BEIJING, Sept. 30 (Xinhua) -- Beijing is fighting an invasive pest with an army of natural enemies. Since Monday, the Chinese capital has been releasing another 400 million parasitic wasps to control a surge of fall webworms.
These wasps, known scientifically as Chouioia cunea Yang, are dominant parasitic natural enemies of the pest and safe for humans and livestock. "Earlier this year alone, Beijing unleashed nearly 700 million of them," said Yang Zhongqi, chief scientist at the Chinese Academy of Forestry and also the discoverer of the wasp.
The fall webworm, a major invasive pest native to North America, produces three generations a year, each passing through four life stages, namely egg, larva, pupa and adult. Beijing is currently in the peak damage period of third-generation fall webworm larvae, with a surge of mature larvae set to descend from trees to pupate, Yang said.
The fall webworm can damage more than 300 plant species. In the capital, over 200 species of trees, fruit trees, flowers and crops are under threat, with ash, mulberry and plane trees among its favorite targets. The pest only damages plants -- neither its larvae nor adults are toxic or harmful to humans, the expert added.
In response to residents' reports that fall webworms have been noticeably more numerous in Beijing this year compared with previous years, Yang Sihan, with the Beijing municipal landscape and greenery resource protection center, attributed the increase mainly to warmer winters and frequent summer rainfall.
Warmer winters in recent years have pushed up the survival rate of the pest's overwintering pupae. "Our five-year survey of overwintering populations in some areas shows that the survival rate of overwintering pupae rose from 65.3 percent in 2023 to 84.2 percent this year," Yang noted, adding that frequent rainfall in Beijing this summer also hampered pest control operations.
Experts explained that the difficulty of controlling the fall webworm is directly tied to the pest's own characteristics and the practical challenges involved.
The fall webworm has an extremely strong reproductive capacity. A single female moth lays an average of 300 to 600 eggs, and up to 2,000 under favorable conditions. Even a small number of surviving insects can allow the population to rebound rapidly. Moreover, the fall webworm showed pronounced generation overlap this year, with multiple life stages present at the same time.
Urban operational conditions also pose challenges. Narrow spaces, tall trees with dense canopies, and the limited range of some ground sprayers can all reduce the effectiveness of pest control.
Despite these challenges, local authorities have rolled out a coordinated response combining early warning and control measures.
According to Yang Sihan, almost 3,000 monitoring sites have been set up across the city under a grid-based management system. Based on pest patterns, meteorological data and expert consultation, officials issue rolling long-, medium- and short-term warnings to guide precise action.
On the control front, beyond releasing parasitic wasps for biological control, crews manually remove larval webs and wrap corrugated paper and non-woven fabric around tree trunks to trap mature larvae descending to pupate.
Traps and insect-killing lamps are also deployed to trap and kill adult moths, thereby breaking the reproductive cycle. In addition, authorities use high-efficiency, low-toxicity, eco-friendly pesticides and carry out ground spraying at staggered times.
The Beijing Municipal Forestry and Parks Bureau is calling on residents to help control this pest.
The bureau advised residents to clear away dead branches, fallen leaves and clutter around their homes to remove places where larvae can pupate. It also suggested cutting off infested branches and leaves when larval webs are spotted, and disposing of them in sealed bags. Mature larvae on tree trunks or the ground, notably, can simply be crushed underfoot.
Meanwhile, anyone who notices chewed leaves, webs or mature larvae on trees in public areas can call the 12345 citizen hotline or report it to their local landscaping and greening department, the bureau added. ■
