Eyal Rosenzweig

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.

Temperature dependence of the electrical resistivity of social wasp cuticle: A comparative study

Resistance to electricity by social wasp cuticle is temperature dependent within the range of 1--40 degrees C. This was measured on the species Vespa orientalis (the Oriental hornet), Vespa crabro (the European hornet) and the wasp Dolichovespula saxonica. The resistance at first decreases with increased temperature, reaching a nadir which differs according to species, and then rises again up to 40 degrees C, the highest temperature tested. It is suggested that the cuticular changes in resistivity at different temperatures reflect the wasps mechanism for detecting and regulating the temperature in their normal environment.

Longevity of hibernating queens in Vespa orientalis (Hymenoptera: Vespinae). Effects of physical and chemical treatments

Abstract Young queens of V. orientalis collected from nests in the field at the end of the season, just before the hornets naturally enter hibernation, were evaluated for longevity under varying laboratory conditions. Queens kept under full illumination and heating had a briefer life span than did queens kept under full illumination alone or under complete heating alone. All, however, were shorter lived than control queens kept under the thermal and photoperiodic conditions prevailing at that time in nature. Feeding of theophylline to the queens caused them to emerge from hibernation and succumb to an early death. Feeding of allopurinol to the queens diminished their activities relative to control queens but did not abbreviate their life span compared to the control queens.

Regeneration of guinea pig facial nerve: The effect of hypergravity

Exposure to moderate hypergravity improves the regenerative capacity of sectioned guinea-pig facial nerve. The improvement in regeneration is tri-directional as follows: a) an average 1.7 fold increase in rate of regeneration in guinea pigs subjected to hypergravity; b) a 25% enhancement of facial muscle activity following the exposure to hypergravity; and c) improvement in the quality of regeneration from an esthetic standpoint. A good correlation was recorded between the histological structure of the severed nerve at the end of the regeneration and the clinical results.

Geotropic sensitivity of hornets.

Oriental Hornet workers, Vespa orientalis (Hymenoptera: Vespinae) were measured for their responses to changes in the direction of the gravitational field and this under both static and kinetic (centrifugal) conditions. The hornets can build a comb (oriented towards the gravitational force) when their multifaceted eyes are covered. Building activity is undertaken in the dark as well as by hornets that had been blinded or had eclosed in the dark and had never seen any light. If the frons plate of hornets is damaged, there is no or little building, and the comb direction is distorted. Hornets eclosing from and developing in combs subjected to centrifugal spinning build combs whose direction is affected both by rotation and by the resultant of the gravitational and centrifugal forces.