Public
Release: 1-Jul-2015
What's
in your landscape? Plants can alter West Nile virus risk
University
of Illinois at Urbana-Champaign
CHAMPAIGN,
Ill. -- A new study looks at how leaf litter in water influences the abundance
of Culex pipiens mosquitoes, which can transmit West Nile virus to humans,
domestic animals, birds and other wildlife.
The
study found that different species of leaf litter in standing water influence
where Culex pipiens mosquitoes deposit their eggs, how quickly the larvae grow,
how big they get and whether they survive to adulthood. Because the mosquitoes
feed on bacteria that grow on leaf litter, the team also measured how native
and non-native leaf species influenced bacterial abundance and diversity.
The
study is reported in the journal Parasites and Vectors.
When
added to standing water, the leaves of two non-native, invasive plants, Amur
honeysuckle (Lonicera maackii) and autumn olive (Elaeagnus umbellata), yielded
significantly higher numbers of adult mosquitoes than other leaf species did,
the researchers report.
"The
invasive honeysuckle was definitely the highest quality habitat in terms of the
adult mosquito emergence rates, even when you had very high densities of the
larvae," said graduate student Allison Gardner, who led the research with
University of Illinois entomology professor Brian Allan and Illinois Natural
History Survey entomologist Ephantus Muturi. The INHS is a division of the
Prairie Research Institute at the U. of I.
A
third invasive plant, multiflora rose (Rosa multiflora) was associated with low
numbers of eggs laid and low survival of the larvae, the researchers found.
The
team also made an unexpected, but promising, discovery: One of the plants
studied, a native blackberry (Rubus allegheniensis), seemed to encourage Culex
pipiens mosquitoes to deposit a lot of eggs on the water's surface - but very
few of the resulting larvae survived to adulthood.
"The
blackberry was one of the most attractive habitats to the mosquitoes, but also
one of the lowest quality habitats in terms of the larval survival rate,"
Gardner said.
"Blackberry
was a really poor habitat: It took the larvae a long time to develop and the
adult mosquitoes that eventually emerged were small," Allan said.
"What's exciting about this is that it suggests that blackberry functions
as a kind of ecological trap, enticing mosquitoes to lay their eggs in a place
where the larvae are unlikely to survive."
This
finding could lead to new, biological methods of controlling Culex pipiens
mosquitoes, he said.
Two
other native plants, elderberry (Sambucus canadensis) and serviceberry (Amelanchier
laevis), had different effects on the mosquitoes. Elderberry attracted
mosquitoes looking for a place to lay their eggs, and the larval survival rates
were low, but not as low as for blackberry. The mosquitoes deposited the lowest
number of eggs in water infused with serviceberry leaves, but the survival of
the larvae was a fairly robust, 62 percent. (See graphic.)
The
team also analyzed the bacteria that colonized the different leaf types.
"We
wanted to understand the mechanism by which plants differ in their ability to
support mosquito oviposition, development and survival," Muturi said.
Sites
with more bacterial diversity had higher numbers of mosquito eggs than those
with less diversity, the researchers found. But bacterial abundance, not diversity,
was associated with better larval survival.
This
finding could explain the unexpected role of blackberry leaves as an ecological
trap, Muturi said. Blackberry leaf debris in water hosted a high diversity of
bacterial species, but bacterial abundance was rather low, giving the
developing larvae little sustenance.
"If
you are a mother, you want your kids to develop in an area that has more
resources, more food to eat," Muturi said. "But sometimes a mother
makes a mistake and chooses the wrong habitat. An ecological trap is a mismatch
between the choice that the mother makes and the quality of the habitat."
Future
studies will explore whether blackberry leaves can be used to undermine the
viability of disease-carrying mosquitoes, Allan said.
In
the meantime, those working to stop the advance of invasive plants like
honeysuckle and autumn olive have another reason to do so, Allan said.
"These
are some of the most widespread invasive exotics in North America," he
said. "Plants like honeysuckle are having very significant ecological
impacts, displacing a lot of native species. And now we're seeing that some of
them also enhance the transmission of a dangerous disease."
The
U.S. Environmental Protection Agency, the Institute for Sustainability, Energy
and the Environment at the U. of I., and the Illinois Used Tire Management Fund
supported this research.
Editor's
notes:
To
reach Allison Gardner, email amgardn2@illinois.edu.
To
reach Ephantus Muturi, email emuturi2@illinois.edu.
James
H Burgess, CDM
Manager,
Mosquito Surveillance
and
Mosquito-Borne Disease Surveillance
Lee
County Mosquito Control District
15191
Homestead Road
Buckingham,
Florida
33971-9749
o
239 694 2174
f
239 694 2243
