Auburn researcher identifies emerging mosquito challenges

Though most people see them as only a nuisance, mosquitoes are the world’s deadliest animal, transmitting diseases that kill hundreds of thousands of people worldwide. That’s why Nannan Liu, endowed professor of entomology and plant pathology at Auburn University’s College of Agriculture, studies mosquitoes’ resistance to insecticides. 

Liu’s goal is to understand how mosquito populations function and how they develop resistance to insecticides. Her project is designed to improve the control of pests that jeopardize agriculture, the environment and human health. The project is part of the Alabama Agricultural Experiment Station. 

“Mosquitoes are vectors — an animal or insect that transmits diseases — and they move from host to host, which is why they are hard to control,” Liu said. “But our surveillance of mosquito populations and their responses to conventional insecticides continues to tell us more.” 

For decades, insecticides have played a key role in managing mosquito populations. Pyrethroid‑based formulations remain among the most widely used and effective options for mosquito control today, but the development of resistance in mosquito populations can reduce their effectiveness.  

Like other insects, mosquitoes have regulatory factors that affect gene responses on a molecular level, in the same way humans have hormone and stress responses acting like switches that turn certain genes on and off.  

Scientists already know that mosquitoes can break down common insecticides before the products can kill them. What they do not know is which regulatory factors tell mosquitoes to “turn on” the P450 genes — genes that help them make the insecticides less effective.  

Liu’s research analyzes why certain insecticides fail, but she is also looking beyond that to identify additional pathways that influence resistance.  

Beyond P450s, Liu is also investigating additional signaling pathways that may influence insecticide resistance. One focus is G-protein coupled receptors, or GPCRs, which are involved in cellular signaling. These are internal signals that help mosquitoes recognize scents and find hosts. 

Her team studies how these signaling pathways may help regulate genes involved in insecticide resistance, including genes that help mosquitoes break down insecticides. 

In the laboratory, Liu and her team examine gene-expression patterns in mosquitoes with different levels of insecticide resistance. By identifying regulatory pathways associated with resistant populations, they hope to better understand how mosquitoes develop resistance in the first place.  

Liu and her team collect mosquitoes and their larvae near water bodies across the state. Once collected, they return to the laboratory to study the resistance of adults and larvae to multiple insecticides and assess mortality. 

The team collects mosquitoes statewide so they can also assess resistance regionally. Liu said this approach shows that mosquitoes in more urbanized areas tend to show higher levels of resistance to conventional insecticides. 

As part of the lab work, Liu uses insecticide bioassays — controlled tests to see how mosquitoes react to different concentrations of insecticides. Then, the researchers assess mortality rates, short-term paralysis and see which populations show greater survival. This gives them a broader view of what is working and what can be improved.  

The resulting datasets give researchers a more detailed picture of how mosquitoes develop resistance and where it occurs in the environment. With that information, researchers can help communities adjust control strategies for better planning and protection. 

As she discovers more details through the project, Liu says sharing data regionally is key to improving overall mitigation. 

She said her core puzzle is to better understand the mechanisms behind insecticide resistance in mosquitoes — and this project is one piece of that puzzle. 

Ultimately, this research can help protect the health of livestock while defending humans from life-threatening mosquito-borne diseases, including malaria and West Nile virus. Liu said current mosquito-control tools, including pyrethroid insecticides and larvicides remain important, but their efficacy varies as resistance develops. 

“We do not fully understand the big picture yet of mosquito resistance, but my long-term research goal is to fill the gaps of what we don’t understand,” she said. 

Through Liu’s work, Auburn research builds on the knowledge that safeguards agriculture and public health, advancing resistance management for a safer environment.