Japanese Beetle

• In Japan it is an unobtrusive insect kept in check by its natural enemies; it reached the United States around 1916 in a consignment of bulbs and became a devastating pest there.
• It feeds in groups because the beetles already feeding release compounds that attract more of their kind, so that a plant can be covered in beetles within hours.
• It has entered Europe through northern Italy and Switzerland, and its advance is under plant health surveillance across the European Union.
• It reached the United States in 1916, detected in a New Jersey nursery, probably in the root ball of irises imported from Japan. Today it is found throughout the east of the country.
• In Japan it is an unobtrusive insect, kept in check by its natural enemies; outside Japan, without them, it becomes a pest.
• It is doubly harmful: the larva ruins lawns by eating roots from below, and the adult skeletonises leaves from above, leaving nothing but the veins.
• It feeds on more than three hundred plant species, from roses and grapevines to maples and apple trees.
• The adults aggregate in response to a pheromone and to the smell of damaged leaves, so damage attracts more damage and attacked plants become bait.
• It was detected in Italy in 2014 and in Switzerland in 2023, and it is one of the European Union's priority pests: its arrival in Spain is an active risk.

Skeleton type

Invertebrate - chitin exoskeleton (insect)

Habitat and environment

Grasslands, gardens and crops; the larva lives in the soil eating grass roots, and the adult devours the leaves, flowers and fruit of more than three hundred plant species

Size at birth

White, spherical and almost translucent egg about 2 mm across; the C-shaped larva reaches 25 to 32 mm

Sexual maturity

The adults emerge in late June or early July and live 30 to 45 days; virgin females release a sex pheromone and the first individuals to emerge release an aggregation pheromone that draws in the rest

Gestation / incubation

The eggs hatch between 8 and 14 days; the larvae go through three instars feeding on roots, overwinter 10-20 cm deep, move up as the soil warms and pupate in June, with a pupal stage of 8 to 20 days

Litter / clutch size

40 to 60 eggs per female over her lifetime, laid one to five at a time at between 5 and 15 cm deep, in several batches during July and August

Sources consulted: https://es.wikipedia.org/wiki/Popillia_japonica; CABI (Fleming 1972, Dalthorp et al. 2000); UMN Extension; Ohio State University Extension; ScienceDirect (Hughes 1989); Science Advances, How colonial animals evolve; Wikipedia, Zooid; NC State Extension, ficha Japanese beetle; Animal Diversity Web (Fleming 1972); CABI (Hadley & Hawley 1934, Barrows & Gordh 1978); Animal Diversity Web; NC State Extension

Best time: From June to August, when the adults feed in numbers