ユスリカ幼蟲の造巣行動
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概要
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While the nest of Chironomus-larva is normally a single tube of slightly bended kind, its shape is variable according to the size and amount of sand-grains used in nest-building. It the grains are plentiful, the larva instantly makes an inroad upon them; but if not so plentiful, it holds the grains with the prothoracic appendages and the mouth part, and sticks them together with a thread-like secretion from the salivary gland to make a tube around its own body. It makes first the middle part of the tube and then the anterior and the posterior parts respectively, so that a complete nest-tube of this form has no preliminary sheath or jugendlicher Rohrteil, which is found in the case of the caddis-fly larva. The present form is able to nest with the sand-grains of different sizes, but the larva tends to become difficult or impossible to nest, it the sand is given in small amount and all the grains are too large to be held between the prothoracic appendages and the mouth part. The time required for building nest varies according to the size and amount of the sandgrains. The larva is also able to make nest with powder of carbon, grass leaves, pine-needles, pieces of paper and others, when put into glass vessels where it lives. But the Chironomus-larva is unable to cut off these foreign materials as seen in Trichoptera-larva. On the occasion of pine-needles cut off into pieces one centimetre long, about eighty per cent. of the experimental larvae made an incomplete nest with two or three needles which were glued together and arranged generally parallel to the long body axis. In the case of grass leaves with the same size, the larvae easily built the nest and the materials were arranged in much the same manner as in the former case. When the pine-needles or the grass leaves were cut off into pieces about 3mm long, and given to them respectively, the nest formed with the former material appeared a very rude structure, while that of the latter resembled its usual nest. In the case of paper, if cut off into small and irregular pieces, the nest-building easily took place, but if cut off into large pieces (3mm. sq.) it did not take place. Whenever any of these foreign materials is mixed together with some amount of small sand-grains, the larva makes nest by gluing it together with the sand grams. The Chironomus-larva seems to prefer to have some special kind of building materials, but this preference is not so remarkable as in the case of a caddis-fly larva. The present larva makes nests at temperatures from 25 to 35℃. Miall ('22) considers the negative phototaxis as the motive factor of nesting habit in Chironomus-larva. This opinion seems not to be true, for the larvae make their nests even in dackness, and also the newly hatched larvae, when they are of the positive phototaxis, are ready to make nests as in the second instar, when they first become negative, or in the later instars. Oishi ('35) assumes that the motive factor is food items (diatoms, algae etc.) which happen to adhere to sand grains. But this also does not agree with the results of my experiments with different kinds of materials for its nesting abilities. From other analytical studies on the nesting behavior, I found out that the Chironomus-larva develope a remarkable positive thigmotaxis. This fact leads me to consider that the thingmotaxis probably is the motive of nesting behaviour.
- 1942-10-15