The stimuli evoking the aerial-righting-posture of falling pea aphids

Abstract

Some wingless insects possess aerial righting reflexes, suggesting that adaptation for controlling body orientation while falling through air could have preceded flight. When threatened by natural enemies, wingless pea aphids (Acyrthosiphon pisum) may drop off their host plant and assume a stereotypic posture that rotates them in midair to land on their feet. The sensory information triggering aphids to assume this posture has so far been unknown. We subjected aphids to a series of tests, isolating the sensory cues experienced during free-fall. Falling aphids assumed the righting posture and landed upright irrespective of whether the experiments were carried out in the light or in complete darkness. Detachment of the tarsi from the substrate triggered the aphids to assume the posture rapidly, but only for a brief period. Rotation (mainly roll and yaw) of the body in air, in the light, caused aphids to assume the posture and remain in it throughout rotation. In contrast, aphids rotated in the dark did not respond. Acceleration associated with falling or airflow over the body per se did not trigger the posture. However, sensing motion relative to air heightened the aphids' responsiveness to rotation in the light. These results suggest that the righting posture of aphids is triggered by a tarsal reflex, but, once the aphid is airborne, vision and a sense of motion relative to air can augment the response. Hence, aerial righting in a wingless insect could have emerged as a basic tarsal response and developed further to include secondary sensory cues typical of falling.

Turning in mid‐air allows aphids that flee the plant to avoid reaching the risky ground

“…First, we tested whether live aphids had a better chance of clinging onto a plant after dropping. Because 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 Y. Meresman et al 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 dead aphids do not actively assume the righting position (Meresman et al 2014) we expected them to cling only coincidentally.…”

“…3). We arbitrarily chose a 2.5-cm radius for measurement because, based on our observations during previous works (Ribak et al 2013;Meresman et al 2014), the aphids undergo a vertical path, and with regard to their size (our colony was measured in a previous work by Ribak et al [2013]; average body length: 4.19 ± 0.15 mm; body mass: 4.16 ± 0.21 mg), the chosen area seemed sufficient for our measurements.…”

“…To allow the adhesive organs to attach to the plant, aphids must position their legs towards the encountered leaves quickly enough, before passing all plant material. By quickly reacting to the detachment of their tarsi from the plant surface (Meresman et al 2014), most pea aphids (75%) can rotate within a 5-cm drop and almost all (90%) within under 14 cm (Ribak et al 2013). Righted aphids, with their tarsi facing down, were able to better grasp an artificially placed surface on their drop-path (Ribak et al 2013) or coincidentally attach to lower plant material (Meresman, pers.…”

“…First, we assessed the effects of both the amount of foliage in the dropping path and the ability of the aphids to actively align their body in the air on their clinging ability by dropping live and dead aphids upon plants from a fixed position, and exposing them to variable foliage coverages. Because dead aphids do not assume the righting posture (Meresman et al 2014), this experiment enabled us to quantify the effect of the actively achieved aerial righting on the clinging success of the dropping aphids. We then released aphids in a commercial alfalfa (Medicago sativa) field to settle on plants (hereafter, self-positioned aphids) and measured their success in avoiding the ground after dropping from a plant.…”

The descent of ant: field-measured performance of gliding ants

“…1A. In laboratory experiments, given sufficiently high resolution video data, righting phase duration can be estimated by directly observing body pose (Meresman et al, 2014;Ribak et al, 2013). Without access to pose information, we chose a fixed short distance (0.2 m), and defined the righting phase duration for a given trajectory as the elapsed time between the initiation of descent and the point in the trajectory where the net horizontal distance traveled became greater than this fixed distance.…”