Insecticide targeting juvenile mosquitoes can enhance Zika transmissions

Posted 11/5/21

Can warm or cool temperatures change whether juveniles of a common, virus-spreading mosquito resist insecticides?

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Insecticide targeting juvenile mosquitoes can enhance Zika transmissions

Posted

VERO BEACH — 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.”

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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