The prevalence of olfactory- versus visual-signal encounter by searching bumblebees

Abstract

While the phrase ‘foraging bumblebee’ brings to mind a bumbling bee flying flower to flower in a sunny meadow, foraging is a complicated series of behaviors such as: locating a floral patch; selecting a flower-type; learning handling skills for pollen and nectar extraction; determining when to move-on from a patch; learning within-patch paths (traplining); and learning efficient hive-to-patch routes (spatial navigation). Thus the term ‘forager’ encompasses multiple distinct behaviors that rely on different sensory modalities. Despite a robust literature on bumblebee foraging behavior, few studies are directly relevant to sensory-guided search; i.e. how workers locate novel patches. The first step in answering this question is to determine what sensory information is available to searching bumblebees. This manuscript presents a computational model that elucidates the relative frequency of visual and olfactory cues that are available to workers searching for floral resources under a range of ecologically relevant scenarios. Model results indicate that odor is the most common sensory cue encountered during search flights. When the likelihood of odor-plume contact is higher, odor-encounter is ubiquitous. While integrative (visual + olfactory) cues are common when foragers are searching for larger flowers (e.g. Echinacea), they become rare when foragers are searching for small flowers (e.g. Penstemon). Visual cues are only encountered in isolation when foragers are seeking large flowers with a low odor-plume contact probability. These results indicate that despite the multisensory nature of floral signals, different modalities may be encountered in isolation during search-behavior, as opposed to the reliably multimodal signals encountered during patch-exploitation or nectar/ pollen acquisition.

Compounds without borders: A mechanism for quantifying complex odors and responses to scent-pollution in bumblebees

“…Unfortunately, agrochemicals are not the sole source of odor pollutants that pollinators contend with-previous work has shown that air pollutants, such as diesel exhaust and ozone, react with floral odorants [11][12][13][14][15]. This reduces the distance that floral odors travel, which could have impacts on signal encounter by searching foragers [8,12]. In addition, the reaction of floral odorants with air pollutants changes the blend structure-in some cases pushing a learned odor far enough that honeybees no longer respond normally [13][14][15].…”

“…Flowers provide multiple sensory advertisements to pollinators; such as shape, color, and scent [5][6][7]. Recent computational work indicates that odor is consistently available to searching bumblebees [8] and labbased experiments indicate that bumblebees are capable of using odor information alone to locate floral resources [9,10]. Floral-scent is likely an important sensory cue for bumblebee foragers; unfortunately anthropogenic activity has modified their olfactory landscape in urban, suburban and agricultural ecosystems [11][12][13][14][15].…”

Heatwave-Like Events During Development Are Sufficient to Impair Bumblebee Worker Responses to Sensory Stimuli

“…Bumblebees are an important model for this work because they tightly regulate both their colony (Schultze-Motel, 1991;Jones and Oldroyd, 2006;Gardner et al, 2007) and brood temperatures (Vogt, 1986;Weidenmüller et al, 2002). The proper development and function of sensory systems in bumblebees is essential for their pollination activities as they rely heavily on visual, olfactory, gustatory and mechanosensory information to navigate between flower patches and their colony (Dyer and Chittka, 2004;Orbán and Plowright, 2014;Wilmsen et al, 2017;Sprayberry, 2018) and to optimise their foraging (Spaethe et al, 2001;Chittka et al, 2003;Kulahci et al, 2008). Furthermore, bumblebees are already experiencing range shrinkage and population declines in both Europe (Kerr et al, 2015) and North America (Cameron et al, 2011;Kerr et al, 2015) as a result of a warming climate.…”

Warm Temperatures Reduce Flower Attractiveness and Bumblebee Foraging

“…Plants attract pollinators to their flowers using several signals, including flower display, size, shape, color, and odor [18][19][20][21][22][23]. Each signal is relevant for pollinators foraging for floral rewards, pollen, and nectar [24], as pollinators often exhibit innate preferences [25].…”