Scientists have found that the effectiveness of some insecticides
depends on what time of day they're used. The results may also have
implications for how people respond to medicines and to toxic
When is a good time to kill a fly? We don't
normally think about it, but researchers at Oregon State University say
the time of day does matter. Jaga Giebultowicz and her colleagues
tested four insecticides to see if their effect on fruit flies changed
at different times of the day. Timing made a big difference for one bug
"You could kill the same number of insects but with
one-third of the pesticide applied at one time of day versus another,"
Another insecticide was
almost twice as effective depending on the time. Dusk appears to be the
best time to spray, "but, of course, it's hard -- you don't want to
spray your orchard when it's dark," she adds.
later in the day you spray, Giebultowicz says, the less pesticide
you'll need to use -- at least with some chemicals.
produce a number of enzymes that break down toxic chemicals and protect
them from the poison. The researchers found the amount of several of
these enzymes was controlled by the fruit fly's biological clock,
rising and falling in sync with the sun.
Many plants naturally
produce chemicals that are toxic to insects, and Giebultowicz suggests
the fruit flies' biological rhythm may boost these enzymes at the best
time to detoxify the chemicals without wasting the insect's resources.
all of the insects' detox enzymes are cyclical. Time didn't affect how
the flies reacted to the other two chemicals Giebultowicz's lab tested.
And they only tested fruit flies -- other insects may respond
But Giebultowicz adds that the implications of her research extend far beyond the insect world.
clocks in insects and in humans are similar genetically," she says. So
that means we may respond differently at different times of day when
we're exposed to insecticides and other toxic chemicals; and it could
also mean that medications may work better or worse depending on the
Giebultowicz says future studies should look into how
both people and insects respond to chemicals over the course of the
day. When it comes to flies, though, the fly swatter appears equally
effective morning, noon, or night.
The research appears in the July issue of the journal PLoS One