Investigation of the sensory organs on antennae of the horseflies Hybomitra bimaculata and Tabanus bovinus (Diptera: Tabanidae) by scanning electron microscope

Sensory organs on the antennae of the horseflies Hybomitra bimaculata Macq. and Tabanus bovinus Loew are represented by the same morphological types of sensilla. Never differences in the topographical distribution of the sensilla on antennae have been also found, which can be explained by the similarity of ecological and behavioural adaptations of these insects. First and second antennal segments are found to be supplied with tactile hairs and proprioceptors. Other antennal segments bear sensory organs of several morphological types. Short thin olfactory hairs are most numerous among them. They are present on all segments of the antennal flagellum and belong to two morphological types different by the hair length. In the upper parts of the antennal segments from third to seventh several sensilla trichoidea are present, which probably serve as tactile and taste receptors.     

昆虫触角感器类型及其功能研究进展

触角感器是昆虫对环境变化产生行为响应的重要基本结构单元,作为昆虫内部神经系统与外部环境进行信息交流的关键接口,受到广泛关注。由于不同环境压力的作用,长期适应性进化使昆虫触角上着生有不同类型的感器,且执行着差异化的生物学功能。触角感器在昆虫识别寄主、寻找配偶、躲避天敌等行为变化中具有重要作用,若深入理解昆虫行为变化的内在机理,则有必要清晰认识昆虫触角感器类型与潜在功能。本文对已有研究结果进行系统性综述与总结。截止目前,共发现有61种昆虫触角感器类型,且触角感器存在种内与种间特征差异。同时针对12种常见的触角感器功能进行梳理,提出昆虫触角感器未来可深入开展的研究方向。本文全面了解各昆虫触角感器类型特征和功能,为从形态结构方面进行昆虫分类研究提供新视角,也为今后从化学生态学角度深入开展昆虫行为对环境改变的适应性等研究提供科学依据。     

Changes associated with laboratory rearing in antennal sensilla patterns of Triatoma infestans, Rhodnius prolixus, and Rhodnius pallescens (Hemiptera, Reduviidae, Triatominae)

We examined changes in the array of antennal sensilla of three species of Triatominae (Triatoma infestans, Rhodnius prolixus, and R. pallescens) following their establishment for different periods in laboratory culture. In each case, the laboratory colonies were compared with conspecific samples taken directly from the field, by quantitative analysis of the sensilla arrays on the three distal segments of the antenna in terms of the densities of three types of chemoreceptors (basiconics and thick and thin walled trichoids) and one type of mechanoreceptor (bristles). Sensilla densities were compared by ANOVA or non-parametric tests, and by multivariate discriminant analysis. Strains of the same species reared in different laboratories showed significant differences in their sensilla arrays, especially when compared to field-collected material from the same geographic origin. A Bolivian strain of T. infestans reared in the laboratory for 15 years and fed at monthly intervals, showed greatest differences from its conspecific wild forms, especially in terms of reductions in the number of chemoreceptors. By contrast, an Argentine strain of T. infestans reared for 25 years in the laboratory and fed weekly, showed a relative increase in the density of mechanoreceptors. A Colombian strain of R. prolixus reared for 20 years and fed weekly or fortnightly, showed only modest differences in the sensilla array when compared to its wild populations from the same area. However, a Colombian strain of R. pallescens reared for 12 years and fed fortnightly, did show highly significant reductions in one form of chemoreceptor compared to its conspecific wild populations. For all populations, multivariate analysis clearly discriminated between laboratory and field collected specimens, suggesting that artificial rearing can lead to modifications in the sensory array. This not only supports the idea of morphological plasticity in these species, but also suggests caution in the use of long-established laboratory material for experimental studies designed to extrapolate the natural behaviour and physiology of these species.     

Juvenile hormone inhibits differentiation of olfactory sense organs during postembryonic development of cockroaches

The density of olfactory sense organs on the antenna of the cockroach, Leucophaea maderae, is relatively constant throughout larval development (average 400 sensilla/mm²), but undergoes a substantial increase at the adult state (to about 620 sensilla/mm²). Experimental manipulations of juvenile hormone (JH) activity result in either supernumerary larval instars (induced by unilaterla antennectomy or addition of exogenous JH), or premature adulthood (induced by allatectomy). The density of antennal sensilla remains at the larval level during the extra instars, but increases to the adult level or surpasses it at the terminal ecdysis following the induction of extra instars. Adultoids resulting from allatectomized sixth instars also have the high density of antennal olfactory sensilla characteristic of the normal adult. These data suggest that an interplay of surface area effects and an inhibitory action of JH controls the pattern of postembryonic development of antennal olfactory sensilla. Limited behavioural observations of the insects resulting from these experiments are consistent with the hypothesis that sex attractant-specific olfactory receptors appear only at the adult stage. However, electrophysiological data will be needed to confirm or negate this hypothesis.     

Inter-specific and developmental differences on the array of antennal chemoreceptors in four species of Triatominae (Hemiptera: reduviidae)

The aim of the work was to investigate the pattern of chemoreceptor sensilla in adults and fifth stage nymphs of Rhodnius prolixus, R. neglectus, Triatoma infestans and T. sordida in order to study differences and similarities between genera and species. Three types of sensilla were analyzed by light microscopy: thin-walled trichoidea, thick-walled trichoidea and basiconica. The number of sensilla of each three types were counted. The length of the antennal segments were also used as a variable for the analysis. The statistical analysis showed that the number of these antennal chemoreceptors had significant differences between species and between adults and nymphs of each species. Discriminant analysis separates incompletely the fifth stage nymphs of the four species and showed similarity between them. Discriminant analysis performed with 12 variables of the antennae, allowed a complete separation of the adults of the four species.     

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.     

Antennal sensory organs and glands of the harlequin ladybird,Harmonia axyridis

Harmonia axyridis (Pallas) (Coleoptera: Coccinellidae) is a sub‐cosmopolitan species. Native to Asia, it has been released during the 20th century for classical and augmentative biological control of several herbivorous insects, mostly aphids and coccids. Despite its recognized positive impact on biological control, H. axyridis is now considered among the most dangerous invasive species in Europe and in most places where it has established. This is mostly due to its ability to reduce the populations of native predatory species of the same trophic guild. When exploring a new area, H. axyridis adults use semiochemical cues to acquire information about the habitat. Presumably, these cues are perceived by the sensilla located on the antennae. Surprisingly, in spite of the huge literature existing on H. axyridis, the antennal sensory organs have been poorly characterized. Here, we used scanning and transmission electron microscopy (SEM, TEM) techniques to study H. axyridis antennae, with focus on the various types of sensilla and their distribution in male and female individuals. The presence of various classes of antennal sensilla belonging to the main types described in insects (chemoreceptors, mechanoreceptors, and thermo‐hygroreceptors) was highlighted, as well as the widespread presence of antennal glands. The investigations showed some peculiar characteristics not known in Coccinellidae, such as the concentration of sensory structures at the level of the distal part of the apical antennomere and the discovery of antennal glands associated with it. No sexual dimorphism was revealed, neither for the general structure of the antenna (similar number of antennomeres and presence of modifications), nor for the total length and width of the antenna, the relative size of the antennomeres, the types of antennal sensilla, of their distribution and abundance. The potential relevance of these sensory structures and antennal glands, reported for the first time in Coccinellidae, is discussed in the context of intra‐ and interspecific communication.     

三种花蓟马触角感器的超微结构

采用扫描电子显微镜对花蓟马Frankliniella intonsa (Trybom)、 禾花蓟马F. tenuicornis (Uzel) 和西花蓟马F. occidentalis (Pergande) 3种国内危害严重的农业害虫的两性成虫触角感器超微结构进行观察和比较, 旨在明确3种花蓟马两性成虫触角上的感器类型、 数量、 分布及超微形态特征, 明晰3种花蓟马触角感器差异, 进而补充蓟马感器详细资料、 完善蓟马形态学研究。结果表明： 3种花蓟马两性成虫触角上均有8种感器类型, 即Böhm氏鬃毛、 钟形感器、 毛形感器、 刺形感器、 锥形感器、 腔锥形感器、 腔形感器和特殊结构感器。触角各节上感器的分布和数量并不均匀。分析结果显示, 各类感器在触角上的分布相对稳定, 具有一定规律; 近缘种间和同种两性间触角感器的形态及分布无明显差异。     

Sense organs on the antennal flagellum of the green stink bug,Nezara viridula (L.) (Heteroptera : Pentatomidae): Sensillum types and numerical growth during the post-embryonic development

The sensilla on the antennal flagellum of Nezara viridula (Heteroptera : Pentatomidae) were studied with the scanning and transmission electron microscopes. Seven morphologically distinct types of sensilla were identified in adults. The number and distribution of six types were studied. Male and female antennae bear the same numbers and types of sensilla. As in other Heteroptera, the flagellum comprises two segments. The second flagellar segment bears more sensilla than the first segment. Sensilla are evenly distributed over the flagellum surface. The total number of sensilla increases during the post-embryonic development. Individual numerical growths of each type follow simple exponential laws when expressed as functions of developmental stage. The growth in number shows positive allometry in respect to body size for sensillum types 1, 2 + 5 and 4, but negative allometry for types 3 and 6. The density of sensilla remains constant. These findings are compared with previously published data from other heterometabolous insects. Adaptation to the increase in body size during the post-embryonic development seems to be the main determinant of the growth of the olfactory system in N. viridula.     

六斑月瓢虫触角及感觉器扫描电镜观察

[目的] 明确六斑月瓢虫雌雄成虫触角感觉器种类、分布及形态特征。[方法] 利用扫描电子显微镜对六斑月瓢虫雌、雄成虫触角形态及触角感受器超微结构进行观察。[结果] 六斑月瓢虫成虫触角由柄节、梗节和鞭节组成,柄节长度与宽度显著大于梗节长度与宽度;鞭节分为9个亚节,末端3节横向膨大呈锤状。雌雄成虫触角上共有8种感觉器:刺形感觉器(SC)、毛形感觉器(ST)、锥形感觉器(SB)、腔形感觉器(CaS)、钟形感觉器(CS)、哑铃形感觉器(DS)、香肠形感觉器(SS)及B?hm氏鬃毛感觉器(BB)。以毛形感觉器和刺形感觉器分布最广,遍布触角;B?hm氏鬃毛仅存在于触角柄节与梗节;触角鞭节第9亚节顶端密布7种触角感觉器。六斑月瓢虫雌雄成虫触角长度、触角感觉器类型及分布无显著差异。[结论] 六斑月瓢虫成虫触角上共有8种感觉器,其触角可能具有感知机械刺激、识别化学信息素及感受温湿度变化的作用。本研究为进一步了解六斑月瓢虫触角与其行为间的关系提供基础资料。     

Peripheral and central nervous effects of lozenge3: a Drosophila mutant lacking basiconic antennal sensilla

The third antennal segment (= funiculus) of wild-type Drosophila melanogaster shows a sexually dimorphic distribution of sensilla: Males possess about 20% less of large basiconic sensilla, but approx 30% more trichoid sensilla than the female. The funiculus of the mutant lozenge3 is much reduced in size. Moreover, basiconic sensilla are completely lacking, and the number and density of trichoid sensilla are reduced. In contrast, the number and density of coeloconic sensilla are increased. The loss of sensilla in lozenge3 leads to a corresponding loss of sensory fibers in the antennal nerve. The antennal commissure of the wild type consists essentially of afferents from the funiculus which extend into the contralateral half of the brain. In the antennal commissure of lozenge3, more than twice the number of fibers lacking in the antennal nerve have disappeared which suggests that most afferents establish purely ipsilateral terminals. A highly specific change in the brain of lozenge3 is the loss of a particular subunit of the antennal center, the glomerulus V. This has previously been shown to be a major target of fibers from basiconic sensilla. Mosaic flies exhibiting a lozenge3 antenna demonstrate that the elimination of glomerulus V is causally related to the change in the sensilla pattern. This implies that the development and/or survival of particular target regions in the antennal center depends on sensory input. Furthermore, it shows that glomerulus V is specifically involved in the processing of information from basiconic sensilla.     

沟眶象触角感器的扫描电镜观察

应用扫描电镜观察沟眶象触角感器的类型、数量和分布。结果表明,沟眶象触角上共有5类10种感器,分别为4种锥形感器、2种刺形感器、2种毛形感器、1种栓锥形感器和1种柱形感器。根据感器的分布、形态特征结合已有的文献描述,推测了感器可能的功能。触角感器在每节上的数量和分布不同,在背腹面的分布差异不显著。雌雄成虫触角上感器总的数量存在显著差异。     

Analysis of antenal sensilla patterns of Rhodnius prolixus from Colombia and Venezuela

Antennal sensilla patterns were used to analyze population variation of domestic Rhodnius prolixus from six departments and states representing three biogeographical regions of Colombia and Venezuela. Discriminant analysis of the patterns of mechanoreceptors and of three types of chemoreceptors on the pedicel and flagellar segments showed clear differentiation between R. prolixus populations east and west of the Andean Cordillera. The distribution of thick and thin-walled trichoids on the second flagellar segment also showed correlation with latitude, but this was not seen in the patterns of other sensilla. The results of the sensilla patterns appear to be reflecting biogeographic features or population isolation rather than characters associated with different habitats and lend support to the idea that domestic R. prolixus originated in the eastern region of the Andes.     

Comparative dissection of the peripheral olfactory system of the Chagas disease vectors Rhodnius prolixus and Rhodnius brethesi

American trypanosomiasis, or Chagas disease, is transmitted by both domestic and sylvatic species of Triatominae which use sensory cues to locate their vertebrate hosts. Among them, odorants have been shown to play a key role. Previous work revealed morphological differences in the sensory apparatus of different species of Triatomines, but to date a comparative functional study of the olfactory system is lacking. After examining the antennal sensilla with scanning electronic microscopy (SEM), we compared olfactory responses of Rhodnius prolixus and the sylvatic Rhodnius brethesi using an electrophysiological approach. In electroantennogram (EAG) recordings, we first showed that the antenna of R. prolixus is highly responsive to carboxylic acids, compounds found in their habitat and the headspace of their vertebrate hosts. We then compared responses from olfactory sensory neurons (OSNs) housed in the grooved peg sensilla of both species, as these are tuned to these compounds using single-sensillum recordings (SSRs). In R. prolixus, the SSR responses revealed a narrower tuning breath than its sylvatic sibling, with the latter showing responses to a broader range of chemical classes. Additionally, we observed significant differences between these two species in their response to particular volatiles, such as amyl acetate and butyryl chloride. In summary, the closely related, but ecologically differentiated R. prolixus and R. brethesi display distinct differences in their olfactory functions. Considering the ongoing rapid destruction of the natural habitat of sylvatic species and the likely shift towards environments shaped by humans, we expect that our results will contribute to the design of efficient vector control strategies in the future.     

External morphology of antennal sensilla of four species of adult flea beetles (Coleoptera : chrysomelidae : alticinae)

External morphology of antennal sensilla of both sexes of Phyllotetra cruciferae (Goeze) and Psylloides punctulata Melsh, both of which feed on the mustard family Cruciferae, and Epitrix cucumeris (Harris) and Psylloides affinis (Paykell), both of which feed on the nightshade family Solanaceae, was studied using scanning electron microscopy. All belong to Alticinae (Coleoptera : Chrysomelidae). The number and distribution of antennal sensilla were also determined. Eight types of sensilla could be distinguished on the flagella of the species examined: sensilla chaetica; sensilla trichodea I and II; long sensilla basiconica I and II; and short sensilla basiconica I, II and III. The sensilla chaetica are probable tactile mechanosensilla, whereas both types of sensilla trichodea and long sensilla basiconica likely function in olfaction. Suggested functions for the short sensilla basiconica I, II and III include hygro-/thermoreception and chemoreception.The lack of sexual dimorphism in antennal structure and in types as well as number of sensilla, indicates that the sensilla probably have similar functions in both sexes. Probably most of the antennal olfactory sensilla are involved in host location and recognition. Any correlation between number of a particular type of sensillum or total number of all types and general host preference is not apparent.     

New scenarios of Trypanosoma cruzi transmission in the Orinoco region of Colombia

Rhodnius prolixus, a blood-sucking triatomine with domiciliary anthropophilic habits, is the main vector of Chagas disease. The current paradigm of Trypanosoma cruzi transmission in Columbia includes a sylvatic and domiciliary cycle co-existing with domestic and sylvatic populations of reservoirs. The aim of this study is to evaluate the population densities and relative abundance of triatomines and mammals that may be involved in the sylvatic cycle of Chagas disease to clarify the epidemiological scenario in an endemic area in the province of Casanare. Insect vectors on Attalea butyracea palms were captured using both manual searches and bait traps. The capture of mammals was performed using Sherman and Tomahawk traps. We report an infestation index of 88.5% in 148 palms and an index of T. cruzi natural infection of 60.2% in 269 dissected insects and 11.9% in 160 captured mammals. High population densities of triatomines were observed in the sylvatic environment and there was a high relative abundance of reservoirs in the area, suggesting a stable enzootic cycle. We found no evidence of insect domiciliation. Taken together, these observations suggest that eco-epidemiological factors shape the transmission dynamics of T. cruzi, creating diverse scenarios of disease transmission.     

Central projections of olfactory receptor neurons from single antennal and palpal sensilla in mosquitoes

In insects, olfactory receptor neurons (ORNs) are located in cuticular sensilla, that are present on the antennae and on the maxillary palps. Their axons project into spherical neuropil, the glomeruli, which are characteristic structures in the primary olfactory center throughout the animal kingdom. ORNs in insects often respond specifically to single odor compounds. The projection patterns of these neurons within the primary olfactory center, the antennal lobe, are, however, largely unknown.We developed a method to stain central projections of intact receptor neurons known to respond to host odor compounds in the malaria mosquito, Anopheles gambiae. Terminal arborizations from ORNs from antennal sensilla had only a few branches apparently restricted to a single glomerulus. Axonal arborizations of the different neurons originating from the same sensillum did not overlap.ORNs originating from maxillary palp sensilla all projected into a dorso-medial area in both the ipsi- and contralateral antennal lobe, which received in no case axon terminals from antennal receptor neurons. Staining of maxillary palp receptor neurons in a second mosquito species (Aedes aegypti) revealed unilateral arborizations in an area at a similar position as in An. gambiae.     

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.