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T biological control of the snails intermediate hosts of Schistosoma mansoni* is one of the accepted options to fight schistosomiasis . For the control of schistosomiasis , one strategy is based on the premise that resistant snails to parasite infection could be used as biological competition agents to replace existing susceptible snails in endemic areas. Therefore , the current studv was designed to investiuatejihe influence of] environmental iactors on copulation behaviour of Biomphalaria snails under various laboratory conditions^ These factors are : light, darkness , starvation , pH and association with nontarget snail species mseid^r to obtain information on the ecological conditions for reproduction of the resistant species. The data obtained showed that , copulation behavior was enhanced by different environmental factors and revealed the best modular system for snail reproduction . Itoaas-aBo noticed that, non-target snail species or the resistant snails affect crossing among the target snails .Moreover, resistant snails recorded more tolerance against abnormal environmental conditions. INTRODUCTION Outcrossing and self fertilization are common modes of reproduction in pulmonate gastropods ( Jarne & Stadler , 1995 ). Biomphalaria snails are simultaneous hermaphrodite with ability of selffertilization, however , in the presence of partner ( when paired ) cross 2 Abdel Hamid Z. Abdel Hamid et ah fertilization is preferred ( Vidigal et ah, 1994 & 1998 a & b ) . Selfing snails often have a lower fecundity than cross fertilizing snails (Bayomy & Joose , 1987 ) . Biological methods for control of freshwater snails were reviewed by Madsen (1992 ), who concluded that more emphasis should be put on searching for pathogens or microparasites as agent for control that can affect directly or indirectly on the intermediate snail hosts . These include bacteria , fungi, Protozoa , Amphibia and fish ( Slootweg et ah, 1993 ) , other competitor snails ( Abdel Hamid & Ali , 1998 ) and Muschovy ducks ( Cairina maschata) (Ndlela & Chimbari, 2000). Although physical, chemical, and biological factors have a significant effect on population dynamics, temperature, water chemistry, current speed, light, shade, snail 's leeding and association among species are of particular importance in the natural history of planorbid snails ( Brown , 1994 ) . Water chemistry includes calcium concentration , total dissolved chemical elements and oxygen. The densities of all snail species appear very low in salt water, high in medium water and somewhat lower in hard water ( Beadle, 1981 ). The level of oxygen may have an important influence on distribution within habitats. Certain environmental factors have pronounced effects on the susceptibility of snails to infection. For example, a decrease in the temperature has a substantial influence on the development of S. mansoni infection in B glahrata (Coelho & Bezerra , 2006 ) . However, Richards ( 1984 ) suggested that , the susceptibility of snails to infection is a hereditary character. Unfavourable conditions , however , can be caused by dense floating vegetation, preventing snail from reaching the surface when there is a shortage of dissolved oxygen ( Brown , 1994 ) . Snail hosts for schistosomes were reported for several generations in almost total darkness ( Appleton , 1978 ) . Shaded sites were unfavourable for Biomphalaria pfeifferi and shading by trees was suggested as a mean for controlling this snail. Dense shade beneath mats of floating vegetation is generally unfavourable for snails ( Nidifon & Ukoli, 1989 ). Most aquatic habitats contain rich microflora which , together with decaying vegeTable matter , provide the snails diet and are probably important in conditioning the habitat ( Malek , 1958 ) . Food in the habitat seemed to influence the reproduction of the snail hosts and their population dynamics. EFFECT OF ENVIRONMENTAL PARAMETERS ON CROSSING 3 PROCESS OF TARGET SNAILS TO S. MANSONI INFECTION MATERIAL AND METHODS Target and non-target snail species for Schistosoma infection ( Biomphalaria alexandrina, Biomphalaria glabrata , Lymnaea truncatula and Physa acuta ) were obtained from the Field ( Giza governorate , Egypt ) . Five liter glass aquaria were used in the experiment. To breed the snails , 500 ml beakers and some crystallizing dishes were used . Snail conditioned water ( SCW ) was used in'the aquaria and at weekly intervals , the aquaria were cleaned and their water changed . The snails were fed on fresh lettuce leaves supplemented with tetramin ( fish food ) . After careful selection on the basis of health , size and age , methods of separating schistosome resistant and susceptible strains from both B. alexandrina and B. glabrata were performed according to the method described by ZanottiMagalhaes et al. ( 1997 ) . Adult snails were exposed individually to 10 freshly hatched miracidia of S. mansoni-Egyptim strain obtained from Schistosome Biological Supply Project (SBSP),(Theodur Bilharz Research Institute , Egypt ) in vials containing 3 ml water for 3 4 hours . Each tested snail was returned and reared singly in a beaker containing 500 ml SCW . Snails were examined at 10 days post exposure and checked for infection with a binocular microscope . Snails with developing sporocysis were transferred to another flask and kept for cercarial emergence for 10 weeks post exposure . As described by Theron & Coustau ( 2005 ). snails that became infected are considered susceptible hosts and those which are not infected are traditionally determined as resistant. Selfing / out crossing : Both susceptible and resistant parent stocks of either B. alexandrina or B, glabrata snails were isolated and reared singly for selffertilization These self fertilized snails were used for breeding and for current studies as following: Different developmental stages ; juvenile ( J ) , adult ( Ad ) and senescent ( Se ) from either susceptible or resistant strains were obtained in successive generations by rearing snails singly each in 500 ml plastic container containing SCW . On the other hand , crosses among adult and senescent snails were performed. To confirm hybridization phenomenon within both B, alexandrina and B. glabrata , the following experiment was conducted . Four groups of snails each contains one B. alexandrina (either susceptible or resistant) and one B. glabrata (susceptible or resistant) were left to live in pairs in 4 Abdel Hamid Z. Abdel Hamid et ah clean plastic containers (500 ml). Crossing numbers and duration of each cross were recorded during 6 hours of pairing with 15 min. interval. The experiments were repeated 5 times. Effect of some environmental conditions on the snails reproduction: 1 Effect of light and darkness: a) Both B. alexandrina and B. glabrata , either susceptible or resistant were maintained individually for 24 hours in a clean plastic containers ( each of 250 ml ) containing sew in order to acclimatize the snails to environmental conditions before starting laboratory experiments. b ) The snails of each species and strain were divided into two groups: the first group was allowed to live in pairs under light, while the second one was put in darkness for 6 hours. Twenty four observations with intervals of 15 min. during 6 hours were recorded for each group and ihe number of crossing and the duration of each cross were recorded for each species, strain and stage. 2 Effect of starvation: The effect of starvation on reproduction of both susceptible and resistant within B. alexandrina and B. glabrata snails populations was examined according to the method described by 1'inheiro et ai ( 2001 ) . The first group was fed on fresh lettuce leaves supplemented with tctramin (fish food) [ingredient statement: fish meat, shrimp meat, aquatic plants, oat Hour yeast various vitamins, chlorophyll], while the second one was starved for 24 hours . 3 Effect ufpll : Adult stages of both B. alexandrina and B. glabrata snails were left to live in pairs under suiTable environmental conditions except pH levels. Six pairs of the acclimatized experimental snails were maintained in clean plastic containers, each contains 500 ml sew at different pH that ranged from 4 -9 . The numbers of crossing and duration of each cross were recorded with intervals of 15 min. for 6 hrs. . The experiment was repeated 3 times with exchanging the place of the containers. 4-lnfluence of non-target snail species on the ability of both B. alexandrina and B. glabrata to crossing: Each pair of snails ( either B. alexandrina or B. glabrata ) was left to live in clean plastic container containing 500 sew under the suiTable environmental conditions. Physa acuta and L. truncatula ( as nontarget snails to Schistosoma parasite) were added to live in the containers EFFECT OF ENVIRONMENTAL PARAMETERS ON CROSSING 5 PROCESS. OF TARGET SNAILS TO S. MANSONI INFECTION together with the target snail of B. alexandrina or B. glabrata . Numbers of crossing and the duration of each cross were recorded for 6 hrs. with intervals of 15min. Statistical analysis Statistical analysis of results was carried out using analysis of variance ( ANOVA) according to Campbell ( 1989 ) . RESULTS Factors affecting the crossing process : 1 Effect of light and darkness : The longest total crossing period was recorded under lighted conditions in groups of both B. alexandrina and B. glabrata as shown in Tables (1 & 2 ) .The resistant individuals at adult stage of each group has longest total crossing period which recorded 64.5 and 83.3 min. for B. alexandrina and B. glabrata respectively .However , the susceptible forms at senescent stage had the shortest total crossing period which recorded 10.4 and 14.7 min. of B. alexandrina and B. glabrata respectively. It was also observed that , B. glabrata was more tolerant to darkness than B. alexandrina , since there was no recorded crossing period in most B. alexandrina groups in the darkness . The longest c

EFFECT OF SOME ENVIRONMENTAL PARAMETERSON CROSSING PROCESS OF TARGET SNAILS TO SCHISTOSOMA MANSONI INFECTION