what do the japanese hornets do to give a signal to the others in their colony that a european honeybee nest is in the area?

Japanese hornets do to give a signal to the others in their colony that a European honeybee nest is in the area that is called as Pheromone marks

Explanation:

The Japanese giant hornets are very large and aggressive. Its sting is so dangerous that it disturbs the nervous system and causes damage to the victim’s tissue. Once a Japanese Hornet locates a hive of the European honey bee, it quickly leaves a mark known as the pheromone which helps attract its nest mates.

The Japanese hornet has the capability of killing 40 honey bees in one minute. Hence a group of 30 can destroy 30,000 bees in a matter of four hours. Then these hornets take these savaged bees to their nests to feed their larvae.