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

Hornet ( , 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° and 180°. The tests were run on non-blind and blind hornets, at temperatures ranging between 18°C and 35°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° declination, queens at 4–5° and males at a declination of 8–19° 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°C for workers, 23.2°C for queens and 20.8–21°C for males.