Hierarchical use of chemical marking and path integration in the homing trip of a subsocial shield bug

Abstract

The female shield bug Parastrachia japonensis provisions its young by dragging fruit to its burrow. Field observations showed that the bug took a winding path when searching for a suitable fruit, but took the shortest route when homing to the burrow. Displaced homing bugs always walked straight towards the fictive burrow, suggesting that they use path integration to orient. After a homing bug neared the entrance of its burrow, it stopped and started beating the surface of fallen leaves with its antennae. To determine whether these bugs use navigational cues other than those used for path integration, when in the vicinity of the burrow, we blocked their sensory organs and presented them with their own burrows in a laboratory experiment. Although nearly all bugs whose eyes had been blocked found their burrows, the antennae-blocked bugs did not. Homing bugs encountering various experimentally manipulated burrows, such as those containing their own nymphs with an alien burrow's substrate or their own burrow's substrate with alien nymphs, entered burrows only if they were made of the original substrate. When we presented bugs with their own burrows along the homing route, they entered their burrows at every homing point, even at the earliest stage of the homing process. These results suggest that the chemical cues marked around a female's burrow can suppress the use of path integration, and that P. japonensis uses cues hierarchically to accomplish precise homing.