Posts Tagged: pollinators
There is a purpose
Without their keen sense of smell, mosquitoes wouldn't get very far. They rely on this sense to find a host to bite and spots to lay eggs.
And without that sense of smell, mosquitoes could not locate their dominant source of food: nectar from flowers.
"Nectar is an important source of food for all mosquitoes," said Jeffrey Riffell, a professor of biology at the University of Washington. "For male mosquitoes, nectar is their only food source, and female mosquitoes feed on nectar for all but a few days of their lives."
Yet scientists know little about the scents that draw mosquitoes toward certain flowers, or repel them from others. This information could help develop less toxic and better repellents, more effective traps and understand how the mosquito brain responds to sensory information -- including the cues that, on occasion, lead a female mosquito to bite one of us.
Riffell's team, which includes researchers at the UW, Virginia Tech and UC San Diego, has discovered the chemical cues that lead mosquitoes to pollinate a particularly irresistible species of orchid. As they report in a paper published online Dec. 23 in the Proceedings of the National Academy of Sciences, the orchid produces a finely balanced bouquet of chemical compounds that stimulate mosquitoes' sense of smell. On their own, some of these chemicals have either attractive or repressive effects on the mosquito brain. When combined in the same ratio as they're found in the orchid, they draw in mosquitoes as effectively as a real flower. Riffell's team also showed that one of the scent chemicals that repels mosquitoes lights up the same region of the mosquito brain as DEET, a common and controversial mosquito repellant.
Their findings show how environmental cues from flowers can stimulate the mosquito brain as much as a warm-blooded host -- and can draw the mosquito toward a target or send it flying the other direction, said Riffell, who is the senior author of the study.
The blunt-leaf orchid, or Platanthera obtusata, grows in cool, high-latitude climates across the Northern Hemisphere. From field stations in the Okanogan-Wenatchee National Forest in Washington state, Riffell's team verified past research showing that local mosquitoes pollinate this species, but not its close relatives that grow in the same habitat. When researchers covered the flowers with bags -- depriving the mosquitoes of a visual cue for the flower -- the mosquitoes would still land on the bagged flowers and attempt to feed through the canvas. Orchid scent obviously attracted the mosquitoes. To find out why, Riffell's team turned to the individual chemicals that make up the blunt-leaf orchid's scent.
"We often describe 'scent' as if it's one thing -- like the scent of a flower, or the scent of a person," said Riffell. "Scent is actually a complex combination of chemicals -- the scent of a rose consists of more than 300 -- and mosquitoes can detect the individual types of chemicals that make up a scent."
Riffell describes the blunt-leaf orchid's scent as a grassy or musky odor, while its close relatives have a sweeter fragrance. The team used gas chromatography and mass spectroscopy to identify dozens of chemicals in the scents of the Platanthera species. Compared to its relatives, the blunt-leaf orchid's scent contained high amounts of a compound called nonanal, and smaller amounts of another chemical, lilac aldehyde.
Riffell's team also recorded the electrical activity in mosquito antennae, which detect scents. Both nonanal and lilac aldehyde stimulated antennae of mosquitoes that are native to the blunt-leaf orchid's habitat. But these compounds also stimulated the antennae of mosquitoes from other regions, including Anopheles stephensi, which spreads malaria, and Aedes aegypti, which spreads dengue, yellow fever, Zika and other diseases.
Experiments of mosquito behavior showed that both native and non-native mosquitoes preferred a solution of nonanal and lilac aldehyde mixed in the same ratio as found in blunt-leaf flowers. If the researchers omitted lilac aldehyde from the recipe, mosquitoes lost interest. If they added more lilac aldehyde -- at levels found in the blunt-leaf orchid's close relatives -- mosquitoes were indifferent or repelled by the scent.
Using techniques developed in Riffell's lab, they also peered directly into the brains of Aedes increpitus mosquitoes, which overlap with blunt-leaf orchids, and a genetically modified strain of Aedes aegypti previously developed by Riffell and co-author Omar Akbari, an associate professor at UC San Diego. They imaged calcium ions -- signatures of actively firing neurons -- in the antenna lobe, the region of the mosquito brain that processes signals from the antennae.
These brain imaging experiments revealed that nonanal and lilac aldehyde stimulate different parts of the antenna lobe -- and even compete with one another when stimulated: The region that responds to nonanal can suppress activity in the region that responds to lilac aldehyde, and vice versa. Whether this "cross talk" makes a flower attractive or repelling to the mosquito likely depends on the amounts of nonanal and lilac aldehyde in the original scent. Blunt-leaf orchids have a ratio that attracts mosquitoes, while closely related species do not, according to Riffell.
"Mosquitoes are processing the ratio of chemicals, not just the presence or absence of them," said Riffell. "This isn't just important for flower discrimination -- it's also important for how mosquitoes discern between you and I. Human scent is very complex, and what is probably important for attracting or repelling mosquitoes is the ratio of particular chemicals. We know that some people get bit more than others, and maybe a difference in ratio explains why."
The team also discovered that lilac aldehyde stimulates the same region of the antenna lobe as DEET. That region may process "repressive" scents, though further research would need to verify this, said Riffell. It's too soon to tell if lilac aldehyde may someday be an effective mosquito repellant. But if it is, there is an added bonus.
"It smells wonderful," said Riffell.
Mosquitoes are Drawn to Flowers as Much as People
Caption: An Aedes mosquito with pollen sacs on its eyes feeding from Platanthera flowers.
Credit: Kiley Riffell
mosquitoes and flower
You've seen honey bees buzzing past you to reach a good nectar or pollen source. But there's much...
What's in store for this honey bee? It is heading for an Anisodontea sp.'Strybing Beauty.' Image taken in pollinator garden in Vacaville, Calif. (Photo by Kathy Keatley Garvey)
The global decline of pollinators ought to concern everybody, and everybody ought to get involved,...
Keynote speaker Lynn Dicks (far left) of the School of Biological Sciences, University of East Anglia, United Kingdom, with conference co-chair Neal Williams, pollination ecologist, UC Davis Department of Entomology and Nematology, and speaker Rachel Vannette of the UC Davis Department of Entomology and Nematology, who addressed the crowd on her hummingbird research. (Photo by Kathy Keatley Garvey)
Vince Jones (far right) of Washington State University, Pullman, Wash., addressing the crowd on "Implementing a Honeybee Foraging Model and REDAPOLL Fruit Set Predictions in Washington State's Decision Aid System." (Photo by Kathy Keatley Garvey)
It's break time in the ARC Ballroom, UC Davis, for the attendees at the International Pollinator Conference. (Photo by Kathy Keatley Garvey)
A reception for the crowd at the International Pollinator Conference. The site: the UC Davis Honey and Pollination Center, Robert Mondavi Institute. (Photo by Kathy Keatley Garvey)
Discussing the conference are these members of the Neal Williams lab. From left pollination ecologist Neal Williams, professor, UC Davis Department of Entomology and Nematology, and Nick Rosenberger, Colin Fagan and Anna Britzman. (Photo by Kathy Keatley Garvey)
Keynote speaker Christina Grozinger (left), distinguished professor of entomology and director of the Center for Pollinator Research, Pennsylvania State University, with conference co-chair Extension apiculturist Elina Lastro Niño, UC Davis Department of Entomology and Nematology. Grozinger served as Niño's major professor at Penn State. (Photo by Mea McNeil)
The organizers: From left are Elizabeth "Liz" Luu, events manager, UC Davis Honey and Pollination Center; conference co-chairs Elina Lastro Niño and Neal Williams of the UC Davis Department of Entomology and Nematology; and Amina Harris, director, the UC Davis Honey and Pollination Center. (Photo by Kathy Keatley Garvey)
Research to help plant growers
protect bees and manage pests.
A group of scientists from the IR-4 Project is doing research to explore the relationships between bees, environmental horticulture plants, and pesticides. This group has put together a database allowing users to create customized plant lists for bees, to research articles, to find pollinator news updates and to research best management practices documents. Check it out:
The research is primarily targeted towards helping environmental horticulture growers, but the information should also produce valuable resources for home gardeners or anyone interested in the interplay between bees, plants, and pesticides.
This website is their hub to:
- Share our research and updates
- Provide customized plant lists to help gardeners
- Provide resources to plant growers
- Share related pollinator information and news
bee on marigold
(June 17-23 is National Pollinator Week.) "How many species of bees are there in the world?" asks...
Wendy Mather (left) program manager of the California Master Beekeeper Program, explains the life cycle of bees to a group of third graders from Amador County. (Photo by Kathy Keatley Garvey)
Wendy Mather (left) program manager of the California Master Beekeeper Program shows the third graders how to use a bee vacuum in a catch-and-release activity. (Photo by Kathy Keatley Garvey)
I can see the bee! There it is! (Photo by Kathy Keatley Garvey)
What kind of butterfly is this? The answer: Monarch! (Photo by Kathy Keatley Garvey)
Wendy Mather, program manager of the California Master Beekeeper Program (CAMBP), tells the students she hopes to see them study entomology at UC Davis. (Photo by Kathy Keatley Garvey)
Volunteer Julia Wentzel introduced the concept of "pollinator specialists" and engaged the students in creating a "pollinator." They then transferred "pollen" to different shaped flowers. (Photo by Kathy Keatley Garvey)
Volunteer Robin Lowry, who managed the “Planting for Pollinators” and “Be a Beekeeper” station, displays a frame. (Photo by Kathy Keatley Garvey)
Students placed "pollinators" inside flowers. (Photo by Kathy Keatley Garvey)
Time to take a photo! Don't say "cheese!" Say "honey!" (Photo by Kathy Keatley Garvey)
Matthew Hoepfinger, staff research associate in the E. L. Niño lab, presented the live bee demonstration. (Photo by Kathy Keatley Garvey)
Hey, I'm a bee! (Photo by Kathy Keatley Garvey)
A little beekeeper shapes a heart. Students took turns trying on the beekeeper protective suits. (Photo by Kathy Keatley Garvey)