TRAIL FOLLOWING AND STOWAWAY BEHAVIOR OF THE MYRMECOPHILOUS STAPHYLINID BEETLE, HOMOEUSA-ACUMINATA, DURING FORAGING TRIPS OF ITS HOST LASIUS-FULIGINOSUS (HYMENOPTERA, FORMICIDAE)

The behaviour of adult Homoeusa acuminata on trails of its host Lasius fuliginosus was investigated both in the field and in the laboratory. The beetles were active from May to September, accurately following t he foraging trails of their hosts up to 20 metres from the nest. Most of the time, they were ignored by the ants, but if attacked they raise d their abdomen as a possible appeasement or defensive behaviour. On t rails the beetles most probably act as food robbers, feeding on prey c ollected by ants. The following method, called stowaway behaviour, was used by the beetles: when a beetle encountered an ant carrying a prey back to the nest it jumped on the prey, probably feeding on it while being transported. Laboratory experiments on circular artificial trail s demonstrated that H. acuminata follows a water extract of hindguts o f the ants, the source of the trail pheromone. Both beetles and ants r esponded to an artificial trail of 0.03 hindgut equivalent per cm, but the mean distance followed by the beetles was about twelve times high er than that covered by the ants themselves. In contrast, experiments with solutions of the six fatty acids reported as the active component s of the trail pheromone showed that the beetles did not respond at al l, and that the ants only respond to the fatty acids at a very high co ncentration.