Genetic exchange between two freshwater apple snails, Pomacea canaliculata and Pomacea maculata invading East and Southeast Asia

Two species of apple snails, Pomacea canaliculata and Pomacea maculata (formerly Pomacea insularum), have invaded many countries of East and Southeast Asia from their native range in South America. This study investigated the genetic structure of the two species invading these areas. Phylogenetic analysis based on sequences of the nuclear gene elongation factor 1-alpha (EF1α) detected two well-supported clades (Clade C and Clade M). Both P. canaliculata and P. maculata were represented in each clade. Some snails had both Clade C and Clade M EF1α sequences. These results suggest genetic exchange between snails of the two clades. A mating experiment between P. canaliculata with Clade C EF1α sequences and P. maculata with Clade M EF1α sequences resulted in viable F1 progeny under laboratory conditions. The genetic exchange was also inferred in some populations collected from Argentina, suggesting an existence of hybrid in the native range. Simple identification of EF1α types using a restriction enzyme, ApaLI, detected significant geographical structure of the EF1α variants in the invaded area. The divergent geographical structure could have resulted from either the founder effect or the bridgehead effect, although further genetic analysis is needed to clarify this. Average individual egg weight, which is an indicator of egg size, was higher in P. canaliculata than P. maculata in both field and laboratory reared samples, suggesting that some (probably most) P. canaliculata and P. maculata invading East and Southeast Asia still maintain species-specific populations.     

Eleven microsatellite loci for two invasive freshwater apple snails, <Emphasis Type="Italic">Pomacea canaliculata</Emphasis> and <Emphasis Type="Italic">P. maculata</Emphasis> (Ampullariidae)

Pomacea canaliculata and P. maculata are major invasive species that continue to spread and negatively impact aquatic habitats globally. Herein we report the development of a set of highly polymorphic microsatellite loci that readily amplify in both species, and that will be informative for understanding the pathways of spread and population structure across the native and non-native range. The high polymorphism of these markers should also provide substantial power for refining the estimated origins of the introduced populations. However, they are uninformative for assessing introgressive hybridization between the two species because of shared alleles.     

Life history traits determine the differential vulnerability of native and invasive apple snails (<Emphasis Type="Italic">Pomacea</Emphasis> spp.) to a shared juvenile-stage predator

The vulnerability of gastropods to their predators varies with life history traits such as morphology, body size, behavior, and growth rates as well as predator size. A recent study suggested that the invasive apple snail, Pomacea maculata, was considerably more vulnerable to crayfish predators than the native Florida apple snail, P. paludosa. The difference was hypothesized to be caused by the relatively small hatchling size of P. maculata. To test this hypothesis, we conducted a series of feeding assays designed to quantify maximum feeding rates and selective foraging of crayfish on apple snails. The rate at which crayfish killed individual P. maculata (i.e., kill rates) decreased with snail size, and kill rates on both species increased with crayfish size. Kill rates on juvenile P. maculata were higher than kill rates on size-matched hatchling P. paludosa, and crayfish fed selectively on P. maculata when offered mixed groups of size-matched snails. Further analyses revealed that hatchling P. paludosa possess shells 1.8× heavier than size-matched P. maculata suggesting differences in vulnerability to crayfish were consistent with interspecific differences in shell defenses. Differences in hatchling size and defensive traits in combination make crayfish kill rates on hatchling P. maculata approximately 15.4× faster than on hatchling P. paludosa, but the relative contribution of hatchling size to differences in apple snail vulnerability was >3× greater than the contribution of defensive traits.     

Factors affecting the distribution and abundance of the commensal <Emphasis Type="Italic">Temnocephala iheringi</Emphasis> (Platyhelminthes: Temnocephalidae) among the southernmost populations of the apple snail <Emphasis Type="Italic">Pomacea canaliculata </Emphasis>(Mollusca: Ampullariidae)

Temnocephala iheringi is the most common temnocephalan inhabiting the mantle cavity of the apple snail Pomacea canaliculata, a freshwater neotropical gastropod that has become a serious rice pest in Southeastern Asia. T. iheringi has been recorded from Mato Grosso (Brazil) to water bodies associated with the Río de la Plata river (Argentina). During an extensive survey in the southern limit of the native area of P.␣canaliculata the presence of T. iheringi eggs was recorded in several apple snail populations, extending the known distribution of the commensal more than 400 km southwards. The aim of this study was to understand the factors affecting the distribution and abundance of T. iheringi among populations of P.␣canaliculata. Only 23% of the apple snail populations inhabiting streams harboured temnocephalans while the occurrence among lentic ones was 71%. T. iheringi was found mostly in populations of apple snails living in non-alkaline sites and where snails attaining sizes larger than 4 cm were very common. The prevalence of the temnocephalans in lentic populations was higher than 90%. The number of eggs on the shell (not including the umbilicus) ranged between 0 and 470 and was different among populations of P.␣canaliculata. The prevalence and number of eggs were lower in the lotic populations, except for a stream population immediately downstream of a lake with commensals. There was no difference between males and females of P. canaliculata neither in the prevalence nor in the number of eggs on the shell. The southernmost population of the world of P. canaliculata harbours commensals that tolerate cold winter water temperatures (4–5 °C) as well as its host. On the other hand, T. iheringi was found only in sites with bicarbonate concentrations lower than 6.6 meq l⁻¹, suggesting that the tolerance of the commensal is very much lower than that of the apple snail (up to 9.95 meq l⁻¹). The number of worms inside each snail or the life history variation of P. canaliculata could explain the influence of the size of the snails on the occurrence of T. iheringi. In the big-sized snails, where the number of commensals is higher, the probability of survival of at least one worm is also higher, specially during the hibernation period, when crawling and feeding are null and snails remain buried. On the other hand, P. canaliculata snails from lentic populations are generally bigger and mostly iteroparous, while those inhabiting streams are smaller and semelparous. In these populations the snails have access to mate only with snails of their same cohort, while in iteroparous populations they can copulate with individuals of other cohorts, allowing the inter-generation transmission of worms and the long term persistence of the population of commensals.     

Complex interactions among fish, snails and macrophytes: implications for biological control of an invasive snail

The golden apple snail (Pomacea canaliculata), a native of freshwater wetlands of South America, has invaded many Asian countries and grazed heavily in agricultural and wild areas. Common carp (Cyprinus carpio) has been proposed as a biological control agent against this snail, but little is known about its impact on non-target aquatic plants and animals. In a 8-week enclosure experiment, we quantified the impact of common carp on three species of aquatic macrophytes and nine species of snails, including the apple snail, in a shallow pond. The results showed that the apple snail or carp alone significantly reduced the plant biomass, although the apple snail had a stronger overall herbivorous effect than the carp. The carp completely removed juvenile apple snails, but had only a weak predatory effect on larger apple snails and no effect on the adults’ oviposition frequency. Furthermore, the carp significantly reduced the populations of most species of other snails that occurred naturally in the pond. Our results thus indicate that common carp can be an effective biological control agent against the invasive apple snail, but caution should be taken about its potential to reduce wetland floral and faunal diversity.     

Invasive apple snails (Pomacea canaliculata) are predators of amphibians in South China

Invasive species are one of the most serious threats to amphibian populations. We investigated the effects of two invasive (Pomacea canaliculata and Physella acuta) and one native (Radix sp.) snail species on five species of wetland-breeding frogs in Hong Kong. We quantified embryonic survivorship and determined whether particular attributes of amphibian egg masses influenced consumption by snails. P. canaliculata preyed on four of the species, consuming >90 % of eggs of Microhyla fissipes and Fejervarya limnocharis, nearly 70 % of eggs of Kaloula pulchra, approximately 40 % of eggs of Duttaphrynus melanostictus, but no eggs of Polypedates megacephalus. P. acuta and Radix sp. consumed only the eggs of K. pulchra, but those eggs were probably non-viable. This study shows that P. canaliculata, which occurs at high densities in tropical East Asia, may be an important predator of amphibian eggs. Future research should evaluate their effects on amphibian populations, community structure, and food web dynamics.     

Biological control of invasive apple snails by two species of carp: Effects on non-target species matter

Molluscivorous fish, especially carp, have been adopted as bio-control agents of the invasive apple snail Pomacea canaliculata, but previous studies have focused on their effectiveness, with little attention paid to their undesirable effects on non-target plants and animals. We conducted an 8-week mesocosm study to compare the effectiveness of two indigenous fish, common carp (Cyprinus carpio) and black carp (Mylopharyngodon piceus), in removing P. canaliculata, and their potential side effects on macrophytes and non-target mollusks in a freshwater wetland. Three species of macrophytes and a community of mollusks in the wetland sediment were enclosed in 1 × 1 × 1 m enclosures either with apple snails (AS), with apple snails and common carp (AS + CC), with apple snails and black carp (AS + BC), or without apple snails and fish. Both species of carp were effective predators of P. canaliculata, removing most of the individuals in the enclosures except a few that were too big to fit into their mouth. By reducing apple snail population, black carp reduced grazing of apple snail on macrophytes. In contrast, although common carp controlled apple snail population, it did not reduce overall loss in plant biomass as the fish might also fed on macrophytes. Both species of carp preyed on non-target mollusks. Application of bio-control agents in invasive species management needs to consider their effects on both the pest and non-target plants and animals. Adoption of common and/or black carp to control apple snail populations thus depends on the weight given to their effectiveness and subtle different effects on non-target organisms by wetland management authority.     

Growth and survival of juvenile Pomacea canaliculata (Gastropoda: Ampullariidae) in plain streams associated to different land uses

Pomacea canaliculata is an apple snail that has become an invasive species in several countries. In this research, through two simultaneous experiments, we assessed the effects of different land uses (urban, agriculture, cattle grazing, farms and recreation) on the growth and survival of snails from native populations. The survival was not affected by the water quality of the three streams studied, whereas the growth of snails exposed to the water of the urban stream was impaired. Therefore, our results suggest that the growth rate of P. canaliculata could be useful for the assessment of a moderate urban impact.     

Impact of invasive apple snails in Hong Kong on wetland macrophytes,nutrients, phytoplankton and filamentous algae

1. Grazing by invasive species can affect many aspects of an aquatic system, but most studies have focused on the direct effects on plants. We conducted mesocosm and laboratory experiments to examine the impact of the invasive apple snail Pomacea canaliculata on macrophytes, filamentous algae, nutrients and phytoplankton. 2. In a freshwater pond, we confined 500 g of Myriophyllum aquaticum or Eichhornia crassipes with 0, 2, 4 or 8 apple snails in 1 m × 1 m × 1 m enclosures for approximately 1 month. Apple snails grazed heavily on both species of macrophytes, with higher overall weight losses at higher snail densities. The damage patterns differed between the two macrophytes. In M. aquaticum, both leaves and stems suffered from substantial herbivory, whereas in E. crassipes, only the roots suffered significant weight reduction. 3. In addition to grazing on macrophytes, apple snails appeared to have controlled the growth of filamentous algae, as these did not develop in the snail treatments. The ability of P. canaliculata to control filamentous algae was supported by a laboratory experiment where the consumption was as high as 0.25 g g⁻¹ snail DW d⁻¹. Because of a lack of native herbivorous snails in the pond, the growth of filamentous algae (mainly Spirogyra sp.) reached 80.3 g m⁻², forming a spongy pond scum in the no‐apple snail control. Together with previous reports that apple snails could eat the juveniles and eggs of other freshwater snails, our results indicated that P. canaliculata could have out‐competed native herbivorous snails from the pond by predation on their juveniles or eggs. Alternatively, P. canaliculata might have out‐competed them by monopolisation of food resources. 4. Nitrogen and phosphorous concentrations remained low throughout both experiments and were not correlated with apple snail density. The treatment effects on chlorophyll a (Chl a) and phytoplankton composition varied in the two experiments. In the M. aquaticum experiment, with increasing snail density, Chl a increased, and the phytoplankton community became dominated by Cryptophyceae. In the E. crassipes experiment, Chl a level was independent of snail density, but with increasing snail density, the phytoplankton community became co‐dominated by Cryptophyceae, Chlorophyceae and Bacillariophyceae. 5. Given the multiple effects of P. canaliculata on wetland biodiversity and function, management strategies should be developed to prevent its further spread. In invaded wetlands, strategies should be developed to eradicate the apple snail and re‐introduce native snails which can control the development of filamentous algae.     

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

This 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.     

Tolerance of embryos and hatchlings of the invasive apple snail Pomacea maculata to estuarine conditions

One of the most successful groups of invasive consumers worldwide is freshwater snails of the family Ampullariidae, including Pomacea maculata, yet little is known about snail survival and growth in the range of conditions found in estuarine ecosystems. Here, we provide an experimental assessment of P. maculata survivability in estuarine conditions, documenting: (1) egg susceptibility to tidal inundation (2) salinity tolerance of snails, and (3) salinity effects on hatchling growth. Results indicate that estuarine conditions will not limit apple snail colonization in oligohaline and mesohaline reaches of estuaries, with eggs remaining viable when exposed to periodic inundations typical of a tidal regime and modest, albeit reduced, growth and survival at moderate salinities (5 and 10 ppt). For this reason, rapid detection and eradication of P. maculata in estuarine areas is needed to avoid the invasion of snails in these vital, productive environments.     

Dispersal and local environment affect the spread of an invasive apple snail (<Emphasis Type="Italic">Pomacea maculata</Emphasis>) in Florida,USA

Dispersal and local environmental factors are major determinants of invasive species distribution. We examined how both dispersal-related geospatial characteristics and environmental factors influence an ongoing invasion of wetlands in a south-central Florida ranchland by non-native apple snails (Pomacea maculata, Ampullariidae). We found P. maculata in 73 (43%) of a random set of 171 wetlands in 2014. We used model selection to evaluate multiple hypotheses of predictors of P. maculata occurrence in 95 wetlands with standing water, including spatially-explicit distances in ditches from wetlands to the presumed entry point, Euclidean (overland) distances, presence/absence of ditches in wetlands, and environmental variables (e.g. pH). We also performed a 5-month field experiment in 20 wetlands to evaluate if snail absence was associated with conditions that limit survival and growth (i.e. unfavorable habitats). Snail occurrence was primarily associated with presence of ditches in wetlands and more neutral wetland pH. These variables more plausibly explained snail occurrence than did Euclidean (overland) distance and minimum ditch travel (rectilinear) distance from propagule sources (a major waterway). Wetland pH best explained survival and growth under the experimental conditions. We found no evidence that prior occupancy by conspecifics affected survival and growth, suggesting that dispersal limitation may contribute to lack of occupancy of wetlands, despite suitable pH. Our study supports man-made conduits as facilitators of dispersal by non-native species, where environmental characteristics (here pH) then also affect colonization within habitats. An understanding of both dispersal mechanisms and local environmental factors is necessary to better predict invasive species distribution.     

Comparing applesnails with oranges: the need to standardize measuring techniques when studying <Emphasis Type="Italic">Pomacea</Emphasis>

Although invaders come in all shapes and sizes, several mollusks have recently achieved notoriety as both economically and ecologically costly invaders. Applesnails of the genus Pomacea get their name from reaching the size of an apple. Native to South America, the species P. insularum has recently established reproducing, and potentially invasive, populations in Texas, Alabama, Georgia, and Florida. In contrast to the widely invasive golden applesnail (P. canaliculata), few studies of the channeled species P. insularum exist. In studying similar invasive applesnail species, scientists use several methods of measurement. We have explored the relationships among shell height, operculum width, and weight among juvenile and adult P. insularum and tested their inter-measurer reliability. We also investigated the use of shell height, shell length, and operculum width measurements in P. canaliculata studies and observed whether or not those studies defined their measurements. We found that operculum width served as a significantly more reliable measure among researchers. Furthermore, operculum width better predicted weight than shell height. The majority of articles that measured P. canaliculata did not define their measurements, which may cause problems when comparing studies between native and exotic populations or when comparing the two species. We recommend that future studies of P. insularum use operculum width to measure snails and explore a possible sex dimorphism in the operculum width of adult P. insularum.     

Feeding and growth of native,invasive and non-invasive alien apple snails (Ampullariidae) in the United States: Invasives eat more and grow more

The United States hosts one native and five non-native species of aquatic apple snails (Ampullariidae). All are currently found in or around the Everglades in Florida. Two of these introduced species have devastated wetlands in Southeast Asia, but little is known about how they may impact the Everglades. To evaluate potential impacts of introduced apple snails relative to the native species, we investigated plant species preference, consumption rates, growth rates, and growth efficiencies in five introduced and the single native species across eight native macrophytes common in the Everglades. Three of the non-native snails are invasive, one has shown no tendency to expand, and one appears to have minimal direct impact on macrophytes due to its diet. All snails exhibited similar feeding preferences, with Utricularia sp. being the most preferred, Bacopa caroliniana, Sagittaria latifolia, and Nymphaea odorata being of intermediate preference, and Eleocharis cellulosa, Pontederia cordata, Panicum hemitomon and Typha sp. being least preferred (avoided as foods). Consumption and growth was minimal for P. diffusa on all macrophytes. On Utricularia sp. and Bacopa caroliniana, the invasive species Pomacea insularum and P. canaliculata tended to eat more, grow more, and have higher conversion efficiencies than the native P. paludosa or the non-invasive P. haustrum. These contrasts were more often significant for P. insularum than for P. canaliculata. The greater rates of expansion by the invasive species may derive from their enhanced feeding and growth rates.     

Variation in reproductive output of marine turtles

Most marine turtle species are non-annual breeders and show variation in both the number of eggs laid per clutch and the number of clutches laid in a season. Large levels of inter-annual variation in the number of nesting females have been well documented in green turtle nesting populations and may be linked to environmental conditions. Other species of marine turtle exhibit less variation in nesting numbers. This inter-specific difference is thought to be linked to trophic status. To examine whether individual reproductive output is more variable in the herbivorous green turtle (Chelonia mydas Linneaeus 1758) than the carnivorous loggerhead (Caretta caretta Linneaeus 1758), we examined the nesting of both species in Cyprus over nine seasons. Green turtles showed slower annual growth rates (0.11 cm year⁻¹ curved carapace length (CCL) and 0.27 cm year⁻¹ curved carapace width (CCW)) than loggerhead turtles (0.36 cm year⁻¹ CCL, 0.51 cm year⁻¹ CCW). CCL was highly correlated to mean clutch size in both green (R²=0.51) and loggerhead turtles (R²=0.61) and maximal clutch size of green turtles (R²=0.58). Larger females did not lay a greater number of clutches or have a shorter remigration interval than smaller females of either species. On average, the size of green turtle clutches increased and that of loggerhead turtles decreased as the season progressed. Individual green turtles, however, produced more eggs per clutch through the season to a maximum in the third or fourth clutch. In loggerhead turtles, clutches 1-4 were very similar in size but the fifth clutch was 38% smaller than the first. No individuals of either species were recorded laying more than five clutches. Green turtles may not be able to achieve their maximum reproductive output with respect to clutch size throughout the season, whereas only loggerhead turtles laying five clutches (n=5) appear to become resource depleted. Green turtles nesting in years when large numbers of nests were recorded laid a greater number of clutches than females nesting in years with lower levels of nesting.     

Agglutinating Activity and Structural Characterization of Scalarin,the Major Egg Protein of the Snail Pomacea scalaris (d’Orbigny, 1832)

Apple snail perivitellins are emerging as ecologically important reproductive proteins. To elucidate if the protective functions of the egg proteins of Pomacea canaliculata (Caenogastropoda, Ampullariidae), involved in embryo defenses, are present in other Pomacea species we studied scalarin (PsSC), the major perivitellin of Pomacea scalaris. Using small angle X-ray scattering, fluorescence and absorption spectroscopy and biochemical methods, we analyzed PsSC structural stability, agglutinating activity, sugar specificity and protease resistance. PsSC aggluttinated rabbit, and, to a lesser extent, human B and A erythrocytes independently of divalent metals Ca²⁺ and Mg²⁺ were strongly inhibited by galactosamine and glucosamine. The protein was structurally stable between pH 2.0 to 10.0, though agglutination occurred only between pH 4.0 to 8.0 (maximum activity at pH 7.0). The agglutinating activity was conserved up to 60°C and completely lost above 80°C, in agreement with the structural thermal stability of the protein (up to 60°C). PsSC was able to withstand in vitro gastrointestinal digestion, and showed no trypsin inhibition activity. The presence of lectin activity has been reported in eggs of other Pomacea snails, but here we link for the first time, this activity to an apple snail multifunctional perivitellin. This novel role for a snail egg storage protein is different from closely related P.canaliculata defensive proteins.     

Clutch frequency affects the offspring size-number trade-off in lizards

Background

Studies of lizards have shown that offspring size cannot be altered by manipulating clutch size in species with a high clutch frequency. This raises a question of whether clutch frequency has a key role in influencing the offspring size-number trade-off in lizards.

Methodology/Principal Findings

To test the hypothesis that females reproducing more frequently are less likely to tradeoff offspring size against offspring number, we applied the follicle ablation technique to female Eremias argus (Lacertidae) from Handan (HD) and Gonghe (GH), the two populations that differ in clutch frequency. Follicle ablation resulted in enlargement of egg size in GH females, but not in HD females. GH females switched from producing a larger number of smaller eggs in the first clutch to a smaller number of larger eggs in the second clutch; HD females showed a similar pattern of seasonal shifts in egg size, but kept clutch size constant between the first two clutches. Thus, the egg size-number trade-off was evident in GH females, but not in HD females.

Conclusions/Significance

As HD females (mean  = 3.1 clutches per year) reproduce more frequently than do GH females (mean  = 1.6 clutches per year), our data therefore validate the hypothesis tested. Our data also provide an inference that maximization of maternal fitness could be achieved in females by diverting a large enough, rather than a higher-than-usual, fraction of the available energy to individual offspring in a given reproductive episode.     

Maternal investment in reproduction and its consequences in leatherback turtles

Maternal investment in reproduction by oviparous non-avian reptiles is usually limited to pre-ovipositional allocations to the number and size of eggs and clutches, thus making these species good subjects for testing hypotheses of reproductive optimality models. Because leatherback turtles (Dermochelys coriacea) stand out among oviparous amniotes by having the highest clutch frequency and producing the largest mass of eggs per reproductive season, we quantified maternal investment of 146 female leatherbacks over four nesting seasons (2001–2004) and found high inter- and intra-female variation in several reproductive characteristics. Estimated clutch frequency [coefficient of variation (CV) = 31%] and clutch size (CV = 26%) varied more among females than did egg mass (CV = 9%) and hatchling mass (CV = 7%). Moreover, clutch size had an approximately threefold higher effect on clutch mass than did egg mass. These results generally support predictions of reproductive optimality models in which species that lay several, large clutches per reproductive season should exhibit low variation in egg size and instead maximize egg number (clutch frequency and/or size). The number of hatchlings emerging per nest was positively correlated with clutch size, but fraction of eggs in a clutch yielding hatchlings (emergence success) was not correlated with clutch size and varied highly among females. In addition, seasonal fecundity and seasonal hatchling production increased with the frequency and the size of clutches (in order of effect size). Our results demonstrate that female leatherbacks exhibit high phenotypic variation in reproductive traits, possibly in response to environmental variability and/or resulting from genotypic variability within the population. Furthermore, high seasonal and lifetime fecundity of leatherbacks probably reflect compensation for high and unpredictable mortality during early life history stages in this species.     

Control the egg hatchling process of Pomacea canaliculata (Lamarck) by water spraying and submersion

Pomacea canaliculata (Lamarck) is an invasive snail species that has become a serious pest of rice and other hydrophytes. Usually it is aquatic but likes to lay its eggs higher than the waterline. In order to seek a feasible and efficient way to control the egg hatchling of this pest, here we systematically studied the effects of water spraying and submersion on its egg hatchling rates and durations. Our results demonstrated that water spraying and submersion could dramatically decrease the hatchling rates to maximal 5.8% and increase the hatchling duration up to 26.4 days on P. canaliculata. Not only the beginning time of water treatment, but also the frequencies of the water spraying is critical to control the hatchling rate and duration of P. canaliculata. Water submersion that began in 12 h after the eggs laid and lasted at least 48 h will significantly decrease the snails’ hatchling rates and extend the hatchling time. In addition, compared to spraying, the water submersion could achieve more remarkable effects. The capsule of the snail’s egg is able to withstand the water treatment. Based on our water spraying and submersion results, it can be inferred that 0–6 h after egg being laid, egg capsule precipitates are beginning to form, and this process will complete after 12–24 h. This special breeding characteristic of P. canaliculata makes the physical control by water treatment become feasible.