Tarsal Hairs Research Articles

Salt-Sugar Interactions in Tarsal Taste Hairs of the Blowfly, Calliphora Vicina Robineau-Desvoidy

With adaptation taken as criterion, it was found that in terminal tarsal taste hairs of Calliphora vicina NaCl and sucrose can stimulate the same sense cells. This result cannot be satisfactorily explained as a secondary effect of water or by the proximity of the dendrites in the taste hairs. It supports, albeit indirectly, the hypothesis that tarsal taste discrimination in the blowfly is based on a central evaluation of relative impulse frequencies from a number of stimulated cells per sensillum.

Taste receptors of the mosquito Anopheles atroparvus Van Thiel.

Taste receptors of Anopheles atroparvus Van Thiel arc located on the labella, tarsi, and probably within the cibarium. All the longer hairs on the outer surfaces of the labella are chemosensory. Stimulating these hairs with water or 1 M sucrose evokes several feeding responses. Labellar hairs have blunt tips, arise from sockets and are 26–48μ in length. Sensilla trichodea are present on the inner surfaces of the labella and are probably chemosensory. These sensilla are 16μ in length, have sharp tips and occur in a row of 3 on each labellum. Tarsal hairs of the blunt type are present on all segments. These are sensitive to water and 1 M sucrose and mediate the proboscis response. By means of the unsheathed stylets technique, evidence was obtained for receptors posterior to the proboscis, probably in the cibarium.

Tarsal Taste Discrimination in the Blowfly, Calliphora Vicina Robineau-Desvoidy

This paper deals with the problem of the specificity of the sense cells in terminal tarsal taste sensilla on the forelegs of the blowfly, Calliphora vicina Rob.-Desv. (= Calliphora erythrocephala Meigen), in relation to the discrimination these flies are capable of making, as judged by their behavioural responses, between water and weak sugar (sucrose) solutions. First, electrophysiologically recorded responses to pure water are described. As many as three receptor cells in the blowfly terminal tarsal taste hairs can be stimulated by water. Next, the reactions of sense cells to both water and weak sucrose solutions are analysed, showing that up to concentrations of several hundredths of Molar sucrose the responses are indistinguishable from those to water. It is therefore surmised that water and sucrose stimulate the same sense cells in these taste hairs, which raises doubts concerning the specificity generally ascribed to these cells. These doubts are confirmed by the results of experiments showing that water and sucrose adapt, and therefore stimulate, the same sense cells. This finding implies that some mechanism other than specificity of sugar- and water-sensitive cells is required to explain the behavioural distinction shown by blowflies between water and sucrose. Before an alternative was formulated, the comparability of the proboscis response in fixed and in free-moving flies was discussed, and also to what extent single-hair stimulations (such as are usually applied in electrophysiological methods) are comparable with multiple-hair stimulations (as usually applied in behavioural experiments). Both questions could be answered satisfactorily and consequently an alternative for cellular specificity is given. It involves the concept that discrimination occurs in the intact animal on the basis of the input from many tarsal hairs, the cells of each of which respond with different relative impulse frequencies to stimulation with water and to stimulation with weak sucrose solutions.

Structure and function of tarsal sensilla in the spider Araneus diadematus

AbstractThe tarsal hairs of the spider Araneus diadematus (Clerck) were examined by light and electron microscopy and for surface structures with a scanning electron microscope. Three different types of hairs could be found: (1) straight, sharp‐pointed hairs, (2) serrated bristles, (3) curved, blunt‐tipped hairs. The third type of hair shows all typical features of chemosensitive hairs, such as multiple innervation and an open tip, and was not included in the present study. The firs two types share the same histological characteristics of having the dendrite of one bipolar neuron attached proximally to the hair base. Also, most of the fine structural details, such as the presence of an extracellular space, a scolopale and a tubular body, correspond to tactile hairs as described in insects. However, in Araneus diadematus the nerve terminal has a three‐lobed structure and seems to be fastened to the socket cuticle which is not known from other arthropods. The five or six serrated bristles at the tip of the tarsus, together with the middle hook, grasp the thread. This relationship was suggested by Nielsen ('31) and was verified by means of the scanning electron microscope. The importance of this mechanism for grasping the thread was demonstrated in ablation experiments with quantitative evaluation of changes in web geometry.

Tarsal and Labellar Taste Hairs of Calliphora Vicina Robineau-Desvoidy: Location, Sensitivity To NaCl

In both males and females of the bluebottle, Calliphora vicina, the labellar hairs are arranged in a systematic pattern, so that the hairs can be identified individually. The hair patterns on the two labellar lobes are mirror images of each other. The relatively long hairs of two of the labellar rows-the and adoral row-and the long tarsal hairs on prothoracic legs have a chemoreceptor function. The responses elicited in these hairs by 1/2, 1/4, 1/8, and 1/16 M NaCl were compared with each other. The number of sense cells active varied from 0 to 3 in all three groups of hairs. Two types of cells were recognized: P cells and N cells, responding positively and not or negatively, respectively, to the change from 1/4 to 1/2 M. In aboral hairs 0, 1, or 2 P cells were found; in adoral and tarsal hairs only 0 or 1 P cell was present. The sensitivity of these cells to NaCI, tested at 1/2 M, was highest in aboral hairs, intermediate in tarsal hairs, and lowest in adoral hairs. Tarsal hairs contained 0, 1, or 2, aboral hairs 0, 1, 2, or 3 and adoral hairs 1 or 2 N cells. Adoral N cells appeared to respond most sharply to changes in NaCl concentration. The number of P and N cells to a hair varied independently of the type of hair within a given group. In all three groups of hairs the combination 1P + 1N was most frequently found. For both P and N cells variation in response between topographically the same hairs (on opposite sides of the body or in flies) is as great as the variation between different hairs.

Behavioral studies of inhibition and integration in the mosquito Culiseta inornata (Williston).

AbstractA study was made of the interaction in the central nervous system of sensory input arising from the simulatneous application of opposing stimuli to receptors on the tarsi and labella of the mosquito. Stimulating chemosensory hairs on the tarsi with 5 M NaCl failed to inhibit the labeller response to sucrose at concentrations above 0.125 M. At lower sucrose concentrations there was a decrease in the number of mosquitoes responding. The application of 5 M NaCl to the tarsal receptors elevated the labellar threshold for sucrose in all subjects tested. This influence of the salt was expressed whether acting on the tarsi in an ipsilateral or contralateral manner. Stimulating the tarsal hairs with 2 M sucrose resulted in a labellar response to NaCl at concentrations of 0.50 M and lower. Ordinarily NaCl is rejected at all concentrations by this mosquito. Evidence was obtained which indicated that the labellar response to NaCl was mediated by the water receptor rather than by the salt receptor.

Responses of tarsal hairs of the bluebottle, Calliphora erythrocephala Meig., to sugar and water

Using a specially designed high-input impedance a.c. preamplifier it was possible to record the responses of tarsal chemoreceptive hairs of Calliphora erythrocephala Meig. to pure sucrose solutions (0·5 M, 0·1 M, and 0·02 M) and water. Sugar always evoked two types of impulses of which the smaller one probably originated in a water receptor, whereas the larger one was fired by a cell sensitive to sugar. In about 90 per cent of the water stimulations two types of spikes were recorded. The larger of these spike types was presumably fired by a water receptor. The possibility that the smaller type of water spike was discharged by a cation or anion receptor, or represented spontaneous activity in any of the sense cells at the base of the tarsal hairs, is discussed. In the remaining 10 per cent of the water stimulations we probably recorded spikes of a water cell only.

Sensory Hairs with Permeable Tips on the Tarsi of the Yellow-Fever Mosquito, Aedes aegypti

The female yellow-fever mosquito, Aedes aegypti (L.), possesses approximately 100 tarsal hairs which stain at the tip when dye is applied to the external surface of the insect. The male has about 60 of these hairs. In both sexes the largest number occurs on the prothoracic tarsi and the smallest on the metathoracic. None were found elsewhere on the legs. The location and distribution of the hairs correlates well with the results of experimental work reported by earlier authors in which the sensitivity of the legs was tested to a variety of salt and sugar solutions. Little doubt now remains that the hairs with stainable tips are the tarsal gustatory receptors of the mosquito.

Initiation of spike potentials in contact chemosensory hairs of insects. II. The effect of electric current on tarsal chemosensory hairs of vanessa.

Initiation of spike potentials in contact chemosensory hairs of insects. II. The effect of electric current on tarsal chemosensory hairs of vanessa.

Bryobia arborea n. sp. and Morphological Characters Distinguishing It from B. praetiosa Koch (Acarina: Tetranychidae)

The clover, or brown, mite, Bryobia praetiosa Koch, was described in 1836 from specimens collected an shrubbery in Germany. The systematics of the species is complex and confusing. By 1838, Koch had described four species in the genus Bryobia but he preserved no type specimens and his descriptions do not agree with his illustrations (7, 12). Subsequent workers either placed Koch's species in synonomy nor described new species. Two species, speciosa Koch and ribis Thomas, have created the most controversv. B. speciosa was accepted as valid by Koch, Berlese, Canestrini and Fanzago, ind Oudemans, but rejected by von Hanstein and Trägårdh (2, 12). The gooseberry mite, B. ribis, was recognized as a valid species by Thomas and von Hanstein but Oudemans and Trägårdh placed it in synonomy with B. praetiosa (12). Further confusion was caused by the descriptions of additional new species of Bryobia and by descriptions of immature stages of B. praetiosa (8). The following taxonomic characters used by early acarologists in describing species of Bryobia have since been considered too variable for distinguishing species: number of femoral and tarsal hairs on the foreleg, body size, concavity of dorsum, and size and shape of cephalothoracic plate (7, 8, 12). Consequently, taxonomists have been at a loss to interpret Koch's original descriptions and subsequent redescriptions became inevitable. Because of the lack of morphological distinctions the modern trend has been to group all previously proposed species into one valid species (7, 8). As a result, 20 synonyms are now recognized for B. praetiosa (8).