Mosquitoes'
thirst for sugar could prove to be the answer
for eliminating malaria and other mosquito-transmitted
diseases, says Hebrew University researcher
Prof. Yosef Schlein in a study published in
the American Science magazine and the International
Journal for Parasitology.
We have all suffered the
irritation of being the food source for hungry
mosquitoes. While it is generally well known
that female mosquitoes need a meal of blood
before laying their eggs, less has been written
about their appetite for sweet snacks between
meals.
It is this diet of "sweets"
-- derived from nectar from flowers and nectaries
on plant leaves and stems - that provide mosquitoes
with their persistent energy.
Schlein and his co-researcher,
Günter Müller, in the Department
of Parasitology at the Hebrew University-Hadassah
Medical School's Kuvin Center for the Study
of Infectious and Tropical Diseases, decided
to exploit the mosquitoes' thirst for sweets
to bring about their demise - by spraying
acacia trees with a sugar solution that had
been spiked with the oral insecticide Spinosad.
The experiment was carried
out in an oasis in the southern desert region
in Israel where some scattered trees flower
most of the year, including during a long,
dry and otherwise flowerless season. Schlein
assumed that in the absence of other sugar
sources nectar-searching mosquitoes would
be attracted to these plants.
The oasis was chosen
for its isolated mosquito population, so that
the experiment could be carried out effectively
without influx and exchange of mosquitoes
from neighboring areas.
Sucrose solution spiked
with the oral insecticide Spinosad was sprayed
on acacia trees in the oasis. The spraying
of insecticide had the effect of eliminating
almost the entire mosquito population in the
oasis. The few mosquitoes that were trapped
after spraying were thought to be newly emerging
adults, and cumulative population growth was
prevented by continuous effect of the insecticide.
Thus, the oasis was completely depleted of
its mosquito population.
Schlein says that in
a desert area, in the dry season, the flowers
of sparse perennial trees or bushes are key
elements in the habitat of adult mosquitoes,
since they are the only source of sugar. In
dry areas, the shortage of sugar sources may
even limit the life span of mosquitoes and
thus decrease their ability to transmit diseases.
Even when a large variety of flowers is available,
the number of sugar sources is limited by
the preferences of the mosquitoes. For example,
among 77 flowering plants in Wisconsin, mosquitoes
concentrated on four dominant ones.
Schlein believes that
blossoms that are nectar-feeding centers may
be used for efficient mosquito-control, if
sprayed with the Spinosad-sugar solution bait.
Spinosad is an environmental "reduced-risk"
oral insecticide that has little effect on
several insect groups, and has low toxicity
to birds and mammals.
Places that might be
suitable for using floral centers for control
of mosquitoes are desert and savannah regions,
particularly in sub-Saharan Africa, where
the burden of malaria is increasing due to
environmental changes, drug resistance and
mosquito resistance to conventional insecticides.
These areas include large-scale irrigation
projects in arid and semi-arid areas that
cover nearly half of the arable land in Africa
and similar projects in the desert in Pakistan.
In these regions, irrigated crops, such as
rice, are not a source of nectar for adult
mosquitoes, while sugar meals are scarce in
the surrounding arid areas.
Therefore, the planting
of mosquito-attracting trees or bushes in
suitable habitats, sprayed with oral insecticide,
could provide a relatively easy and cheap
way to supplement the limited arsenal against
mosquitoes -- and the fight against malaria.
