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image - Abdullah Alomar is a doctoral candidate at Florida Medical Entomology Laboratory who led a story on insecticide resistance in juvenile Aedes aegypti mosquitoes and impacts on Zika transmission rates.

Insecticide targeting juvenile mosquitoes can enhance Zika transmissions

  • Insecticide resistance among the Aedes aegypti mosquito remains a source of frustration for public health and mosquito control agencies, medical entomologists and ecologists.
  • Known as the yellow fever mosquito, this species poses a public health risk because it is the primary source transmitting multiple viruses including Zika, chikungunya, dengue and yellow fever to humans.
  • University of Florida researchers at the Institute of Food and Agricultural Sciences (UF/IFAS) released a study illustrating a development in the species’ ability to transmit the Zika virus from the juvenile stage when they overcome an otherwise lethal dose of a commonly used insecticide.

Abdullah Alomar, UF/IFAS doctoral candidate at FMEL, looked into transmission rates of insecticide-resistant juvenile Aedes aegypti mosquitoes.

VERO BEACH, Fla. – Can warm or cool temperatures change whether juveniles of a common, virus-spreading mosquito resist insecticides? If so, will these young mosquitoes be more likely to transmit mosquito-borne illnesses to humans?

The widespread species, known scientifically as Aedes aegypti and commonly referred to as the yellow fever mosquito, is a primary source for transmitting the Zika virus to humans. In the latest published study, scientists at UF/IFAS Florida Medical Entomology Laboratory (UF/IFAS FMEL) looked at what happens when juvenile Aedes aegypti mosquitoes are exposed to a chemical known as juvenile hormone analog (JHA) at varied climates.

JHA is commonly used in insecticides to prevent the larvae from growing into adults. The study recorded the mosquitos’ development, lifespan, population growth and ability to transmit the Zika virus when exposed to JHA. The study looked specifically at those juveniles that survived an otherwise lethal dose of the chemical.

“Our research provides empirical evidence that exposure to insecticide pyriproxyfen, also known as JHA, during immature stages can produce adults with higher infection and transmission rates of the Zika virus,” said Barry Alto, a co-author in the study and an associate professor at UF/IFAS FMEL “It may also have significant consequences for Zika virus epidemiology.”

Barry Alto, a co-author in the study and an associate professor at UF/IFAS FMEL, at work in the biosecurity lab of Florida Medical Entomology Laboratory.

Insecticides are a common way to control mosquitoes and thus, the diseases they can transmit such as Zika, chikungunya, dengue and yellow fever viruses. Relying on these insecticides for long periods has led some mosquito species to develop resistance to them.

“Our findings support the need to consider the status of insecticide resistance during times of virus transmission and to implement insecticide-resistance management and mitigation strategies in mosquito-control programs,” said Abdullah Alomar, lead author of the study published in Scientific Reports, and a UF/IFAS doctoral candidate.

During the study, scientists recorded the reactions of juvenile Aedes aegypti mosquitoes after being exposed to JHA at cool and warm temperatures. Those temperatures were 68 degrees Fahrenheit and 86 degrees Fahrenheit, respectively. From that, scientists saw the simultaneous effects on the development and life stages of the mosquitoes from larvae to adults.

The temperatures influenced the juvenile’s molting, development time, wing lengths and size as they reached adulthood. For example, under cooler temperatures, the time to develop from a juvenile to an adult took longer in comparison to warmer temperatures. The size and wing lengths of the mosquitoes could also be correlated to exposure of JHA in cooler or warm weather.

The study also looked at the responses of 399 adult female mosquitoes to the Zika virus, following the juveniles’ exposure to JHA under different temperatures.

Zika virus infection and transmission rates were higher among adult mosquitoes previously exposed to JHA during the juvenile stages. Assessing the effects of mosquito control methods on mosquito biology — including their susceptibility to virus infection and transmission — is essential to evaluate the overall outcomes on epidemiology of arboviruses, Alto said.

“This research shows that while the application of JHA has potential for reducing mosquito populations, it may enhance adult mosquito infections, and transmissions which may lead to enhancement of Zika virus infectivity in Floridian Aedes aegypti mosquito vector,” said Alomar. “This may ultimately compromise the control efforts.”

Next, researchers need to determine whether JHA can alter Zika virus incubation periods in the mosquitoes. They will also need to take a closer look at whether JHA alters transmission rates of the Zika virus when infection is passed from parent to offspring. Finally, they will need to conduct field trials to determine how JHA exposure affects mosquito biology, including viral infection and transmission, in natural environmental conditions.

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By: Lourdes Mederos, 954-577-6363 office, rodriguezl@ufl.edu

The mission of the University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) is to develop knowledge relevant to agricultural, human, and natural resources and to make that knowledge available to sustain and enhance the quality of human life. With more than a dozen research facilities, 67 county Extension offices, and award-winning students and faculty in the UF College of Agricultural and Life Sciences, UF/IFAS brings science-based solutions to the state’s agricultural and natural resources industries and all Florida residents.

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