Visual ground pattern modulates flight speed of male Oriental fruit moth Grapholita molesta

Abstract

Insects flying in a horizontal pheromone plume must attend to visual cues to ensure that they make upwind progress. Moreover, it is suggested that flying insects will also modulate their flight speed to maintain a constant retinal angular velocity of terrestrial contrast elements. Evidence from flies and honeybees supports such a hypothesis, although tests with male moths and beetles flying in pheromone plumes are not conclusive. These insects typically fly faster at higher elevations above a high-contrast ground pattern, as predicted by the hypothesis, although the increase in speed is not sufficient to demonstrate quantitatively that they maintain constant visual angular velocity of the ground pattern. To test this hypothesis more rigorously, the flight speed of male oriental fruit moths (OFM) Grapholita molesta Busck (Lepidoptera: Tortricidae) flying in a sex pheromone plume in a laboratory wind tunnel is measured at various heights (5-40 cm) above patterns of different spatial wavelength (1.8-90 ∘ ) in the direction of flight. The OFM modulate their flight speed three-fold over different patterns. They fly fastest when there is no pattern in the tunnel or the contrast elements are too narrow to resolve. When the spatial wavelength of the pattern is sufficiently wide to resolve, moths fly at a speed that tends to maintain a visual contrast frequency of 3.5 ± 3.2 Hz rather than a constant angular velocity, which varies from 57 to 611 ∘ s −1 . In addition, for the first time, it is also demonstrated that the width of a contrast pattern perpendicular to the flight direction modulates flight speed.

Extremely low neonicotinoid doses alter navigation of pest insects along pheromone plumes

“…Similarly, sublethal exposure to imidacloprid alters the motion-detection neural system of a hoverfly pollinator 30 . Since visual flow across the retina provides essential cues for regulating orthokinetic (movement) and taxis (steering) components of the flight tracks 31 , a potential effect of TIA on the visual system could explain some of the effects that we have observed. On the other hand, the reduction in the number of males taking flight, together with an increased wind-induced drift angle, suggest that TIA could have attenuated male muscular activity.…”

Effects of floor pattern on flight behaviour of the smaller tea tortrix, Adoxophyes honmai, during orientation flight in a sex pheromone plume

“…We observed faster flight speeds of A. honmai over a solid black floor than over a solid white floor or stripes (Figures 4 and 5). A solid white floor has been used as an unpatterned floor (Kuenen et al, 2014; Kuenen & Gilbert, 2014; Vickers & Baker, 1994), but coloured, unpatterned floors have not been used. Differences in speed over solid white and black floors suggest that moths may use visual cues not only from the floor pattern, but also from wavelengths reflected by the floor.…”

“…Flight tracks were digitized to obtain x and y coordinates ( x is the distance from the pheromone source and y is the height) of moth locations using Matlab. Flight trajectories obtained from the side were considered a sufficient indicator of changes in behaviour, because changes in net upwind flight speed of male moths with different floor patterns are almost exclusively the result of a positive orthokinetic responses (Foster & Howard, 1999; Kuenen et al, 2014; Kuenen & Gilbert, 2014). In addition to the net upwind flight speed, the flight height and number of backward movements were also analysed.…”

“…Kennedy (1951) hypothesized that insects maintain a constant preferred visual angular velocity of image flow, and this hypothesis qualitatively explains changes in flight speeds caused by visual cues described above. However, there are some reports that moths do not maintain constant angular velocities (Foster & Howard, 1999; Kuenen & Gilbert, 2014). In these cases, moths may use visual cues other than angular velocity, as reported for Grapholita molesta (Kuenen & Gilbert, 2014).…”

“…However, there are some reports that moths do not maintain constant angular velocities (Foster & Howard, 1999; Kuenen & Gilbert, 2014). In these cases, moths may use visual cues other than angular velocity, as reported for Grapholita molesta (Kuenen & Gilbert, 2014). To investigate the influence of visual cues on the flight of moths, a solid white floor pattern has sometimes been used as a control, but patternless floors of other colours, which reflect different wavelength, have not been used (Kuenen et al, 2014; Kuenen & Gilbert, 2014; Vickers & Baker, 1994).…”