beneficial insect; useful insect
Refers to insects that are helpful to humans, such as pollinators or natural pest controllers. Often contrasted with 害虫 (pest).
Ladybugs are beneficial insects that eat aphids.
The farmer reduced pesticide use to encourage beneficial insects.
害虫 refers to insects that harm crops, spread disease, or otherwise trouble humans, while 益虫 refers to insects that are beneficial, such as ladybugs that eat aphids.
Compound of 益 (benefit) and 虫 (insect). The reading is on'yomi.