Scientists explore new ways to target mosquitos as warming climate expands threat

Mosquitoes are the deadliest animals on Earth, killing more people than any other creature. As the climate warms, mosquito season is extending, allowing them to spread diseases like Zika, West Nile virus, and dengue fever for longer periods. Ben Tracy from Climate Central explores how scientists are combating this threat. Ben Tracy: It isn't equipped with sharp teeth or claws, but a mosquito's bite claims more lives than any other animal on the planet.

As global warming intensifies, mosquito season is expanding, providing them with additional opportunities to transmit dangerous diseases. Ben Tracy: With assistance from Climate Central, we delve into the innovative methods scientists are employing to tackle this issue. Ben Tracy: It's delivery day in the San Gabriel Valley, located just east of Los Angeles.

Tristan Hallum, Director of Scientific Programs at the San Gabriel Valley Mosquito and Vector Control District, shares his recent shipment. Tristan Hallum: These 25 tubes are now in front of me. Ben Tracy: The contents of these tubes consist of 600 male Aedes aegypti mosquitoes, recently delivered from Kentucky. Ben Tracy: Hallum is in charge of the scientific programs for the San Gabriel Valley Mosquito Control District.

Tristan Hallum jokes, "Do you enjoy mosquitoes?" Tristan Hallum replies, "I appreciate working with them, but I enjoy killing them." (Laughter) Ben Tracy: Hallum targets invasive mosquitoes capable of spreading diseases, including Zika, West Nile virus, and dengue fever. Tristan Hallum explains that San Gabriel Valley was among the first areas to witness local dengue transmission.

Ben Tracy: Oh, no. They released 30,000 mosquitoes every week, all containing a bacterium that inhibits disease transmission. Tristan Hallum: In total, we will release just under half-a-million mosquitoes. Ben Tracy: How effective is this approach? Tristan Hallum: Previous studies have observed reductions in the range of disease transmission by 80 to 95 percent in areas where they have released these mosquitoes.

Ben Tracy: As the climate warms, mosquito seasons are enduring. Climate Central's analysis found that nearly 95% of the cities studied now have more days annually suitable for mosquitoes to spread diseases, approximately 18 days more on average than in the early 1970s. Tristan Hallum: Traditionally, the mosquito season was considered May to September.

However, now, mosquito control activities are needed throughout the entire season. Ben Tracy: During these releases, they don't require bug spray. I don't observe any bites on your arms. This is because they are all male mosquitoes, and males do not bite. Stephen Dobson, President of MosquitoMate in Lexington, Kentucky, supplies these mosquitoes.

Stephen Dobson: The common name for this mosquito is the yellow fever mosquito, and yellow fevers are indeed dangerous. Ben Tracy: His team breeds this specific species of mosquito in their laboratory and delivers them to control districts across the country. These male mosquitoes carry a naturally occurring bacterium called Wolbachia, which renders them sterile when they attempt to mate with females.

Stephen Dobson: This bacterium is not genetically modified; we are simply transferring it from one mosquito to another. Ben Tracy: Is this process considered genetic modification? Stephen Dobson: No, it is not. We are merely moving the bacterium from one mosquito to another. Ben Tracy: This EPA-approved method can reduce certain mosquito populations by 70 to 95 percent.

The World Mosquito Program employs similar strategies in 16 countries, including Brazil, where they produce 110 million Wolbachia mosquitoes weekly. Some Brazilian communities have experienced a 89% decrease in dengue cases. Stephen Dobson: These are the mosquito larvae. Ben Tracy: Dobson notes that new tools are necessary because climate change is not only prolonging mosquito seasons but also expanding their range.

Stephen Dobson: The general trend is that mosquitoes are moving northward into areas that were previously too cold. Ben Tracy: Overall, temperatures are rising, and the atmosphere is becoming more humid. Is this favorable for mosquitoes in terms of their survival? Stephen Dobson: Unfortunately, yes. For these mosquitoes, a warm and humid environment is precisely what they prefer.

Tristan Hallum: Let's check what's inside. Ben Tracy: Tristan Hallum states that if his traps capture fewer disease-carrying females this summer, it will indicate the effectiveness of the male mosquitoes in controlling the population. Tristan Hallum: As long as we do not observe females being collected in this trap, it confirms a reduction in the population in that area. Ben Tracy: For PBS News Hour, I am Ben Tracy, reporting for Climate Central.