Abstract

The main aim of this work was to determine the consumption capacity of five aquatic insects (as predators) on four species of medical snails (as preys) tested under four values of pH at a constant and controlling temperature in the laboratory. The predators were represented by adults of two hemipterous species (Limnogeton fieberi Mayr, Sphaerodema urinator Duf.) and three nymph odonatous species (Anax imperator Leach, Crocothemis erythraea Brulle and Ischnura pumilio Charp.). Moreover, the four water-pH values were 5, 7, 9, and 11 at 30°C. On the other hand, the four prey of the medical snails were Bulinus truncates Audouin, Biomphalaria alexandrina Ehrenb, Cleopatra bulimoides Olivier and Melanoides tuberculata Muller. All of individual fauna were collected from the River Nile in Qena. The acidic media were adjusted as a mixture of three acids phosphoric acid acetic acid boric acid. In contrast, the alkalinic solution was prepared by sodium hydroxide. The results illustrate that, the maximum predation occurred under 7 pH and 9 pH at 30°C regardless of the laboratory conditions. It appeared that Bulinus truncates was highly preferable snail species to these predators. Biomphalaria alexandrina which is the intermediate host of Schistosoma mansoni Bilharz, may be the lastly preferable snail species to these predators. The belostomatids (Limnogeton fieberi and Sphaerodema urinator), and the odonats (Anax imperator, Crocothemis erythraea and Ischnura pumilio), could be the highest successful predators on the harmful snails (Bulinus truncates, Melanoides tuberculata,  Biomphalaria alexandrina and  Cleopatra bulimoides). Therefore, its use should be encouraged to be reared in large numbers and then released in the natural places of snails under 7 to 9 range values of water pH.

Key words: Bulinus truncates, Biomphalaria alexandrina, Schistosoma mansoni, The belostomatids (Limnogeton fieberi and Sphaerodema urinator), and the odonats (Anax imperator, Crocothemis  erythraea and  Ischnura pumilio), predation Odonata,  Hemiptera, snails  and  pH values.