Deficiency of gustatory sensitivity to some deterrent compounds in "polyphagous" mutant strains of the silkworm, Bombyx mori

Abstract

Sawa-J, CSJ02 and N601 x C601 are selected mutant strains of Bombyx mori, which grow on various artificial diets or temporarily ingest various plant leaves. To examine the mechanisms mediating diet breadth of caterpillars, gustatory spike responses of the silkworms, called 'polyphagous" strains, were compared with normal strains, N137 x C146 and C02. There were notable differences in their feeding habits and in their sensitivity to salicin in deterrent cells in the maxillary medial styloconic sensilla and the epipharyngeal sensilla. By contrast, the deterrent cells of all strains responded similarly to strychnine nitrate in a dose-dependent manner. In additional comparisons of Sawa-J and N137 x C146, Sawa-J maxillary deterrent cells were significantly less sensitive to phloridzin, amygdalin and arbutin, but responded to some alkaloids and 20-hydroxyecdysone with similar or even higher firing rate. These results suggest that the deficiency of the sensitivity to some deterrent compounds on the deterrent cell of the polyphagous strains may be caused by mutant genes and affects the diet breadth of caterpillars.

Ligand carrier protein genes expressed in larval chemosensory organs of Bombyx mori

“…Two B. mori strains, N137  C146 and Kinshu  Showa, were reared with the Silkmate artificial diet (Nosan Corporation, Japan) at 25 C. The former strain was used for the electrophysiology experiments of the gustatory sensilla reported in previous studies (Asaoka, 2000;Asaoka and Shibuya, 1995).…”

“…Morin, b-sitosterol, n-hexacosanol and n-octacosanol from insoluble or slightly soluble fractions have been shown to stimulate feeding Hamamura et al, 1962;Mori, 1982). However, several o-glycosides, alkaloids, and lactones in non-host plants were recognized by the deterrent cells on the maxillary galea, suggesting that these compounds may act as tastants to avoid feeding (Asaoka, 2000). Amputation of the maxilla from the silkworm expanded food preference to include non-host plants, such as cabbage and cherry leaves (Torii and Morii, 1948;Ito et al, 1959).…”

Molecular neurophysiology of taste in Drosophila

“…The silkworm, for example, is a monophagous insect, but one mutant strain has a wide range of diet. The deterrent cells in this mutant were found to have lost their sensitivity to some of the deterrent compounds tested [44]. In Manduca sexta, although dietary exposure to caffeine desensitizes deterrent cells to caffeine, dietary exposure to salicin or aristolochic acid does not desensitize the deterrent cells to those compounds [45].…”

Temporal Coding Mediates Discrimination of “Bitter” Taste Stimuli by an Insect

“…They show that M. sexta can discriminate compounds that are detected by the same bitter-sensitive taste cells, as long as the compounds generate distinct discharge patterns. Given that at least one other species of caterpillar (e.g., Bombyx mori) has bitter-sensitive taste cells that generate different discharge patterns in response to different plant compounds (Asaoka, 2000), it is likely that the discrimination phenomenon described herein is more taxonomically widespread.…”