Overwintering Colorado potato beetles found again in Lahti

Overwintering Colorado potato beetles have been discovered in the Lahti region, Finland’s Food Authority (Ruokavirasto) reports. Adult beetles, larvae, and eggs were found during an inspection at a site where they were detected last year.

The agency urges professional and home growers to monitor potato crops for signs of the pest. Potatoes are the beetle’s primary host plant, and even small quantities can attract them.

In 2025, multiple Colorado potato beetle sightings were confirmed in Finland, with some populations believed to have overwintered in the country. Overwintered beetles emerge in early summer, lay eggs in potato fields, and produce a new generation.

The beetles can also enter Finland from Russia or Estonia. The adult beetle is about one centimetre long, with a yellow back marked by ten black stripes and an orange thorax with black spots. Larvae are plump, orange, and feed on potato leaves, creating bare patches. Fully grown larvae are slightly over one centimetre long, with black heads and two rows of black spots along their sides. Eggs are yellow-orange and laid in dense clusters on the undersides of leaves.

If the beetle establishes itself permanently in Finland, it would cause significant damage to domestic potato production. As a quarantine pest, authorities order eradication measures to prevent its spread.

Suspected sightings should be reported immediately to the Food Authority. Growers are advised to stop all cultivation activities in the affected field, mark the location, photograph the insects, and collect a few specimens in a sealed container without disturbing the site further. Do not attempt independent control measures, as this may hinder official eradication efforts.