Geotropism of hornet comb construction under persistent acceleration.

Social wasps (Vespinae) are insects which build in a precise geotactical orientation. The effect of persistent acceleration on comb construction by Oriental hornet (Vespa orientalis) workers was assessed experimentally within breeding boxes of various size and shape. Groups of hornets at the building phase were subjected to a centrifugal and gravitational force with a resultant ranging between 26 degrees and 45 degrees. The comb construction within such boxes was compared to that within control boxes under ordinary gravitational pull. It was found that: a) juvenile hornets (1-2 days of age) placed in quasi-rectangular boxes built in the direction of the resultant force; b) juvenile and adult hornets (3-7 days of age) placed in spherical shaped containers also built in the direction of the resultant force; c) adult hornets who had spent their first days of life in a stationary rectangular box, apparently learned the direction of the gravitational force and "tried" to build in this direction when exposed to a centrifugal force; d) adult hornets made to spin in quasi-rectangular boxes tilted in the direction of the calculated resultant force built in the direction of the resultant. These results suggest that hornets learn the direction of the gravitational force during the first days of life and that geometrical cues within the breeding box enable them to build in the direction of the force to which they have become habituated. From the standpoint of geometric cues, only the roof of the breeding box is of critical importance.