A Breath of Fresh Air in Foraging Theory: The Importance of Wind for Food Size Selection in a Central-Place Forager

Bumblebees compensate for the adverse effects of sidewind during visually guided landings

Flying animals often encounter winds during visually guided landings. However, how winds affect their flight control strategy during landing is unknown. Here, we investigated how sidewind affects the landing performance and sensorimotor control of foraging bumblebees (Bombus terrestris). We trained bumblebees to forage in a wind tunnel, and used high-speed stereoscopic videography to record 19,421 landing maneuvers in six sidewind speeds (0 to 3.4 m s-1), which correspond to winds encountered in nature. Bumblebees landed less often in higher windspeeds, but the landing durations from free flight were not increased by wind. By testing how bumblebees adjusted their landing control to compensate for adverse effects of sidewind on landing, we showed that the landing strategy in sidewind resembled that in still air, but with important adaptations. Bumblebees landing in a sidewind tended to drift downwind, which they controlled for by performing more hover maneuvers. Surprisingly, the increased hover prevalence did not increase the duration of free-flight landing maneuvers, as these bumblebees flew faster towards the landing platform outside the hover phases. Hence, by alternating these two flight modes along their flight path, free-flying bumblebees negated the adverse effects of high windspeeds on landing duration. Using control theory, we hypothesize that bumblebees achieve this by integrating a combination of direct aerodynamic feedback and a wind-mediated mechanosensory feedback control, with their vision-based sensorimotor control loop. The revealed landing strategy may be commonly used by insects landing in windy conditions, and may inspire the development of landing control strategies onboard autonomously flying robots.

Spatial cognition in the context of foraging styles and information transfer in ants

Ants are central-place foragers: they always return to the nest, and this requires the ability to remember relationships between features of the environment, or an individual's path through the landscape. The distribution of these cognitive responsibilities within a colony depends on a species' foraging style. Solitary foraging as well as leader-scouting, which is based on information transmission about a distant targets from scouts to foragers, can be considered the most challenging tasks in the context of ants' spatial cognition. Solitary foraging is found in species of almost all subfamilies of ants, whereas leader-scouting has been discovered as yet only in the Formica rufa group of species (red wood ants). Solitary foraging and leader-scouting ant species, although enormously different in their levels of sociality and ecological specificities, have many common traits of individual cognitive navigation, such as the primary use of visual navigation, excellent visual landmark memories, and the subordinate role of odour orientation. In leader-scouting species, spatial cognition and the ability to transfer information about a distant target dramatically differ among scouts and foragers, suggesting individual cognitive specialization. I suggest that the leader-scouting style of recruitment is closely connected with the ecological niche of a defined group of species, in particular, their searching patterns within the tree crown. There is much work to be done to understand what cognitive mechanisms underpin route planning and communication about locations in ants.

Plant odors trigger clearing behavior in foraging trails- do they represent olfactory obstacles?

Foraging trails of leaf-cutting ants may be exposed to plant material that interferes with foragers' flux either by physically blocking it or due to secondary metabolites which affect insect behavior. We hypothesized that plant secondary metabolites such as plant volatiles may interfere with pheromone communication, triggering clearing behavior. We impregnated small pieces of paper with different plant odors from native and exotic species and placed them in the middle of foraging trails of the leaf-cutting ant Acromyrmex lobicornis. As a control, we used papers impregnated with trail odor. The paper used as substrate for the odors did not constitute a physical obstacle based on its small surface area. Papers treated with trail odor did not interfere with ant flux and were not removed from the trail. However, when papers were treated with plant odors, they were removed from the trail in most of the cases and ant flux was reduced significantly by 15-28%. We found that ants tapped the tip of their gaster against the ground around the treated papers only when they were impregnated with foreign odors. The number of gaster tappings as well as the time between the placement of the paper and its removal increased with plant odor concentration. However, the decision to remove the paper was not correlated with the number of gaster tappings. Interestingly, clearer ants were smaller than forager ants, suggesting there is morphological differentiation in clearing behavior of the trail. Results from the current study also suggest that odors trigger clearing behavior on foraging trails and affect trail marking behavior. Our results provide information about the potential for plant compounds to constitute obstacles, even when they do not physically obstruct the trail. We conclude that odors may trigger clearing behavior by interfering with pheromone communication.