As the population of the summer pest "lovebug (red-tipped woolly bear caterpillar)" is expected to decrease after July, concerns are rising that the fall webworm may thrive this time.
On the 10th, the National Forest Service's National Institute of Forest Science raised the occurrence forecast for the fall webworm from "concern" to "caution."
The fall webworm larvae are pests that chew on the leaves of street trees and ornamental trees in urban areas. They occur 2 to 3 times a year, and large infestations can disrupt residents' lives and destroy urban landscapes. They are believed to have invaded North America in 1958.
The damage rate of the first generation (the entire life cycle from hatching from eggs to larvae, pupae, and then becoming an adult before laying eggs again) of fall webworm larvae collected from 1,600 broadleaf trees in 32 fixed survey sites across the country, as monitored by the National Institute of Forest Science, was found to be 15.8%. The damage rate for the second generation of larvae is predicted to be 26.9%.
This is higher than 8.9% in the 2000s and 6.7% in the 2010s, indicating that damage is gradually increasing.
The cause is estimated to be an increase in the number of generations due to climate change. In particular, the rise in temperatures during spring and autumn is elongating the activity period, increasing the likelihood of a third generation occurrence.
Researcher Kim Min-jung from the Forest Pests and Diseases Research Division said, "To reduce larval damage in summer (August) and autumn (October), concentrated monitoring and control measures are necessary from mid-July to early August, when the second generation of larvae begins to appear."