Vector-borne diseases are illnesses that can be transmitted to humans by
blood-feeding insects, such as mosquitoes, ticks and fleas. Mosquitoes
are known to contribute to the spread of a number of vector-borne
diseases, including malaria, dengue, yellow fever and Zika.
According to the World Health Organization (WHO), this class of diseases
accounts for 17% of all infectious diseases in the world, causing over 1
million human deaths per year. Developing methods to reduce the spread
and prevalence of these diseases is thus of utmost importance, as it
could ultimately save countless human lives.
In recent years, scientists have devised a number of control methods to
reduce or manage harmful insect populations without injecting harmful
chemicals into the environment. One of these methods is the sterile insect technique
(SIT), a form of insect birth control that entails the use of radiation
to sterilize male mosquitoes, which are then released into the air in a
target area and start mating with wild female insects.
As a sterile male and a fertile female do not produce any offspring
after they mate, SIT produces a decline in the insect population. In
order to reduce the incidence of vector-borne diseases, however, large
amounts of good quality sterile insects need to be released continuously
over affected geographical areas. Techniques for the cost-effective
aerial release of sterile mosquitoes over extended geographical regions
are thus a bottleneck to enabling the application of SIT on a large
scale.
With this in mind, researchers at the Joint Food and Agriculture
Organization of the United Nations (FAO)/ International Atomic Energy
Agency (IAEA) Insect Pest Control Laboratory in Vienna, WeRobotics and
Biofábrica Moscamed Brasil have recently developed a system to apply the
SIT using unmanned aerial vehicles (UAVs), or drones, to manage and
reduce vector-borne-disease-transmitting mosquito populations. This
unique system, presented in a paper published in Science Robotics, entails the release of sterile mosquitoes in the air over large geographical areas using UAVs.
"We report on a fully automated mosquito release system operated via
drone," said Jeremy Bouyer, a medical entomologist who carried out the
study, who also works within the joint FAO/IAEA division of nuclear
techniques in food and agriculture. "The system, tested in Brazil,
enabled a uniform dispersal of sterile male Aedes aegypti mosquitoes
while maintaining their quality, leading to a consistent sterile-to-wild
male ratio."
The key goal of the study carried out by Bouyer and his colleagues was
to measure the survival, dispersal and sexual competitiveness of sterile
male mosquitoes after they were mass-produced, sorted, handled,
irradiated, marked and released within a geographical area using UAVs.
The UAV-based release system they devised uses a canister in which
mosquitoes are chilled down to 8-12 °C and compacted. Each canister can
contain up to 50,000 sterile males. When the canister opens, the
mosquitoes fall into a rotating cylinder that releases them into the
open air with each of its rotations.
"The rotation speed controls the number of sterile males released per
minute," Bouyer said. "It is fully automated, and release rates can be
controlled depending on the location and speed of the drone. Our
findings represent a major breakthrough in the application of SIT
against mosquitoes. It supports cost-efficient releases, also over areas
densely populated by humans."
So far, the researchers have evaluated the system in Brazil, with the
aim of reducing the population of Aedes aegypti, a species of mosquito
that can spread vector-borne diseases. Overall, they found that the
sterile male insects that they released into the environment were able
to compete with wild males in mating with females. This means that they
effectively induced sterility in the overall Aedes aegypti mosquito
population within that geographical region.
The UAV-based system for the release of sterile mosquitoes could
significantly reduce the costs of SIT implementations, making them
easier to carry out on a large scale. Their method could also prove to
be ideal for SIT operations, as it might overcome limitations such as
inaccessibility, enabling the release of sterile male mosquitoes in areas that are difficult to reach.
"In the future, it is envisioned that adult mosquitoes are irradiated
when already packed into cassettes that can be shipped via courier
services to release sites," Bouyer said. "These cassettes would be
loaded directly into the drones for release, eliminating the need for a
release center."
In Brazil, the researchers evaluated their mosquito release system
using a drone that weighs approximately 12kg. In their next studies,
however, they plan to develop a smaller UAV prototype that weighs 900g,
conforms to the C1 European drone category, can take on a 200g payload
of mosquitoes (~30,000 individuals) and can fly up to 15 minutes over
urban areas.
"Another challenge for the large-scale application of SIT against mosquitoes
is the use of more cost-effective sex-sorting technologies," Bouyer
said. "This is important to ensure no mass-reared female mosquitos are
released, as they bite and transmit diseases. The IAEA, in partnership
with the FAO and collaboration with other partners, is developing the
technology to address this, with some trials planned soon.
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