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| Citrus flatid planthopper. Korea Times file |
By Ko Dong-hwan
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| This photo posted on Twitter by former lawmaker Lee Jae-oh, July 18, shows stick insects invading a park on Mount. Bong in the Gusan-dong area of Seoul's Eunpyeong District. Capture from Twitter |
Eunpyeong and the adjacent Goyang city offices, alongside the Forest Management Service, tried to eradicate the insects twice ― in July and August. They deployed drones to drop pesticides, an extreme measure never before used in Seoul for such a purpose.
The incident, experts say, does not have a clear cause. It only led to hypotheses, one of which was that the insects hatched from eggs that survived the unusually warm winter last year.
Another was that for some reasons the balance of the ecosystem in the park area had collapsed, most likely because of human intervention.
"Stick insects are hard to find in Korea, much harder than grasshoppers," Jung Boo-hee, a Korea University professor and the founder of the Woori Entomological Institute in Yangpyeong County in Gyeonggi Province, told The Korea Times. Instead of being worried, the expert who has conducted research in forests and fields for nearly 30 years was elated to learn about the insects' mass emergence in the city.
Jung was especially excited because Seoul is losing more natural habitats for insects with the increasing construction of apartment buildings and development projects. With their disappearance, the city's grassy zones were becoming "silent grass."
"One stick insect lays hundreds of eggs. So it is possible that just a few of those eggs could have brought about the mass infestation. It is also possible that the collapsed ecosystem removed the insects' natural predators such as frogs and birds. In a normal natural balance, if thousands of insects appear, then naturally so do their predators.
"Those stick insects in Eunpyeong have now been killed by natural predators, all right ― humans, who keep interrupting the balance of natural cycles."
She doubts such an incident will happen again next year, saying it was rather random, as any species can mushroom in huge numbers "anywhere if the conditions are right."
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| Spotted lantern fly. Korea Times file |
Another random mass infestation of stick insects was witnessed several decades ago by Park Kyu-tek, an emeritus professor at Kangwon University and entomological expert in his late 70s. His published field research made him popular among global researchers wishing to identify unknown insect species.
"I saw the insects when I was part of an environmental impact assessment group for Yongpyeong ski resort in Gangwon Province's Pyeongchang County in 1975," Park told The Korea Times. "They swarmed a verdant valley behind the site in numbers so many that I couldn't even discern any green spot. The following year, I was curious to see if they were still there. I visited again and couldn't see a single stick insect. And I haven't seen another outbreak of a similar kind.
"What caused that outbreak? I still don't know. This mass infestation is certainly happening more frequently than before. It is a sign that our ecosystem has sustained a penetration, like a hole. If the system was intact, we wouldn't be able to notice any changes."
Collapsed natural balance
Entomological experts in Korea mentioned a "collapsed natural balance" as the most plausible reason behind random insect infestations in out-of-proportional scales that have occurred in recent years here. This year has seen an unusually large number of gypsy moths and mosquitoes that carry the Japanese encephalitis virus, like culex pipiens, nationwide. Chuncheon city in Gangwon Province in 2018 was engulfed by moths, while spotted lantern flies and citrus flatid planthoppers were also among species that have left a massive footprint.
Climate change is believed to be one of the strongest factors behind the broken natural balance.
"Many experts, including myself, believe that climate change and its global warming effect are linked to mass infestations by certain insects," Nam Young-woo, a researcher from Forest Insect Pests and Diseases Division at the National Institute of Forest Science, told The Korea Times.
"Insects are sensitive to ambient temperature. So, with a high temperature, bugs grow faster and their number grows faster as well. The mass infestation of stick insects and gypsy moths this year is because much of their eggs survived hibernation during last winter, which was unusually warm and thus had a low fatality rate for them."
A warm climate, together with enough humidity, can speed a larva's cocoon stage, slashing its duration from 30 days in half for all kinds of insects, according to Jung.
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| Jung Boo-hee felt a 'serious change' in climate conditions in Korea five years ago which was beginning to become unfavorable to insects. Courtesy of Jung Boo-hee |
Jung sensed in 2015 that climate conditions were becoming seriously unfavorable for insects in Korea as days with high temperatures were increasing. The ever-shortening duration of the spring season also worried her.
"There are insects ― such as longhorn beetles ― that fully mature and emerge during a brief period in spring, for about a week or two, when early spring flowers wither and late spring flowers begin to bloom," Jung said. "But these insects could not adapt to the climate that began to heat up in about May, bringing an earlier than usual summer. While flowers are naturally more adaptable to weather, insects, whose functions are more locked into their daily lifecycles than weather conditions, cannot keep up with such climate change."
Korea does not yet have enough data to establish a firm causal relationship between climate change and the insect population, according to Jung. "While climate change certainly seems to influence the ecosystem, at least five to 10 years of monitoring is required to confirm the relationship," she said.
Winning species
In the absence of certain insects in any ecosystem, others naturally take their place. The problem is, they could seriously disrupt the previous natural order. These disruptors, often referred to as "hazardous species" here, are those with exceptional survival strengths such as mosquitoes and cockroaches, or foreign species that find ideal habitats in new ecosystems including the spotted lantern fly and citrus flatid planthopper in Korea.
But Park said such replacements eventually even out naturally ― unless there is human interference.
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| Seongnam city officials fumigate the Sunae-dong area in Bundang District to kill citrus flatid planthoppers in this August, 2016, file photo. Courtesy of Seongnam City Government |
"With international trading by people comes foreign insect species. Once they leave their natural grounds and arrive in new environment where there are no natural predators, they start to thrive. But nature's intricate control measures keep things in balance eventually bringing their predators.
"But when humans step in and try to quell the situation by sprinkling chemicals from the sky or use other artificial forces, they not only kill the overabundant species but also affect the natural predators. It kills the natural balance. Humans' artificiality also cheats on the natural rivalry between them and bugs on agricultural crops, disrupting the sub-ecosystems on farmlands."
Jung said the disrupted natural balance had lowered the number of natural predators and instead given help to intrinsically strong insects that can adapt to extreme conditions.
Gypsy moths are one such example ― they feed on virtually all kinds of fresh leaves on any tree, unlike other moths that eat only certain types. Mosquitoes also have strong adaptability, being able to live in dirty water where their natural predators such as Chinese mud loaches and other fish cannot live. It leads to a boost in mosquito' larvae. This adaptability to the changing environment has even made mosquitoes able to resist various chemicals designed to kill them.
"As the country is becoming warmer due to climate change, those that are more susceptible to this will disappear while stronger bugs will survive," Jung said.
