Geotropic sensitivity exhibited by single hornets: the influence of caste, age, light and temperature

Hornet Vespa orientalis, Hymenoptera: Vespinae) workers, queens and males, aged 0-24 hours (i.e. juveniles) and 24 hours and more (i.e. adults) were tested for their responses to changes in the direction of the gravitational force while placed on a flat surface gradually tilted between 0.5 degree and 180 degrees. The tests were run on non-blind and blind hornets, at temperatures ranging between 18 degrees C and 35 degrees C, in daylight as well as in the dark. Up to 18 hours of age, negative phototaxis prevailed among the hornets, which displayed a clear preference for remaining in the dark regardless of the geotropic position. Between 18-24 hours of age, there was gradual appearance of a sensitivity to change in the geotropic position. Above 24 hr of age, the hornets became sensitive to changes in their declinations, with workers becoming sensitive at a 3-5 degrees declination, queens at 4-5 degrees and males at a declination of 8-l9 degrees from the horizontal. Hornet response takes the form of an upward climb, to the highest point of the test surface. Such response required a temperature exceeding 24.8-25 degrees C for workers, 23.2 degrees C for queens and 20.8-21 degrees C for males.