Effect of the plant Azolla pinnata on survival, growth rate, fecundity and hatchability of egg-masses of Biomphalaria alexandrina snails

Data indicated that Azolla pinnata plants variously reduce the growth rate of Biomphalaria alexandrina snails expressed as net increase in shell diameter (direct or indirect exposure). The plant density played an important role in this respect. The higher the plant density was the lower the growth rate and vice versa. Too, indirect exposure of newly hatched B. alexandrina resulted from exposed treated eggs reduced the growth rate of these snails. Data revealed that direct and/or indirect exposure to the abnormal high density (50,000 plants/L) resulted in complete kill of B. alexandrina snails after two weeks from continuous exposure. Snails exposed directly to Azolla at 50,000 and 25,000 plants/L failed to lay eggs. On the other hand, sanils exposed to 10,000 plants/L laid few eggs, resulted in low reproductive rate (57.94) compared with unexposed ones (110.6). The same trend of results was recorded with hatchability of Biomphalaria eggs.

The influence of self-fertilization performance and copulation behaviour in reproduction by cross-fertilization in groups of Biomphalaria tenagophila (Mollusca, Planorbidae)

The following hypotheses were tested for groups of simultaneous hermaphrodites Biomphalaria tenagophila: (a) snails that have low reproductive success during the process of self-fertilization do not increase their reproductive success after the end of grouping; (b) the copulation behaviour and the presence of one snail whose eggs have a low viability rate influence the partner's reproductive success by cross-fertilization. Groups were constituted by a homozygous pigmented snail and two albinos: one with a viability rate higher than 70% ("good reproducers") and the other less than 10% ("bad reproducers"). All pigmented snails had viability rates higher than 70%. The "good" and "bad" reproducer albino snails had similar copulation behaviour. However, after the end of grouping, the "bad reproducers" continued to have viability rates less than 10% over 30 days. In 100% of the cases that pigmented snails copulated (performing either a male role or simultaneously male and female roles) exclusively with "good" reproducer albinos, they presented high reproductive success (producing, on average of 8.4 pigmented embryos/egg-mass). However, in 100% of the cases that pigmented snails copulated with both partners, the "good" reproducer albino snails produced none or very few embryos (the highest average was 2.2 pigmented embryos/egg-mass). Therefore, the production of viable embryos by cross-fertilization was more influenced by self-fertilization performance than by copulation behaviour. The presence of a snail whose eggs have a low viability rate could decrease their partners reproductive success.

[Relationship between pathogenicity of Schistosoma mansoni in mice and the susceptibility of the vector mollusk. IV--Infectiousness of miracidia]

OBJECTIVE

The infection ability of miracidia of BH and SJ strains of S. mansoni, obtained from mice infected with cercariae taken from Biomphalaria glabrata and Biomphalaria tenagophila, genetically selected for susceptibility is compared with the infection ability of miracidia obtained from mice infected with larvae from non-selected mollusks.

MATERIAL AND METHOD

Progeny of S. mansoni resulting from successive infections of selected mollusk sproduced various generations of selected miracidia. Selection of B. glabrata and B. tengophila was carried out by autofertilization of mollusks susceptible to the BH and SJ strains of S. mansoni. Five generations of mollusks (from parental down to F4), were used in the experiment. Tests for the infectiousness of the miracidia used 10 larvae: susceptibility was checked starting on day 30 after infection, for 90 days, through observation for the presence of cercariae.

RESULTS

The results showed that susceptibility of the selected mollusks in the face of the respective sympatric strains was not altered by the selection process of S. mansoni. However F4 miracidia of the BH strain were more infectant for non-selected B. glabrate than parental miracidia of the same strain. Miracidia of BH and SJ strains, parental generation, and BH strain, F3 generation, showed the same infectiousness in selected B. glabrata. Nevertheless, these mollusks had distinct infection rates from allopatric selected miracidia (SJ strain, F4 generation). The generation of successive infections of S. mansoni SJ in selected B. tenagophila resulted in the adaptation of the worm strain to the species of mollusk. B. tenagophila was never susceptible to the BH strain, even when selected mollusks and trematodes were employed. The susceptibility/infectiousness of the pair B. tenagophila-SJ S. mansoni strain was only changed by the selection process of the mollusks.

CONCLUSION

As non-selected B. glabrata were more intensively infected by selected BH miracidia than by non-selected BH miracidia, one is led to surmise that the greater pathogenicity of S. mansoni from susceptible mollusks implies the greater infection ability of these miracidia.

Phenoloxidase activity in the reproductive system of Biomphalaria glabrata: role in egg production and effect of schistosome infection

Infection by larval trematodes often causes a cessation of egg production in its molluscan intermediate host and is referred to as parasitic castration. Because phenoloxidase (PO) has been shown to be involved in egg formation in other invertebrate species, we investigated the role of PO in normal egg production in the snail, Biomphalaria glabrata, and the effects of Schistosoma mansoni infection on the PO pathway in this snail. Our data showed that PO activity in the albumen gland (AG) is initially expressed when snails reach a size of approximately 8 mm in shell diameter and continues to increase as snails grow, indicating a developmental link between snail size and AG PO expression. Egglaying was also shown to be coincidental with the onset of PO expression in the AG, thereby supporting a direct association between PO activity and egg production. In addition, exposure of snails to diethyldithiocarbamate (DDC), a PO inhibitor, affected normal in vivo egg production, as evidenced by a significant decrease in the numbers of eggs laid in DDC-treated groups compared to nontreated groups. Normal resumption of egg-laying activity in treated snails following withdrawal of the drug indicated that inhibition was reversible. Taken together, the results of our developmental and DDC-exposure studies provide strong support for a crucial role of PO in normal egg production in this animal. Finally, AG PO activities of infected and uninfected control snails were measured over the course of S. mansoni infection. Our results showed that both total and specific enzyme activities in the AG of infected snails were significantly decreased at 28 and 33 days postinfection (PI) when compared to those of control snails. Results of subsequent experiments assessing the effects of larval infection on L-tyrosine (PO substrate) levels in AG and ovotestis revealed a significant increase in the levels of this compound in both organs over the course of infection. It is concluded that AG PO activity is functionally linked to egg formation in normal snails and that a strong association exists between parasite-mediated decrease in AG PO activity and parasitic castration. However, from the data presented, a direct causal relationship linking infection, decreased PO, and castration has yet to be established.

Effects of Bayluscide WP 70 on the survival and water-leaving behaviour of Biomphalaria straminea, snail host of schistosomiasis in northeast Brazil

The toxic and behavioural effects of niclosamide (Bayluscide WP 70) on Biomphalaria straminea from a highly endemic area of schistosomiasis in northeastern Brazil were investigated through laboratory bioassays. The LD50 and LD90 were 0.114 mg/l and 0.212 mg/l, respectively. Water-leaving behaviour occurred among 14% to 30% of the snails in the presence of sublethal doses of niclosamide and among 16% of the controls. It was concluded that both the relatively low susceptibility to niclosamide and water-leaving behaviour of local B. straminea may be responsible for the recolonization of transmission foci after mollusciciding. It was suggested that recently improved measures of snail control, such as controlled-release formulations of niclosamide and plant molluscicides should be considered in areas where snail control is recommended.

Susceptibility of three successive snail generations from positive and negative laboratory bred Biomphalaria alexandrina from different localities in Egypt to infection with Schistosoma mansoni from Giza

Susceptibility of snail vectors to schistosome infection varies between geographical areas, populations in the same area and among individuals in the same population. It is also affected by biological factors of which are snail size (age), number and age of miracidia exposed to water, temperature, illumination and darkness. Our preview studies indicated that snails 4-6 mm in diameter exposed to 5 freshly hatched miracidia under light and in water at 25 degrees C are optimum conditions for infection of Biomphalaria alexandria from various localities in Egypt with Schistosoma mansoni (TBRI strain maintained in hamsters). In the present study, groups of 16 snails from three successive generations from positive and negative laboratory bred B. alexandrina from Giza, Alexandria, Menoufia, Cairo and Minia were exposed to S. mansoni miracidia (TBRI Strain) from Giza under the above mentioned optimum conditions. From the 20th day infection snails were checked from cercariae shedding to estimate the prepatent period and their number from each snail light for one hour. B. alexandrina from the various localities in Egypt were susceptible to S. mansoni (TBRI strain) infection. Snails from Alexandria were the most susceptible, followed by those from Cairo, Giza, Menoufia and Minia. Snails from positive generations were more susceptible to infection than those from negative ones. However, there has been a decline in the susceptibility of snails from one generation to the next. The prepatent period for shedding of cercariae was 27 days in case of snails from positive generations and it was extended to 38 days among snails from negative ones. It can be concluded that: (1) There are different levels of susceptibility between B. alexandrina from the various localities in Egypt and infection with S. mansoni from Giza. (2) Unsusceptibility (refractory character) of B. alexandrina to S. mansoni infection could be a heritable character like susceptibility. Consequently, it would be beneficial to select actively resistant snails and mass culture them to increase the proportion of alleles for insusceptibility as a possible mean for biological control of schistosomiasis in natural population.

Comparative histopathology of Biomphalaria glabrata, B. tenagophila and B. straminea with variable degrees of resistance to Schistosoma mansoni miracidia

A comparative histopathological study of three snails species--Biomphalaria glabrata, B. tenagophila and B. straminea--which had been infected with Schistosoma mansoni miracidia revealed similar qualitative features; consisting of areas of sporocyst proliferation and differentiation associated with reactive host reaction, at the time they were actively eliminating great number of cercariae. However, in specimens that were exposed to miracidia but failed to eliminate cercariae later on, different histopathological pictures were observed in different snail species. While B. glabrata exhibited frequent focal (granulomatous) proliferation of amebocytes in several organs, B. tenagophila and B. straminea only rarely showed such reactive changes, suggesting that the mechanism of resistance to miracidial infection probably follows different pathways in the snail species studied.

Fecundity changes induced by low-doses of gamma radiation on Biomphalaria straminea (Dunker, 1848)

A population of 420 snails Biomphalaria straminea, an intermediate host of Schistosoma mansoni, received gamma-rays obtained from a 60Co source in low-doses (0/2,5/5/7,5/10/15/20 and 25 Gy); half population was kept in colonies (allowing cross fertilization) and the other half was maintained in sexual isolation (allowing self fertilization). Results showed that 15 Gy stimulates the fertility of both groups but the colonies were more sensitive and at this dose its fertility overpasses the control group dose. The possible hormonal role played in the observed phenomena is under investigation.

Evaluation of chemical and physical-morphological factors as potential determinants of Biomphalaria pfeifferi (Krauss, 1848) distribution

This study was carried out in five sites along a small perennial river system in south-central Tanzania, which had been identified as the focus for transmission of intestinal schistosomiasis in the area. Malacological surveys preceding the study showed a focal distribution of Biomphalaria pfeifferi, intermediate host snail of Schistosoma mansoni, the snails being present in three sites but absent from the other two sites. The objective of this study was to evaluate to what extent chemical and/or physical-morphological factors determine the distribution of B. pfeifferi between these five sites. It was found that none of the chemical constituents in the waters examined were outside the tolerance range of B. pfeifferi snails. Moreover, the composition of water from B. pfeifferi-free sites was not different from that in those sites where snails occurred. Furthermore, none of the physical-morphological constituents seemed likely to be a determinant for the absence of B. pfeifferi. In view of these findings, and those of previous studies, it is concluded that the focal distribution of B. pfeifferi cannot be associated with a single environmental factor and is rather the result of more complex interactions of habitat factors.

A comparative study of the organic acid content of the hemolymph of Schistosoma mansoni-resistant and susceptible strains of Biomphalaria glabrata

The freshwater snail Biomphalaria glabrata is an intermediate host of the trematode Schistosoma mansoni. However, some strains of B. glabrata are resistant to successful infection by S. mansoni larvae. The present work examines the profile of organic acids present in S. mansoni-resistant and -susceptible strains of B. glabrata, in order to determine whether the type of organic acid present is related to susceptibility. The organic acids were extracted from the hemolymph of two susceptible B. glabrata strains (PR, Puerto Rico and Ba, Jacobina-Bahia from Brazil), and from the resistant strains 13-16-R1 and 10R2, using solid phase extraction procedures followed by high performance liquid chromatography. The organic acids obtained were analyzed and identified by comparison with known standards. Pyruvate, lactate, succinate, malate, fumarate, acetate, propionate, beta-hydroxybutyrate and acetoacetate were detected in all hemolymph samples. Under standard conditions, the concentration of each of these substances varied among the strains tested and appeared to be specific for each strain. An interesting variation was the low concentration of pyruvate in the hemolymph of PR-snails. Only the concentration of fumarate was consistently different (p < or = 0.05) between resistant and susceptible strains.

Studies on the sacculant portion of the kidney of Biomphalaria glabrata Say (1818) as a haemopoietic organ

The term immunity signifies all those properties of the host which confer resistance to a specific infectious agent. This resistance may be of all degrees ranging from complete to incomplete susceptibility. The defensive functions is performed by various cellular and humoral components which interact with each other producing a co-ordinated immune response directed towards eliminating the pathogen or minimizing its danger. Snails as other members of the Animal Kingdom have their own immune system. The present study concentrated on the sacculant portion of the kidney of B. glabrata as a haemopoietic stem cell. The histological picture of this portion in the kidney as well as in-vitro culture was studied. (I) The histological studies showed that (a) the sacculant portion constituted the last fifth of the kidney highly folded with primitive epithelial tissue, (b) amoebocytes (10.7 +/- 0.98m) rounded, oval or amoeboid, showing flattening and spreading when encapsulated around foreign particles, when doing so, both the cytoplasm and nucleus were more basophilic, (c) the haemocytes in the sacculant portion were distributed either as clustering forming amoebocytic plugs or dense aggregation or being normal in distribution (d) there was a significant correlation between haemocytic diameter and shell weight and between shell weight and shell diameter but no significant correlation between haemocytic diameter and shell diameter. (II) The in-vitro studies showed that (a) The medium 199 and fetal calf serum (3:1) produced higher number of granulocytes, (b) the cells differed in shape and size from those shown in histological studies of the kidney itself (c) the majority of the cells were large sized granulocytes and very few small sized hyalinocytes, (d) granulation of cytoplasm took place in the culture medium used more than in the sacculant portion, (e) only the smaller granulocytes showed greater ability for mitotic division. The results were photographed and discussed.

Differences in susceptibility of Biomphalaria alexandrina to Schistosoma mansoni from Gize and Dakahlia Governorates, Egypt

Biomphalaria alexandrina snails were collected from irrigation canals at Gize and Dakahlia Governorates. They were exposed to strains of Schistosoma mansoni from these localities. The snails showed different rates of susceptibility to the parasite. There was a high range of snail sensitivity to S. mansoni infection (53.9%-60.7%) when snail populations and parasite strains were from the same governorate. Supporting this was the high cercarial production from infected snails of these cases (288.2 cercariae/ snail/week of Dakahlia-Dakahlia group). However, snail populations and parasite strains from different Governorates (Gize-Dakahlia) exhibited poor values of snail sensitivity and cercarial production with significant variations from those of the group of the same governorate.

Effect of X-ray on the snails of schistosomiasis in Egypt

Biomphalaria alexandrina and Bulinus truncatus snails were exposed to sublethal doses 0.2, 3, 5, 10 and 20 rad of X-ray. The survival and reproductive rates of these snails were highly affected by these doses. The maximum survival periods of laboratory populations of Biomphalaria snails were less than those of field ones which means a high sensitivity of laboratory snails to X-ray. The reproductive capacity of irradiated Biomphalaria and Bulinus snails was highly suppressed and this will interrupt Schistosomiasis transmission. A deleterious effect of gametogenesis of irradiated Biomphalaria was histologically proved. After 3 weeks of snail irradiation with high dose (40 rad) the hermaphrodite gland became completely evacuated.

Male reproductive success of Schistosoma mansoni-infected Biomphalaria glabrata snails

Infection of Biomphalaria glabrata by Schistosoma mansoni results in a dramatic reduction in the snail's ability to produce eggs. We studied the ability of such parasitically castrated snails to fertilize the eggs of uninfected snails. Pigmented B. glabrata snails (13141 stock) were infected with S. mansoni miracidia and reared individually until they ceased laying eggs. These infected snails were then given the opportunity to mate with uninfected albino (NMRI) snails. Each of the infected snails was paired with a different albino partner each subsequent week. Sperm transfer by the infected snails was evident from the production of pigmented progeny by the uninfected albino snails. Infected snails successfully acted as males for up to 6 wk after parasitic castration had occurred. The duration of allosperm use by uninfected recipients was lengthy, regardless of the infection status of the pigmented sperm donor.

Current advances on the study of snail-snail interactions, with special emphasis on competition process

Field work research on population dynamic of snails from the regions of Belo Horizonte and Lagoa Santa give much information about interactions among two or more species of mollusks: Pomacea haustrum, Biomphalaria glabrata, B. tenagophila, B. straminea and Melanoides tuberculata. Data ranging from two years to several decades ago suggest that the Pampulha reservoir is like a cemetery of B. glabrata and B. straminea, species that coexist for more than 14 years in a small part of a stream, whereas only B. glabrata lives in all the streams of the basin. In the last ten to twenty years B. tenagophila has coexisted with P. haustrum and M. tuberculata in the Serra Verde ponds and in the Pampulha dam. However these species have not settled in any of the brooks, except temporarily. The data suggest that the kind of biotope and the habitat conditions are decisive factors for the permanence of each species in its preferencial biotope. B. glabrata, natural from streams and riverheads, quickly disappears from the reservoirs and ponds where it coexists with other species for a short time, independently of the competitive process. Competition needs to be better studied, since in Central America and Caribean islands this kind of study has favored the biological control of planorbid species.

Schistosoma mansoni: relationship between low fecundity and reduced susceptibility to parasite infection in the snail Biomphalaria glabrata

Biomphalaria glabrata snails which were not susceptible as juveniles to infection by Schistosoma mansoni were selectively bred (by self-fertilization) from the highly susceptible NMRI laboratory snail stock. The susceptibility rate among juvenile snails derived from interbreeding NMRI parents was initially 85-95%, but after several generations of selection, less than 5% of exposed snails became infected by the parasite. Selection for low susceptibility also resulted in a large proportion of snails that displayed low fecundity and produced abnormal egg masses. Individual adult snails which were isolated from an interbreeding population of nonselected NMRI snails usually produced well-developed egg masses each containing 15-30 embryos. However, when juvenile snails from this same population were reared in isolation and not allowed to cross-fertilize, many displayed a pattern of low fecundity and abnormal egg production similar to that observed in the selected low susceptible line. Furthermore, it was found that many of the isolated snails which exhibited low egg production were also not susceptible to parasitic infection.

Surface membrane polypeptides associated with hemocytes from Schistosoma mansoni-susceptible and -resistant strains of Biomphalaria glabrata (Gastropoda)

Previous studies have shown that hemocytes from inbred susceptible and resistant strains of the snail, Biomphalaria glabrata, differentially react to primary sporocysts of the blood fluke, Schistosoma mansoni. It has been hypothesized that this differential reactivity may be due to differences in the expression of hemocyte surface determinants serving as parasite recognition and/or hemocyte activating factors. In order to begin addressing this hypothesis the hemodynamics and surface polypeptides of circulating hemocytes from susceptible and resistant B. glabrata strains were compared in two morphologically distinct cellular subpopulations that differed in their substrate adherence properties. When compared to a S. mansoni-resistant snail strain, two susceptible strains exhibited overall lower total circulating cell numbers and a consistently lower proportion of nonadherent hemocytes. Exposure of snails to S. mansoni miracidia induced significant increases in total circulating cell number in all strains by 2 days postexposure (PE). However, the proportion of adherent and nonadherent hemocytes remained constant in each snail strain at 2 and 4 days PE. A sensitive technique involving biotin labeling of polypeptides at the surface of living hemocytes, followed by nonreducing SDS-PAGE separation and electrotransfer to nitrocellulose, revealed a similar pattern of hemocyte surface polypeptides ranging in apparent molecular weights from 210 to 30 kDa in the three B. glabrata strains. One exception was the presence of a 66-kDa polypeptide expressed at the surface of both adherent and nonadherent hemocytes in the two susceptible snail strains, which was only weakly expressed or absent from hemocytes of the resistant 13-16-R1 B. glabrata strain.(ABSTRACT TRUNCATED AT 250 WORDS)

[Molluscacidal activity of spiro-alpha-methylene-gamma-butyrolactone]

The alpha-methylene-gamma-butyrolactones 1-28 were tested in vitro for molluscicidal activity against Biomphalaria glabrata. The racemic compound 25 shows the best activity. The synthesis was carried out by modified Reformatzky reaction of the corresponding carbonyl compounds and bromomethylacrylic acid ethyl ester. 7-10, 17 and 22-27 have been synthesized for the first time.

Synthesis and molluscicidal activity of new derivatives of 1-(hydroxy/substituted phenyl)-3-arylpropenones

Several 1-(hydroxy/substituted phenyl)propenones were tested as molluscicidal agents among which the 1-(2-hydroxy/substituted phenyl)-3-(2-furyl)propenones 1a-c show the most promising results. In an attempt to improve their activity, new dihydropyrazolo[1,5-c][1,3]benzoxazines, their thio and their dehydrogenated derivatives were prepared. The pyrazolo[1,5-c][1,3]benzoxazines 4a,b were hydrolyzed affording the 3-(2-furyl)-5-(2-hydroxy/substituted phenyl) pyrazoles 8a,b. The hydroxyimino derivatives 10a-c were synthesized together with their corresponding isoxazole derivatives 11a-c. -Molluscicidal assay indicated that the oximes 10b,c, the isoxazole 11b, the pyrazole 8b, and its N-carbamoyl derivative 9b are most effective. They have in common the conjugated system shown in Fig. 1 which is presumably the active core.

Factors conditioning the habitat and the density of Biomphalaria tenagophila (Orbigny, 1835) in an isolated schistosomiasis focus in Rio de Janeiro city

The present work was carried out in a watercress garden in Alto da Boa Vista, in the city of Rio de Janeiro, Brazil. The investigation was carried out in two phases. The first one (1985-86) involved the sampling of Biomphalaria tenegophila in two areas to determine its relative populational densities. The results showed that the populations presented similar densities and dynamics. The second phase (1988-89) involved the study of the influence of some environmental factors on the establishment of B. tenagophila in watercress garden. Two factors were identified as responsible for the establishment of B. tenagophila in the garden: (1) the quality of the water entering the irrigation system, to which domestic sewage is added, and (2) alterations in the nature of the substrate, due to inadequate fertilization techniques, which employ organic matter from adjacent pigsties. Aquatic plants and hydrological parameters of the irrigation system were subsidiary factors to the establishment of B. tenagophila in the garden.

Ecology of Biomphalaria alexandrina the snail vector of Schistosoma mansoni in Egypt

The patterns of spreading and seasonal variation of population density of Biomphalaria alexandrina, the snail vector of Schistosoma mansoni in Egypt, in correlation with some environmental parameters were studied for 1988-1990 in four irrigation canals in Giza and Qalyoubiya Governorates. Results shown that the spreading patterns of snails along canals are changeable because of water current and irrigation activities. The snail population density showed two peaks, different in height, in April-May and November-December separated by two bottoms following the Winter Closure and during the hot summer season. The height of the peaks appears to be dependent on the extent of the "Winter Closure" and the prevailing water temperature. Two snail sampling tools, the dip-net and drag scoop, were used concurrently in this study. No considerable difference in sampling efficacy was recognized between these tools in the case of Biomphalaria. However, the dip-net appears to be more efficient in sampling other pulmonates while the drag scoop is more efficient in sampling prosobranchs. It is also realized that double sampling of 50% of sampling sites the next day should be satisfactory as a quality control system in snail population studies.

Biomphalaria occidentalis Paraense, 1981 in the State of Minas Gerais, Brazil

A population of Biomphalaria occidentalis was found for the first time in the State of Minas Gerais. It was probably introduced into the Várzea das Flores dam, in the municipality of Contagem, the area of study, during fish stocking in 1985. There is the possibility of "competitive exclusion" between that species and B. glabrata, previously the only Biomphalaria found in the region. The present geographical distribution of B. occidentalis in Brazil is listed.

Schistosoma mansoni infection in diapausing Biomphalaria glabrata snails: studies of temperature and genetic influences on diapausing behavior

Snails that are capable of undergoing diapause can circumvent unfavorable environmental conditions, including long periods of drought. Studies were performed to investigate possible temperature and/or genetic factors that may trigger lamella formation and diapausing behavior. The influence of diapause in Biomphalaria glabrata snails on susceptibility to Schistosoma mansoni infection and levels of cercarial production was also investigated. Rearing temperatures of 23 degrees C or higher did not induce lamella formation or diapause, regardless of the parental phenotype. However, substantial percentages of progeny from lamellated or lamellated/diapausing parental snails developed lamellae at 18 degrees C and underwent diapause. Only a small percentage of offspring from nonlamellated parents formed lamellae at this temperature. Juvenile snails exposed just prior to diapause, or immediately following a diapause period of three weeks, were highly susceptible to infection by S. mansoni miracidia. Snails that underwent diapause produced comparable or only slightly fewer cercariae than did nondiapausing snails. These studies indicate that diapause in B. glabrata does little to decrease a snail's ability to act as an intermediate host for S. mansoni or to interrupt the development of the parasite. For these reasons, we believe that greater attention should be given to diapausing snail populations when planning field surveys or mollusciciding programs.