Morphology and function of ovipositorial and tarsal sensilla of female Asian citrus psyllid

The Asian citrus psyllid (ACP), Diaphorina citri Kuwayama (Hemiptera:Psyllidae), is one of the most important pests of citrus plants worldwide, due to be the dominant vector of the devastating citrus disease Huanglongbing (HLB). Selection of suitable oviposition site is a crucial event of phytophagous insect life. Usually, the chemical and physical characteristics of a host plant were recognized by sensilla on the ovipositor and tarsi of a phytophagous insect after settling on a plant surface. In this study, the morphology, number, and distribution pattern of the ovipositorial and tarsal sensilla of adult female psyllids, were observed by scanning electron microscopy (SEM) techniques. The effect of these sensilla on oviposition was investigated by sensilla deactivation using hydrochloric acid (HCl). The results showed that sensilla trichoid (ST), sensilla chaetica (ChS) and sensilla basiconica (SB) were distributed on ovipositor, while sensilla trichoid (ST) were distributed on the external genitalia. Sensilla chaetica (ChS) and basiconica (SB) were mainly distributed on the end of the ovipositor back plate, and on the base of the sternum. On tarsus, sensilla trichoid (ST), sensilla chaetica (ChS), sensilla triangular (TeS) and sensilla ear ball (SE) were observed. However, whole tarsal segments were covered with Böhm's mane, which was arranged in a circular line. Oviposition assay revealed that a significantly lower number of eggs were laid on the Murraya paniculata seedlings confined by the psyllids with deactivated ovipositorial sensilla followed by protarsal sensilla, mesotarsal sensilla and hindtarsal sensilla. These results suggested that the ovipositorial and tarsal sensilla of citrus psyllid have an important role in the oviposition.     

Tarsal chemoreception in the polyphagous grasshopper Schistocerca americana: behavioural assays, sensilla distributions and electrophysiology

ABSTRACT Behavioural and electrophysiological responses of Schistocerca americana (Drury) (Orthoptera: Acrididae) to chemical stimulation of the tarsi were investigated. Using restrained insects, differences in leg-waving behaviour were observed following stimulation by sucrose and nicotine hydrogen tartrate (NHT), compared to control stimulations by water. Furthermore, free-walking insects were able to detect NHT on leaf surfaces, resulting in leg-raising to avoid tarsal contact.
SEM studies showed the presence of numerous peg chemoreceptor sensilla on the ventral surface of the tarsus. Tip recordings from such pegs showed activity from up to three chemosensitive neurones, plus a mechanoreceptor neurone. Stimulation by NaCl and KC1 elicited similar responses from two or three neurones in all sensilla tested, with increased firing rates at higher concentrations. Sucrose caused an increase in firing rate in few sensilla. In such cases several neurones were stimulated, and there was no evidence of a specific neurone sensitive to sucrose. In contrast, NHT elicited rapid firing in a single neurone, which was not sensitive to NaCl. Stimulation by NHT also inhibited the activity of the NaCl-sensitive neurones.
Possible mechanisms for chemical discrimination in S. americana tarsi are compared with those previously proposed for grasshopper mouthpart sensilla, and the significance of a NHT-sensitive neurone in tarsal sensilla is discussed.     

Positive force feedback in development of substrate grip in the stick insect tarsus

The mechanics of substrate adhesion has recently been intensively studied in insects but less is known about the sensorimotor control of substrate engagement. We characterized the responses and motor effects of tarsal campaniform sensilla in stick insects to understand how sensory signals of force could contribute to substrate grip. The tarsi consist of a chain of segments linked by highly flexible articulations. Morphological studies showed that one to four campaniform sensilla are located on the distal end of each segment. Activities of the receptors were recorded neurographically and sensilla were identified by stimulation and ablation of their cuticular caps. Responses were characterized to bending forces and axial loads, muscle contractions and to forces applied to the retractor apodeme (tendon). The tarsal sensilla effectively encoded both the rate and amplitude of loads and muscle forces, but only when movement was resisted. Mechanical stimulation of the receptors produced activation of motor neurons in the retractor unguis and tibial flexor muscles. These findings indicate that campaniform sensilla can provide information about the effectiveness of the leg muscles in generating substrate adherence. They can also produce positive force feedback that could contribute to the development of substrate grip and stabilization of the tarsal chain.     

Behavioural and chemosensory responses of the turnip root fly (Delia floralis) to glucosinolates

This study investigates the behavioural and neural mechanisms involved in the oviposition behaviour of the turnip root fly,Delia floralis (Fallen). Behavioural studies showed that glucosinolates modulated the oviposition behaviour of the flies on artificial leaves as well as the number of eggs laid in the soil at the base of these leaves. Electrophysiological responses to glucosinolates were obtained from type A and type D sensilla on the prothoracic and mesothoracic tarsi, as well as from the long contact sensilla on the labellum. The neural responses from these sensilla were positively correlated with the oviposition behaviour of the flies and with the number of eggs laid. Of the eleven glucosinolates tested in the behavioural and electrophysiological tests, the flies were most responsive to glucobrassicanapin, gluconapin and glucobrassicin. The type D tarsal sensilla were more responsive to the glucosinolates than either the type A tarsal sensilla or the labellar sensilla. The structure-activity investigations showed that slight modifications to the chemical composition of the glucosinolates resulted in changes in neural activity.     

Morphology and distribution of sensilia on the cephalic appendages,tarsi and ovipositor of the European sunflower moth,Homoeosoma nebulella Den. & Schiff. (Lepidoptera : Pyralidae)

Sensilla on male and female antennae, mouthparts, tarsi and on the ovipositor of the European sunflower moth, Homoeosoma nebulella (Lepidoptera : Pyralidae) have been investigated by means of scanning electron microscope. The antennal flagellum bears multiporous sensilla (trichodea, basiconica, auricillica, coeloconica) and uniporous sensilla (chaetica, styloconica). A sexual dimorphism is found in the numbers of sensilla trichodea (8300 in males and 6000 in females) and sensilla basiconica (1150 in females and 650 in males). The proboscis has uniporous s. styloconica, multiporous s. basiconica (described for the first time in Lepidoptera), aporous s. chaetica, and some rare uniporous s. basiconica in the food channel. The labial palp-pit organ houses multiporous s. coeloconica, while the maxillary palps have aporous sensilla. Tarsi of both sexes possess one type of aporous s. chaetica and 2 types of uniporous s. chaetica. There is no significant difference in the distribution of tarsal sensilla between males and females. The surface of each lobe of the ovipositor is covered by 3 types of aporous s. trichodea of different lengths and about 60 multiporous s. basiconica, sensilla unusual on the ovipositor of Lepidoptera. The role of sensilla in the oviposition site selection is discussed.     

Morphology and distribution of ovipositor sensilla of female cotton leaf worm Spodoptera littoralis (Lepidoptera: Noctuidae), and evidence for gustatory function

The ovipositor of Spodoptera littoralis has many sensilla, which implies a distinct sensory function of this organ in the assessment of the egg laying substrates and placement of eggs. The ovipositor is composed of two papillae densely packed with sensilla. Scanning electron microscopy showed that there are four categories of sensilla chaetica (s. chaetica), characterized based on differences in distribution, length and morphology, distributed on each papilla: Type I with 69 ± 2.9 sensilla on each papilla (length: 29–163 μm) distributed at the base; Type II with 19 ± 1.8 sensilla (length: 287–446 μm) distributed medially; Type III with 120 ± 7.8 sensilla (length: 62–156 μm) distributed distally; and Type IV 8 ± 0.9 sensilla (length: 72–91 μm) scattered between Type III sensilla. The structure of s. chaetica Types I–III suggests a mechanosensory function, whereas electrophysiological analysis of s. chaetica Type IV showed responses from four gustatory neurons and one mechanosensory neuron. Of the chemoreceptive neurons, one responded to salt, one to the secondary compound caffeine, one to sugars, mainly sucrose and fructose, and lastly one potentially to water. Behavioral studies are needed to verify the role of these sensilla during choice of oviposition site.     

Behavioural evidence for hygro- and mechanoreception by ovipositor sensilla of Dacus tryoni (Diptera: Tephritidae)

ABSTRACT. Gravid female Queensland fruit flies Dacus tryoni (Froggatt) readily oviposit when the ovipositor sensilla are stimulated either by a relatively thick (≥2 mm) surface layer, or by moisture under a relatively thin (<0.5 mm) or thick surface layer. A single layer of Parafilm over dry air elicits almost no oviposition; significantly more oviposition occurs when the underside of the Parafilm is coated with a 2 mm thick layer of petroleum jelly; even more oviposition occurs when the Parafilm is floated on liquid paraffin; greatest oviposition is elicited when moist media (agar gel, water or moist air) are presented under the Parafilm. Hollowed-out domes of apple skin elicit significant oviposition only when sealed basally, to give high internal concentrations of water vapour. The previously identified groove sensilla on the tephritid ovipositor are inferred as being a source of mechanical and chemical information used by the fly in such ovipositional decisions. The ovipositor also has two other types of tactile sensilla. The three types of ovipositor sensilla of tephritids are considered to play roles analogous to those of certain labial receptors of flies with piercing mouthparts.     

两种小菜蛾寄生蜂产卵器感器的形态和超微结构

半闭弯尾姬蜂和菜蛾盘绒茧蜂是两种重要的小菜蛾寄生蜂.采用扫描电镜对该两种寄生蜂雌蜂产卵器上的感受器的形态和超微结构进行了观察和研究,结果显示半闭弯尾姬蜂和菜蛾盘绒茧蜂的产卵器形态结构基本相同,都是由两个独立的腹产卵瓣和两个愈合在一起的背产卵瓣包围形成产卵道,与其它种类的寄生蜂相似.借背产卵瓣上的脊与腹产卵瓣的沟连锁在一起,腹产卵瓣可以沿背产卵瓣上的脊前后相对滑动.在半闭弯尾姬蜂产卵器上观察到1种钟形感器、2种腔锥感器、浅凹状感器和分泌毛孔.在菜蛾盘绒茧蜂产卵器上同样观察到了这几种感器,但菜蛾盘绒茧蜂产卵器端部的钟形感器突起较狭长,顶部开有气孔.此外菜蛾盘绒茧蜂产卵器上还存在第3种腔锥感器,其中央突起较低而长,表面有网孔.对各种感受器的形态和分布进行了描述,并对其功能进行了探讨,认为半闭弯尾姬蜂的产卵器较细长,且刺突部位有6个倒钩状突起,背、腹产卵瓣上分布更多的感受器,显示出更强的寄主搜寻定位和产卵寄生能力.     

Contact chemoreception related to host selection and oviposition behaviour in the monarch butterfly, Danaus plexippus

Abstract. Behavioural events during host selection by ovipositing monarch butterflies (Danaus plexippus (L.), Danainae, Nymphalidae) include tapping the leaf surface with fore-tarsi and touching this surface with mid-tarsi (‘drumming’) and antennae. Flavonoids identified from host plant extracts are known to stimulate oviposition. Scanning electron microscopy revealed the presence of contact-chemoreceptor sensilla on all appendages that contact the leaf surface. This electrophysiological study was conducted to identify the contact chemoreceptors that are sensitive to the known oviposition stimuli and are therefore probably involved in host recognition. Receptor cells of conspicuous sensilla grouped in clusters on fore-tarsi of females were sensitive to the behaviourally active butanol fraction of host plant (Asclepias curassavica) extract. However, these receptors generally had low sensitivity to three oviposition-stimulating flavonoids identified from this fraction, but they were also sensitive to the butanol fraction of a non-host (Brassica oleracea). Chemoreceptors in sensilla of the tarsomers 2–4 of the mid-legs also responded to the behaviourally active fraction of host plant extract and showed some sensitivity to two of the flavonoids that stimulate oviposition. Similar results were obtained from receptor cells in sensilla on the tip of the antennae. Most of these sensilla had cells responding to the butanol fraction of A. curassavica extract but only 25% of them were also sensitive to one of the behaviourally active flavonoids. These electrophysiological results, in combination with behavioural observations, suggest that host selection in monarch butterflies relies on a complex pattern of peripheral sensory information from several types of tarsal and antennal contact chemoreceptors.     

Detecting substrate engagement: responses of tarsal campaniform sensilla in cockroaches

Sensory signals of contact and engagement with the substrate are important in the control and adaptation of posture and locomotion. We characterized responses of campaniform sensilla, receptors that encode forces as cuticular strains, in the tarsi (feet) of cockroaches using neurophysiological techniques and digital imaging. A campaniform sensillum on the fourth tarsal segment was readily identified by its large action potential in nerve recordings. The receptor discharged to contractions of the retractor unguis muscle, which engages the pretarsus (claws and arolium) with the substrate. We mimicked the effects of muscle contractions by applying displacements to the retractor apodeme (tendon). Sensillum firing did not occur to unopposed movements, but followed engagement of the claws with an object. Vector analysis of forces suggested that resisted muscle contractions produce counterforces that axially compress the tarsal segments. Close joint packing of tarsal segments was clearly observed following claw engagement. Physiological experiments showed that the sensillum responded vigorously to axial forces applied directly to the distal tarsus. Discharges of tarsal campaniform sensilla could effectively signal active substrate engagement when the pretarsal claws and arolium are used to grip the substrate in climbing, traversing irregular terrains or walking on inverted surfaces.     

Effect of age on the responsiveness of peripheral chemosensory sensilla of the turnip root fly (Delia floralis)

The effect of insect age on the neural responsiveness of gustatory sensilla was investigated. Electrophysiological recordings were obtained from type A and type D sensilla on the pro- and meso-thoracic tarsi, and from sensilla on the labellum of the turnip root fly,Delia floralis (Fallen) in response to potassium chloride, sucrose and sinigrin. The age of the fly did have an effect on the numbers of sensilla responding to the test stimuli and on the magnitude of the response, but there was no consistent pattern in these effects among sensilla. The labellar sensilla were more responsive to sucrose than the tarsal sensilla and the proportion of flies whose labellar sensilla responded to sucrose was initially low, but increased after day 2 of adult life. In contrast, the number of flies whose tarsal sensilla responded to stimulation with sucrose was initially high and decreased as the flies aged. There was a similar decline in the proportion of tarsal sensilla responding to potassium chloride. Neither the proportion of flies whose tarsal sensilla responded to sinigrin nor the magnitude of the response was influenced by the age of the fly. These finding are discussed in relation to the feeding and host selection behaviour of the fly.     

黑肩绿盲蝽外生殖器及其感器的超微结构

黑肩绿盲蝽Cyrtorhinus lividipennis Reuter是稻飞虱重要天敌之一.为分析黑肩绿盲蝽成虫生殖器上与生殖有关的感器类型,本文通过扫描电镜对黑肩绿盲蝽雌成虫交配孔和产卵器,雄成虫交配器感器分布进行了观察.结果表明,黑肩绿盲蝽雌成虫交配孔有毛形感器Ⅱ(TSⅡ)和锥形感器Ⅱ(BSⅡ)2种感器;产卵器上...     

Sex-specific non-pheromonal taste receptors in Drosophila

Taste receptors have recently been reported in Drosophila [1,2], but little is known of the relation between receptor and response. Morphological studies of the distribution of chemosensory sensilla indicate that the fruit fly has two major sites of gustation: the proboscis and the legs [3]. The taste sensilla on both these sites are similar in structure and each sensillum generally houses four gustatory neurons [4]. Early anatomical observations have demonstrated a sexual dimorphism in the number of tarsal sensilla [5] and in their central projections [6]. We measured the electrophysiological responses of the prothoracic taste sensilla to non-pheromonal substances--salts, sugars and water--and found a clear sexual dimorphism. From the response profile of individual sensilla, we were able to distinguish three types of tarsal sensilla in females as against only two types in males. The female-specific type, which responded specifically to sugar, was absent in males except when male gustatory neurons were genetically feminised. The fact that tarsal gustatory hairs exhibit a sexual dimorphism that affects the perception of non-pheromonal compounds suggests that sexual identity is more complex than has previously been thought [7,8].     

Receptors and neurons for fly odors in Drosophila

Remarkably little is known about the molecular and cellular basis of mate recognition in Drosophila[1]. We systematically examined the trichoid sensilla, one of the three major types of sensilla that house olfactory receptor neurons (ORNs) on the Drosophila antenna, by electrophysiological analysis. We find that none respond strongly to food odors but that all respond to fly odors. Two subtypes of trichoid sensilla contain ORNs that respond to cis-vaccenyl acetate (cVA), an anti-aphrodisiac pheromone transferred from males to females during mating [2-4]. All trichoid sensilla yield responses to a male extract; a subset yield responses to a virgin-female extract as well. Thus, males can be distinguished from virgin females by the activity they elicit among the trichoid ORN population. We then systematically tested all members of the Odor receptor (Or) gene family [5-7] that are expressed in trichoid sensilla [8] by using an in vivo expression system [9]. Four receptors respond to fly odors in this system: Two respond to extracts of both males and virgin females, and two respond to cVA. We propose a model describing how these receptors might be used by a male to distinguish suitable from unsuitable mating partners through a simple logic.     

Sex-specific non-pheromonal taste receptors in Drosophila

Taste receptorshave recently been reported in Drosophila [1] and [2], but little is known of the relation between receptor and response. Morphological studies of the distribution of chemosensory sensilla indicate that the fruit fly has two major sites of gustation: the proboscis and the legs [3]. The taste sensilla on both these sites are similar in structure and each sensillum generally houses four gustatory neurons [4]. Early anatomical observations have demonstrated a sexual dimorphism in the number of tarsal sensilla [5] and in their central projections [6]. We measured the electrophysiological responses of the prothoracic taste sensilla to non-pheromonal substances—salts, sugars and water—and found a clear sexual dimorphism. From the response profile of individual sensilla, we were able to distinguish three types of tarsal sensilla in females as against only two types in males. The female-specific type, which responded specifically to sugar, was absent in males except when male gustatory neurons were genetically feminised. The fact that tarsal gustatory hairs exhibit a sexual dimorphism that affects the perception of non-pheromonal compounds suggests that sexual identity is more complex than has previously been thought [7] and [8].     

Neuroanatomical and electrophysiological studies of identified contact chemoreceptors on the ventral ovipositor valve of 3rd instar larvae of lubber grasshoppers (Taeniopoda eques)

A large number of contact chemoreceptors are located on the ovipositor valves of adult female grasshoppers. These receptors play an important role in many aspects of grasshopper life such as detecting the chemical composition of the soil before and during oviposition. It is surprising, however, to find these types of receptors on the ovipositor valves of instar larvae which are not able to oviposit. Thus, these receptors may serve functions other than to search for a suitable site for egg laying. Observation under the scanning electron microscope revealed the presence of uniporous basiconic contact chemoreceptors in addition to different types of trichoid mechanoreceptors on the ovipositor valve of lubber grasshopper 3rd instar larvae. Neuroanatomical studies have shown that these sensilla are multiply innervated, containing one mechanosensory neuron and four chemosensory neurons that project locally and intersegmentally. The tip recording technique from single basiconic sensilla demonstrated mechanosensory responses to deflections of the sensillum as well as gustatory activity when in contact with different chemical solutions. The electrophysiological studies have shown that these sensilla serve as contact chemoreceptors and not as olfactory receptors.     

The fine structure of sense organs in the ovipositor of the parasitic wasp, Orgilus lepidus Muesebeck

Three types of sensilla were observed in the ovipositor, including a multicellular sensillum presumed to respond to both chemical and mechanical stimuli, plus two types of campaniform sensilla. Four or five bipolar chemosensory cells innervate each multicellular sensillum, witln the dendrites terminating at an 800 ,Å dia. pore in the cuticular wall. The dendrite of an associated mechanosensory neuron is inserted upon a slender shaft of cuticle which extends inward from the wall of the ovipositor. This mechanosensory neuron may he activated by stretching when the ovipositor is bent. The dendrite of each campaniform sensillum ends in a cavity in the wall of the ovipositor, and are probably activated by stresses and vibrations as the wasp probes for a host. Sensilla of each type are present in the medial and lateral stylets of the ovipositor. Earlier behavioral studies indicated that the parasite probably uses these sense organs to locate hosts and distinguish healthy from already parasitized hosts.     

Comparison of the egg-laying behaviour and electrophysiological responses of Delia radicum and Delia floralis to cabbage leaf compounds

Abstract.  The behaviour and the sensitivity of adult cabbage root fly, Delia radicum and turnip root fly, Delia floralis are compared with host-plant extracts and isolated crucifer compounds previously identified as oviposition stimulants for D. radicum . The oviposition behaviour of both species is similar; 7–10-day-old females are stimulated to lay eggs by the methanol extract of cauliflower leaves that contains thia-triaza-fluorenes (CIF) as well as glucosinolates. The glucosinolate fraction is mainly composed of glucobrassicin, which alone stimulate both fly species to lay eggs. The C₅ and D_3,4 sensilla on the prothoracic tarsae of newly-emerged D. radicum contain neurones sensitive to the glucosinolate fractions tested and to glucobrassicin, whereas the CIF specifically stimulate a neurone in the C₅ sensillum. By contrast, newly-emerged D. floralis respond less to glucosinolates, especially to glucobrassicin, and have sensitive neurones to CIF in other sensilla than D. radicum . Recordings are also made from the longest sensilla present on the labellum because they are apparently sensitive to glucosinolates. By contrast to earlier investigations, no remarkable phasic-tonic responses of these neurones are seen. The two species are difficult to discriminate visually, have the same host plants, show identical host-selection behaviour, apparently respond to the same physical and chemical properties of their host-plants, but have a clearly different distribution of receptor neurones in the tarsal sensilla.     

Tarsal taste sensilla of the autumn gum moth, Mnesampela privata: morphology and electrophysiological activity

Mnesampela privata Guenée (Lepidoptera: Geometridae: Ennominae) is a native Australian geometrid that conducts considerable host assessment prior to ovipositing on its host plants, which belong to the genus Eucalyptus . The leaves of some of their hosts are covered with a particularly thick and waxy cuticle and we have shown that epicuticular waxes influence the oviposition preferences of females. This necessitates that M. privata has evolved specific chemosensory organs to assess the identity and perhaps even the quality of its hosts. In this work, we examined the morphology of tarsal taste sensilla and the sensitivity of their sensory neurones to a range of primary metabolites possibly influential on host assessment and oviposition. The ventral surface of the fifth tarsomere of females bear two parallel rows of up to eight sensilla, each loosely aligned with two parallel rows of five spines. Salts, sugars, and amino acids elicited phasi-tonic multicellular neuronal responses of variable magnitude and form. Two pairs of sensilla are closely apposed to the most distal spine in each row; the sensory neurones associated with these sensilla exhibited notably larger responses to alanine and serine compared with those of all other sensilla. The arrangement of the taste sensilla in close proximity to prominent tarsal spines is unique and could represent an adaptation that enables them to penetrate the wax layer and be brought into contact with primary metabolites present closer to the leaf surface.     

Responses of a population of antennal olfactory receptor cells in the female moth Manduca sexta to plant-associated volatile organic compounds

Extracellular electrophysiological recordings were made from individual type-A trichoid sensilla on the antenna of the female sphinx moth Manduca sexta. A single annulus of the antenna bears about 1,100 of these sensilla, and each is innervated by two olfactory receptor cells. We tested the responses of these receptor cells to a panel of 102 volatile compounds, as well as three plant-derived odor mixtures, and could discern three different functional types of type-A trichoid sensilla. One subset of receptor cells exhibited an apparently narrow molecular receptive range, responding strongly to only one or two terpenoid odorants. The second subset was activated exclusively by aromatics and responded strongly to two to seven odorants. The third subset had a broad molecular receptive range and responded strongly to odorants belonging to several chemical classes. We also found receptor cells that did not respond to any of the odorants tested but were spontaneously active. Certain odorants elicited excitatory responses in some sensilla but inhibitory responses in others, and some receptor cells were strongly excited by certain odorants but inhibited by others. Impregnation of groups of receptor cells in type-A trichoid sensilla with rhodamine-dextran demonstrated that their axons project mainly to the large female glomeruli of the antennal lobe.