As lovebugs begin their summer swarm, pest-control plans to curb population

Dozens of wriggling larvae emerged after damp soil and fallen leaves were brushed aside on the slopes of Mount Gyeyang in Incheon around noon on Wednesday. The larvae belonged to summer's notorious nuisance, the lovebug.

“[The larvae] will become adults, mate and start flying around by late June,” Kim Dong-gun, head of the Institute of Environmental Ecology at Sahmyook University, explained while placing one of the larvae on his palm. “There is a strong possibility they will appear in large numbers across several regions again this year.”

Plecia longiforcep, commonly known as the lovebug, is an invasive fly native to humid parts of southern China, Taiwan and Japan, was first detected in Korea around 2018. As climate change has made the Korean Peninsula warmer and wetter, the insects have swarmed the greater Seoul area in growing numbers every summer since 2022. With no natural predators to keep populations in check, authorities are racing to contain them before they emerge as adults in late June, deploying everything from biological sprays to rose-scented traps designed to lure the bugs away from urban areas.

Near the summit of Mount Gyeyang, workers were busy spraying BTI, a biological control agent used against the insects. Hoses continuously sprayed water mixed with the treatment solution, while generators loudly pumped water uphill from the base of the mountain to the treatment site.

Researchers from Sahmyook University and representatives from the National Institute of Biological Resources (NIBR), who were leading the operation, mixed 2 kilograms (4.4 pounds) of brown-colored BTI with 1 ton of water brought up from the mountain slope.

A passing hiker asked, “Are you spraying pesticides?” But BTI differs from conventional pesticides. The biological agent specifically targets members of the fly order, including lovebugs, and does not affect other animals or plants.

Researchers and pest control teams began the control operation in spring while the larvae were still growing in soil and leaf litter. Controlling insect numbers becomes far more difficult once they become adults in the summer. The treatment becomes ineffective after the insects enter the pupal stage.

Adult lovebugs survive only three to seven days, but a single mating pair can lay around 500 eggs.

The operation also serves as a research experiment to measure the effectiveness of control methods and identify the insects’ preferred habitats.

Researchers intentionally left larvae found outside designated control zones untouched. Teams instead collected samples from 16 separate areas with varying environmental conditions such as altitude, slope direction and terrain.

Researchers hope the data will help determine which environments the insects prefer. The results will later be combined with geographic information system mapping to identify high-risk areas for intensive management.

There's a possibility that the insects’ habitat perimeter could spread even further this year.

“Surveys conducted across 102 locations nationwide found high larval densities in Seoul and northern Gyeonggi regions such as Dongducheon,” Park Sun-jae, a researcher at the NIBR, explained. “Larvae were discovered in the majority of the parks across Seoul’s 25 districts.”

Larvae have also been found in southern Gyeonggi areas such as Seongnam.

Researchers also point to the insects’ “hitchhiking” behavior — attaching themselves to vehicles and moving to new regions — as another factor behind their expanding range.

Complaints last year were concentrated in northwestern and southwestern Seoul as well as Incheon, but experts worry the insects could spread to far more regions this year.

The invasive species was first discovered in Korea around 2018. Native to hot and humid regions such as southern China, Taiwan and Okinawa in Japan, the insects have repeatedly appeared in massive numbers around the Seoul metropolitan area since 2022 as climate change has changed Korea’s climate to become warmer and more humid.

The lack of natural predators contributes to the outbreaks.

“Lovebugs do not appear in massive outbreaks in China,” Kim explained. He conducted field research in Jiangxi Province in southeastern China. “Their habitats in China are surrounded by a wider variety of species, making them more likely to face natural predators or competition for food from other insects.” 

Korea’s thick and humid leaf-litter soil is also believed to provide favorable conditions for larvae growth.

Researchers are also testing new control methods this year, including using rose scents to lure lovebugs out of urban areas and toward city outskirts.

The strategy is based on studies showing that some species within the same fly family are strongly attracted to the scent of roses. Korean researchers have also partially confirmed the effectiveness through domestic experiments.

“We plan to install 1,300 traps using rose scents near parks and mountains across 19 districts in Seoul during June and July,” Song Eun-cheol, an official at the infectious disease control division of the Seoul Metropolitan Government, explained.

Additional traps, including light traps and 3-meter-high (9.8-foot-high) aerial traps, will also be installed in areas including Mount Baengnyeon in Eunpyeong District, northern Seoul, and Mount Buram in Nowon District, northern Seoul.

Some experts are also calling for clearer systems and guidelines that would allow local governments to respond more aggressively to outbreaks.

“We need clearer standards for when authorities should begin full-scale pest control measures based on insect population levels,” Kim said. “One example worth referencing is Japan’s encephalitis warning system, which issues alerts when mosquito numbers exceed a certain threshold.”

This article was originally written in Korean and translated by a bilingual reporter with the help of generative AI tools. It was then edited by a native English-speaking editor. All AI-assisted translations are reviewed and refined by our newsroom.

BY HEO JEONG-WON [[email protected]]