Some Effects of Tube Shape on the Feeding of Chironomus plumosus L. (Diptera: Chironomidae)

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Abstract
Feeding in the 3 types of tube constructed by larvae of C. plumosus L. was studied in the laboratory. U-shaped, J-shaped and horizontal tubes, normally located in different parts of the lake bottom, were imitated in 2 mm diameter black polythene tubing. Two tube types were compared at a time, replicates of each type being arranged in the same aquarium so as to expose larvae to identical conditions, apart from tube shape, during each experiment. Peat, homogenized to produce the desired range of particle sizes, were used as a food. Larval feeding was assessed by the measurement of particle sizes selected and by the rate at which fecal pellets were produced. These 2 criteria were taken to reflect method of feeding and feeding efficiency, respectively. Each tube imposed a characteristic type of feeding on the larvae inhabiting them. U-tubes were particularly suited to suspension feeding, while horizontal tubes, although at least as efficient, were better suited to deposit feeding activities. J-tubes were associated with deposit feeding and lower efficiency. Because of the feeding patterns characteristic of each tube shape, larvae inhabiting tubes which occur together in the field, like the U- and J-tubes in the lake center, will not be in direct competition for food. The feeding characteristics associated with each tube type also enable larvae to make the best use of food locally available in the field. For example, the horizontal tubes at the lake perimeter are especially suitable for deposit feeding in a habitat where benthic diatoms predominate. In the lake center where suspended material is more abundant, filter feeding is imposed by U-tubes.

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