By Josh Lancette
Certain mosquitoes are more likely to lay eggs in water sources near flowers than in water sources without flowers, according to an article published in the Journal of Medical Entomology.
Researchers from the USDA and the University of Florida studied the Asian tiger mosquito (Aedes albopictus) and its egg-laying preferences. This mosquito is known to transmit yellow fever, dengue, and chikungunya, and it has been spreading throughout the United States.
Asian tiger mosquitoes prefer to lay eggs in containers. In fact, it is believed that they made it to the U.S. as stowaways in tires that were imported from Japan back in 1985. So the first thing the scientists decided to test was whether the size of the containers made any difference. They were also curious about whether or not the presence of flowers might affect the egg-laying behavior.
Flowers? “Why flowers?” some might ask.
Although they are mostly known as blood-feeders, mosquitoes also drink nectar from flowers. In fact, male mosquitoes do not feed on blood at all, so their only food sources are nectar and other forms of sugar from plants.
The scientists chose the butterfly bush (Buddleja davidii) for their experiment because it’s a very hardy plant that flowers throughout the year, and mosquitoes are attracted to it.
“From my visual observations, when I brought the truck filled with these flowering plants to the field sites and parked, I could see the mosquitoes fly to the plants,” said Dr. Timothy Davis, one of the authors.
The researchers used “blood sausages” — sheep or pig intestines that are filled with cattle blood — to feed female mosquitoes that had been released in large cages containing the flowers and water containers.
They found significantly more eggs in the largest containers, and they found more eggs in containers next to flowering butterfly bushes than in containers without flowers.
These findings could lead to new methods of controlling the mosquito.
“One of the potential outcomes of this study might be that someone could look at the flower fragrances as a way to lure egg-laying female mosquitoes to some sort of trap,” said Dr. Phil Kaufman, one of the researchers.
“This study provides evidence of the attractiveness of flowering butterfly bushes to ovipositing (i.e., egg-laying) Aedes albopictus,” said Dr. Davis. “Ovipositing mosquitoes are those that have taken a bloodmeal and, in instances where pathogen transmission is occurring, are the potential vectors as they may have acquired the pathogen through the bloodmeal. Therefore, exploiting the attractiveness of flowering butterfly bushes in developing control techniques could assist in stopping pathogen transmission.”
The researchers suggest that female mosquitoes lay eggs near flowers for a variety of possible reasons. Nectar is an important energy source, so pregnant females are obviously attracted to the flowers in order to feed themselves. But it could also have something to do with providing food for the next generation in the form of nectar.
“Putting eggs in water near a nectar source may be a way of provisioning for the offspring, which do need sugar upon emergence,” said Dr. Kaufman.
While these findings might tempt people to remove flowers to keep mosquitoes away, the researchers doubt it would help much.
“The mosquitoes we studied were blood-fed already and were looking for a place to lay eggs,” said Kaufman. “We found that flowers by your house may attract mosquitoes that have already blood fed, so they would not be interested in biting. We did not evaluate host-seeking mosquitoes, so I cannot comment on whether the flowers would attract mosquitoes that are seeking a blood meal. I suspect that they are just as likely to come in, but we have no data on that. Sounds like a project for the next student…”
However, the findings of this study may be used one day to increase the effectiveness of mosquito trapping and monitoring efforts, especially if the attractants from the butterfly bush can be isolated and replicated.
“Incorporation of phytochemicals that are produced by butterfly bush may enhance ovitrap effectiveness, thereby improving surveillance and control efforts,” according to the authors.
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Josh Lancette is Manager of Publications at the Entomological Society of America.
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