The structure of bimodal chemo-, thermo-, and hygroreceptive sensilla on the antenna of Locusta migratoria

Abstract

Coeloconic sensilla on the antenna of Locusta migratoria were investigated electrophysiologically, labeled and then examined under the scanning or transmission electron microscope. They can be categorized into two main morphological types: 1) sensilla with wall pores and two concentric cuticular walls (wp-dw sensilla), and 2) sensilla lacking wall pores (np-sensilla). Hygroreceptors were observed only in np-sensilla. Olfactory receptors were observed in wp-dw sensilla, but not in np-sensilla. Cold-sensitive units were fund in both types. Wp-dw sensilla with a cold-sensitive unit also manifest a fatty acid olfactory receptor. This cold-sensitive unit appears to be less sensitive to drops in temperature than the cold receptor combined with hygroreceptors in np-sensilla. Recordings from both types revealed up to three or sometimes four units that could be distinguished on the basis of impulse amplitude. The number of np-sensilla on each antennal segment ranges from 0 to 6. These sensilla are pegs 4--5 micrometer long with a terminal swelling. The dendritic outer segments of two sensory cells fit tightly into these pegs. The dendrite of the third sensory cell ends at its base. All three are up to 1 micrometer thick, unbranched, and densely filled with microtubules. The cuticular wall and socket of the peg are characterized by (1) an electron-dense inner layer surrounding the dendrites and continuous with electron dense clusters at the base of the peg, and (2) clefts in the cuticle at the insertion of the peg. The present observations favor the hypothesis that insect sensilla combining the triad of moist air, dry air and cold receptors generally lack pores. Specifically, though still alternative roles in stimulus transduction can be suggested for substructures demonstrated in the present and previous electron microscopic investigations.

Electron microscope study on workers antennae and sting lancets of three subspecies of honey bee Apis mellifera L. (Hymenoptera: Apidae) and its bearing on their phylogeny

“…The coeloconic sensillum described in this study similar to that observed in L. migratoria (Altner et al, 1981) and the basiconic sensillum of P. americana are reported to possess stimulus-conducting pores similar to those of olfactory sensilla (Steinbrecht, 1969;Altner et al, 1973, 1977and Yokohari et al, 1975.…”

“…This is explained as hygroreceptors of honey bees were shown to respond to a deformation of the sensillum, similar to that shown for cockroach hygroreceptors (Yokohari, 1978). Sensilla of similar structure have been identified as hygro-and thermoreceptors (Altner et al, 1978;Tichy, 1979 andAltner et al, 1981). Thermoreceptors of the cockroach are found in both the capitular sensillum (Yokohari et al, 1975) and in the grooved sensillum (Altner et al, 1977 andYokohari, 1983).…”

“…Other investigators described similar structure to these sensilla to be poreless as in Carausius morosus (Altner et al, 1978); P. americana (Schaller 1978;Yokohari, 1978; L. migratoria (Altner et al, 1981) and in Leucophaea maderae (Schaller, 1982). The outer cavity of the sensillum communicates directly with the exterior (Schaller, 1978).…”

“…Some studies have shown that the hygroand thermoreceptors can be identified electrophysiologically in structures morphologically similar to olfactory sensilla (Steinbrecht, 1969;Altner et al, 1973 andAltner et al, 1977). Many studies indicate that these receptors are found in the poreless sensilla (Yokohari et al, 1975Altner et al, 1978Altner et al, , 1981Yokohari, 1978Yokohari, , 1981Schaller, 1978.…”

“…On the other hand, Altner et al (1981) found the cleft at the base of the cuticular apparatus associated with deposits of electron-dense material in the poreless coeloconic sensillum of L. migratoria, and discussed its possible role in stimulus transduction. In the present study, the centro-apical part of the coeloconica sensillum in worker honey bee, and may be plugged by electrondense node, is found in all poreless hygro-and thermoreceptive sensilla.…”