Snail Survival Research Articles

Reviewing Fasciola hepatica transmission in the West Indies and novel perceptions from experimental infections of sympatric vs. allopatric snail/fluke combinations

Fasciolosis is an important food-borne parasitic disease affecting over two million people worldwide with economic losses related to cattle production of up to US$ 3 billion annually. Despite the long known presence of Fasciola hepatica in the Caribbean islands its transmission is not well known. This study reviews historical and recent data on fasciolosis in the West Indies, revealing for the first time the outcomes of sympatric and allopatric fluke/snail interactions in the area by exploring the susceptibility of four lymnaeid species after exposure to F. hepatica isolates from Cuba, the Dominican Republic and France. Overall, Galba cubensis showed a mean prevalence of 71.8% and appears to be the most suitable intermediate host species irrespective of the isolate used. Sympatric combinations (snail and parasite from the same country) were generally more compatible (higher susceptibility, parasite intensity and snail survival post-exposure) and only the allopatric interaction of French G. truncatula/Cuban F. hepatica attained 100% prevalence and mean intensity over 33 rediae/snail. However, certain Dominican populations of Pseudosuccinea columella showed high parasite intensities (>30 rediae/snail) when infected with Cuban flukes, highlighting the potential risks of biological introductions. Overall, high compatibility in most sympatric combinations compared to low or moderate compatibility in allopatric ones, suggests the existence of local adaptation from a long sustained interaction that has led to high rates of transmission. Interestingly, attempts to infect G. schirazensis with sympatric and allopatric flukes failed and coupled with the lowest survival rates which supposes a low risk of fasciolosis transmission in areas where this is the only snail species. Although there are significant gaps in the actual status of fasciolosis transmission from several islands in the West Indies these results show a permanent risk. We conclude that fasciolosis transmission is high in areas where the local snail, G. cubensis, occurs, and will be even higher in the presence of the invasive P. columella.

Surveillance of potential transmission factors of schistosomiasis in Xiuzhou District of Jiaxing City from 2013 to 2015

To understand the potential risk of schistosomiasis transmission in Xiuzhou District of Jiaxing City, so as to provide the scientific evidence for consolidating schistosomiasis control achievements. Fixed and mobile surveillance sites were set up in Xiuzhou District of Jiaxing City from 2013 to 2015. Oncomelania hupensis snails was surveyed historical snail habitats, current snail habitats, and suspected snail habitats. The schistosome infections were identified using serological and parasitological testing among local residents and mobile populations. In addition, the survival and reproduction of snails imported into Xiuzhou District was observed, and the schistosome infection in wild reservoir hosts was detected. A total of 540.14 hm2 of settings were surveyed in Xiuzhou District, Jiaxing City from 2013 to 2015, and 1.65 hm2 of snail habitats were identified. The snail habitats were mainly located in dry lands, and no infected snails or importation of snails were found. During the period from 2013 to 2015, a total of 7 668 local residents and mobile populations were examined in Xiuzhou District, and no new local infections were detected; however, three imported schistosomiasis cases were identified. Field simulation experiment showed that the imported snails laid eggs and reproduced in Xiuzhou District, and no schistosome infections were found in wild animals. There are still residual Oncomelania snails and imported schistosomiasis patients in Xiuzhou District of Jiaxing City; therefore, the surveillance and management of local Oncomelania snails and imported schistosomiasis should be intensified to reduce the risk of schistosomiasis transmission.

Heat-wave tolerance in tropical intertidal animals: accounting for thermal and desiccation tolerances

Abstract We investigated whether thermal tolerance is useful in predicting the responses of tropical snails to heat-waves - unusually warm periods of weather. Studying four sympatric high-rocky-shore species, we assessed thermal tolerance from the lethal limit following a constant rate of acute warming, as well as from an ecologically-relevant heat tolerance measure accounting for midday thermal exposure times. These thermal tolerance assessments were then compared with the survival of snails under three laboratory-simulated heat-wave treatments, each constituting four days of cycling temperatures but varying in daily maximum temperature (45, 48 and 50 °C). Additionally, water loss of individual snails was measured daily to assess the effect of desiccation due to heat-wave exposure. We found that responses to heat-wave exposure are complex and are not always predictable from thermal tolerance traits. This arises from a mismatch in thermal tolerance and desiccation tolerance, such that variation in daily thermal maximum and duration of the heat-waves produced different survival responses for each species. This study highlights the need to consider both thermal and desiccation tolerance traits when building frameworks to predicting heat-wave vulnerability in benthic intertidal ectotherms.

The effects of oil on blue crab and periwinkle snail interactions: A mesocosm study

We examined the sub-lethal effect of Macondo oil from the Deepwater Horizon oil spill on predator-prey interactions using blue crabs (Callinectes sapidus) and periwinkle snails (Littoraria irrorata). A 2 × 2 factorial mesocosm design determined the effect of oil (no oil vs. oil) and blue crabs (no blue crab predator vs. one blue crab predator) on periwinkle snail climbing and survival. Sixteen mesocosm tanks were used in the experiment, which were replicated three times. Each tank contained water, sand, and Spartina marsh stems. The sixteen tanks were divided between two, temperature-controlled chambers to separate oil treatments (no oil vs. oil). Oil was buried in the sand to prevent direct coating of mesocosm organisms. Half of the tanks contained only snails, while the other half contained snails and (one) blue crab in each chamber. Snail climbing behavior and survival were documented every 12 h over 96 h. Snails exposed to oil without a blue crab predator survived as well as snails not exposed to oil and no blue crab predator. Oil reduced snail survival in the presence of a blue crab predator. The increase in snail mortality can be attributed to changes in snail climbing behavior. Oil significantly reduced snail climbing height in the presence and absence of a blue crab predator. This change in behavior and subsequent decrease in snail survival could be beneficial for Spartina during recovery after an oil spill. A decrease in snail populations would reduce grazing stress on Spartina. However, field research immediately after an oil spill would be more useful in determining predator-prey interactions and further food web effects.

English

Cameroon south-west region offers favorable climatic conditions for survival of land snails whose meat is known for their nutritional benefits. Besides, conventional livestock (beef, chicken, etc.) cannot satisfy the high demand in Cameroon. Hence, snail meat could be suitable alternative source of protein. Therefore, this article investigated the perception and identified the main determinants of land snail meat consumption in the Fako division (south-west region Cameroon). A multistage random sampling method was used to select a total of 211 respondents. Descriptive statistics has highlighted that snail meat is quite consumed in Fako with 76.30% of respondents. Majority of respondents where Christians (95.26%) and have their origin from south-west region (56.40%). Additionally, regression analysis has pointed out that snail meat consumption depends on marital status, household size, income, snail origin and religion. The amount of snail meat consumed was shown to be influenced by its price and price variation between seasons. At the end of this study, two recommendations were made: snail farming should be increased in order to reduce scarcity of snail during dry season as well as its price and educate the people coming from other region of Cameroon on the nutritional benefits of snail meat. Key words: Snail consumption, African garden snails, Cameroon.

EFFECTS OF AESTIVATION DURATION ON REPRODUCTIVE TRACT DIMENSION AND SPERMATOZOA PRODUCTION OF GIANT AFRICAN LAND SNAIL (Archachatinamarginata) DURING DRY SEASON

Aestivation is a process of metabolic suspension which plays a key role in the survival of land snails during a period of drought. Human shave also used this process to transport the animal for commercial purpose. To examine the effect of this physiological process on reproductive apparatus, thirty (30) Giant African Land snail (Archachatinamarginata) with average weight of 130 -150g were used for this study. The snails were allotted to three different treatments with ten (10) replicate each after four weeks of acclimatization period which include: zero (0) week, three (3) weeks and six (6) weeks of aestivation. Parameters measured were: Internal organ weight, ovo-testis weight, reproductive tract length (cm) and weight (g). Also gonado-somatic index and spermatozoa concentration were also determined. Results showed that aestivation duration had significant influence on organ weight, ovo-testis weight, reproductive tract length and weight and spermatozoa concentration. However, gonado-somatic index (GSI) was not significantly influenced. It was observed that organ weight decreased as aestivation duration increased. For ovo-testis, snails with aestivation duration of six weeks had smaller weight compared to the control (0 week) while those at three weeks aestivation duration were not significantly different from the control group and those of six weeks aestivation duration. For reproductive tract weight, there was a significant(P<0.01)decrease in weight of the tract for both snails under three and six weeks aestivation duration compared to the control group (0 week). Spermatozoa count also decreased as aestivation duration increased. It can therefore be concluded that aestivation duration had significant effect on organ weight, ovo-testis weight, reproductive tract weight and spermatozoa concentration. For quick target of reproduction and snail economic value, it is recommended that aestivation duration should not be allowed to reach three weeks and above for whatever reason.
 
 

A simple method to improve the adsorption properties of drinking water treatment residue by lanthanum modification

The loading of La can substantially enhance the adsorption capability of drinking water treatment residue (DWTR) for better recycling. Normally, the modification was based on incubation of DWTR and La solution at a certain ratio, following by solid-liquid separation and drying processes. This study attempted to simplify La loading procedures by adopting high ratio of DWTR and La solution to eliminate the solid-liquid separation, aiming to promote the potential actual production. According to the results of the short- (2 d) and long-term (30 d) P adsorption tests, the N2 gas sorption and desorption analysis, the X-ray photoelectron spectroscopy analysis, and the metal fractionation, the substantial enhanced adsorption capability of the modified DWTR was maintained and the La loading mechanisms to DWTR changed little after eliminating solid-liquid separation processes during modification; typically, La loading increased the initial P adsorption rates from 1.00 (raw DWTR) to 6.08 and 6.03 mg g-1 d-1 for the modified DWTR with and without the separation processes. Furthermore, the DWTR before and after modification had little unfavorable effect on the survival of snail Bellamya aeruginosa, while eliminating the separation processes tended to reduce the bioavailability of Al, Fe, and La in the modified DWTR. These results demonstrated that solid-liquid separation was not the key step for DWTR modification and that the developed simple modification method was feasible for La loading to DWTR, promoting the beneficial recycling in environmental remediation.

Inhibition of Fasciola hepatica infection in Galba truncatula snails by application of monosaccharides to the aquatic environment

Fasciola hepatica is one of the etiological agents of fasciolosis, a widespread disease in domestic animals and occasionally in humans. Fasciolosis may be reduced by blocking the parasite transmission through its intermediate hosts. In the present work, different monosaccharides have been tested for their ability to impact on ligand/receptor interactions at the interface between the parasite and the intermediate host. Laboratory snails were subjected to miracidia in the presence of methyl-α-D-mannopyranoside (MetMan), α-D-glucose (Glc), N-acetyl-D-glucosamine (GlcNAc), D-(+)-galactose (Gal), N-acetyl-D-galactosamine (GalNAc) or L-(−)-fucose (Fuc), in 10 mM concentration. The snail survival rates and the prevalence of infection were determined after 50 days. Survived snails in the study groups varied from 78% to 97%. A remarkable reduction in the number of parasite-infected snails was observed in groups subjected to MetMan, Glc, or GlcNAc – 36.9%, 10.9%, and 11.9%, respectively, compared to 92.7% in the control group. Other tested monosaccharides had a low impact on snail infection. The results point to the implication that surface carbohydrate/receptor interactions are among the determining factors concerning the transmission of F. hepatica by the specific vector Galba truncatula. Biological recognition between the two organisms can be interfered with appropriate monosaccharides and this can be used to develop an alternative method for control of fasciolosis at the intermediate host level.

Fasciola hepatica-Pseudosuccinea columella interaction: effect of increasing parasite doses, successive exposures and geographical origin on the infection outcome of susceptible and naturally-resistant snails from Cuba

BackgroundPseudosuccinea columella is one of the most widespread vectors of Fasciola hepatica, a globally distributed trematode that affects humans, livestock and wildlife. The exclusive occurrence in Cuba of susceptible and naturally-resistant populations to F. hepatica within this snail species, offers a fascinating model for evolutionary biology, health sciences and vector control strategies. In particular, resistance in P. columella is characterized by the encapsulation of the parasite by host’s immune cells and has been experimentally tested using different Cuban F. hepatica isolates with no records of successful infection. Here, we aimed to explore for the first time, the effect of different parasite doses, successive exposures and different parasite origins on the infection outcomes of the two phenotypes of P. columella occurring in Cuba.MethodsTo increase the chances for F. hepatica to establish, we challenged Cuban P. columella with increasing single parasite doses of 5, 15 or 30 miracidia and serial exposures (three-times) of 5 miracidia using a sympatric F. hepatica isolate from Cuba, previously characterized by microsatellite markers. Additionally, we exposed the snails to F. hepatica from different geographical origins (i.e. Dominican Republic and France). Parasite prevalence, redial burden and survival of snails were recorded at 25 days post-exposure.ResultsNo parasite development was noted in snails from the resistant populations independent of the experimental approach. Contrastingly, an overall increase in prevalence and redial burden was observed in susceptible snails when infected with high miracidia doses and after serial exposures. Significant differences in redial burden between single 15 miracidia and serial 3 × 5 miracidia infected snails suggest that immune priming potentially occurs in susceptible P. columella. Compatibility differences of allopatric (Caribbean vs European) F. hepatica with susceptible snails were related to the geographical scale of the combinations.ConclusionsHere, the effectiveness of P. columella resistance to F. hepatica does not decline with increasing parasite doses, successive infection or different geographical origins of parasite isolates, while presenting new evidence for specificity for infection in susceptible P. columella snails. Understanding the peculiarities of the P. columella-F. hepatica interaction and the extent of the resistant phenotype is crucial for an effective parasite control and for developing alternatives to tackle fasciolosis transmission.

Thermal preferences of bird schistosome snail hosts increase the risk of swimmer's itch

Ambient temperature strongly affects host parasite interactions, especially when both are ectothermic. Bird schistosomes, which cercariae are known as agents of swimmer's itch and their snail hosts can be a good example of this phenomenon. The snails of these parasites play the key role, as the source of harmful larvae. Cercarial dermatitis is noted even in areas when prevalence of parasites in snail populations is very low. The main question is what adaptation in snail-fluke association can lead to a sufficient number of cercariae causing swimmer's itch in lake water? The influence of ambient temperature on snail survival and cercarial production as well as the thermal preferences of two host species naturally infected with bird schistosomes were studied. The 24-h preferences of Lymnaea stagnalis infected with Trichobilharzia szidati, and Planorbarius corneus infected with Bilharziella polonica were recorded using an oblong thermal gradient set (OTGS). Both cercariae releasing hosts of bird schistosomes preferred a significantly lower temperature than non-infected snails. Additionally, at a higher temperature, the survival of snail hosts was shortened as a result of the increase in daily cercarial expulsion. An especially interesting result concerns the release of a significantly larger total cercariae number by L. stagnalis at lower than at higher temperatures. These data indicate that preferences of infected snails to low temperature microhabitats can increase host survival and parasite success, as well as affecting the increase in the number of invasive larvae in the environment increasing the risk of swimmer's itch.

Simulation of population dynamics of Bulinus globosus: Effects of environmental temperature on production of Schistosoma haematobium cercariae.

BackgroundTemperature is an important factor that influences the biology and ecology of intermediate host (IH) snails and the schistosome parasites they transmit. Although temperature shifts due to climate change has been predicted to affect the life history traits of IH snails and parasite production, the mechanisms of how this may affect parasite abundance and disease risks are still not clear.Materials and methodsUsing data from laboratory and field experiments, we developed a deterministic compartmental simulation model based on difference equations using a weekly time step that represented the life cycle of Bulinus globosus. We simulated snail population dynamics and the associated production of cercariae assuming current environmental temperatures as well as projected temperature increases of 1 °C and 2 °C.ResultsThe model generated snail fecundity and survival rates similar to those observed in the laboratory and also produced reasonable snail population dynamics under seasonally varying temperatures representative of generally favorable environmental conditions. Simulated relative abundances of both snails and cercariae decreased with increasing environmental temperatures, with maximum snail abundances decreased by 14% and 27%, and maximum cercariae productions decreased by 8% and 17%, when temperatures were increased by 1 °C and 2 °C, respectively.ConclusionThe results indicate that future rise in temperature due to climate change may alter the abundance of B. globosus and impact on the prevalence of schistosomiasis. Furthermore, increased temperatures may not linearly influence the abundance of S. haematobium. These results may have important implications for schistosomiasis control programmes in view of temperature driven changes in the life history traits of B. globosus and S. haematobium. Our study recommends that the use of deterministic models incorporating the effects of temperature on the life history traits of IH snails would be vital in understanding the potential impact of climate change on schistosomiasis incidences and prevalence.

The Three Gorges Dam: Does the Flooding Time Determine the Distribution of Schistosome-Transmitting Snails in the Middle and Lower Reaches of the Yangtze River, China?

Background: Schistosomiasis is one of the most devastating tropical diseases in the world. Oncomelania hupensis is the only intermediate host of Schistosoma japonicum, and its growth and development are sensitive to environmental factors. The Three Gorges Dam has substantially altered the water level in the Yangtze River. This study focused on the impact of the flooding time on the occurrence of Oncomelania snails in Hunan Province, China. Methods: The data regarding Oncomelania snails were collected from the Schistosomiasis Atlas of the People’s Republic of China. Air temperature, hours of daylight and relative humidity from 1995 to 2002 were collected from the China Meteorological Data Sharing Service System. The data for rainfall and days inundated with water were collected from the Hunan flood control information system and hydrological stations in Hunan Province. A generalized additive model was used to estimate the impact of these factors on the presence or absence of snails. Results: The number of days inundated with water in the areas with snails ranged from 56 to 212 days. However, 82 percent of the areas without snails were inundated with water less than 60 days. The lowest air temperature in a year in the areas without snails ranges from −2.88 °C to −2.10 °C, and the range was from −2.88 °C to −2.34 °C for areas with snails. Annual rainfall in the areas with snails ranged from 989 to 1565 mm, and the range was from 1230 mm to 1647 mm for the areas without snails. The results from the generalized additive model showed that the number of days inundated with water, lowest air temperature in a year, annual rainfall, days of daily rainfall greater than 0.1 mm, and hours of daylight were the factors that significantly affect the occurrence of snails in Hunan Province, China. Conclusions: The number of days inundated with water may be a key factor determining the geographical distribution of Oncomelania snails in Hunan Province and the favorable number of days inundated with water for the survival of snails ranges from about 2 to 7 months.

Effects of Density and Food Deprivation on Growth, Reproduction, and Survival of Lissachatina fulica

Abstract: Population density commonly affects snail biology and is an important ecological factor to consider in any pest control program because population growth rates can be affected. Lissachatina fulica (Bowdich, 1822) is a pest of plants throughout the worldwide tropics; however, its biology is not completely known. We studied the effects of three rearing densities: low (5 snails per 25 × 38 × 17 cm (L × W × H) cage), medium (15 snails), or high (35 snails), on L. fulica growth, reproduction, and survival. High rearing density reduced growth, affected the initiation of egg laying, and reduced the number of eggs laid per snail and per clutch. Mortality did not increase with high rearing density, nor was any cannibalism observed, even when snails were deprived of food. Juvenile snail survival was more affected by lack of food than was adult survival, and availability of calcium did not compensate for lack of food. High-density rearing effects were not likely caused by limited food, calcium, or oxygen.

Effect of body size and sub-optimal water quality on some hemato-immunological parameters of spotted babylon snail Babylonia areolata

Cellular and humoral effectors are imperative for the innate defense mechanisms of invertebrates, including the spotted babylon snail Babylonia areolata, a marine gastropod belonging to the family Buccinidae. In this study, we have investigated the influence of body size [5–8 g (small), 10–12 g (medium) and 15–17 g (large)], and culture waters of varied quality [natural seawater, low salinity, low alkalinity, high total ammonia nitrogen (TAN) and artificial seawater] on some hemato-immunological parameters [total hemocytic counts (THC), hemolymphatic glucose, total protein concentration, phenoloxidase (PO), agglutinating and lysozyme activity] of the snail. Growth performance measures and survival of test snails were also evaluated after rearing them in culture water of varied quality. Body size did not influence most parameters assessed, except that the lysozyme and PO activities of medium and large-size snails were higher than those of the small-size snails. Sub-optimal culture water quality affected hemato-immunological factors, growth and/or survival of the spotted babylon snail. Seawater with low salinity, low alkalinity and a high TAN level caused decreased THC, hemolymphatic glucose, and PO activity; increased lysozyme activity; and clearly retarded growth of the snail. The snails held in artificial seawater could not survive after 4 weeks, suggesting the lack of certain essential factors necessary for their survival.

System productivity alters predator sorting of a size-structured mixed prey community.

Predator-prey interactions are often size-structured and focused on smaller vulnerable size classes. Predators are also predicted to sort prey communities according to relative vulnerabilities. Increased system productivity and juvenile growth may benefit some species more than others, making relative vulnerability non-static and growth-mediated. We hypothesized that increased system productivity would weaken juvenile-stage predation generally, and potentially shift the community sorting effects of a predator. Using replicated wetland mesocosms we quantified the effects of a generalist size-specific crayfish predator (Procambarus fallax) on juveniles of two species of apple snails (Pomacea spp.) under two levels of system productivity (low vs. high). After 6weeks of exposure, we quantified predator and productivity effects on snail survival, biomass, and composition of the assemblage. Crayfish depressed the final density and biomass of snails, and sorted the assemblage, selectively favoring survival of the native P. paludosa over the intrinsically more vulnerable invasive P. maculata. Both snails grew faster at higher productivity, but growth differentially increased survival of the invasive snail in the presence of crayfish and weakened the sorting effect. The native P. paludosa hatches at a larger less vulnerable size than the invasive P. maculata, but higher productivity reduced the relative advantage of P. paludosa. Our results are inconsistent with predictions about the sorting effects of predators across productivity gradients because the more resistant prey dominated at low productivity. Our findings highlight that the relative vulnerabilities of prey to a common predator are not always fixed, but can be growth-mediated.

The ecophysiology of apple snails in rice: implications for crop management and policy

AbstractThis review relates the ecology and physiology of apple snails (Ampullariidae) to their impact on rice‐production systems. Two species in particular, Pomacea canaliculata and Pomacea maculata, have been introduced to several rice‐growing regions. Flooded rice systems represent a high‐quality habitat for these apple snails because of similarities in the environmental conditions (water temperature, salinity, pH, water flow velocity) necessary for both rice production and for snail survival and development. Furthermore, amphibious respiration, a capacity to aestivate during dry periods, as well as cold acclimation and tolerance (particularly in P. canaliculata), increases the resilience of apple snails to rice farming practices, including agrochemical applications, intermittent drainage and crop rotations – under a wide range of climatic conditions. Risks to regional rice production depend on four principal factors: these are (a) regional climate, (b) regional rice‐production systems, (c) prevailing production practices, and (4) the presence/absence of invasive, non‐native apple snails. Based on these criteria, lowland irrigated rice in tropical and subtropical regions that is wet‐direct seeded is most vulnerable to damage from both native and non‐native apple snails (albeit with greater losses from non‐native snails because of normally higher densities). Adequate quarantine regulations, particularly in vulnerable tropical regions that are adjacent to centres of recent outbreaks (e.g. India and Bangladesh adjacent to Myanmar, Peru and Colombia adjacent to Ecuador) and attention to the preparedness of farming systems could reduce potential impacts as these highly invasive snails continue to spread. The urgent development of labour‐saving crop‐establishment methods that reduce dependencies on chemical molluscicides is necessary to achieve sustainable rice production in regions at risk from non‐native apple snails.

Cost of resistance to trematodes in freshwater snail populations with low clonal diversity

BackgroundThe persistence of high genetic variability in natural populations garners considerable interest among ecologists and evolutionary biologists. One proposed hypothesis for the maintenance of high levels of genetic diversity relies on frequency-dependent selection imposed by parasites on host populations (Red Queen hypothesis). A complementary hypothesis suggests that a trade-off between fitness costs associated with tolerance to stress factors and fitness costs associated with resistance to parasites is responsible for the maintenance of host genetic diversity.ResultsThe present study investigated whether host resistance to parasites is traded off with tolerance to environmental stress factors (high/low temperatures, high salinity), by comparing populations of the freshwater snail Melanoides tuberculata with low vs. high clonal diversity. Since polyclonal populations were found to be more parasitized than populations with low clonal diversity, we expected them to be tolerant to environmental stress factors. We found that clonal diversity explained most of the variation in snail survival under high temperature, thereby suggesting that tolerance to high temperatures of clonally diverse populations is higher than that of populations with low clonal diversity.ConclusionsOur results suggest that resistance to parasites may come at a cost of reduced tolerance to certain environmental stress factors.

Effects of glyphosate-based herbicides on survival, development and growth of invasive snail (Pomacea canaliculata)

This study tests the hypotheses that whether environmental relevance of glyphosate would help control spread of the invasive snail Pomacea canaliculata, or benefit its population growth worldwide. Our results showed that glyphosate induced acute toxicity to the snail only at high concentrations (96h LC50 at 175mg/L) unlikely to occur in the environment. Long-term exposures to glyphosate at sublethal levels (20 and 120mg/L) caused inhibition of food intake, limitation of growth performance and alterations in metabolic profiles of the snail. It is worth noting that glyphosate at 2mg/L benefited growth performance in P. canaliculata. Chronic exposures of glyphosate significantly enhanced overall metabolic rate and altered catabolism from protein to carbohydrate/lipid mode. Cellular responses in enzyme activities showed that the exposed snails could increase tolerance by their defense system against glyphosate-induced oxidative stress, and adjustment of metabolism to mitigate energy crisis. Our study displayed that sublethal concentrations of glyphosate might be helpful in control of the invasive species by food intake, growth performance and metabolic interruption; whether environmental relevance of glyphosate (≤2mg/L) benefits population growth of P. canaliculata is still inconclusive, which requires further field study.

Identification of Potential High-Risk Habitats within the Transmission Reach of Oncomelania hupensis after Floods Based on SAR Techniques in a Plane Region in China.

Schistosomiasis japonica is an infectious disease caused by Schistosoma japonicum, and it remains endemic in China. Flooding is the main hazard factor, as it causes the spread of Oncomelania hupensis, the only intermediate host of Schistosoma japonicum, thereby triggering schistosomiasis outbreaks. Based on multi-source real-time remote sensing data, we used remote sensing (RS) technology, especially synthetic aperture radar (SAR), and geographic information system (GIS) techniques to carry out warning research on potential snail habitats within the snail dispersal range following flooding. Our research result demonstrated: (1) SAR data from Sentinel-1A before and during a flood were used to identify submerged areas rapidly and effectively; (2) the likelihood of snail survival was positively correlated with the clay proportion, core area standard deviation, and ditch length but negatively correlated with the wetness index, NDVI (normalized difference vegetation index), elevation, woodland area, and construction land area; (3) the snail habitats were most abundant near rivers and ditches in paddy fields; (4) the rivers and paddy irrigation ditches in the submerged areas must be the focused of mitigation efforts following future floods.

Dynamic change of population structure of Oncomelania hupensis

Objective To understand the successive dynamic change of population structure of Oncomelania hupensis during a one-year period, so as to provide the evidence for snail control. Methods A river beach and a ditch infested with O. hupensis snails were selected and longitudinally investigated in the midmonth during one year. The snail survey indices included the survival status, gender, number of whorls, length and width of shell, and gonad development status (measured by the color depth of gonad and the length ratio of gonad to liver), and the monthly snail eggs in the soil were collected and counted simultaneously. In addition, the temperature and humidity of the soil and the daily data of air temperature and precipitation were measured or collected during the study period (every month). Results Both survival rate of snails and live snail density at the two environments were positively correlated with the temperatures of air and soil. With a slight bimodal distribution, the snail survival rate peaked from May to June, and in September. The living snail densities got the highest level in July and September in the river beach, and from April to May in the ditch. The regression equations of snail length (L) and width (W) were Lbeach = 2.355 + 1.678W (F = 2 989.43, P < 0.01) and Lditch = 0.478 + 2.091W (F = 2.989.43, P < 0.01), respectively. The snails were the ones with 4.07-11.81 mm in the length (8.98 ± 0.92) mm in the river beach, and the snails were the ones with 3.63-9.92 mm in the length (7.03 ± 0.82) mm in the ditch. The main snails were the ones with five to eight whorls of shell in the river beach and four to seven whorls of shell in the ditch. The proportions of snails with less than or equal to five whorls (in the river beach) and four (in the ditch) were the highest in May and September, about 20%. The ratios of male and female snails were 1.66 in the river beach and 1.22 in the ditch, respectively. The gonad development status of male and female snails was basically synchronous and had a bimodal abundance period - from April to May and September to October. The numbers of snail eggs in the soil among months were significantly different, reaching the highest in June in the river beach (100.8/0.1 m2), and May in the ditch (82.5/ 0.1 m2). Conclusion The principal periods of breeding and alternation of generations of snails are April-May and SeptemberOctober every year, which should also be the optimal time for mollusciciding in schistosomiasis susceptible zones.