Active tactile exploration for adaptive locomotion in the stick insect

Insects carry a pair of actively movable feelers that supply the animal with a range of multimodal information. The antennae of the stick insect Carausius morosus are straight and of nearly the same length as the legs, making them ideal probes for near-range exploration. Indeed, stick insects, like many other insects, use antennal contact information for the adaptive control of locomotion, for example, in climbing. Moreover, the active exploratory movement pattern of the antennae is context-dependent. The first objective of the present study is to reveal the significance of antennal contact information for the efficient initiation of climbing. This is done by means of kinematic analysis of freely walking animals as they undergo a tactually elicited transition from walking to climbing. The main findings are that fast, tactually elicited re-targeting movements may occur during an ongoing swing movement, and that the height of the last antennal contact prior to leg contact largely predicts the height of the first leg contact. The second objective is to understand the context-dependent adaptation of the antennal movement pattern in response to tactile contact. We show that the cycle frequency of both antennal joints increases after obstacle contact. Furthermore, inter-joint coupling switches distinctly upon tactile contact, revealing a simple mechanism for context-dependent adaptation.     

The antennal motor system of the stick insect Carausius morosus: anatomy and antennal movement pattern during walking

The stick insect Carausius morosus continuously moves its antennae during locomotion. Active antennal movements may reflect employment of antennae as tactile probes. Therefore, this study treats two basic aspects of the antennal motor system: First, the anatomy of antennal joints, muscles, nerves and motoneurons is described and discussed in comparison with other species. Second, the typical movement pattern of the antennae is analysed, and its spatio-temporal coordination with leg movements described. Each antenna is moved by two single-axis hinge joints. The proximal head-scape joint is controlled by two levator muscles and a three-partite depressor muscle. The distal scape-pedicel joint is controlled by an antagonistic abductor/ adductor pair. Three nerves innervate the antennal musculature, containing axons of 14-17 motoneurons, including one common inhibitor. During walking, the pattern of antennal movement is rhythmic and spatiotemporally coupled with leg movements. The antennal abduction/adduction cycle leads the protraction/retraction cycle of the ipsilateral front leg with a stable phase shift. During one abduction/adduction cycle there are typically two levation/depression cycles, however, with less strict temporal coupling than the horizontal component. Predictions of antennal contacts with square obstacles to occur before leg contacts match behavioural performance, indicating a potential role of active antennal movements in obstacle detection.     

Olfactory receptor responses of the nymphal American cockroach to sex pheromones and their mimics

1. EAG responses to highly purified sex pheromones (periplanone-A and -B), sex pheromone mimics [germacrene-D, (+)-verbanyl acetate and (+)-trans-verbenyl acetate] and general odor (camphor) were recorded from both sexes of adult and three nymphal stages (7, 10 and 11th instars) of the American cockroach. 2. The M/F ratios were evaluated for each stage by stimulation with the above chemicals. 3. The ratio values indicated undeveloped sex pheromone receptor on the antennae of 7th male instar and females of all the stages. On the other hand, precursory development of the receptor was expected on the antennae of males of the old-aged nymphal instars and full development on the adult male antennae.     

Electroantennogram responses to the sex pheromone and other odours in the American cockroach

Electroantennogram responses of adult American cockroaches were recorded for the sex pheromone and 30 kinds of monoterpenoids. Strong responses to the sex pheromone were obtained from the antennae of male adults, but not from females. The compounds possessing a hydroxyl or carbonyl group produced significant EAG responses in the antennae. Bornyl acetate, however, was an exception and gave strong responses in both male and female antennae. There was basically no difference between the antennal responsiveness to monoterpenoids tested in both sexes.     

Response to host plant odors and aggregation pheromone by larvae of the Colorado potato beetle on a servosphere

Using a servosphere (locomotion compensator), locomotory behavior of Colorado potato beetle Leptinotarsa decemlineata Say (Coleoptera: Chrysomelidae) larvae was measured in detail in response to pulsed and non-pulsed odors of hostplant and conspecific pheromone. Second instars showed decreased straightness of movement, and all larvae showed decreased speed, in response to potato odor. Change in straightness by 2nd instars was also significantly affected by the interaction of pheromone and pulsing treatments. Fourth instars showed increased positive anemotaxis in response to the combined hostplant and pheromone odors. To our knowledge, this is the first demonstration of larval behavioral responses to adult pheromone in a holometabolous insect.     

Transplant Antennae and Host Brain Interact to Shape Odor Perceptual Space in Male Moths

Behavioral responses to odors rely first upon their accurate detection by peripheral sensory organs followed by subsequent processing within the brain’s olfactory system and higher centers. These processes allow the animal to form a unified impression of the odor environment and recognize combinations of odorants as single entities. To investigate how interactions between peripheral and central olfactory pathways shape odor perception, we transplanted antennal imaginal discs between larval males of two species of moth Heliothis virescens and Heliothis subflexa that utilize distinct pheromone blends. During metamorphic development olfactory receptor neurons originating from transplanted discs formed connections with host brain neurons within olfactory glomeruli of the adult antennal lobe. The normal antennal receptor repertoire exhibited by males of each species reflects the differences in the pheromone blends that these species employ. Behavioral assays of adult transplant males revealed high response levels to two odor blends that were dissimilar from those that attract normal males of either species. Neurophysiological analyses of peripheral receptor neurons and central olfactory neurons revealed that these behavioral responses were a result of: 1. the specificity of H. virescens donor olfactory receptor neurons for odorants unique to the donor pheromone blend and, 2. central odor recognition by the H. subflexa host brain, which typically requires peripheral receptor input across 3 distinct odor channels in order to elicit behavioral responses.     

Olfaction in dragonflies: electrophysiological evidence

The problem of olfaction in Paleoptera (Odonata, Ephemeroptera) cannot be considered fully elucidated until now. These insects have been traditionally considered anosmic, because their brain lacks glomerular antennal lobes, typically involved in Neoptera odor perception. In order to understand if the presumed coeloconic olfactory receptors described on the antennal flagellum of adult Odonata are really functioning, we performed an electrophysiological investigation with electroantennogram (EAG) and single cell recordings (SCR), using Libellula depressa L. (Odonata, Libellulidae) as a model species. Odors representing different chemical classes such as (Z)-3-hexenyl acetate (acetate ester), (E)-2-hexenal, octanal (aldehydes), (Z)-3-hexen-1-ol (alcohol), propionic acid, butyric acid (carboxylic acids), and 1,4-diaminobutane (amine) were tested. Most of the tested chemicals elicited depolarizing EAG responses in both male and female antennae; SCR show unambiguously for the first time the presence of olfactory neurons in the antennae of L. depressa and strongly support the olfactory function of the coeloconic sensilla located on the antennal flagellum of this species. Electrophysiological activity may not necessarily indicate behavioral activity, and the biological role of olfactory responses in Odonata must be determined in behavioral bioassays. This study represents a starting point for further behavioral, electrophysiological, neuroanatomical and molecular investigation on Odonata olfaction, a research field particularly interesting owing to the basal position of Paleoptera, also for tracing evolutionary trends in insect olfaction.     

Discrimination of conspecific individuals via cuticular pheromones by males of the cricket Gryllus bimaculatus

Cuticular substances on the body surface of crickets serve as pheromones that elicit a variety of different behaviors in male crickets. Antennal contact between males and females resulted in courtship behavior, and that between two males resulted in aggressive displays. As a first step in elucidating how crickets recognize and discriminate individuals, behavioral responses of male individuals to cuticular substances of conspecific males or females were investigated. The behavioral responses of males to antennal or palpal stimulation with an isolated antenna from a male or a female were recorded. To both antennal and palpal stimulation with female antennae, the majority of males responded with courtship behavior; to stimulation with male antennae, males responded with aggressive displays. To gain insight into the chemical nature of the behaviorally relevant components, isolated antennae were washed in either n-hexane, acetone or ethanol before behavior assays. Washed antennae no longer elicited courtship or aggressive responses in males. Next, polypropylene fibers were smeared with substances from the body surface of females and used for antennal stimulation. This experiment showed that the quality and quantity of cuticular substances appear to be highly age-dependent. Significantly more males responded with courtship behavior to cuticular substances from younger females. Isolated males generally showed higher levels of aggression than males reared in groups. Grouped males also were more likely to display courtship behavior towards antennae from younger females, and aggressive behavior towards antennae from older females. These results suggest that male discrimination of mating partners depends on the nature of female cuticular substances.     

Cautious cannibals: Behavioral responses of juvenile and adult blue crabs to the odor of injured conspecifics

Blue crabs are cannibalistic, and therefore the scent of injured conspecifics represents both a potential food cue, as well as an indicator of predation risk. We examined the response of blue crabs to conspecific odor alone, as well as in mixtures of attractive cues to determine how animals evaluate and respond to this odor. We explicitly manipulated risk-sensitivity based on either animal size (an indicator of susceptibility to predation) or hunger state (susceptibility to starvation) as ways to evaluate theories of risk-allocation, which suggest that decreases in predation risk, or increases in the risk of starvation, ought to result in diminished responses to sensory cues that signal predator presence or activity. Large and small blue crabs were challenged to locate the source of odor plumes consisting of the scent of injured conspecifics (risk cue), attractive food odors (attractive cue), or their mixture (conflicting cue). Neither large nor small blue crabs tracked aversive cues, but large blue crabs consistently tracked conflicting treatments to their source. Responses to conflicting and aversive treatments also involved diminished movement and reduced tracking speed relative to behaviors displayed in attractive plumes. Thus, even cannibalistic crabs seem to respond more prevalently to the apparent predation risk then to food reward, and risk-sensitive behaviors have a likely cost in terms of reduced food intake. Starved animals were more likely than unstarved animals to track conflicting plumes. Both the ontogenic shift and the response of starved animals support the notion that the cost of risk-aversive behaviors results in this strategy being allocated in proportion to the degree of potential risk. Since risk-aversive responses to chemical cues can produce strong effects in communities, the size-dependent nature of these responses in blue crabs may introduce considerable complexity in interactions between blue crabs, their predators, and their prey.     

Appetence behaviours of the triatomine bug <Emphasis Type="Italic">Rhodnius prolixus</Emphasis> on a servosphere in response to the host metabolites carbon dioxide and ammonia

A combination of 1,000 ppm CO(2) plus 30-40 ppb NH(3) in an air stream induced Rhodnius prolixus nymphs walking on a servosphere to perform a series of appetence behaviours. Shortly after the onset of stimulation the nymphs turned sharply upwind towards the source of the chemostimuli (within 13 +/- 9 s) from mostly downwind and crosswind walks in the air stream alone. The mean vector angles of these upwind tracks were concentrated in a cone 60 degrees either side of due upwind. The upwind walking bugs stopped more frequently but for a shorter duration and walked at a higher speed than before stimulation. During stops in the presence of the chemostimuli the bugs frequently corrected their course angles and extended their forelegs to reach higher with their antennae in the air. In the air stream alone, R. prolixus nymphs frequently sampled the sphere surface with the antennae and cleaned their antennae with the foreleg tarsi. However, the nymphs only briefly tapped the left or right antennal flagellum on the corresponding first leg tarsus and never touched the servosphere surface in the presence of the chemostimuli. After chemostimulus removal from the air stream the bugs continued to respond with the same appetence responses as during stimulation, but walked more tortuously in a crosswind direction in an effort to regain contact with the chemostimuli.     

Bilateral and unilateral antennal lesions alter orientation abilities of the crayfish, Orconectes rusticus.

Numerous animals use chemical cues within their environments to execute various behaviors. One of these behaviors is orientation to an odor source. Crayfish, in particular, can orient to food sources under a number of different conditions. It has not been determined, however, what kind of search strategy these animals employ to successfully locate a food source. To determine the role of antennae and antennules in this behavior and to investigate different modes of orientation behavior, the orientation patterns of crayfish with complete and partial antennal lesions were examined. Detailed analysis of orientation paths confirmed that crayfish could not locate odor sources with either bilateral or unilateral lesions. This suggests that crayfish are using the spatial information obtained from these appendages to successfully orient. Animals using information from the bilaterally paired appendages in the control group exhibited increased walking speed, increased speed to source and decreased heading angles towards the source compared to these measurements taken from lesioned groups. There was no significant difference in any parameters between animals with unilateral or bilateral lesions. This strongly suggests that these animals are reliant on the spatial comparison of differences between bilaterally paired olfactory appendages for successful orientation.     

Antennal glands in Psylliodes chrysocephala, and their possible role in reproductive behaviour

Abstract. The antennal morphology of Psylliodes chrysocephala L. (Coleoptera: Chrysomelidae), an important pest of oilseed rape ( Brassica napus ), was studied. Two types of tricellular, integumentary glands were found. The common antennal glands are distributed under all sensilla-bearing parts of male and female antennae. The male-specific antennal glands are only located under a glabrous area found on antennomeres 6–10 of male beetles. The common antennal glands are synthetically active in both pre- and post-diapause adults, but the male specific antennal glands are only active in post-diapause (reproductively active) males. During studies of mating behaviour, the antennae of the males were highly active at the beginning and end of copulation, and in response to increased female activity. The male specific antennal glands may secrete a sex pheromone, and the glabrous area on the male antennae could be the release site for such a pheromone.     

油松萜烯成分变化与红脂大小蠹的反应特性

采用顶空采样方法,比较健康油松、人工损伤油松以及抗性油松在单萜烯成分组成上的差异。GC-MS分析表明,在自然状况下,油松树干释放的萜烯类成分很少,以α-蒎烯占绝对优势(>97%);人工损伤后,油松萜烯类成分明显增多,除α-蒎烯为主要成分外,还包括β-蒎烯、月桂烯、柠檬烯、萜品油烯、β-水芹烯、长叶烯等;而抗性油松萜烯类成分更为复杂。对3类油松主要单萜类成分的相对含量方差分析表明,α-蒎烯的相对含量呈显著降低;3-蒈烯在损伤寄主中相对含量最高,在抗性寄主中相对含量与自然状态下没有差异。柠檬烯、莰烯、萜品油烯在抗性寄主中相对比率显著增加。而β-蒎烯、月桂烯、β-水芹烯相对含量在3个处理中变化不大。在此基础上,比较红脂大小蠹Dendroctonus valens LeConte对油松主要单萜类成分的触角电位及嗅觉行为反应。结果表明,室内触角电位、嗅觉试验与先前林间试验结果相一致,即红脂大小蠹对(+)-3-蒈烯表现出最强的电生理和行为反应。对R-(+)-α-蒎烯和S-(-)-α-蒎烯研究发现,红脂大小蠹对α-蒎烯2个对映体的触角电位、嗅觉行为无显著不同。结合油松单萜类含量变化特点与红脂大小蠹行为反应,认为3-蒈烯相对含量上升可能作为易感寄主特点;而柠檬烯、莰烯、萜品油烯相对比率增加则代表了抗性或者非适合寄主的特征。     

Modification of cockroach behavior to environmental humidity change by dehydration (Dictyoptera: Blattidae)

Effects of dehydration on the behavioral response to humidity have been examined in the cockroach, Periplaneta americanaL. Under normal conditions cockroaches prefer lower humidity, but the preference is reversed by dehydration. Dehydrated cockroaches can distinguish smaller differences between two air streams compared with normal individuals. Cockroach behavioral responses to humidification include swing of antennae and locomotion. The period from onset of humidification to behavioral response decreases with increasing dehydration, indicating that the humidity threshold required for behavioral response decreases. Observed modulations of the behavioral response are discussed in relation to the contribution of the antennal hygroreceptors.     

Behavioral responses to odorants in drosophila require nervous system expression of the beta integrin gene myospheroid

Integrins are cell adhesion molecules that mediate numerous developmental processes in addition to a variety of acute physiological events. Two reports implicate a Drosophila beta integrin, betaPS, in olfactory behavior. To further investigate the role of integrins in Drosophila olfaction, we used Gal4-driven expression of RNA interference (RNAi) transgenes to knock down expression of myospheroid (mys), the gene that encodes betaPS. Expression of mys-RNAi transgenes in the wing reduced betaPS immunostaining and produced morphological defects associated with loss-of-function mutations in mys, demonstrating that this strategy knocked down mys function. Expression of mys-RNAi transgenes in the antennae, antennal lobes, and mushroom bodies via two Gal4 lines, H24 and MT14, disrupted olfactory behavior but did not alter locomotor abilities or central nervous system structure. Olfactory behavior was normal in flies that expressed mys-RNAi transgenes via other Gal4 lines that specifically targeted the antennae, the projection neurons, the mushroom bodies, bitter and sweet gustatory neurons, or Pox neuro neurons. Our studies confirm that mys is important for the development or function of the Drosophila olfactory system. Additionally, our studies demonstrate that mys is required for normal behavioral responses to both aversive and attractive odorants. Our results are consistent with a model in which betaPS mediates events within the antennal lobes that influence odorant sensitivity.     

Mating behavior of the eucalyptus longhorned borer (Coleoptera: Cerambycidae) and the adaptive significance of long “horns”

Sexual dimorphism in insect antennal structure is often attributed to differences between the sexes in sensitivity to pheromones, the antennae of one sex being more elaborately structured (for example, plumose). Males of the family Cerambycidae (order Coleoptera) often have longer antennae than females, but of a similar general structure, suggesting that selective factors other than sensitivity to pheromones are at work. Both sexes of the eucalyptus longhorned borer, a cerambycid, were attracted to eucalyptus logs that were larval hosts. There, males located females by antennal contact, and male mating success therefore depended on the walking rate and width of the antennal spread. Elongate antennae may benefit males by increasing antennal spread width, but have no such advantage for females, suggesting an evolutionary explanation for sexual dimorphism.     

Central gustatory projections and side-specificity of operant antennal muscle conditioning in the honeybee

Gustatory stimuli to the antennae, especially sucrose, are important for bees and are employed in learning paradigms as unconditioned stimulus. The present study identified primary antennal gustatory projections in the bee brain and determined the impact of stimulation of the antennal tip on antennal muscle activity and its plasticity. Central projections of antennal taste hairs contained axons of two morphologies projecting into the dorsal lobe, which is also the antennal motor centre. Putative mechanosensory axons arborised in a dorso-lateral area. Putative gustatory axons projected to a ventro-medial area. Bees scan gustatory and mechanical stimuli with their antennae using variable strategies but sensory input to the motor system has not been investigated in detail. Mechanical, gustatory, and electrical stimulation of the ipsilateral antennal tip were found to evoke short-latency responses in an antennal muscle, the fast flagellum flexor. Contralateral gustatory stimulation induced smaller responses with longer latency. The activity of the fast flagellum flexor was conditioned operantly by pairing high muscle activity with ipsilateral antennal sucrose stimulation. A proboscis reward was unnecessary for learning. With contralateral antennal sucrose stimulation, conditioning was unsuccessful. Thus, muscle activity induced by gustatory stimulation was important for learning success and conditioning was side-specific.     

Antennal responses of Cydia pomonella (L.) exposed to surfaces treated with methoxyfenozide

Electroantennogram (EAG) measurements were recorded from the antennae of male and female codling moth, Cydia pomonella L., to determine whether adult moths exposed to surfaces treated with the ecdysteroid agonist methoxyfenozide experience a decline in their antennal reception and thus olfactory sensitivity. Such a phenomenon would offer a possible mechanism for the previously reported decreased responsiveness from moths treated with methoxyfenozide to pheromone‐ and plant volatile‐based monitoring lures. Mean EAG data revealed that the antennae from methoxyfenozide‐treated male moths appear to be just as sensitive to various doses of synthetic codlemone as the antennae from the control and surfactant‐treated moths, but they appeared to be less sensitive to the pheromone component 12OH (collected from female effluvia) than the control male antennae. Mean male EAG responses to the pheromone components E8,E10‐12Al and codlemone collected from methoxyfenozide‐treated females were significantly less than the responses towards those two pheromone components collected from the control and surfactant‐treated females. Female moth exposure to methoxyfenozide did not negatively impact the sensitivity of female antennae to the plant volatile pear ester, but it did towards the apple volatile butyl hexanoate. Data from this study show that adult C. pomonella exposure to methoxyfenozide‐treated surfaces does appear to negatively impact, in a minor way, the (i) olfactory sensitivity (or detection) of male antennae towards some components of the female sex pheromone, (ii) the female antennal sensitivity towards a key apple volatile and (iii) the attractiveness of female pheromone effluvia.     

High-content behavioral analysis of Caenorhabditis elegans in precise spatiotemporal chemical environments

To quantitatively understand chemosensory behaviors, it is desirable to present many animals with repeatable, well-defined chemical stimuli. To that end, we describe a microfluidic system to analyze Caenorhabditis elegans behavior in defined temporal and spatial stimulus patterns. A 2 cm × 2 cm structured arena allowed C. elegans to perform crawling locomotion in a controlled liquid environment. We characterized behavioral responses to attractive odors with three stimulus patterns: temporal pulses, spatial stripes and a linear concentration gradient, all delivered in the fluid phase to eliminate variability associated with air-fluid transitions. Different stimulus configurations preferentially revealed turning dynamics in a biased random walk, directed orientation into an odor stripe and speed regulation by odor. We identified both expected and unexpected responses in wild-type worms and sensory mutants by quantifying dozens of behavioral parameters. The devices are inexpensive, easy to fabricate, reusable and suitable for delivering any liquid-borne stimulus.     

Tactile localisation: the function of active antennal movements in the crayfishCherax destructor

Video recordings and single frame analysis were used to study the function of the second antennae of crayfish (Cherax destructor) as a sensory system in freely behaving animals. Walking crayfish move their antennae back and forth through horizontal angles of 100 degrees and more, relative to the body long axis. At rest, animals tend to hold their antennae at angular positions between 20 and 50 degrees. Movements of the two antennae are largely independent of each other. Before and during a turn of the body the ipsilateral antenna is moved into the direction of the turn. Solid objects are explored by repeatedly moving the antennae towards and across them. Both seeing and blinded crayfish can locate stationary objects following antennal contact. On antennal contact with a small novel object, a moving animal withdraws its antenna and attacks the object. When the antenna of a blinded crayfish is lightly touched with a brush the animal turns and attacks the point of stimulation. The direction taken and the distance covered during an attack can be correlated with: the angle at which the antenna is held at the moment of contact and the distance along the antennal flagellum at which the stimulus is applied. From behavioural evidence we conclude that crayfish use information about the angular position of their antennae and about the position of stimulated mechanoreceptors along the antennal flagellum to locate objects in their environment. We suggest ways in which an active tactile system-like the crayfish's antennae--could supply animals with information about the three-dimensional layout of their environment.