The best time to kill a bug

Insects’ circadian rhythms can signal “die time,” and with further research, it may be possible to tap into this genetic characteristic and identify the times that a target insect is most vulnerable to a specific pesticide. This information could increase the effectiveness, reduce costs and decrease the amounts of pesticide necessary for insect control.
“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,” said Louisa Hooven, a postdoctoral fellow in the OSU Department of Zoology. “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.”
In the newest work, circadian rhythms appear to coordinate “xenobiotic metabolizing” genes, or the genes responsible for breaking down and detoxifying various poisons, such as pesticides. It’s possible that circadian clocks may also affect absorption, distribution, excretion, and molecular targets of toxicity.
The OSU 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.
“A fundamental understanding of the functional significance of circadian rhythms in chemical exposures may facilitate strategies to reduce adverse events in humans, promote control of pest species and reduce pesticide use,” the researchers wrote in their report. “Our study strongly suggest that time of day should be included in insect control strategies and human risk assessment of chemical exposures, including pesticides.”