Photo/Illutration Aedes albopictus (Provided by the U.S. Centers for Disease Control and Prevention)

The refreshing autumn breeze now blowing most days is a welcome respite after the hottest September on record. And yet, it comes at a price.

There’s a familiar buzz in the air, from mosquitoes, although the sound is normally associated with the height of midsummer.

The scorching summer, it seems, sucked the lifeblood out of mosquitoes, which probably explains their annoying presence so late in the year, say experts.

“Recently, I was bitten by a mosquito while I enjoyed watching the moon from my balcony,” said a 67-year-old resident of Tokyo’s Chuo Ward. “I don’t recall them being around in the summer.”

The man promptly went out to a drugstore to buy hanging mosquito repellent.

“When I was a child, I couldn’t believe there would be mosquitoes in October,” he said.

DEMAND FOR REPELLENT RISES

Sales of anti-mosquito products were sluggish from June to August but picked up in September, according to Fumakilla Ltd., a Tokyo-based company dealing in insecticides.

“It’s rare for sales of mosquito products to surge in late September,” a spokesperson said.

Sales of repellent and insecticides across the entire pesticide industry in the fourth week of September were up 1.43-fold over the same week of the previous year.

“Since the prevalence of cockroaches and ticks typically subsides by August, the increase is likely due to mosquitoes,” the official said.

According to Fumakilla, the peskiest mosquito species on Japan’s main island of Honshu is the “Aedes albopictus.”

The critters are more active when temperatures range between 25 and 30 degrees, but they tend to rest in the shade of trees when the mercury hits 35 degrees or higher, the company said.

Yoshikazu Shirai, who heads the Institute of Pest Control Technology in Chiba Prefecture, noted that daily temperatures this summer frequently exceeded 35 degrees in many areas, which explains the insects’ inactivity during the daytime.

“Due to the intense heat, fewer people went out and about, and even mosquitoes sought the shade of trees,” he said. “Now that the temperature has cooled down, mosquitoes may be more active in laying eggs.”

EXPANDING HABITAT

The lifespan of the Aedes albopictus ranges from two weeks to a month. They lay eggs several times during their lifetime--through the act of sucking blood.

Conventionally, mosquito eggs remain dormant in October, when daylight hours become shorter. But they hatch when the temperature is relatively high.

“Year after year, the period when mosquitoes increase has shifted, and recently, more people are being bitten in April and October,” Shirai said.

In addition, puddles of warm water that form from sudden evening showers are favored breeding grounds for mosquitoes.

“There was a lot of such rainfall in many areas this year, so it is likely that an unusual outbreak is occurring,” he said.

Their habitats are also expanding.

In 1950, the northernmost habitat of the Aedes albopictus was Tochigi Prefecture, but in 2016, the insects were confirmed to have settled in Aomori Prefecture, according to a survey by the National Institute of Infectious Diseases.

In Hokkaido, the species currently identified in the region is “Aedes flavopictus,” which primarily inhabits mountainous areas.

“It wouldn’t be surprising if the Aedes albopictus establishes a solid presence in Hokkaido anytime soon,” said Yuki Eshita, a visiting professor of infectious diseases at Hokkaido University International Institute for Zoonosis Control.

The Aedes albopictus is adept at detecting carbon dioxide emitted from human breath. When they become adults, they target people.

“Sometimes they even enter a house with you through the door,” Eshita said. “Don’t let your guard down just because it’s autumn.” 

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