Central projections from contact chemoreceptors of the locust ovipositor and adjacent cuticle

Contact chemoreceptors (basiconic sensilla) located on the ovipositor and genital segments of the locust serve to control the chemical features of the substrate before and during oviposition. They occur dispersed and also crowded in fields between mechanosensory exteroceptors sensitive to touch or wind (trichoid and filiform sensilla). The central nervous projections of the four chemosensory and one mechanosensory neurons from single basiconic sensilla were stained selectively, focusing on receptors on the ovipositor valves, which usually contact the substrate during the pre-oviposition probing movements. All axons and neurites from one contact chemoreceptor usually stay close together in most of their projections. Segregation occurs mainly when single axons terminate in one neuromere while the others proceed to a different neuromere or ganglion. For projections from one chemoreceptor, there is evidence neither for functional segregation of mechanosensory from chemosensory afferent terminals nor for specific segregation between different chemosensory afferents. The projections from sensilla of dorsal cuticle tend to project rather uniformly along the midline of the terminal ganglion. Comparative staining of touch- and wind-sensitive hair receptor neurons shows mostly central projections, similar to those of neighbouring contact chemoreceptors. From the typical intersegmental projections of most primary afferents and from the lack of segregation into glomerular structures, we conclude that integration of chemosensory information from the genital segments is distributed in the terminal and the 7th abdominal ganglion.     

Distribution of chemo- and mechanoreceptors on the antennae and maxillae of Busseola fusca larvae

The stem borer Busseola fusca (Fuller) (Lepidoptera: Noctuidae) is a major pest of maize, Zea mays L., and sorghum, Sorghum bicolor (L.) Moench (both Poaceae), in sub-Saharan Africa. Like in many other lepidopteran insects, the success of B. fusca in recognizing and colonizing a limited variety of plants is based on the interaction between its sensory systems and the physicochemical characteristics of its immediate environment. The sensilla on the maxillary galeae of B. fusca larvae are typical of Lepidoptera and comprise two uniporous styloconic sensilla, which are contact chemoreceptors, three basiconic sensilla, and two aporous sensilla chaetica. The maxillary palp is two-segmented and has eight small basiconic sensilla at the tip, which were also found to be gustatory. The antennae of B. fusca larvae are short and simple. The sensilla of the antenna are composed of two aporous sensilla chaetica, three multiporous cone-shaped basiconic sensilla, three small basiconic sensilla, and one aporous styloconic sensillum. The basiconic sensillum located on the third antennal segment displayed a contact chemoreception response. The other basiconic sensilla did not show any action potential activity in tip-recording tests. The significant and positive dose–response curve obtained for the antennal basiconic sensillum with sucrose indicated for the first time the presence of gustatory chemoreceptors on the antennae of a lepidopteran larva.     

Morphology and untrastructure of the antennal sense organs in tenebrionid larvae <Emphasis Type="Italic">Tenebrio molitor</Emphasis> L. and <Emphasis Type="Italic">Zophobas rugipes</Emphasis> Kirsch (Coleoptera: Tenebrionidae)

The distribution, external morphology, and ultrastructure of various types of sensilla in the antennae of tenebrionid larvae Tenebrio molitor and Zophobas rugipes are studied by means of scanning and transmission electron microscopy. On the antennae of T. molitor there are sensilla of four basic morphological types: basiconic, styloconic, trichoid, and papillate sensilla. On the antennae of Z. rugipes, in addition to the aforementioned ones, there are placoid sensilla. Ultrastructure points to olfactory function of basiconic and placoid sensilla. Other sensillum types are contact chemoreceptors.     

七星瓢虫唇须感器分布和统计特征的雌雄差异

应用扫描电镜观察七星瓢虫Coccinella septempunctata的唇须和附节,以便确认在感应农药残留时起主要作用的化学感受器。研究证明分布在下颚须上的感器类型包括两种锥形感器（兼有机械感受器和化学感受器的功能）和一种钟形感器。同时本文首次报道了对这些感器精确的形态测量,明确了其性二型性。对下颚须的测量表明其左右末节的长度差异与七星瓢虫的性别之间有明显的相关性。文中还记述了下唇须上一种新的钟形感器,其在每个下唇须上的数量大约为12～17个。经测量这些机械感受器的平均直径为2.4 μm。早期研究中所记述的锥形感器被证实是下唇须上仅有的化学感应器,并且首次证明这些锥形感器的数量与性别相关,雄性平均为18个,雌性平均为16个。附节上也存在性别差异： 第2跗节跗垫的宽度在雄性中是从后向前逐渐增大,而在雌性中刚好相反。本文还就这些差异的意义以及新发现感器的功能进行了讨论。     

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.     

Functional bases of host-acceptance behaviour in the aphid parasitoid Aphidius ervi

Abstract.  The host acceptance behaviour in Aphidius ervi is investigated, assessing the role of both external and internal host-associated cues, offered to the experimental parasitoids with parafilm-made aphid dummies. The reaction to internal cues present in the host haemolymph is clearly evident, and its intensity is enhanced by external cues. Parasitoid females lay few eggs in aphid dummies filled with host haemolymph. A significant increase in the number of both oviposition reactions (host stinging) and egg laying is observed only when these dummies are coated with cornicle secretion. However, this enhancement is not observed when the aphid dummies contain distilled water. Thus, the host acceptance behaviour of A. ervi females appears to be controlled by the integration of both external and internal chemical cues. The physiological basis of this behavioural response is investigated with a detailed study on the anatomy and ultrastructure of A. ervi ovipositor. The detection of chemical cues present in the host haemolymph that act as kairomones is made possible by the presence of gustatory sensilla on the tip of the ovipositor. These sensilla consist of porous areas, reached by unbranched dendrites running inside both the lower valves (i.e. first valvulae) and the unpaired upper valve (i.e. second valvulae). The mechanosensory function during oviposition appears to be provided mostly by the basiconic sensilla found on the tip of external valves (i.e. third valvulae). A tentative functional model accounting for the observed oviposition behaviour of A. ervi is proposed.     

Development of phenotypic differences in sensillum populations on the antennae of a grasshopper,Schistocerca americana

The development of diet-induced phenotypic differences in numbers of sensilla on the antennae of the grasshopper Schistocerca americana was studied using the exuviae produced at each molt. This made it possible to follow changes within an individual insect. In the first instar, insects had similar numbers of four sensillum types: uniporous trichoid sensilla, coeloconic sensilla, and large and small multiporous basiconic sensilla. Rearing on lettuce resulted in sixth instars with greater numbers of three sensillum types than siblings reared on an artificial diet. The first statistically significant differences between treatments in numbers of trichoid sensilla and large basiconic sensilla occurred in the third and fourth instars, respectively. No major reductions in sensillum numbers occurred at any time and the phenotypic differences resulted from differences in the numbers added at each molt.     

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.     

Reproductive strategies and parasitization behavior of Ageniaspis citricola, a parasitoid of the citrus leafminer Phyllocnistis citrella

We describe the number, distribution, and function of sensilla located on different organs of Lobesia botrana (Lepidoptera: Tortricidae) females using scanning electron microscopy, selective staining, and contact electrophysiology. The tarsi of the prothoracic legs bear contact chemo‐mechanoreceptor sensilla chaetica (5–13 per tarsomere), arranged in rings mainly concentrated on ventral surfaces, and different mechanosensory structures (sensilla chaetica, sensilla squamiformia, sensilla campaniformia, and spines). A single contact chemo‐mechanoreceptor sensillum chaeticum is present between the claws on the pretarsus. The ventral surface of the ovipositor lobes is covered with numerous mechanosensory sensilla chaetica of different types, out of which 10 have a contact chemosensory function. Putative contact chemo‐mechanoreceptor sensilla were also observed on the proboscis and antenna. Longitudinal rows of alternated sensilla styloconica and basiconica are present on the distal part of the proboscis, and rings of sensilla chaetica are present at the antennal tip. The sensilla on these body parts may play different roles in the selection of an oviposition site.     

木瓜榕传粉榕小蜂雌蜂触角感器的分布和超微形态

为探索木瓜榕传粉榕小蜂Ceratosolen emarginatus寄主定位机制, 应用扫描电镜和透射电镜观察了其雌蜂触角感器的类型、 分布和超微形态。结果显示： 木瓜榕传粉榕小蜂雌蜂触角呈膝状, 由柄节、 梗节和11个鞭小节组成的鞭节组成, 第3鞭小节着生一坚固的脊骨突。触角上共发现7类11种感器, 分别为毛形感器、 刺形感器、 锥形感器（包括单孔形和多孔形）、 多孔板形感器（包括长形和圆形）、 腔锥形感器（分为3种类型）、 栓锥形乳突状感器、 角锥形感器。结合表面特征和内部结构, 锥形感器、 多孔板形感器、 栓锥形乳突状感器和腔锥形感器类型1为有孔型, 为化学感器; 无孔型的毛形感器和刺形感器是机械感器, 但腔锥形感器类型2和3为本体感器或湿热压力感器; 最为特异的为角锥形感器, 其厚壁无孔, 逆向触角主轴, 为该科昆虫所特有, 推测可防止传粉榕小蜂进入榕果时滑脱。这些结果将有助于理解木瓜榕传粉榕小蜂特异性行为, 并为下一步开展电生理研究, 揭示其信息化学物质利用和分配模式奠定基础。