Corixids are found abundantly in freshwater habitats, usually several species living together. The competition between these species was investigated. \ud Corixids are generally believed to be algal and detritus feeders, but are shown to be predators. Observation of feeding behaviour and examination of feeding structures of British and foreign species representing five of the six subfamilies have shown that most corixids feed on small swimming animals and animals dug and scraped up from detritus. Some species, however, are specialised for feeding only on large swimming animals, e.g. Cymatia or only by digging up animals, e.g. Neocorixa. In contrast, to other predatory aquatic heteroptera, the small prey of corixids is held on the short, wide rostrum and over the labial orifice. The short, simple stylets have a unique interlocking and sealing mechanism involving the cuticular protein resilin, A mode of functioning is suggested for the foodpump and the significance of the structural variation is discussed.\ud The freshwater habitats of Leicestershire, and in particular ponds, the commonest habitat, show considerable seasonal variation in the plant life and water level, as well as changes caused by trampling and pollution by cattle. An investigation into the fluctuations of water temperature in ponds showed that for example on a sunny summer's day 25 to 30 degrees centigrade is reached in very shallow water.\ud Competition between the closely related and structurally similar species of the corixinae inhabiting the same water body is reduced by differences in size and therefore in size of prey, differences in feeding behaviour and the areas of the habitat occupied and by variation in the occurence and duration of ovarian, embryonic and nymphal development.\ud Some corixid populations may be more efficient than others because of a greater number of females than males, or a larger proportion of flightless individuals. Some species are more efficient because they are more resistant to attack by the ectoparasitic Hydrocarina which is shown to reduce the fercundity of the over wintering females
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