Response of the antennal receptors of the male Aedes aegypti mosquito

Extracellular recordings of the spike discharge patterns of single chemoreceptor neurons in the antennae of male Aedes aegypti mosquitos were obtained and compared with similar recordings made from homologous sensilla on the antennae of female A. aegypti. In both male and female mosquitos, the grooved-peg sensilla were associated with two types of neurons sensitive to lactic acid—one excited by lactic acid and the other one inhibited by lactic acid. The short, blunt-tipped sensilla trichodea Type II (A2-II) of the male mosquito house chemosensory neurons sensitive to volatile chemical substances associated with sources of plant nectar, whereas in the female this information is provided by the long, sharp-tipped sensilla trichodea and the female A2-II sensilla respond to oviposition-site attractants.     

External morphology of antennal sensilla of trichogramma australicum girault (Hymenoptera : Trichogrammatidae)

External morphology of antennal sensilla on female and male Trichogramma australicum (Hymenoptera : Trichogrammatidae) was examined using scanning electron microscopy. Antennae show strong sexual dimorphism in structure and types of sensilla. The female antenna displays 14 types of sensilla: basiconic capitate peg sensilla (types 1 and 2), campaniform sensilla, chaetica sensilla (types 1–3), coeloconic sensilla, falcate sensilla, placoid sensilla (types 1 and 2), styloconic sensilla and trichoid sensilla (types 1–3). The male antenna displays 12 types of sensilla: basiconic capitate peg sensilla (type 2), campaniform sensilla, chaetica sensilla (types 1–5), coeloconic sensilla, placoid sensilla (type 1), and trichoid sensilla (types 3–5). Falcate and styloconic sensilla occur only on the female antenna. Both sensilla probably are associated with host examination, host discrimination and oviposition behaviour. Male antennal trichoid sensilla types 4 and 5 are probably associated with courtship behaviour, because these types occur only on the male. We propose the term “falcate sensilla” for a unique female antennal sensilla; the number of falcate sensilla may be used for identification of Trichogramma spp. In addition, we report the presence of placoid sensilla type 2 and difference in structure of coeloconic sensilla in T. australicum. Variation in structure and position of antennal sensilla are discussed.     

Structure of female genitalia of glassy-winged sharpshooter, Homalodisca coagulata (Say) (Hemiptera: Cicadellidae)

The functional reproductive morphology of the female glassy-winged sharpshooter, Homalodisca coagulata (Say), is described at both light microscopy and scanning electron microscopy levels. The female has nine abdominal segments; the seventh to the ninth abdominal segments are modified for reproduction; the eighth tergite is reduced to two segments, with the ovipositor partially exposed from the modified ninth segment-the pygofer. The pygofer, covered with trichoid and coeloconic sensilla, almost completely encloses the ovipositor, which consists of three pairs of valvulae and two pairs of valvifers. The first and second valvulae function together for oviposition. The first valvulae are located exterior to the second valvulae, both of which bear many trichoid, campaniform, and coeloconic sensilla. The third valvulae, possessing many coeloconic sensilla, envelope the first and second valvulae. Seven major muscles are found to be associated with the ovipositor and the pygofer. The oviposition process is described with respect to the activity of the valvulae and their associated musculature. The female morphology follows the general pattern of cicadellids as a group.     

Sensing the Plant Surface Prior to Feeding and Oviposition: Differences in External Ultrastructure and Function Among Tarsi of <Emphasis Type="Italic">Heliconius erato</Emphasis>

Adult foretarsi of Heliconius erato Linnaeus (Lepidoptera, Nymphalidae) are reduced in size and are not used for walking. Foretarsi of the female have specialized sensilla that are presumably used to identify the host plant, by drumming. The mid- and hind tarsi also bear sensilla in both sexes, but these have not been described in detail, nor has their chemosensory function been determined. We described and compared the tarsi of H. erato under light and scanning electron microscopy. Behavioral experiments showed that differences in the shape, number, and size of sensilla were related to feeding and oviposition behaviors. Two types of sensillum (chaeticum and trichodeum) were found in similar numbers and size on the mid- and hind tarsi of both sexes. Sensilla on the female foretarsi act in host-plant site selection, strongly affecting oviposition rates when isolated. Male foretarsi lack sensilla, which may have been selected against due to the absence of function and thus lost. Sensilla on the mid- and hind tarsi are involved in sugar detection in both sexes, responding to an effective dose of sucrose (ED₅₀) near 0.01 M, and therefore might be used to identify food resources when the butterflies settle on flowers.     

Ultrastructure of contact-chemoreceptor sensilla found among the genae of female Gasterophilus nasalis

Scanning electron microscopy was used to observe contact-chemoreceptor sensilla in the genae of the anterior vestigial mouthparts of female Gasterophilus nasalis. These were of the uniporous trichoid type and were surrounded by mechanosensory aporous trichoid sensilla of variable size. Contact-chemoreceptor sensilla could be involved in detecting different chemical substances, including the equine kairomones that stimulate females to lay eggs on the hair of the host and/or the short-range sexual pheromones used in precopulatory courtship. The probable functions of these sensilla are discussed with reference to the current literature on the sensorial organs of muscomorphid dipterans.     

Influence of Substrate Color on Oviposition Behavior,Egg Hatchability,and Substance of Egg Origin in the Mosquito Anopheles sinensis (Wiedemann) (Diptera: Culicidae)

Understanding the factors that influence the choice of substrate for oviposition by the malaria mosquito is critical to efforts directed to the management of the disease and vector control measures aimed at modifications of larval habitat. The influence of black and white substrates on Anopheles sinensis (Wiedemann) (Culicidae: Anophelinae) female oviposition behavior and egg-hatching rate and the presence of substances associated with egg laying were studied. Results from the no-choice tests showed that the number of eggs laid on black substrate was significantly greater than that laid on white substrate. Results from the dual-choice tests revealed that gravid females showed stronger preference for the black substrate than that for the white substrate. Furthermore, the egg-hatching rate on white substrate was significantly lower than that observed on black substrate. Results from the three-choice tests showed that substance of egg origin was associated with the black substrates (UBS) that were attractive for and stimulated oviposition. The results of this study suggest that there might be some compounds in the black substrates which play a positive role in the oviposition behavior of female mosquitoes and in the development of eggs and that eggs might produce and release active substances that attract females and stimulate oviposition. These results could be important as regards to the optimization of mosquitoes raised for experimental purposes and the control of malaria mosquitoes by altering the oviposition behavior of gravid females.     

Comparison of the antennal sensilla of females of four fig-wasps associated with Ficus auriculata

A comparison was performed of the antennal sensilla of females of four chalcid wasp species Ceratosolen emarginatus Mayr, 1906, Sycophaga sp., Philotrypesis longicaudata Mayr, 1906, and Sycoscapter roxburghi Joseph, 1957, which are specific and obligatory associated with Ficus auriculata (Lour, 1790). The four species exhibit different oviposition strategies in the fig ovules where their offspring hatch and develop. Antennal sensilla morphology was evaluated using scanning electron microscopy. Females of the four species present 11 morphologically similar types of sensilla: trichoid sensilla, sensilla obscura, chaetica sensilla 1 and 2, which all have mechanosensory functions; uniporous basiconic sensilla, which are presumably contact chemosensilla; basiconic capitate peg sensilla, coeloconic sensilla 1, multiporous basiconic and placoid sensilla, which may be regarded as olfactory sensilla, and coeloconic sensilla 2 and 3, which are presumed to be proprioreceptors or pressure receptors. The four species have significant differences in the abundance and arrangement of trichoid sensilla and chaetica sensilla 1 on the flagellum. The coeloconic sensilla and sensilla obscura only occur on the antennae of C. emarginatus that enter figs. The chemosensilla which are presumably involved in host discrimination, i.e., basiconic sensilla, multiporous placoid sensilla and basiconic capitate peg sensilla, are similar in shape and configuration, although they present some differences in abundance. These findings provide practical information on the adaptations of fig wasps and the relationship between multisensory antennae and functions in fig wasp behaviour.     

Volatile cues can drive the oviposition behavior in Odonata

Selection for the oviposition site represents the criterion for the behavioral process of habitat selection for the next generation. It is well known that in Odonata the most general cues are detected visually, but laboratory investigations on the coenagrionid Ischnura elegans showed through behavioral and electrophysiological assays that adults were attracted by olfactory cues emitted by prey and that males of the same species are attracted by female odor.The results of the present behavioral and electrophysiological investigations on I. elegans suggest the involvement of antennal olfactory sensilla in oviposition behavior. In particular, I. elegans females laid in the laboratory significantly more eggs in water from larval rearing aquaria than in distilled or tap water. Moreover, the lack of preference between rearing water and tap water with plankton suggests a role of volatiles related to conspecific and plankton presence in the oviposition site choice. I. elegans may rely on food odor for oviposition site selection, thus supporting the predictions of the “mother knows best” theory. These behavioral data are partially supported by electroantennographic responses. These findings confirm a possible role of olfaction in crucial aspects of Odonata biology.     

Influence of blood meal on the responsiveness of olfactory receptor neurons in antennal sensilla trichodea of the yellow fever mosquito, Aedes aegypti

In female Aedes aegypti L. mosquitoes, a blood meal induces physiological and behavioral changes. Previous studies have shown that olfactory receptor neurons (ORNs) housed in grooved peg sensilla on the antennae of Ae. aegypti down-regulate their sensitivity to lactic acid, a key component driving host-seeking behavior, which correlates with observed changes in the host-seeking behavior of this species. In the present study, we performed electrophysiological recordings from the most abundant antennal sensillum type, sensilla trichodea. Our results indicate that the response spectra of ORNs contained within most trichoid sensilla do not change in response to blood feeding. However, we observe an increase in sensitivity to primarily indole and phenolic compounds in neurons housed within four of the five functional types of short blunt tipped II trichoid sensilla, both at 24 and 72 h post-blood feeding, which was more pronounced at 24 h than 72 h. Furthermore, sensitivity to undecanone, acetic acid and propionic acid was observed to increase 72 h post-blood meal. Considering the timing of these changes, we believe that these neurons may be involved in driving the orientation behavior of female mosquitoes to oviposition sites, which are known to release these compounds.     

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.     

属模巨齿蛉成虫感器的超微形态

为了解属模巨齿蛉成虫多个部位感器的超微结构及其对生命活动的影响,本文对属模巨齿蛉成虫的触角、大颚、翅缘和生殖器4个部位进行了电镜扫描。研究发现,触角有7种感器,分别是毛形感器Ⅰ型、Ⅱ型、Ⅲ型、Ⅳ型、腔锥感器、锥形感器、柱形感器;大颚有3种感器,分别是腔锥感器、锥形感器、刺形感器;翅缘有4种感器,分别是毛形感器Ⅱ型、Ⅲ型、Ⅳ型、腔锥感器;雌性成虫生殖器有7种感器,分别是毛形感器Ⅱ型、Ⅲ型、Ⅳ型、Ⅴ型、Ⅵ型、锥形感器、钟形感器。柱形感器是触角的特殊感器,钟形感器是雌性成虫生殖器的特殊感器。毛形感器是触角、翅缘和生殖器主要感器,而大颚上没有毛形感器。触角和生殖器上的感器类型最多,且分布最密集,这与触角和生殖器对成虫的交配、产卵行为具有重要作用相吻合。     

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.     

Fine structure and role in behavior of sensilla on the terminalia of Aedes aegypti (L.) (Diptera: Culicidae)

The terminalia of male and female Aedes aegypti (L.) bear numerous hairs of various shapes and lengths, all of which are mechanoreceptors. Each hair is innervated by one bipolar neuron which contains ciliary rootlets, two basal bodies, and a region assuming the structure of a non-motile cilium. At the distal tip of the dendrite is a tubular body, a characteristic of cuticular mechanoreceptors. Covering the outer dendritic segment is a cuticular sheath which ends proximally in a net-like felt-work and distally attaches to the hair base. Each hair sensillum has two sheath cells. Presumed efferent fibers are associated with the sheath cells. On the insula of the female terminalia are a few campaniform sensilla, the domes of which are raised into small pegs. The sensilla on the terminalia function in copulation and oviposition and probably in warning. A sequence of neurological events is traced for copulation and oviposition. Other cuticular structures, viz., scales, microtrichia, acanthae, and aedeagal spines, which occur on the terminalia are not innervated.     

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.     

Oviposition behaviour in Lygus rugulipennis: a morpho-functional study

Before oviposition, a Lygus rugulipennis (Poppius) (Heteroptera: Miridae) female explores the substrate with her mouthparts, performing ‘probing’ behaviour which eventually leads to a choice of oviposition site. In this study, morphological and behavioural observations were carried out in order to define the mechanisms through which female bugs recognise suitable oviposition sites. The morphological study was conducted using electron‐microscopy techniques, while the behavioural experiments aimed at the temporary (using ZnSO₄) or permanent (i.e., cauterization of the rostrum and ablation of both stylets and labium) inactivation of sensory structures located in the labium tip and in the stylets, which are probably involved in oviposition site selection. The tip of the labium of L. rugulipennis females is characterised by the presence of 11–12 uniporous gustatory sensilla which are innervated by 3–6 sensory neurones. One aporous mechanoreceptor is located ventrally on both areas of the labium tip. Other aporous mechanosensilla are found more proximally on the labium. ZnSO₄ labium tip treatment did not affect oviposition site selection, while stylet amputations, as well as rostrum cauterisations, resulted in almost complete oviposition failure. Labium tip‐ablated females oviposited similarly to control females. These results suggest that the sensory neurones associated with the stylets are involved in the location of the oviposition site. Uniporous gustatory sensilla on the labium tip are not involved in the final steps of the oviposition behaviour. However, they seem to play a role in assessing the suitability of the substrate as a food source.     

Consistent pattern in the placement of taste sensilla on the labellar lobes of Aedes aegypti

The long sensilla on the labellar lobes of Aedes aegypti were studied using scanning electron microscopy. The surface of the labella is populated by 3 hair-like structures: long sensilla (female 33.5 μm, SD 3.81 n=114; male 32.0 μm, SD 2.69 n=20), short sensilla (female 4.27 μm, SD 0.550 n=15; male 4.52 μm, SD 0.609 n=15), and microtrichia (female 5.00 μm, SD 0.656 n=55; male 5.27 μm, SD 0.376 n=53). This current study is concerned with the long sensilla. The ventral surface of the labella is consistently populated with 10 long sensilla. The dorsal surface is populated by 5 long sensilla. We assigned the base of each sensillum Cartesian co-ordinates describing its relationship to the other sensilla on the ventral and dorsal surfaces of each individual. These Cartesian co-ordinates were pooled and a stringent form of cluster analysis was used to determine if these sensilla could be identified by location on the labella. Sensilla from different individuals are more closely related by position than sensilla on the same individual, suggesting that these sensilla are located in a consistent pattern over the labellar surface. Sensilla were labeled V1–V10 and D1–D5 on the ventral and dorsal surfaces respectively.     

The role of contact chemoreception in the host location process of an egg parasitoid

Taste allows insects to detect palatable or toxic foods, identify a mate, and select appropriate oviposition sites. The gustatory system strongly contributes to the survival and reproductive success of many species, yet it is rarely studied in insect parasitoids. In order to locate and assess a host in which they will lay their eggs, female wasps actively search for chemical cues using their sensory organs present mainly on the antennae. In this paper, we studied the role of antennal taste sensilla chaetica in the perception of contact semiochemicals in Trissolcus brochymenae (Hymenoptera: Platygastridae), an egg parasitoid of the brassicaceae pest Murgantia histrionica (Heteroptera: Pentatomidae). Methanolic extracts obtained from male and female hosts elicited action potentials in taste neurons housed in antennal sensilla chaetica, indicating that these sensilla are involved in the perception of non volatile host kairomones. In behavioural assays, wasp females displayed an intense searching behaviour in open arenas treated with host extracts, thus confirming that these kairomones are soluble in polar solvents. We further investigated the extracts by Gas Chromatography-Mass Spectrometry (GC-MS) and found that they contain several compounds which are good candidates for these contact kairomones. This study contributes to better understanding contact chemoreception in egg parasitoids and identifying gustatory receptor neurons involved in the host location process.     

Oviposition behaviour of Phlebotomus argentipes - A laboratory-based study

The breeding habitat of sandflies is a little studied and poorly understood phenomenon. More importantly, oviposition behaviour is a largely neglected aspect of sandfly biology and this knowledge gap further undermines our understanding of the biology of sandflies. Pheromones released by the eggs play an important role in identifying good sites for oviposition by female insects. Several recent studies have examined the oviposition pheromone. The present study provides a preliminary report on the oviposition behaviour of Phlebotomus argentipes, the only vector of kala-azar (or visceral leishmaniasis) on the Indian sub-continent. Sandflies prefer to oviposit their eggs on surfaces that contain organic substances, especially substances with an odour of decaying animal products and the remains of conspecific eggs. The results presented here suggest that the odour released by the organic substances of old sandfly colony remains that contain dead flies, old unhatched eggs, larval food containing vertebrate faeces, frass and other organic matter serves as an attractant for the ovipositing females of P. argentipes and hence greatly increases the number of oviposited eggs compared to eggs deposited in controlled oviposition pots. This result will be helpful in maintaining an efficient colony of P. argentipes and may be a promising tool for monitoring and controlling the target insect as part of a synergistic approach.     

Oviposition by Lobesia botrana is stimulated by sugars detected by contact chemoreceptors

Abstract.  The influence of glucose, fructose and sucrose on oviposition site selection by Lobesia botrana is studied by combining behavioural and electrophysiological experiments. Oviposition choice assays, using surrogate grapes treated with grape berry surface extracts of Vitis vinifera cv. Merlot at different development stages, show that L. botrana females are most stimulated by extracts of mature berries containing the highest concentrations of glucose and fructose. Choice assays reveal that the oviposition response to these sugars is dose-dependant (with a threshold of the applied solution = 10 m m and a maximum stimulation at 1  m ) and that females are more sensitive to fructose than to glucose. Tarsal contact-chemoreceptor sensilla are unresponsive to stimulation with sugars but the ovipositor sensilla contain at least one neurone most sensitive to fructose and sucrose with a threshold of approximately 0.5 m m . Corresponding to the behavioural data, glucose is significantly less stimulatory to sensilla than fructose or sucrose. It is argued that fructose may be of special importance for herbivorous insects exploiting fruit as an oviposition site.     

Effects of blood-feeding on olfactory sensitivity of the malaria mosquito Anopheles gambiae: Application of mixed linear models to account for repeated measurements

Olfaction plays an important role in the host-seeking behavior of the malaria mosquito Anopheles gambiae. After a complete blood meal, female mosquitoes will not engage in host-seeking behavior until oviposition has occurred. We investigated if peripheral olfactory sensitivity changed after a blood meal by recording electroantennograms (EAGs) of female mosquitoes at three time points (2 h, 48 h and 72 h) to 15 volatile kairomones of either human origin or documented to emanate from oviposition sites. The EAG-sensitivity was compared with that of females of similar age post eclosion. As is common practice in electrophysiological studies, the EAG recordings were obtained by repeated stimulation of the same antennal preparations. We introduce mixed linear modeling as an improved statistical analysis for electrophysiological data. Two hours after blood ingestion, olfactory sensitivity as quantified through EAG-recording increased significantly and selectively, i.e. for seven compounds, compared to unfed females of the same age. Such short-term electrophysiological sensitization in the olfactory system as a result of feeding has not been documented before for insects. Sensitization to six compounds persisted until 48 h or 72 h post-blood meal at one or more concentrations. Desensitization was observed at 48 and 72 h pbm in response to two and three kairomones, respectively. For several compounds, sensitization at the EAG-level corresponded with sensitization found previously in single sensillum studies on olfactory neurons in antennal sensilla trichodea of An. gambiae females. These effects are likely to reflect sensitization to oviposition cues, as eggs have matured 48–72 h pbm. Knowledge of changes in olfactory sensitivity to kairomones can be applied to increase trap catches of malaria mosquitoes that have taken a blood meal and need to locate oviposition sites.