The effectiveness of insecticides against mosquitoes can vary significantly at different times of day, as well as between day and night. A Florida study found that wild Aedes aegypti mosquitoes resistant to permethrin were most sensitive to the insecticide between midnight and sunrise. Resistance then increased throughout the day, when mosquitoes were most active, peaking at dusk and the first half of the night.
The findings of a study conducted by researchers at the University of Florida (UF) have far-reaching implications for pest control professionals, allowing them to use pesticides more efficiently, save money, and reduce their environmental impact. “We found that the highest doses of permethrin were needed to kill mosquitoes at 6 p.m. and 10 p.m. These data suggest that permethrin may be more effective when applied between midnight and dawn (6 a.m.) than at dusk (around 6 p.m.),” said Lt. Sierra Schloop, a co-author of the study. The study was published in the Journal of Medical Entomology in February. Schloop, an entomology officer with the UF Naval Sealift Command, is a doctoral student in entomology at the University of Florida along with Eva Buckner, Ph.D., the study’s senior author.
It may seem like common sense that the best time to apply an insecticide to mosquitoes is when they are most likely to buzz, flutter, and bite, but that’s not always the case, at least in experiments with permethrin, one of the two most commonly used mosquito control insecticides in the United States, which was used in this study. The Aedes aegypti mosquito bites primarily during the day, both indoors and outdoors, and is most active about two hours after sunrise and a few hours before sunset. Artificial light can extend the time they can spend in the dark.
Aedes aegypti (commonly known as the yellow fever mosquito) is found on every continent except Antarctica and is the vector for the viruses that cause chikungunya, dengue, yellow fever, and Zika. It has been linked to outbreaks of several endemic diseases in Florida.
However, Schluep noted that what is true for one mosquito species in Florida may not be true for other regions. Various factors, such as geographic location, can cause the genome sequencing results of a particular mosquito to differ from those of Chihuahuas and Great Danes. Therefore, she emphasized, the study’s findings only apply to the yellow fever mosquito in Florida.
There is one caveat, however, she said. The findings of this study could be generalized to help us better understand other populations of the species.
A key finding of the study showed that certain genes that produce enzymes that metabolize and detoxify permethrin were also affected by changes in light intensity over a 24-hour period. This study focused on just five genes, but the results can be extrapolated to other genes outside the study.
”Given what we know about these mechanisms and about mosquito biology, it makes sense to extend this idea beyond these genes and this wild population,” Schluep said.
The expression or function of these genes begins to increase after 2 p.m. and peaks in the dark between 6 p.m. and 2 a.m. Schlup points out that of the many genes involved in this process, only five have been studied. She says this may be because when these genes are working hard, detoxification is enhanced. The enzymes can be stored for use after their production slows.
”A better understanding of diurnal variations in insecticide resistance mediated by detoxification enzymes in Aedes aegypti may allow targeted use of insecticides during periods when susceptibility is highest and detoxification enzyme activity is lowest,” she said.
”Diurnal changes in permethrin sensitivity and metabolic gene expression in Aedes aegypti (Diptera: Culicidae) in Florida”
Ed Ricciuti is a journalist, author, and naturalist who has been writing for more than half a century. His latest book is Backyard Bears: Big Animals, Suburban Sprawl, and the New Urban Jungle (Countryman Press, June 2014). His footprints are all over the world. He specializes in nature, science, conservation, and law enforcement. He was once a curator at the New York Zoological Society and now works for the Wildlife Conservation Society. He may be the only person on Manhattan’s 57th Street to have been bitten by a coati.
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Post time: May-26-2025