (glutathione-S-transferase and uridine 5′-diphosphoglucosyltransferase) and dose responses to the pesticides propoxur, deltamethrin, fipronil, and malathion in the model organism Drosophila melanogaster.

The researchers discovered 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. "We found that it took  a triple 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," explains Hooven. "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."

"Our study strongly suggests that time of day should be included in insect control strategies and human risk assessment of chemical exposures, including pesticides," the researchers wrote in the paper. The findings may prove to be useful in programs of integrated pest management (IPM), which aim to minimize pesticide use, prevent development of resistance to pesticides and enhance the effectiveness of an insect control program.

Read the paper published by PLoS ONE at http://dx.doi.org/10.1371/journal.pone.0006469