Hansen K, Wacht S, Seebauer H, Schnuch M
Zoological Institute, University of Regensburg, Germany.
Ann N Y Acad Sci. 1998 Nov 30;855:143-7. doi: 10.1111/j.1749-6632.1998.tb10556.x.
For studies of insect taste the sensory cells of labellar taste hairs on the proboscis of calliphorid flies (e.g., Phormia) are preferred objects. Three sensory cells are electrophysiologically characterized: a sugar cell, a water cell and a cation or salt cell. Studying hairs on legs and proboscis of other families of flies we recently obtained results that extend our knowledge about the complexity of food detection in flies. The hoverfly Eristalis tenax (Syrphidae family) feeds on nectar and pollen of flowers. While nectar is recognized via the sugar cell, the so-called salt cell is activated by low concentrations of a water-soluble substance in extracts of pollen. From several tested pollen constituents only proline, an essential amino acid for pollen germination, stimulates the salt cell. The discrimination between salt and pollen in behavioral tests can be explained by the finding that the water cell remains active in the presence of pollen extract, but is inhibited by salts. Obviously the water cell activity is involved in the feeding decision. We already described a similar situation in Phormia, where the salt cell activity only elicits feeding behavior when the water cell is active too. In contrast to the sugar cells of species of flies studied so far the sugar cell of the house fly Musca domestica (Muscidae family) is highly sensitive to lactose, a disaccharide (beta-galactoside (1-->4) glucoside) naturally occurring only in the milk of mammals. Thus sugar spectra adapt to special environmental food situations. The fifth tarsomere of the forelegs of Musca bears besides two D-hairs 46 hairs of the B-type. The B-hairs are functionally not uniform in contrast to their structural identity. Only two hairs, the 'water hairs,' contain a water cell beside a spontaneously firing cell, but no sugar cell. Other examples of diversity are hairs that contain apart from the classical sugar cells, additional cells which react either to p-nitrophenyl-beta-galactoside, but not to the chemically related lactose, or to p-nitrophenyl-alpha-glucoside. Therefore the rule established for the labellar taste hairs that each hair type contains the same physiological equipment of sensory cells, does not hold for the taste hairs of the legs.
对于昆虫味觉的研究，丽蝇科苍蝇（如伏蝇属）喙上唇叶味觉毛的感觉细胞是首选对象。通过电生理学方法可区分出三种感觉细胞：一个糖细胞、一个水细胞和一个阳离子或盐细胞。我们研究了其他蝇类科的腿部和喙上的味觉毛，最近获得的结果扩展了我们对苍蝇食物检测复杂性的认识。食蚜蝇（食蚜蝇科）以花蜜和花粉为食。花蜜通过糖细胞被识别，而所谓的盐细胞则被花粉提取物中低浓度的水溶性物质激活。在几种经过测试的花粉成分中，只有脯氨酸（花粉萌发所必需的氨基酸）能刺激盐细胞。行为测试中对盐和花粉的区分可以通过以下发现来解释：水细胞在花粉提取物存在时保持活跃，但会被盐抑制。显然，水细胞的活性参与了进食决策。我们已经在伏蝇中描述过类似情况，即只有当水细胞也活跃时，盐细胞的活性才会引发进食行为。与迄今为止研究的蝇类物种的糖细胞不同，家蝇（蝇科）的糖细胞对乳糖高度敏感，乳糖是一种仅天然存在于哺乳动物乳汁中的二糖（β-半乳糖苷(1→4)葡萄糖苷）。因此，糖谱会适应特殊的环境食物情况。家蝇前腿的第五跗节除了两根D型毛外，还有46根B型毛。B型毛在功能上并不一致，尽管它们在结构上相同。只有两根毛，即“水毛”，除了一个自发放电细胞外还含有一个水细胞，但没有糖细胞。多样性的其他例子包括除了经典的糖细胞外，还含有对β-硝基苯基-β-半乳糖苷有反应但对化学相关的乳糖无反应的额外细胞，或者对β-硝基苯基-α-葡萄糖苷有反应的细胞。因此，为唇叶味觉毛确立的规则，即每种毛类型都包含相同生理装备的感觉细胞，并不适用于腿部味觉毛。
