الفهرس 
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Abstract
The aim of the present study was using the Egyptian fresh water predatory insects which may act as biological control agents for snails the intermediate hosts for some parasitic diseases of human and domestic animals.
In general, the biological control is very important method to control the harmful insects or invertebrate animals as snails of Bilharzias and fascioliasis. So, The present study is an attempt to demonstrate number of predators deployed in the ponds and marshes in the governorate of Qena to determine the efficiency of predators under laboratory conditions or other factors such as the temperatures and pH values. Therefore, Five aquatic predators were collected from the field and their efficiency as predators of snails was studied under laboratory conditions. The predators under investigation included: two species of Hemiptera adults Limnogeton fieberi Mayr and Sphaerodema urinator Duf. (Belostomatidae), and nymphs of three species of Odonata, Anax imperator Leach (Aeshnidae), Crocothemis erythraea Brulle (Libellulidae) and Ischnura pumilio Charp. (Coenagrionidae),which they dtudied against different types of snails (preys). Bulinus truncates Audouim (Thiaridae) which it is the main intermediate host of Schistosoma haematobium in Egypt and Middle East countries, Biomphalaria alexandrina (Planorbidae), acts as an intermediate host of Shistosoma mansoni in Egypt. Cleopatra bulimoides (Thiaridae), acts as intermediate host for Gastrodiscus aegypticus and Prohemistomum vivax, Melanoides tuberculata (Thiaridae), as first intermediate host for Lecithodendrium pyramidum which has the adult stage in bats.
The data of these experiments were analysis by the program (statistical package for social science) (SPSS).
The First Experiment
l.Consumption capability of insects (predators)on different types of snails under laboratory and five constant temperatures (°C):
In the present work, the consumption capability of the five predators were examined on four snail species (as preys), Bulinus truncates Audouin, Biomphalaria alexandrina Ehrenberg, Cleopatra bulimoides Olivier and Melanoides tuberculata Muller under five constant degrees of temperatures (20°C, 25°C, 30°C, 35°C and 40°C) in addition to room temperature. Regarding to a comparison between the consumed snails, the maximum consumed number of the preys was represented by Bulinus truncates, to all types of predators, while the minimum number was observed in case of the snail Biomphalaria alexandrina to all types of predators. Except, Limnogeton fieberi which the minimum number was observed in case of the snail Coleopatra bulimoides. These results were confirmed statistically as highly significance at P>0.1% probability level of error for predation of the present predators.
Limnogeton fieberi (the only insect) prefer the snail of Biomphalaria alexandrina after the snail of Bulinus truncates at all experiments.
On the other hand, the current study showed highly consumption of the preys under both 30°C and 35°C. In contrast, the lowest number of consumed snails was under 40°C, and the consumption rate was gradually higher with the increase of temperature from 20°C to 35°C., and had the ability on consumption the different types of snails and tolerate the high temperature. Limnogeton fieberi , the best predator at this experiment which achieved the best results, and the lowest results with Ischnura pumilio. These results indicated that the all predators were active in the different temperatures and had the ability on consumption the different types of snails and showed the important role can be played by these predators under investigation in controlling these harmful snails.
The Second Experiment
2.Consumption capability of insects (predators)on different types of snails under laboratory and four values of pH:
In this experiment, the effect of low and high values of pH on consumption capacity of aquatic insects (predators) on the snails (preys) were studied. The predators under investigation examined against four types of snails (preys), under laboratory conditions and four values of pH (5,7,9 and llpH). The incubator to control was used to the temperature at (30°C), which it was suitable degree to give the best consumed snails. So, the experiments was prepared and placed in incubator (30°C) for ten days. Regarding to a comparison between the consumed snails, the maximum consumed number of the preys was represented by Bulinus truncates, to all types of predators, while the minimum number was observed in case of the snail Biomphalaria alexandrina to all types of predators. Except, Limnogeton fieberi which the minimum number was observed in case of the snail Coleopatra bulimoides. These results were confirmed statistically as highly significance at P>0.1% probability level of error for predation of the present predators.On the other hand, the current study showed highly consumption of the preys under both 7pH and 9pH. In contrast, the lowest number of feed snails was under 1 IpH value.Limnogeton fieberi, the best predator at this experiment which achieved the best results, and the lowest results with Ischnura pumilio,Thereby, the result indicated that the predator L. fieberi had highly predatory efficiency of consumption capacity under the different pH values, while the lowest predatory efficiency of consumption capacity was Ischnura pumilio. In addition, these results indicated that the maximum predation under 7pH value regardless the laboratory result. These results indicated that the all predators were active in the different pH values and had the ability on consumption the different types of snails.
The third Experiment
Prey preference
The experiment was conducted in the laboratory to study the preference of the five predators on the four types of snails which exist in its natural habitat/The consumption capability of the predators in non choice experiment under laboratory conditions was determined.Thereby, the result indicated that when all predators were provided with equal numbers of the snails species recorded above, the first preferred for attack was directed towards Bulinus truncates. However, the tested preys could be arranged descendingly according to the preference as follow: Bulinus truncates, Biomphalaria alexandrina, Melanoides tuberculata and Cleopatra bulimoides. The experiment was repeated again in the laboratory to study the preference of these predators on the three types of snails, Biomphalaria alexandrina, Melanoides tuberculata, and Cleopatra bulimoides, after isolated the preference snail Bulinus truncates. however, the three tested preys could be arranged descendingly by Limnogeton fieberi according to the preference as follow: Biomphalaria alexandrina, Melanoides tuberculata and lastly Cleopatra bulimoides. But, the three tested preys could be arranged descendingly by the other four predators according to the preference as follow: Melanoides tuberculata Cleopatra bulimoides and lastly Biomphalaria alexandrina. The Belostomatidae (Limnogeton fieberi and Sphaerodema urinator), and Odonata (Anax imperator, Crocothemis erythraea and Ischnura pumilio),WQTQ active as predators of harmful snails (Bulinus truncates, Melanoides tuberculata, Biomphalaria alexandrina and Cleopatra bulimoides) thus they can be reared in large numbers and then released in the breeding places of snails to achieve biological control of these pests. So, the results of such studies would enable us to formulate the biological control program in a more effective way. Finely, The current study hope that this study along with the aforementioned studies provide a better understanding of this promising biocontrol agent and the best conditions for rearing and releasing of this important predator of snails to conserve (nature and human health).