SUMMARY Visual identification of targets is an important task for many animals searching for prey or conspecifics. Dragonflies utilize specialized optics in the dorsal acute zone, accompanied by higher-order visual neurons in the lobula complex, and descending neural pathways tuned to the motion of small targets. While recent studies describe the physiology of insect small target motion detector (STMD) neurons, little is known about the mechanisms that underlie their exquisite sensitivity to target motion. Lobula plate tangential cells (LPTCs), a group of neurons in dipteran flies selective for wide-field motion, have been shown to take input from local motion detectors consistent with the classic correlation model developed by Hassenstein and Reichardt in the 1950s. We have tested the hypothesis that similar mechanisms underlie the response of dragonfly STMDs. We show that an anatomically characterized centrifugal STMD neuron (CSTMD1) gives responses that depend strongly on target contrast, a clear prediction of the correlation model. Target stimuli are more complex in spatiotemporal terms than the sinusoidal grating patterns used to study LPTCs, so we used a correlation-based computer model to predict response tuning to velocity and width of moving targets. We show that increasing target width in the direction of travel causes a shift in response tuning to higher velocities, consistent with our model. Finally, we show how the morphology of CSTMD1 allows for impressive spatial interactions when more than one target is present in the visual field.

energy expenditure to track flowers is minimal compared to energy intake; therefore, patterns of net energy gain mimicked patterns of feeding rate. The direction effects of flower motion were greater than the frequency effects. While M. sexta appeared equally capable of tracking flowers moving in the horizontal and vertical motion axes, they demonstrated poor ability to track flowers moving in the looming axis. Additionally, both feeding rates and net energy gain were lower for looming axis flower motions.

Declines in bumblebee populations have led to investigations into potential causes – including agrochemical effects on bumblebee physiology. The indirect effects of agrochemicals (i.e. behavior modulation) have been postulated, but rarely directly tested. Olfactory information is critical in mediating bumblebee-floral interactions. As agrochemicals emit volatiles, they may indirectly modify foraging behavior. We tested the effects of olfactory contamination of floral odor by agrochemical scent on foraging activity of Bombus impatiens using two behavioral paradigms: localization of food within a maze and forced-choice preference. The presence of a fungicide decreased bumblebees’ ability to locate food within a maze. Additionally, bumblebees preferred to forage in non-contaminated feeding chambers when offered a choice between control and either fertilizer- or fungicide-scented chambers.

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.

While plant-pollinator interactions are a classic model system for evolutionary relationships, the relationship between forager energetics and floral motions remains little explored. In this study, we show that hawkmoths preferentially feed on horizontally oscillating flowers, which have previously been shown to yield higher energy gains during feeding bouts than looming flowers. We also analyze natural flower motions exhibited by four hawkmoth-pollinated species. Our analysis shows these flowers have higher amplitude motions in the horizontal axis than that in the looming axis. This work demonstrates the potential for adaptation between the biomechanical determinates of flower motions and the feeding performance of hawkmoths.

Hawkmoths rely on vision to track moving flowers during hovering-feeding bouts. Visually guided flight behaviors require a sensorimotor transformation, where motion information processed by the optic ganglia ultimately modifies motor axon activity. While a great deal is known about motion processing in the optic lobes of insects, there has been far less exploration into the visual information available to flight motor axons. Visual information recorded at this stage has likely arisen from multiple visual pathways, and has potentially been modified by outside sensory information. As a first step, understanding the sensorimotor transformation from transduction of moving flower signals to active flower tracking behavior requires that the visual information available to the thoracic flight control centers be assayed. This paper investigated the response of descending visually sensitive neurons in the cervical connectives of the hawkmoth, Manduca sexta L. (Lepidoptera: Sphingidae), to flower-like stimuli. Because flower structure lends itself to oscillatory (vibratory) motion, the stimuli used in these experiments were discs oscillating in each axis of motion (horizontal, vertical, and looming). Object-sensitive descending-neurons (OSDNs) respond to multiple directions of object motion and do not clearly sort into classes of directional tuning. The broad spatial distribution of directional sensitivities exhibited by OSDNs indicates that the direction of object motion may be encoded on a population scale. Although OSDNs exhibit broad frequency response curves, over the range of frequencies that M. sexta are able to track (0–2 Hz) OSDNs exhibit monotonically increasing response. Additionally, OSDNs respond to discs oscillating at frequencies as high at 6 Hz, indicating that the visual information being sent to thoracic motor control centers is not likely the limiting factor in flower tracking ability.

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Background and AimsBumblebees provide vital pollination services to both natural and agricultural ecosystems. Consequently their declines in species-diversity and population size over the last five decades is alarming. Direct contributors to these declines include pesticides, habitat loss, and disease. However, given that colony fitness is linked to foraging success, successful conservation requires mitigation of any anthropogenic practices that negatively impact foraging. Previous work has shown that agrochemical odor-pollution, including that of fungicides, can modulate bumblebee foraging behavior. This study investigates how odor pollution from three common fungicides (Safer® Brand Garden Fungicide II, Scotts® Lawn Fungus Control, and Reliant® Systemic Fungicide) affects Bombus impatiens’ floral-odor learning and recognition using an associative learning paradigm.MethodsThe effects of fungicide-odor pollution were tested in three ways: (1) background pollution during floral-odor learning; (2) background pollution during floral-odor recognition; and (3) point (localized) pollution during floral-odor recognition. Electroantennogram (EAG) recordings from B. impatiens confirmed the salience of all odor-stimuli and examined impacts of background fungicide-odor on antennal responses to floral-odor. To better understand how fungicide-odor structure related to behavioral data, scents were sampled (Solid Phase Microextraction) and analyzed using gas chromatography–mass spectrometry. Odors were then characterized using the Compounds Without Borders (CWB) vectorization method.ConclusionAll fungicides tested disrupted floral-odor learning and recognition for at least one concentration tested, and Scotts® was universally disruptive at all tested concentrations. All fungicides induced EAG responses, indicating they provide perceivable odor stimuli. Interestingly, two of three tested fungicides (Scotts® and Reliant®) inhibit antennal responses to Monarda fistulosa odor. Odor characterization supports previous findings that sulfurous scents could be disruptive to odor-driven foraging behaviors. Inability for foraging bumblebees to associate to rewarding floral odors in the presence of fungicidal odor pollution could have negative large-scale implications for colony health and reproductive fitness.