Electrophysiological characterization of olfactory cell types in the antennae and palps of the housefly

A set of odours was presented to the housefly Musca domestica and the electrophysiological responses of single olfactory receptor cells in the antennae and palps were recorded. The olfactory cells in the antennae of the housefly showed a large variability of response profiles, but multidimensional cluster analysis suggested a moderate clustering in olfactory response types. Receptor cells with similar or with different odour response profiles can reside in one and the same sensillum. No fixed spatial distribution of olfactory response types over the antennal of palpal surface was found. The odours of 1-octen-3-ol, amyl acetate, 3-methylphenol, 2-pentanone and R(+)limonene elicited the largest responses in antennal cells. Most odours elicited responses in cells of only a few of the clusters, but 1-octen-3-ol was detected by cells of almost all clusters of the antenna. Surprisingly, rather low responses were found to acetic acid, skatole, indole and muscalure, odours that are known to attract flies. Response profiles of palpal cells differed considerably from those of antennal cells. Palpal cells mostly responded to 3-methylphenol and 2-pentanone. In the palps, the clusters of cells responding to 3-methylphenol and 2-pentanone are clearly separated from the other olfactory cells.     

Range and Absolute Odour Intensity Affect Olfactory Generalisation in the Honeybee

The human olfactory psychophysical literature is rich with anecdotal reports of variation in the perceived quality between weak and strong concentrations of the same odour (Wilson and Stevenson 2006). Psychophysical experiments using animals have also found similar effects of concentration on odour quality. The proboscis extension reflex (PER) is an appetitive Pavlovian conditioning assay that has been used to investigate olfactory stimuli in the honeybee. In this series of experiments I aim to identify the sensitivity of honeybees to changes in odorant concentration across the range of a honeybee’s sensorium (0.01–100 Pa). I compared generalisation to test odours that differed in molecular identity, odour concentration or both and found that large changes in odorant concentration (1,000 fold change) can produce greater shifts in perceptual similarity than a change in the odorant’s molecular structure. Our findings suggest a failure in concentration invariance when identical odours differ greatly in concentration. I also found poorer olfactory sensitivity (between identical odours of differing concentration) and acuity (between novel odours of identical concentration) at low odour concentrations (0.01 Pa).     

Preliminary experiments on the olfactory responses of Pterostichus melanarius Illiger (Coleoptera: Carabidae) to intact plants

1 In two successive years, the olfactory responses of Pterostichus melanarius Illiger (Coleoptera: Carabidae) to intact cabbage and white clover plants were studied, using a four‐arm olfactometer. 2 The first set of experiments tested the response to the odours of cabbage, white clover and the two plants grown together against potting compost; in the second and third sets of experiments, white clover and cabbage were tested, respectively. 3 The results indicate that female P. melanarius individuals are arrested by the combined odours of cabbage and white clover, spending significantly more time in the cabbage with white clover odour field than in either the cabbage, white clover or control odour fields. 4 Similar results were not found for males. 5 Cabbage plants alone did not elicit significant responses in either sex. 6 White clover alone did not elicit significant responses by females and the responses of males were not uniform in the two successive years.     

棉铃虫成虫对两种关键花香气味的联系性学习

为了明确棉铃虫对苯乙醛和乙酸苯甲酯两种关键花香气味的联系性学习行为,在室内分别测定了不同学习训练的棉铃虫雌雄成虫对两种关键花香气味的选择偏好性反应和雄成虫的触角电位反应。偏好性测定结果表明,无花香气味接触经历的棉铃虫对苯乙醛和乙酸苯甲酯的选择频次均无显著差异,且单纯的花香气味接触经历也不能诱导棉铃虫气味偏好性的显著改变,唯有花香气味接触经历伴随蔗糖溶液进行强化训练时,才能诱导气味偏好性的显著性改变。从对两种花香气味的联系性学习看,棉铃虫更容易将苯乙醛与蔗糖溶液进行联系性学习,而不容易将乙酸苯甲酯与蔗糖溶液进行联系性学习。从性别差异看,雌虫比雄虫具有更强的将花香气味与蔗糖溶液进行联系性学习的能力。触角电位测定结果表明,不同学习训练的棉铃虫雄成虫对两种花香气味和绿叶气味顺-3-己烯-1-醇的EAG反应值之间不存在显著性差异。总之,花香气味伴随食物资源的联系性学习经历,能够明显提高棉铃虫成虫对花香气味的选择偏好,可以此为基础进一步优化花香引诱剂的配方设计和应用技术。     

The influence of olfactory enrichment on the behaviour of captive black-footed cats,Felis nigripes

The value of olfactory enrichment for captive-housed animals is now well recognised. Large cats have been shown to benefit from the introduction of odours to their captive environment, but to date the effect of odour introduction on the behaviour of small cats remains unknown. This study investigated the behaviour of six zoo-housed black-footed cats, Felis nigripes, in response to four odours (no odour [control], nutmeg, catnip and body odour of prey) introduced individually on cloths into the animals’ pens over a period of 5 days. It was hypothesised that the cats’ behaviour would differ significantly between the control and experimental odours and that interest in the experimental odours would wane over time. All of the experimental odours influenced the cats’ behaviour, resulting in an increase in the amount of time that the animals spent in active behaviours, i.e. moving (average increase of 8.3%), grooming (average increase of 5.9%), exploring the cloth (average increase of 10.9%) and exploring the pen (average increase of 9.2%). The experimental odours also resulted in a decrease in the amount of time that the cats spent in sedentary behaviours, i.e. standing (average decrease of 2.8%), sitting (average decrease of 5.2%) and resting (average decrease of 25.9%). Nutmeg exerted less of an effect on the cats’ behaviour than catnip or odour of prey. The cats’ response to all of the experimental odours waned over the course of the 5-day observation period, suggesting that the animals habituated to the stimuli. The results highlight the potential for odour to be employed as a method of environmental enrichment for small captive-housed felids, if presented in an appropriate manner.     

Evidence for separate perceptive and semantic memories for odours: a priming experiment

Sixty-four subjects participated in an olfactory priming experiment comprising separate study and test phases. Priming was measured within the olfactory modality (intramodal condition) and from the visual modality to the olfactory modality (intermodal condition). In the study phase of the intramodal condition, subjects were exposed twice to a series of odours: once performing a semantic orientation task (deciding which of seven categories odour stimuli belonged to) and once performing a perceptual orientation task (judging the intensity, the hedonicity and the familiarity of odour stimuli). Half of the odour stimuli corresponded to edible products, the other half did not. The study phase of the intermodal condition was similar, with the exception that the names of the odours (instead of the odours themselves) were presented. In the test phase, subjects were presented with primed and non-primed odour targets and had to decide as fast as possible whether the target corresponded to an edible product or not. Response times and types were recorded by a computer. The analysis of response times revealed a priming effect in the intramodal condition only. Results are discussed in terms of separate perceptual and semantic subsystems that store odour representations.     

Smoke,pheromone and kairomone olfactory receptor neurons in males and females of the pine sawyer Monochamus galloprovincialis (Olivier) (Coleoptera: Cerambycidae)

The response of antennal olfactory receptor neurons (ORNs) of Monochamus galloprovincialis to several odourants was tested using single sensillum electrophysiology. Behaviourally active pheromone, and kairomone (host and sympatric bark beetle pheromone) odours were tested alongside smoke compounds released by burnt wood that are potentially attractive to the insect. The antennae bore several types of sensilla. Two plate areas in the proximal and distal ends of each antennal segment were covered with basiconic sensilla that responded to the odour stimuli. Sensilla basiconica contained one or two cells of different spike amplitude. The 32 male and 38 female ORNs tested responded with excitations or inhibitions to the different plant odours. In general the response of male and female receptors was very similar so they were pooled to perform a cluster analysis on ORN responses. Six ORNs were clearly specialised for pheromone reception. Responses to kairomone and smoke odours were less specific than those of pheromone, but a group of 9 cells was clearly excited by smoke compounds (mainly eugenol and 4-methyl 2-methoxyphenol), a group of 8 cells was very responsive to α-pinene, β-pinene and cis-verbenol, and a group of 14 cells responded to a wider range of compounds. The rest of the cells (47%) were either non-responsive or slightly inhibited by smoke compounds. Dose–response curves were obtained for several compounds. Different compounds induced significantly different latencies and these appeared to be unrelated to their boiling point.     

Electrophysiological responses of olfactory bulb neurons to odour stimuli in the frog. A comparison with receptor cells

Extracellular recordings were performed from olfactory bulbneurons in the frog. The odour stimuli were the same as thosepreviously used for studying the receptor cells in the sameanimal species and were delivered at similar concentrations(Revial et al., 1982). The general properties of the neuronresponses are presented and discussed with reference to homologousproperties of olfactory receptor cells. The response rates elicitedby different stimuli from the bulbar neurons were found to behighly correlated with those elicited from receptor cells. Theindividual cell selectivity was better in the bulb than in theolfactory epithelium. The olfactory bulb neurons seemed to improvethe discrimination between stimuli (enantiomers) poorly distinguishedby the receptor cells. Reducing odor concentration caused therate of suppressive response to decrease faster than that ofexcitatory ones, suggesting that the manifestations of inhibitoryprocesses in some neurons requires a high level of excitationin others.     

Inhibition of host-seeking response and olfactory responsiveness in Anopheles gambiae following blood feeding

The effect of a single blood meal on the host-seeking response of Anopheles gambiae was investigated in the laboratory using a behavioural bioassay, whereas possible changes at the chemosensory level were monitored using electroantennogram recording (EAG). To avoid the possible confounding effect of body size, mosquitoes of a large size class only were used. Five-day old female mosquitoes were given a blood meal on a human arm and exposed to the emanations of a human hand in an olfactometer at 3, 24, 40, 48 and 72 h following the meal and their behaviour and EAG response to host stimuli were compared with that of unfed mosquitoes (controls) of corresponding age. During egg development, mosquitoes had access to glucose and an oviposition tray. The ovarian development of blood-fed mosquitoes that responded to host odours was compared with that of blood-fed mosquitoes that had not been exposed to host odours. The EAG response of blood-fed and control mosquitoes to host odour was examined upon stimulation with air led over incubated human sweat, hexanoic acid, indole and geranyl acetone. EAGs were recorded at times after a blood meal corresponding with those used in the behavioural experiment. There was no host-seeking response at 3 and 24 h post blood meal (pbm). Seven percent of the mosquitoes responded to human emanations 40-h pbm, 27% at 48 h and 68% at 72 h following a blood meal. The average response of controls to host stimuli varied from 35 (at t=40 h) to 67%. There was no ovarian development in the unfed group of mosquitoes. Of the mosquitoes that responded to host odour 48 h pbm, 12.5% (n=5) had ovaries in Christophers' stage IV and the remainder in stage V. Of the mosquitoes that responded 72 h pbm, 66.7% (n=94) had ovaries in stage V and 31.2% (n=44) had recently oviposited. Maximum EAG amplitudes recorded from blood-fed and control mosquitoes were similar for mosquitoes in Christophers' stages I-III, whereas in stage IV EAG amplitudes recorded from the blood-fed group were significantly lower than those of the corresponding control group in response to headspace of incubated human sweat and to indole. The results show that there was a strong inhibition of host seeking in An. gambiae for a period of at least 40 h following a blood meal. Host-seeking returned to pre-blood meal levels 72-h post feeding and was associated with egg maturation. The inhibition of host-seeking behaviour was accompanied by an inhibition of olfactory sensitivity to headspace of incubated sweat and indole just before the resumption of the host-seeking response. The implications of these findings for mosquito surveillance with host odours are discussed.     

Ontogeny of electroantennogram responses in the moth, Manduca sexta

The antennae of the moth, Manduca sexta, and the sensilla and sensory neurons they contain, develop during metamorphosis from pupa to adult. To determine when, during their development, antennae become capable of generating electrical responses to various stimuli, we recorded the electroantennogram (EAG), believed to be the summed extracellular record of receptor potentials, from developing and mature antennae. Antennae from male and female moths are similarly responsive to trans-2-hexenal, while only males respond to Manduca sex pheromone; these two odorants presumably stimulate separate receptors. Mechanical stimulation also elicits and EAG response. EAG responses to olfactory and mechanical stimuli are detectable several days before eclosion but not until the neurons are morphologically and biochemically quite mature. Responses increase in magnitude until the end of metamorphosis and then change little during the first 3 days after emergence of the adult. Responses to different stimuli do not develop synchronously.     

美洲大蠊对多种化合物的触角嗅觉电位反应

用多种化合物的气味制激美洲大蠊(Periplaneza americana)触角,诱导、记录触角电位(EAG)反应.试验了各类化合物154种,其中53%能诱发出明显的EAG反应.绝大多数EAG反应是负相慢波,波幅多数为0.5—2mV,时程1.5—3秒.苯等少数化合物能诱发正相EAG反应.剂量-反应曲线大致呈“S”形,还可见适应现象.萜类化合物和挥发性植物油类诱发EAG反应的作用最强,其次是酮、醇、酯、胺类化合物.化合物的含氧功能基团和空间构型与EAG反应的诱发有一定的关系.可能是同一种化合物对不同种的感受器都可能诱发EAG反应.一般性化合物诱发雌、雄、成、幼虫EAG反应的差异不大,但雌虫类提取物仅对雄性成虫触角诱发较强的EAG反应.一些已知的驱、诱、杀虫剂也能诱发EAG反应,但仅表现为对一般化合物的反应特征.     

Background odour induces adaptation and sensitization of olfactory receptors in the antennae of houseflies

The presence of background odour was found to have a small but significant effect on the sensitivity of the antennal olfactory system of houseflies, Musca domestica Linnaeus (Diptera: Muscidae), to new pulses of odour. We show that cross-adaptation and cross-sensitization between a background odour of (+/-)-1-octen-3-ol and pulses of (+/-)-1-octen-3-ol, 2-pentanone and R-(+)-limonene can occur, confirming that olfactory receptor cells are sensitive to different odours. Background odour can increase the responses to low concentration odour pulses and decrease the responses to higher concentration odour pulses. It is suggested that background odour has a larger effect on olfactory receptor cells that respond with a tonic increase of spike frequency, giving information about the level of odour concentration, i.e. the 'static' environment. Cells that respond in a phasic way only provide information on the dynamics of the olfactory environment.     

Nestmate recognition in sweat bees (Lasioglossum zephyrum): Does an individual recognize its own odour or only odours of its nestmates?

We investigated the olfactory mechanism by which guard bees of Lasioglossum zephyrum decide whether to admit conspecifics to their nests. First we set up colonies of young bees, consisting of sisters from a single family or a mixture of bees from two distinct families. These bees were then introduced into colonies other than their own. Our experimental evidence shows that guards learn the odours of their nestmates, then accept or reject other bees on the basis of the similarity of the latters' odours to those of the guards' nestmates. Guards act as though they do not use their own odour as a reference for nestmate recognition. This recognition mechanism enables individuals with different odours to live together; it may also enhance the operation of kin selection by providing a more complete basis for discriminating relatives from non-relatives. No evidence was found that nestmates acquire one another's odours. Such lack of odour transfer may be characteristic of early stages in the evolution of recognition mechanisms.     

Factors affecting the antennal and behavioural responses of the saw-toothed grain beetle Oryzaephilus surinamensis to food odour and aggregation pheromone

ABSTRACT. The effects of insect age, sex, mated state and culture density on the attraction of adult saw-toothed grain beetles, Oryzaephilus surinamensis (L.) (Coleoptera: Silvanidae), to sources of food odour and synthetic aggregation pheromone were investigated. In single-insect behavioural assays, insect age affected the attraction to the food odour, but not to the synthetic aggregation pheromone. Conversely, there were sexual differences in the attraction to the aggregation pheromone, but not to the food odour. The effects of the same factors on the antennal response to food odour and synthetic pheromone were also investigated, using the electroantennogram (EAG) technique. Insect age affected the EAG response to food odour, but not to the synthetic pheromone. There were no sexual differences in the EAG responses to either food odour or synthetic pheromone.
The correlation of factors affecting both behavioural and antennal responses, and the possible role of changes in peripheral olfactory receptor sensitivity in the modulation of behaviour are discussed.     

Peripheral modulation of olfaction by physiological state in the Egyptian leaf worm Spodoptera littoralis (Lepidoptera: Noctuidae)

Insects show behavioural plasticity based on their physiological state. Deprivation from a resource will normally make them more responsive to it or to perform behaviour increasing the probability of encountering such a resource. Modulation of the olfactory system has been shown mainly in the central nervous system, but also in the periphery. In this study, antennal sensitivity of females of the Egyptian cotton leaf worm Spodoptera littoralis to different plant and sex pheromone odours was measured using electroantennography (EAG). Different mating status, age, and feeding status were used to investigate peripheral changes in olfactory responses. Virgin females were found to be more sensitive to plant odours and sex pheromone compared to mated females. Age also had an impact on antennal sensitivity, 2 and 4 days old females being more sensitive than just-emerged ones. Such an increase in sensitivity could be explained by maturation of olfactory receptor neurons after emergence or by an increase in motivation as the available expected life time remaining decreases. Finally, feeding status did not modify the antennal sensitivity of females. A peripheral modulation could thus be demonstrated in the olfactory system of female Spodoptera littoralis at certain life stages.     

Odours stimulate neuronal activity in the dorsolateral area of the hippocampal formation during path integration

The dorsolateral area of the hippocampal formation of birds is commonly assumed to play a central role in processing information needed for geographical positioning and homing. Previous work has interpreted odour-induced activity in this region as evidence for an ‘olfactory map’. Here, we show, using c-Fos expression as a marker, that neuronal activation in the dorsolateral area of the hippocampal formation of pigeons is primarily a response to odour novelty, not to the spatial distribution of odour sources that would be necessary for an olfactory map. Pigeons exposed to odours had significantly more neurons activated in this area of the brain than pigeons exposed to filtered air with odours removed. This increased activity was observed only in response to unfamiliar odours. No change in activity was observed when pigeons were exposed to home odours. These findings are consistent with non-home odours activating non-olfactory components of the pigeon''s navigation system. The pattern of neuronal activation in the triangular and dorsomedial areas of the hippocampal formation was, by contrast, consistent with the possibility that odours play a role in providing spatial information.     

Calcium responses to pheromones and plant odours in the antennal lobe of the male and female moth Heliothis virescens

In male moths, the primary olfactory integration centre, the antennal lobe, consists of two systems. The macroglomerular complex processes pheromone information, while the ordinary glomeruli process plant odour information. Females lack a macroglomerular complex. We measured the spatial representation of odours using in-vivo optical recording. We found that: (1) pheromone substances elicited activity exclusively in the MGC. No response was found in female antennal lobes. (2) Plant odours elicited combinatorial activity patterns in the ordinary glomeruli in both males and females. No response was found in the MGC of male moths. (3) A clean air puff often led to activity, in both males and females, suggesting that mechano-sensory information is also processed in the antennal lobe. (4) With an interstimulus interval of 5 or 10 s, strongly activated glomeruli were able to follow the temporal structure of the stimulus, while others lost their phase-locking. Some glomeruli showed "off" responses. These properties were odour dependent. This confirms and extends previous studies, showing the functional significance of the two subsystems for processing olfactory information. Pheromones are coded in a combinatorial manner within the macroglomerular complex, with each glomerulus corresponding to one information channel. Plant odours are coded in an across-glomeruli code in the ordinary glomeruli.     

The influence of cultivar and cultivar-aphid odours on the olfactory response of the parasitoid Aphidius colemani

The olfactory response of the parasitoid Aphidius colemani (Viereck) (Hymenoptera: Braconidae) to odours in a tritrophic system involving three cultivars of common cabbage, Brassica oleracea var capitata, characterized by different levels of susceptibility to Myzus persicae (Sulzer) (Hemiptera: Aphididae) was studied in a four‐way olfactometer. Odours influenced A. colemani response in the olfactometer to varying degrees. The magnitude of parasitoid response to odours of uninfested cabbage depended on cultivar, with Derby Day [green‐leaved, susceptible to M. persicae and the crucifer specialist, Brevicoryne brassicae (Linnaeus) (Hemiptera: Aphididae)] and Minicole (green‐leaved, partially resistant with known antibiosis factors for B. brassicae) preferred over Ruby Ball (red‐leaved with antixenosis factors for M. persicae and B. brassicae). The odour of the cabbage cultivar on which the parasitoid had been reared was preferred over the other cultivars. However, when provided with a choice between odours of infested plants, parasitoids did not show a significant preference for the cultivar on which they were reared. Results from the study show that parasitioids differentiated between odour of the three cultivars in dependence of their rearing history when the plant is uninfested.     

Single cell recordings from tsetse (Glossina m.morsitans) antennae reveal olfactory, mechano - and cold receptors

Abstract. Action potentials from individual cells and receptor potentials were recorded from antennae (funiculi) of living tsetse flies, Glossina m.morsitans Westwood, using a 'surface-contact' recording technique. Stimuli were pressure of the electrode, changes in temperature and the vapours of l-octen-3–ol, acetone, 3–methylphenol, dichloromethane and CO₂. Two types of mechano-receptive cells were found. One type only fired action potentials when pressure was increased, the other type continued firing when pressure was maintained. Of the 182 cells tested for their sensitivity to temperature change and the odour stimuli, 19% did not respond to any of the stimuli, suggesting that we are still unaware of cues which may be of import to the flies, and 4% responded to temperature only, increasing and decreasing their activity with a decrement and increment in temperature, respectively. Of the 141 cells which were olfactory receptors, 52% responded to 1-octen-3–ol and 40% were exclusively sensitive to this substance. For 3–methylphenol these percentages were 23 and 18, for acetone 13 and 11, for dichloromethane 12 and 7, for CO₂ 13 and 13. No clustering of cell types in certain areas of the funiculi was found, nor was a difference apparent between the sexes. The majority of the olfactory cells responded by increasing their activities on odour stimulation. Inhibition was found in three cells only, in which spontaneous activity was suppressed on stimulation with 3–methylphenol. Spike responses were phasic-tonic and varied between two extremes: Cells showing relatively rapid cessation of spike activity after the end of stimulation, and cells which continued firing for several seconds or minutes after stimulation. Possible behavioural effects of the activities of the various cell types are discussed.     

Love is in the air: olfaction-based mate-odour identification by jumping spiders from the genus Cyrba

Jumping spiders (Salticidae) are known for having good eyesight, but the extent to which they rely on olfaction is poorly understood. Here we demonstrate for the first time that olfactory pheromones are used by two species from the salticid genus Cyrba (C. algerina and C. ocellata). Using a Y-shape olfactometer, we investigated the ability of adult males and females of both species to discriminate between mate and non-mate odour. A hidden spider or a spider’s draglines (no spider present) were used as odour sources. There was no evident response by females of either Cyrba species to any tested odour. Males of both species chose odour from conspecific females, or their draglines, significantly more often than the no-odour control, but there was no evident response by males to any of the other odours (conspecific male and heterospecific female). Our findings demonstrate that C. algerina and C. ocellata males can make sex- and species-specific discriminations even when restricted to using olfaction alone. Also, by showing that draglines can be a source of olfactory pheromones, our findings illustrate the difficulty of ruling out olfaction when attempting to test for chemotactile cues.