Molluscicidal effect of nicotinanilide and its intermediate compounds against a freshwater snail Lymnaea luteola, the vector of animal schistosomiasis

Sublethal effects of niclosamide on the aquatic snail Pomacea canaliculata

Pomacea canaliculata is a malignant invasive aquatic snail found worldwide, and niclosamide (NS) is one of the primary agents used for its control. NS applied to water will exist in non-lethal concentrations for some time due to degradation or water exchange, thus resulting in sublethal effects on environmental organisms. To identify sublethal effects of NS on Pomacea canaliculata, we studied the aspects of histopathology, oxygen-nitrogen ratio (R_O∶N), enzyme activity determination, and gene expression. After LC₃₀ NS treatment (0.310 g/L), many muscle fibers of the feet degenerated and some acinar vesicles of the hepatopancreas collapsed and dissolved. The oxygen-nitrogen ratio (R_O∶N) decreased significantly from 15.0494 to 11.5183, indicating that NS had changed the metabolic mode of Pomacea canaliculata and shifted it primarily to protein catabolism. Transcriptome analysis identified the sublethal effects of LC₃₀ NS on the snails at the transcriptional level. 386, 322, and 583 differentially expressed genes (DEGs) were identified in the hepatopancreas, gills, and feet, respectively. GO (Gene Ontology) functional analysis and KEGG (Kyoto Encyclopedia of Genes and Genomes) pathway annotations showed that DEGs in the hepatopancreas were mainly enriched for sugar metabolism, protein biosynthesis, immune response, and amino acid metabolism functional categories; DEGs in the gills were mainly enriched for ion transport and amino acid metabolism; DEGs in the feet were mainly enriched for transmembrane transport and inositol biosynthesis. In the future, we will perform functional validation of key genes to further explain the molecular mechanism of sublethal effects.

Molluscicides against the snail-intermediate host of Schistosoma: a review

Schistosomiasis, a neglected tropical disease (NTD), is one of the most prevalent parasitoses in the World. Certain freshwater snail species are the intermediate host in the life cycle of schistosome species. Controlling snails employing molluscicides is an effective, quick, and convenient intervention strategy to prevent the spread of Schistosoma species in endemic regions. Advances have been made in developing both synthetic molluscicides and molluscicides derived from plants. However, at present, the development of molluscicides is not adapted to the actual demand for snails and schistosoma controlling. We undertake a systematic review of exploitation and application of synthetic molluscicides and molluscicides derived from plants to combat intermediate host snails. The detailed molluscicidal activity, structure–activity relationship, structural feature, and possible mechanism of some molluscicides are also highlighted, which may afford an important reference for the design of new, more effective molluscicides with low environmental impact and realize the aim of controlling schistosome at transmission stages.

Lethal Doses of Saponins from Quillaja saponaria for Invasive Slug Arion vulgaris and Non-Target Organism Enchytraeus albidus (Olygochaeta: Enchytraeidae)

Simple Summary

The Spanish slug, known by its scientific name Arion vulgaris, causes significant damage to agriculture and private gardens around the world. To control this pest, the use of saponin-rich plant extracts is gaining importance as they exhibit strong molluscicidal activity against gastropods and are safe (as saponin residues) in agriculture products. However, despite their proven safety in food, they still do not have a widespread application due to their liquid form and the absence of more accurate knowledge of their effects on other organisms. In this study we evaluated an extract from the bark of the soap tree Quillaja saponaria on slugs and on the white worms Enchytraeus albidus. It was found that slugs were significantly more sensitive to saponin extract at 2 and −1 °C compared to 15 °C. The lethal effect of saponins was stronger on adult slugs than on juveniles. However, lethal effect on worms was much stronger than on slugs. Overall, our results show that Q. saponaria saponins may be a successful slug control tool, especially during colder periods, but its concentration should be selected according to the age of slugs. However, high toxicity to white worms limits its use as an environmentally benign alternative means of slug control.

Abstract

The slug, Arion vulgaris Moquin-Tandon, 1855, is a serious pest in agriculture and private gardens. White worm, Enchytraeus albidus Henle, 1837, is an important model of decomposer organism in the terrestrial ecosystem. Saponins, which are secondary metabolites of plants, have previously been shown to have some molluscicidal effect. We investigated which doses of saponins are lethal to the slug, A. vulgaris, and to the non-target organism, E. albidus. An aqueous solution with different concentrations of saponin extract from the bark of the soap tree, Quillaja saponaria Mol., was used in repeat treatments. Slugs were tested in filter paper contact tests as they are naturally exposed to soil contact while crawling. Worms were tested in soil contact tests as they live below ground. It was found that lethality of saponins depends on the slug age group and the environmental temperature. The median lethal concentration (LC₅₀, at 15 °C) on adults was 68.5 g/L, and on juveniles, 96.9 g/L. The slugs were significantly more sensitive at 2 and −1 °C compared to 15 °C. The LC₅₀ (at 6 ℃) on E. albidus was 2.7 g/L (or 0.5 g/kg dry weight of soil), far below those in A. vulgaris (at 15 ℃ and lower). The LC₅₀ for worms at -1℃ was also significantly lower than at 6 ℃. Therefore, we can conclude: (1) that Q. saponaria saponins may be a successful slug control tool used during colder times of the year, but its concentration should be selected according to the age group of A. vulgaris; (2) this measure is more toxic than expected to white worms, which limits its use.

Molluscicidal activity of fatty acids in the kernel of Chimonanthus praecox cv. Luteus against the golden apple snail Pomacea canaliculata

The fatty acid composition of the kernel of Chimonanthus praecox cv. Luteus (FKC) was analyzed by gas chromatography-mass spectrometry (GC-MS), its ability to kill Pomacea canaliculata was detected, and the degree of damage and physiological and biochemical effects of an FKC soaking treatment on the hepatopancreas tissue of P. canaliculata were evaluated. In total, 16 fatty acids were detected in FKC, among which 13 were qualitatively identified; octadecadienoic acid (56.76%) and palmitic acid (17.03%) had the highest contents. After 48 h of treatment with FKC, the hepatopancreas of P. canaliculata had a large area of necrosis. The contents of soluble sugar, soluble protein, and albumin (Alb) in the hepatopancreas of P. canaliculata decreased with increasing FKC concentration. The content of malondialdehyde (MDA) and the activities of cereal third transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (AKP), and acetylcholinesterase (AChE) increased with increasing FKC concentration. The results showed that FKC has an obvious negative effect on the hepatopancreas cell structure and physiological function of P. canaliculata, i.e., has strong molluscicidal activity.

Toxicity of a molluscicide candidate PPU07 against Oncomelania hupensis (Gredler, 1881) and local fish in field evaluation

Schistosomiasis japonica caused by Schistosoma japonicum infection is recognized as a considerable economic and public health concern in Asia. Oncomelania hupensis is the sole intermediate host of S. japonicum. The only molluscicide recommended by World Health Organization (WHO) since 1960s is relative toxic to other aquatic species. In this article, we evaluated the novel molluscicide PPU07 in field trials on their efficiency against O. hupensis and toxicity for local fish. 25% PPU07 sulfate WP exhibited similar molluscicidal effect at 2.0 g/m² and 2.0 g/m³ in the spraying and immersion trials with the WHO recommended molluscicide niclosamide (1 g/m² and 1 g/m³). The mortality rates reached 95% and 96%, respectively. Moreover, little toxicity was observed for local fish and other aquatic organisms at the effective molluscicidal concentrations. In all, 25% PPU07 sulfate WP is a promising molluscicide for snail control, particularly in semi-commercial or commercial aquaculture ponds.

Discovery of the pyridylphenylureas as novel molluscicides against the invasive snail Biomphalaria straminea, intermediate host of Schistosoma mansoni

BACKGROUND

The snail Biomphalaria straminea is one of the intermediate hosts of Schistosoma mansoni. Biomphalaria straminea is also an invasive species, known for its strong capability on peripheral expansion, long-distance dispersal and colonization. Using molluscicides to control snail populations is an important strategy to interrupt schistosomiasis transmission and to prevent the spread of the invasive species. In this study, a series of pyridylphenylurea derivatives were synthesized as potential molluscicides. Their impact on adult snails and egg masses was evaluated. Acute toxicity to fish of the derivatives was also examined to assess their effect on non-target organisms. The preliminary mechanisms of action of the derivatives were studied by enzyme activity assays.

RESULTS

The representative compounds, 1-(4-chlorophenyl)-3-(pyridin-3-yl)urea (compound 8) and 1-(4-bromophenyl)-3-(pyridin-3-yl)urea (compound 9), exhibited strong molluscicidal activity against adult snails with LD₅₀ values of 0.50 and 0.51 mg/l and potent inhibitory effects on snail egg hatchability with IC₅₀ values of 0.05 and 0.09 mg/l. Notably, both compounds showed good target specificity with potent molluscicidal capability observed in snails, but very low toxicity to local fishes. Furthermore, the exposure of compounds 8 and 9 significantly elevated the enzyme activities of acid phosphatase and nitric oxide synthase of the snails, while no significant change was recorded in the activities of alkaline phosphatase, acetylcholine esterase and superoxide dismutase.

CONCLUSION

The results suggested that compounds 8 and 9 of pyridylphenylurea derivatives could be developed as promising molluscicide candidates for snail control.

A New Technique Using Low Volumes: A New Technique to Assess the Molluscicidal Activity Using Low Volumes

Schistosomiasis is a disease endemic in several states of Brazil. The population control of the transmitter mollusks is done with Bayluscide WP 70®, in the control programs. OMS preconize molluscicidal assays using Becker with 500 mL of final volume, restringing the number of natural products and synthetic drugs to be tested in function of high quantity of material necessary. A new technique to assess the toxic effects for Biomphalaria sp. is the purpose of this work, for developing adaptation for this aquatic organism, using a low volume of test solution in 24-well plates. We used Biomphalaria glabrata (10–12 mm size) in a static system, consisting of the following components: Becker containing 10 snails or 24-well plates where snails were individualized for a volume of 2 mL per well for 24 and 48 hours. For the assays, we added aqueous solutions of Bayluscide WP 70, at a concentration of 1–5 mg/L, distilled water, and 1% dimethyl sulfoxide. Data were evaluated using Kappa's coefficient, Z factor validation, and comparison study. This technique to assess the toxic effect has proven to be a useful tool to detect lethal and sublethal effects, which could be used as a new evaluation protocol.

Impact of Taraxerol in combination with extract of Euphorbia tirucalli plant on biological parameters of Lymnaea acuminata

The present work was carried out to evaluate the molluscicidal activity of active ingredient Taraxerol with the acetone extract of Euphorbia tirucalli against Lymnaea acuminata snail. The (fecundity, hatchability and survivability) of snail L. acuminata exposed to this extract was studied. The effects of the tested extracts on life-history traits of harmful snail L. acuminata have also been evaluated, and this study also expounds the inhibitory effects of these extracts singly as well as in binary combination (1:1 ratio). It concluded that these herbal products act as a potential source of molluscicides, and that they would also have the advantage of easy availability, low cost, biodegradability and greater acceptance amongst users than synthetic pesticide.

Comparative toxicity of Euphorbia milii latex and synthetic molluscicides to Biomphalaria glabrata embryos

Plant molluscicides have been regarded as possible alternatives to the costly and environmentally hazardous molluscicides currently available. This study was undertaken to compare the developmental toxicity of a plant molluscicide (Euphorbia milii latex, LAT) with that of three synthetic molluscicidal compounds. Biomphalaria glabrata egg masses (0-15 h after spawning) were exposed to molluscicides for 96 h and thereafter examined up to the 14th day after spawning. Embryo deaths, abnormal embryo development (malformations) and the day of hatching were recorded. Although exhibiting a weak ovicidal effect, LAT markedly impaired the development of snail embryos at concentrations 1000 microg L(-1) and produced anomalies (EC(50)=2040 microg L(-1)) such as abnormal shells, hydropic embryos, cephalic and non-specific malformations. Embryolethal potencies of molluscicides were as follows: triphenyltin hydroxide (TPTH; LC(50)=0.30 microg L(-1))>niclosamide (NCL; LC(50)=70 microg L(-1))>copper sulphate (CuSO(4); LC(50)=2190 microg L(-1)) >>> LAT (LC(50)=34030 microg L(-1)). A few malformations were recorded in embryos exposed to concentrations of TPTH within the range of lethal concentrations, while almost no anomalies were noted among those treated with NCL or CuSO(4). A hatching delay (hatching on day 10 after spawning or later) was observed among LAT-exposed embryos. The effects of NCL, TPTH and CuSO4 on hatching were to some extent masked by their marked embryolethality. The no-observed effect concentrations (NOEC) for embryotoxicity were as follows: TPTH, 0.1 microg L(-1); NCL, 25.0 microg L(-1); CuSO(4), 500.0 microg L(-1) and LAT, 500.0 microg L(-1). Results from this study suggest that, although LAT was not acutely embryolethal after a short-term exposure, it markedly disrupted snail development. The marked embryotoxicity of E. milii possibly contributes to its effectiveness as a molluscicide.

Molluscicidal activity of Hammada scoparia (Pomel) Iljin leaf extracts and the principal alkaloids isolated from them against Galba truncatula

The molluscicidal activity of Hammada scoparia leaf extracts and the principal alkaloids isolated from them (carnegine and N-methylisosalsoline) were tested against the mollusc gastropod, Galba truncatula, the intermediate host of Fasciola hepatica in Tunisia. The results indicated that the molluscicidal activity was correlated with the presence of alkaloids. A significant molluscicidal value, according to the World Health Organization, was found with the methanol extract (LC50 = 28.93 ppm). Further fractionation of the methanolic extract led to the isolation of two principal alkaloids: carnegine and N-methylisosalsoline. These alkaloids are isoquinolines that have not previously been characterised for their molluscicidal activity. The N-methylisosalsoline possesses the highest molluscicidal activity (LC50 = 0.47 microM against G. truncatula).

Synthesis of furo-salicylanilides and their heterocyclic derivatives with anticipated molluscicidal activity

The synthesis of new furo-salicylanilides and their heterocyclic derivatives is described. Twenty-three compounds were screened for their molluscicidal activity against Biomphalaria alexandrina snails, the intermediate host of Schistosoma mansoni. Five of the tested compounds showed no activity, while eighteen compounds showed strong to moderate activity using bayluscide as a reference.

The relative susceptibilities of juvenile and adult Bulinus globosus and Bulinus truncatus to the molluscicidal activities in the fruit of Ghanaian Blighia sapida, Blighia unijugata and Balanites aegyptiaca

The relative susceptibilities of juvenile (2- to 3-week-old) and adult (5- to 7-week-old) Bulinus globosus and Bu. truncatus to the molluscicidal activities of aqueous preparations of the powdered, dried fruits of Blighia sapida, Bl. unijugata and Balanites aegyptiaca were investigated under laboratory conditions. For the extract prepared from the freeze-dried, semi-ripe fruits of Bl. sapida, the concentrations killing 95% of the snails after an exposure for 24 h (LC95) were, respectively, 232.7 and 161.2 ppm for the juveniles and adults of Bu. globosus and 187.6 and 140.2 ppm for the juveniles and adults of Bu. truncatus. The corresponding values for Bl. unijugata were 136.9 and 98.7 ppm for Bu. globosus and 132.2 and 98.5 ppm for Bu. truncatus, respectively. Extracts of the freeze-dried, ripe fruit of Ba. aegyptiaca were much more active, however, giving LC95 of just 16.9 and 19.7 ppm for the juveniles and adults of Bu. globosus, and 14.2 and 12.0 ppm for the juveniles and adults of Bu. truncatus, respectively. In general, similar results were obtained when the fruit were oven-dried rather than freeze-dried but the potency of Balanites extracts produced from oven-dried fruit was relatively low. That the juvenile snails appeared less susceptible than the adults to the molluscicidal activity in each Blighia extract is interesting. This observation may have implications for snail control, in terms of the optimal frequency, timing and concentration of molluscicides applied in a particular habitat.