Humans are highly visual creatures, but other species integrate several senses to get a sense of their surroundings. When foraging for nectar, tobacco hornworm moths appear to rely on their senses of smell and vision to home in on their nectar target. But can they employ other senses to help direct them to their goal? While hovering above an attractive flower, Joaquín Goyret explains that the insect constantly probes the surface with its proboscis. Working with Robert Raguso, Goyret was curious to know whether the moth co-opts mechanosensory information from the proboscis to help locate a nectar treat. Scrutinising moths as they probed fake flowers, the team investigated how successfully the insects read the flower's terrain().
Working with young adult moths, Goyret offered the youngsters an array of bergamot scented paper flower shapes, each with a nectar lure at its centre. Presenting each moth with an array of 12 identical flower shapes, Goyret filmed insects as they foraged for 10 minutes and calculated the foraging success rate from the number of flowers that the moth successfully drained.
Preventing the insects from touching the flower shapes by covering them with a transparent film square, Goyret found that the moth's success rate plummeted when the surface was inaccessible. Even though the insects could see the flower shapes and smell their scent, the loss of reliable tactile information significantly reduced their ability to locate their nectar reward.
Curious to know how aspects of a flower's shape might influence the insects' success rate, Goyret tested their foraging efficiency on a range of flower shapes by varying the surface area and edge-to-centre distances, and found that the insects seemed to find it easier to locate their nectar reward on the flower shapes with the smallest surface areas. Goyret adds that the insects appear to use several probing strategies, raging from random stabs at the surface, to more directed approaches where they locate the flower's edge before tracing a radial path towards the centre.
Having found that the proboscis's mechanosensory input gave the moths a significant foraging advantage, Goyret folded groves into the flower shapes to see whether the insect used three-dimensional cues to home in on the nectary. Sure enough, when the grooves converged on the nectary, the insect's proboscis tracked along them leading the insect directly to its nectar reward. But when the grooves crossed the flower, avoiding the nectar at the flower's centre,the insects rarely reached their goal. The moth seemed able to follow topographic features on the flower's surface with its proboscis.
Goyret is now keen to find out how the moths fare when presented with real flowers, and whether they choose to forage at large attractive but unwieldy model flowers, in preference to smaller model blooms that they handle more efficiently.
