Antennal Position Research Articles

Busy bees need rest, too

1. The behaviour of isolated individual forager honeybees during the night has been investigated with a variety of experimental methods. Prolonged rest in these diurnal insects is accompanied by: reduced muscle tone (Figs. 1, 6, 10–12), decreased motility (Figs. 2, 3, Table 1), lowered body temperature (Figs. 7, 8) and raised reaction threshold (Fig. 9). These phenomena strongly resemble four characteristic features of sleep in humans, mammals and birds. It is thus very likely that the profound rest which forager bees experience at night is sleep. This assumption is further supported by the results of previous investigations of visual interneurones in the bee. 2. The antennae of sleeping bees manifest characteristic postural constellations (Fig. 6). High reaction thresholds are associated with particular antennal positions. 3. The total sleep time (duration of antennal immobility plus duration of small antennal movements) in 24 h for two bees was 7.6 h and 4.9 h (Table 1). 4. Bees which rest in a hive at night also display phenomena which have been encountered during the laboratory investigations. 5. Sleep in mammals is an active, controlled process; the same seems to be true of sleep in honeybees (Figs. 3, 4). Unlike mammals, bees experience their deepest sleep towards the end of the sleep phase (Figs. 3, 9, 10, 12).

Pheromone-triggered flip-flopping interneurons in the ventral nerve cord of the silkworm moth,Bombyx mori

1. A group of extracellularly recorded descending interneurons in the ventral nerve cord of the male silkworm mothBombyx mori share a common flip-flopping input. In response to repeated stimuli these flip-flopping interneurons switch back and forth between long lasting high and low firing rates (Figs. 1, 2). 2. Changes in the level of the female pheromone bombykol in an airstream directed at the antennae were the most effective stimuli in eliciting flip-flopping of the interneurons. Changes in light intensity, up or down, were the only other effective stimuli (Fig. 2, Table 1). 3. The low or high firing frequency states following a single stimulus presentation lasted as long as 4 min, although with some decrement (Fig. 3a). 4. The high and low states corresponded to two different positions of the antennae. Transitions between states were mirrored by changes in antennal position. Immobilizing the antennae did not eliminate flip-flopping (Fig. 5). 5. In intact animals, the two antennal positions corresponded to left and right turning movements of the legs and to left and right ‘ruddering’ of the abdomen (Fig. 6). 6. When bombykol-laden air puffs were presented to a single antenna, the neurons sometimes showed flip-flopping responses, but often remained in a ‘favored’ state between stimuli (Fig. 7). 7. When different concentrations of bombykol were presented to the two antennae, the interneurons assumed a high or low firing rate, consistent with a turn toward the antenna receiving the higher concentration. Different concentrations of bombykal to the two antennae (with equal, constant bombykol levels to the two antennae) elicited the opposite effect, i.e., firing rates consistent with turning away from the higher bombykal concentration (Fig. 8). 8. Most interneurons responded in graded fashion to other stimuli besides those which elicited flip-flopping (Fig. 9). Six response types were discriminated, based upon exclusive combinations of sensory inputs and upon the direction of the correlation between flip-flopping states and animal turning (Table 2). 9. All of the results support the hypothesis that these interneurons carry left and right turning instructions for pheromone-directed turns in the upwind approach of maleBombyx to the female.

Antennal Sensory Organs of Two Melanophila Species (Coleoptera: Buprestidae)1

Examination of the antennae of Melanophila drummondi Kirby and Melanophila acuminata DeGeer reveal a new type of sensory structure containing sensilla basiconica. The distal lobes of antennal annuli 3–11 of M. drummondi and annuli 4–11 of M. acuminata possess a slit structure which contains from 15 to more than 60 sensilla basiconica. The location of these organs with respect to antennal position during flight, and their ability to stain when treated with aqueous crystal violet dye suggest their probable role as chemoreceptors. A campaniformtype organ was also found on the lateral regions of the antennal annuli of the female M. acuminata. Between 20 and 30 of these organs were present on either side of the annulus. These organs were absent from the male M. acuminata antennae. The possible function of this organ as a temperature receptor is discussed.

Antennae: Another Wind-sensitive Receptor in Locusts

FIVE pairs of wind-sensitive hair beds at the upper part of the head control flight posture and wing movement of locusts1–7. But the antennae of flies and bees are airflow receptors which regulate the insect's flight speed relative to the surrounding air and stabilize the flight course in the horizontal plane8–12. During tethered flight these insects hold their antennae in a characteristic flight position. Exposed to the air current of a wind tunnel, they will move their antennae actively against the direction of the air current. This movement is considered as an antennal positioning reaction, which adapts the operating range of the receptor to different air speeds10–12.