How do microplastics alter molluscicidal activity? Effects of weathered microplastics and niclosamide in developing freshwater snails.

Despite the wide distribution and persistence of microplastics (MPs), their interactive effects with molluscicides are unknown. Schistosomiasis, a neglected tropical disease, affects 236.6 million people worldwide. Niclosamide (NCL) is the only molluscicide recommended by the World Health Organization (WHO) and it is used to control the population of Schistosoma spp.'s intermediate host. Thus, this study aimed to evaluate of the interaction between polyethylene (PE) MPs and NCL, and their associated toxicity in the freshwater snail Biomphalaria glabrata (Say 1818). Weathered PE MPs were characterized and theoretical analysis of NCL-MP adsorption nature was made using quantum mechanical calculations. The toxicity of NCL isolated (0.0265 to 0.0809 mg L-1) and under interaction with PE MPs (3400 µg L-1) in B. glabrata embryos and newly hatched snails was analyzed. In silico analysis confirmed the adsorption mechanisms of NCL into PE MPs. PE MPs decreased the NCL toxicity to both B. glabrata developmental stages, increasing their survival and NCL lethal concentrations, indicating concerns regarding NCL use as molluscicide in aquatic environments polluted by MPs. In conclusion, MPs may change the efficiency of chemicals used in snail control programs.

Assessing the molluscicidal and biochemical activities of New-Fort®, an inorganic fertilizer against Theba pisana snails.

Terrestrial snails are a significant issue in agricultural production worldwide. The use of nitrogen - phosphorus - potassium (NPK) based fertilizers played an important role in meeting the food demand throughout the world, so its effectiveness against land snails needs to be investigated. This study was conducted to evaluate toxic lethal effect of New-Fort®, an inorganic NPK based fertilizer, in the field for 3, 7 and 10 days and in the laboratory for 24, 48 and 72 h against Theba pisana snails. Also, the impact of its sub-lethal doses (1/10, 1/5, 1/4 and 1/2 of 48 h-LD50) on biochemical parameters were determined under laboratory conditions. The results showed that the snails percent reduction in the field were 21.4, 61.0 and 80.0 % after 10 days' application of quarter, half and one field rate and the values of LD50 in the laboratory were 4.94, 4.56 and 4.24 mg/g b.w at 24, 48 and 72 h, respectively. New-Fort® sub-lethal doses caused a significant inhibition in catalase, γ-glutamyl transferase and acetylcholinesterase activities. It also elicited a significant elevation in glutathione S-transferase activity post exposure to 1/10 and 1/5 of LD50, whereas an opposite effect was occurred after exposure to 1/4 and 1/2 of LD50. Lipid peroxidation level was reduced in snails treated with 1/10 and 1/5 of LD50, whereas it increased in 1/4 and 1/2 of LD50- treated snails. Moreover, a significant inhibition in alkaline phosphatase activity at all tested doses, with the exception of 1/2 of LD50 was observed. An increase in alanine aminotransferase and aspartate aminotransferase activities were occurred after all tested doses exposure. Our findings highlighted on how biochemical changes can be exploited to better understand the mechanisms underlying New-Fort® fertilizer toxicity against the land snail, T. pisana, as well as how to benefit from NPK fertilizers application in snail control.

Ovicidal, immunotoxic and endocrine disrupting effects of saponin on Bulinus truncatus snails with special emphasize on the oxidative stress parameters, genotoxicological, and histopathological alterations.

Bulinus truncatus snail is one of the most medically important snails. The goal of this study was to evaluate the molluscicidal effect of saponin on these snails and study how it affects their biological functions. The present results showed that saponin had a molluscicidal activity against adult B. truncatus snails after 24h and 72h with LC50 (57.5 and 27.1 ppm, respectively) and had ovicidal acivity on the snails' embryos. By studying the effect of the sublethal concentrations (LC10 48.63 ppm or LC25 52.83 ppm) exposure on B. truncatus snails, they resulted in significant decreases in the survivorship, egg-laying, and the reproductive rate compared to untreated snails. Both concentrations caused morphological changes to the snails' hemocytes, where, after the exposure, granulocytes and hyalinocytes had irregular outer cell membrane and some cell formed pseudopodia. Granulocytes had large number of granules, vacuoles, while hyalinocytes' nucleus was shrunken. Also, these concentrations resulted in significant increases in sex hormone levels (17ß-estradiol and testosterone) in tissue homogenate of B. truncatus snails. It resulted in significant decrease in total antioxidant (TAO) activity, while, significantly increased lipid peroxidase (LPO) level, superoxide dismutase (SOD), nitrogen oxide (NO), and glutathione-S-transferase (GST) as compared to control group. Histopathological and genotoxicological damages occurred in snails' tissue after exposure to these concentrations. Conclusion, saponin has a molluscicidal effect on B. truncatus snails and might be used for the control of schistosomiasis haematobium. Besides, these snails could be used as invertebrate models to reflect the toxic effects of saponin in the aquatic ecosystem.

Bioactivity of substances isolated from natural products on mollusks Biomphalaria glabrata (Say, 1818) (Planorbidae): a review.

Schistosomiasis is a neglected tropical disease caused by parasitic worms of several species of the genus Schistosoma. Transmission occurs by parasitic larvae that stay in freshwater snails of the genus Biomphalaria. Thus, the search for new products that are biodegradable has increased the interest in products of plant origin. The aim of this article is to review the isolated substances from natural products that showed molluscicidal activity against the species Biomphalaria glabrata in order to reevaluate the most promising prototypes and update the progress of research to obtain a new molluscicide. We perform searches using scientific databases, such as Scientific Electronic Library Online (SciELO), Google schoolar, PUBMED, Web of Science and Latin American and Caribbean Literature on Health Sciences (LILACS). From 2000 to 2022, using the keywords "isolated substances", "molluscicidal activity" and "Biomphalaria glabrata". In the present study, it was possible to observe 19 promising molluscicidal molecules with a lethal concentration below 20 µg/mL. Of these promising isolates, only 5 isolates had the CL90 calculated and within the value recommended by WHO: Benzoic acid, 2',4',6'-Trihydroxydihydrochalcone, Divaricatic acid, Piplartine and 2-hydroxy-1,4-naphthoquinone (Lapachol). We conclude that beyond a few results in the area, the researches don't follow the methodological pattern (exposure time and measure units, toxicity test), in this way, as they don't follow a pattern on the result's exposure (LC), not following, in sum, the recommended by WHO.

Bio-molluscicidal potential and biochemical mechanisms of clove oil and its main component eugenol against the land snail, Theba pisana.

The land snail, Theba pisana is a serious pest that adversely affects various crops in sustainable agriculture. Essential oils and their constituents represent an environmentally sound alternative to synthetic pesticides. Our study aimed to investigate the lethal and sub-lethal toxicity of clove oil and its main component eugenol to understand the mechanisms underlying its toxic action against T. pisana. The GC-MS profile of the clove oil composition was characterized. In the laboratory experiment, LD50 of clove oil and eugenol via the contact testing were determined after 48 and 72 h. Moreover, sub-lethal effects of clove oil or eugenol on the survivors following the exposure of snails to the 25 and 50% of the LD50/48 and 72 h were evaluated through using snail tissues for biochemical measurments. The GC-MS analysis showed that eugenol (64.87%) was the major constituent present in the oil. The results also showed that LD50 values at 48 and 72 h were 2006.5 and 1493.5 µg/g b.w for oil and 239.6 and 195.3 µg/g b.w for eugenol, respectively. Compared to control, the sub-lethal effects of clove oil or eugenol at 48 and 72 h showed a significant increase in reduced glutathione (GSH) levels. Catalase (CAT) and glutathione-S-transferase (GST) activities significantly elevated in oil- or eugenol-treated snails, except at low dose after 48 h. After two exposure times, snails exposed to oil or eugenol at both sub-lethal effects had considerably higher γ-glutamyltransferase (γ-GT) and aspartate aminotransferase (AST) activities. Moreover, markedly augmentation in alkaline phosphatase (ALP) and alanine aminotransferase (ALT) activities at all exposure times, with the exception of snails treated with low dose of eugenol after 48 h was observed. Both clove oil and eugenol at the tested doses caused a significant inhibition in acetylcholinesterase (AChE) activity at two exposure times. Our findings highlight the potential of clove oil and eugenol, as an efficient natural molluscicide alternative to its synthetic counterparts for snail control.

Molluscicidal activity of plant alkaloids.

Some snail species pose a serious threat for human health, economy, and the environment due to their widespread distribution and the transmission of dangerous parasites causing, among others, schistosomiasis and fascioliasis. Scientists from around the world have been studying the effects of plant extracts on snails for many years in order to find an alternative to molluscicides of synthetic origin. The main purpose of this study was to collect the results obtained so far on the effect of plant alkaloids on snails in the context of their molluscicidal properties. This work presents the results of publications on the effect of plant alkaloids on snails, which were published in the years 1974-2021. The Solanaceae, Papaveraceae, and Asteraceae are the plant families most frequently cited for containing alkaloids with molluscicidal activity. The alkaloids identified as molluscicidal belonged to various groups, of which the most numerous were pseudoalkaloids and tyrosine-derived alkaloids. Most of the tested alkaloids were characterized by a high mortality rate among the studied groups of snails. Based on the collected research results, it was found that plant alkaloids can be extremely useful in the fight against problematic species of snails and cause much lower harm to the environment than synthetic molluscicides.

Toxicological effects of Saponin on the free larval stages of Schistosoma mansoni, infection rate, some biochemical and molecular parameters of Biomphalaria alexandrina snails.

Saponins have been used as biopesticides. The objective of the present study is to investigate the toxic effects of Saponin against Biomphalaria alexandrina snails. Results showed that Saponin exhibited a molluscicidal activity against adult B. alexandrina snails at LC50 (70.05 mg/l) and had a larvicidal effect on the free larval stages of Schistosoma mansoni. To evaluate the lethal effects, snails were exposed to either LC10 (51.8 mg/l) or LC25 (60.4 mg/l) concentrations of Saponin. The survival, the infection rates, protein, albumin, and total fat levels were decreased, while glucose levels were increased in exposed snails compared to control snails. Also, these concentrations significantly raised Malondialdehyde (MDA) and Glutathione S Transferase (GST) levels, whereas reduced Superoxide dismutase (SOD) activity and the total antioxidant capacity (TAC) in exposed snails. Furthermore, these concentrations resulted in endocrine disruptions where it caused a significant increase in testosterone (T) level; while a significant decrease in Estradiol (E2) levels were noticed. As for Estrogen (E) level, it was increased after exposure to LC10 Saponin concentration while after exposure to LC25 concentration, it was decreased. Also, LC10 and LC25 concentrations of Saponin caused a genotoxic effect and down-regulation of metabolic cycles in the snails. In conclusion, Saponins caused deleterious effects on the intermediate host of schistosomiasis mansoni. Therefore, B. alexandrina snails could be used as models to screen the toxic effects of Saponins in the aquatic environment and if it was used as a molluscicide, it should be used cautiously and under controlled circumstances.

Exposition of Intermediate Hosts of Schistosomes to Niclosamide (Bayluscide WP 70) Revealed Significant Variations in Mortality Rates: Implications for Vector Control.

(1) Background: Schistosomiasis remains a public health issue in Cameroon. Snail control using Niclosamide can prevent schistosome transmission. It is safe to determine lethal concentrations for the population. This study aimed at assessing the toxicity of Niclosamide on different developmental stages of snail populations; (2) Methods: Snails were collected, identified, and reared in the laboratory. Egg masses and adult snails were exposed to Niclosamide, at increasing concentrations (0.06, 0.125, 0.25, 0.5, 1 mg/L for egg embryos and 0.06, 0.08, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2 mg/L for adults). After 24 h exposure, egg masses and snails were removed from Niclosamide solutions, washed with source water and observed; (3) Results: Snail susceptibility was species and population dependent. For egg embryos, Biomphalaria pfeifferi was the most susceptible (LC50: 0.1; LC95: 6.3 mg/L) and Bulinus truncatus the least susceptible (LC50: 4.035; LC95: 228.118 mg/L). However, for adults, B. truncatus was the most susceptible (mortality rate: 100%). The LC50 and LC95 for Bi. camerunensis eggs were 0.171 mg/L and 1.102 mg/L, respectively, and were higher than those obtained for adults (0.0357 mg/L and 0.9634 mg/L); (4) Conclusion: These findings will guide the design of vector control strategies targeting these snail species in Cameroon.

Research on the molluscicidal activity and molecular mechanisms of arecoline against Pomacea canaliculata.

Pomacea canaliculata, as an invasive snail in China, can adversely affect agricultural crop yields, ecological environment, and human health. In this paper, we studied the molluscicidal activity and mechanisms of arecoline against P. canaliculata. The molluscicidal activity tests showed that arecoline exhibits strong toxicity against P. canaliculata, and the LC50 value (72 h) was 1.05 mg/L (15 ± 2 mm shell diameter). Additionally, Molluscicidal toxicity were negatively correlated with the size of snails. Snails (25 ± 2 mm shell diameter) were choosed for mechanisms research and the result of microstructure and biochemistry showed that arecoline (4 mg/L, 20 â„ƒ) had strong toxic effect on the gill, and the main signs were the loss of cilia in the gill filaments. Moreover, arecoline significantly decreased the oxygen consumption rate, ammonia excretion rate and inhibited acetylcholinesterase (AChE). Then, the changes in protein expression were studied by iTRAQ, and 526 downregulated proteins were found. Among these, cilia and flagella-associated 157-like (PcCFP) and rootletin-like (PcRoo) were selected as candidate target proteins through bioinformatics analysis, and then RNA interference (RNAi) was adopted to verify the function of PcCFP and PcRoo. The results showed that after arecoline treated, the mortality and the cilia shedding rate of PcRoo RNAi treated group was significantly lower than control group. The above results indicate that arecoline can bind well with protein PcRoo, and then leads to the drop of gill cilia, affect respiratory metabolism, accelerate its entry into hemolymph, inhibit AChE and finally leads to the death of P. canaliculata.

Toxicological impact of organophosphorus Chlorpyrifos 48%EC pesticide on hemocytes, biochemical disruption, and molecular changes in Biomphalaria alexandrina snails.

Organophosphorus pesticides like Chlorpyrifos 48%EC were widely used to control agricultural pests. The present study aimed to evaluate the toxic effects of Chlorpyrifos 48%EC on B. alexandrina snails, the intermediate host of Schistosoma mansoni. After exposure of snails to serial concentrations to determine the LC50, thirty snails for each sublethal concentration (LC10 2.1 and LC25 5.6 mg/l) in each group were exposed for 24 h followed by another 24 h for recovery. After recovery random samples were collected from hemolymph and tissue to measure the impacts on Phagocytic index, histological, biochemical, and molecular parameters. The current results showed a toxic effect of Chlorpyrifos 48%EC on adult B. alexandrina snails after 24 h of exposure at LC50 9.6 mg/l. After exposure to the sub-lethal concentrations of this pesticide, it decreased the total number of hemocytes and the percentage of small cells, while increased the percentage of hyalinocytes. The granulocyte percentage was increased after exposure to LC10, while after LC25, it was decreased compared to the control group. Also, the light microscopical examination showed that some granulocytes have plenty of granules, vacuoles and filopodia. Some hyalinocytes were contained shrinked nuclei, incomplete cell division and forming pseudopodia. Besides, the phagocytic index of hemocytes was significantly increased than control in all treated groups. Also, these sub-lethal concentrations increased MDA and SOD activities, while, tissue NO, GST and TAC contents were significantly decreased after exposure. Levels of Testosterone (T) and Estradiol (E) were increased significantly after exposure compared with control group. The present results showed that the concentration of DNA and RNA was highly decreased after exposure to LC10, 25 than the control group. Therefore, B. alexandrina snails could be used as a bio monitor of the chemical pollution. Besides, this pesticide could reduce the transmission of schistosomiasis as it altered the biological system of these snails.

Molluscicidal and biochemical effects of green-synthesized F-doped ZnO nanoparticles against land snail Monacha cartusiana under laboratory and field conditions.

The glass clover snail, Monacha cartusiana (M. cartusiana) is one of the most seriously impacting economic animal pests spreading across Egypt which inflicts severe damages to the agriculture. A green route is developed by deploying an abundant Rosemary plant leaves aqueous extract to synthesize ZnO and F-doped ZnO (F-ZnO) nanoparticles (NPs) that display high molluscicidal activities against the M. cartusiana land snails via leaf dipping and contact techniques. The effect of lethal concentrations, that kills 50% of exposed snails (LC50) value of the treatments, is examined on the activity of alkaline phosphatase (ALP), aspartate aminotransferase (AST), alanine aminotransferase (ALT), enzymes, total protein (TP), total lipids (TL) and cholesterol level of snails, including the histopathological evaluation of the digestive gland and foot of M. Cartusiana. Their molluscicidal activity as poisonous baits under field conditions is also evaluated and compared to the recommended molluscicide, Neomyl. The results show that F- doping dramatically improves the snail control capability of ZnO NPs, and promotes a considerable increase in both ALT and AST enzymes with an enhancement of TL and Cholesterol levels, but a significant decrease in TP content and ALP activity in treated snails compared to the control group. The LC50 values are found to be 1381.55 and 2197.59 ppm using the leaf dipping for F-ZnO and ZnO, while 237.51 and 245.90 ppm can be achieved using the contact technique, respectively. The greenly synthesized F-ZnO and ZnO NPs induce severe histological alterations in the digestive gland and foot of M. cartusiana, including a complete destruction of the digestive tubules. The histological evaluation of the foot of M. cartusiana exposed to ZnO, shows a rupture of the epithelial layer of the foot sole, while F- ZnO NPs causes the folds of the foot becoming deeper and the rupture of epithelial layer. Our field experiments further demonstrate that F-ZnO achieves 60.08% reduction, while ZnO attains 56.39% diminution in snail population compared to the commercial, Neomyl (69.55%), exhibiting great potentials in controlling the harmful land snail populations.

Biomphalaria embryotoxicity test (BET): 60 years of research crossing boundaries for developing standard protocols.

Snail's embryotoxicity test is a suitable approach for toxicity assay of traditional and emerging pollutants, environmental risk assessment, as well as screening and development of new molluscicides. Among the snail species, Biomphalaria spp. has been indicated as a promising model system for developing standardized test protocols for assessing the chemical toxicity using early developmental stages. Thus, the current study aimed to review the data available in the scientific literature concerning the experimental approach, type of chemicals and the response of multiple biomarkers (survival, hatching rate, development delays, morphological and behavior changes) in snail embryos applied in toxicity tests. Revised data showed that the use of Biomphalaria embryos to assess chemical toxicity began in 1962. Snail's embryotoxicity test was applied mainly for analyzing the toxicity and development of new molluscicides, while its use in ecotoxicological studies is emerging. Biomphalaria glabrata was the main species analyzed. Embryos exposed to chemicals showed bioaccumulation, mortality, hatching inhibition, development delays, and morphological malformations, which were classified into four categories (hydropic, shell, cephalic and unspecified malformations). Besides, research gaps and recommendations for future research are indicated. Overall, the results showed that the Biomphalaria embryotoxicity test (BET) is a suitable tool for toxicity and health risk assessment.

Molluscicidal and cercaricidal activities of the essential oil of Dysphania ambrosioides (L.) Mosyakin & Clemants: Implications for the control of schistosomiasis.

Schistosomiasis is one of the most important tropical diseases. A fundamental strategy to control its spread is the use of natural products against its vectors, which are snails of the genus Biomphalaria. The present study evaluated the chemical composition, the molluscicidal and cercaricidal effects, and the ecotoxicity of the essential oil from the aerial parts of Dysphania ambrosioides (L.) Mosyakin & Clemants (DAEO). The essential oil was obtained by hydrodistillation and analyzed by gas chromatography-mass spectrometry (GC-MS). Molluscicidal and cercaricidal activities were determined by the immersion method. Environmental toxicity was assessed from bioassays using Artemia salina larvae and Danio rerio fish. DAEO presented a 0.8% yield. The GC-MS analysis revealed the predominance of hydrocarbon monoterpenes in the oil. A total of 32 constituents was identified, with α-terpinene (50.69%) being the major compound, followed by p-cymene (13.27%) and ascaridole (10.26%). DAEO was active against adult Biomphalaria glabrata snails and demonstrated lethal effect against Schistosoma mansoni cercariae, with LC50 values of 25.2 (22.7-27.8) and 62.4 (61.8-62.9) µg/mL, respectively. Regarding toxicity to non-target aquatic organisms, the oil showed LC50 values of 86.9 (84.7-87.6) and 18.6 µg/mL (15.5-22.8) for A. salina and D. rerio, respectively. DAEO proved to be a promising natural product for the control of schistosomiasis, acting on both the vectors and the etiological agent of the disease. However, the use of the oil is safer in transmission sites where there are no non-target organisms, as it has showed toxicity to D. rerio fish.

Emamectin benzoate as a potential molluscicide against white garden snail, Theba pisana in association with biochemical defects.

BACKGROUND: The white garden snail, Theba pisana, is distributed worldwide and is a serious molluscan pest of different crops. Emamectin benzoate (EMB) 'an avermectin derivative' is a novel biorational agent and highly effective pesticide. This study focused on the lethal and in vivo sublethal toxic effect of EMB on the energy reserves (glycogen, lipids and proteins), total energy reserves and activities of glutathione S-transferase (GST), γ-glutamyl transferase (γ-GT), lactate dehydrogenase (LDH), aspartate aminotransferase (AST) and alanine aminotransferase (ALT) in the hepatopancreas of T. pisana for up to 7 days of exposure. RESULTS: The median lethal dose (LD50 ) at 48 h of EMB treatment was 5.34 µg g-1 body weight (b.w.). Sublethal doses of 1.07 and 3.20 µg g-1 b.w. (i.e., 20% and 60% of the LD50 ) led to significant dose- and time-dependent decreases in glycogen and lipids; these doses increased the total protein level. Overall, the tested sublethal doses significantly decreased the total energy reserves. Moreover, GST and γ-GT activities were elevated, whereas the activities of AST and ALT were inhibited in the exposed snails. A decrease in LDH activity after 1 and 3 days of exposure and an increase after 7 days of exposure were seen in snails treated with EMB. CONCLUSION: EMB exerted lethal toxicity on T. pisana and consequently caused changes in energy reserve levels and enzyme activities in the animal. © 2022 Society of Chemical Industry.

Control of the Invasive Agricultural Pest Pomacea canaliculata with a Novel Molluscicide: Efficacy and Safety to Nontarget Species.

The golden apple snail Pomacea canaliculata is an invasive pest that causes extensive damage to agricultural production. P. canaliculata is also an intermediate host of Angiostrongylus cantonensis, which causes human eosinophilic meningitis. In this study, the molluscicidal activity and safety profile of a novel molluscicide PBQ [1-(4-chlorophenyl)-3-(pyridin-3-yl)urea] were evaluated. PBQ exhibited strong molluscicidal potency against adult and juvenile snails (LC50 values of 0.39 and 0.07 mg/L, respectively). In field trials, PBQ killed 99.42% of the snails at 0.25 g a.i./m2. An acute toxicity test in rats demonstrated that PBQ is a generally nonhazardous chemical. PBQ is also generally safe for nontarget organisms including Brachydanio rerio, Daphnia magna, and Apis mellifera L. Transcriptomics analysis revealed that PBQ had a significant impact on the carbohydrate and lipid metabolism pathways, which provided insights into its molluscicidal mechanism. These results suggest that PBQ could be developed as an effective and safe molluscicide for P. canaliculata control.

Evaluating the Life-History Responses of Adult Invasive (Bithynia tentaculata) and Native (Physa gyrina) Snails Exposed to a Cu-Based Pesticide (EarthTec® QZ).

The faucet snail, Bithynia tentaculata, is an invasive snail that facilitates outbreaks of waterfowl disease in the Upper Mississippi River of the United States. In response, there is interest in identifying strategies that mitigate its population and spread. In this study we assessed the effects of a copper (Cu) molluscicide, EarthTec® QZ, at three concentrations (0, 0.1 and 0.6 mg/L Cu) on adult B. tentaculata and a coexisting native species, Physa gyrina. We found that in the 0.6 mg/L Cu treatment, ~ 68% of B. tentaculata snails remained alive after a 4-day exposure whereas all P. gyrina snails died. In contrast, a majority of both snail species remained alive and active after 4 days in the control and 0.1 mg/L Cu treatments. Although B. tentaculata demonstrated higher survivorship, it bioaccumulated more Cu than P. gyrina. Additionally, examination of B. tentaculata individuals revealed that females tended to exhibit higher mortality than males.

Contact toxicity and biochemical impact of metaldehyde against the white garden snail Theba pisana (Müller, 1774).

BACKGROUND: Terrestrial snails are one of the most damaging threats to sustainable agriculture. Chemical control using molluscicides is the main approach used to combat these agricultural pests. Metaldehyde is the active ingredient in most snail control products in use. However, its toxicity indices and mode of action have scarcely been investigated. For the first time, we characterized the metaldehyde contact toxicity indices against the white garden snail Theba pisana. The biochemical impact of metaldehyde on acetylcholinesterase (AChE), aspartate aminotransferase (AST) and alanine aminotransferase (ALT), alkaline phosphatase (ALP) and glutathione S-transferase (GST) activities and the lipid peroxidation (LPO) level was investigated. RESULTS: The median lethal dose (LD50 ) values at 24, 48 and 72 h of treatment were 11.33, 8.53, and 6.87 µg g-1 body weight (BW), respectively; while, the median lethal time (LT50 ) values were 88.16, 55.85, and 25.67 h when doses of 6, 8, and 12 µg g-1 BW were applied, respectively. In the snails treated with 2.83 and 5.67 µg g-1 BW (» and ½ LD50 at 24 h of treatment) and 2.13 and 4.27 µg g-1 BW (» and ½ LD50 at 48 h of treatment), higher AChE, GST, AST, ALT, and ALP activities as well as higher levels of LPO were observed compared with that of untreated snails. CONCLUSION: Metaldehyde displayed dose- and time-dependent contact toxicity. The biochemical results suggest that metaldehyde may have neurotoxic and cytotoxic actions in terrestrial snails. Application of metaldehyde in ways that could control pest snails and slugs and reduce its negative impact on the environment are discussed. © 2021 Society of Chemical Industry.

Molluscicidal activity of Persea americana Mill. (Lauraceae) stem bark ethanolic extract against the snail Biomphalaria glabrata (Say, 1818): a novel plant-derived molluscicide?

Plant-derived molluscicides have been indicated as biodegradable and low-cost strategies for control of Biomphalaria spp., intermediate host for the Schistosoma. This study evaluated whether the crude ethanolic extract of the Persea americana stem bark has molluscicidal activity against embryos, newly-hatched and adults of Biomphalaria glabrata. The extract was obtained, characterized and its toxicity analyzed by snail embryotoxicity test (144 h) and acute toxicity test with newly-hatching and adult snails (96 h). Results showed the presence of flavonoids, anthraquinone heterosides, coumarins and tannins in the crude ethanolic extract, which showed molluscicidal activity against all life cycle stages of B. glabrata. The LC50 for embryos, newly-hatched and adults were 27.06, 30.60 and 55.55 ppm, respectively. Embryos exposed to the extract at 50 ppm showed hatching inhibition and at 6.2 and 25 ppm had the highest rates of morphological alterations, such as shell malformations and coagulation of the perivitelline substance. Adult snails exposed to the extract at 75 ppm showed a peak of behavioral changes, such as lethargy and shell reclusion, in addition to answers like hemolymph release in most concentrations. Further studies are required, prioritizing toxicity testing on non-target organisms and further elucidation of the active molecules.

[Acute toxicity of four heavy metal ions to Oncomelania hupensis].

OBJECTIVE: To assess the acute toxicity of Cu2+, Cd2+, Hg2+ and Pb2+ to Oncomelania hupensis. METHODS: Cu2+, Cd2+, Hg2+ and Pb2+ solutions were prepared at five concentrations, and 10 snails were exposed to each concentration for 24, 48, 72 h and 96 h. Then, the inhibition of snail activity and snail death was observed, and the half maximal effective concentration (EC50) and median lethal concentrations (LC50) were estimated. RESULTS: The 24, 48, 72 h and 96 h EC50 values of Cu2+, Cd2+, Hg2+ and Pb2+ were 0.74, 0.56, 0.46, 0.37 mg/L, 4.79, 3.52, 1.70, 1.26 mg/L, 1.90, 1.49, 0.83, 0.76 mg/L and 21.40, 9.98, 7.90, 5.42 mg/L for snails, respectively. The 96 h LC50 values of Cu2+, Cd2+, Hg2+ and Pb2+ were 0.43, 2.96, 1.12 mg/L and 12.22 mg/L for snails, the safe concentrations were 0.004 3, 0.029 6, 0.011 2, 0.122 2 mg/L, respectively. CONCLUSIONS: Cu2+ shows a high acute toxicity to snails, and Cd2+ and Hg2+ exhibit a moderate acute toxicity to snails, while Pb2+ is lowly toxic to snails.

Microcapsulated biocides for the targeted control of invasive bivalves.

Invasive alien species (IAS) are one of the greatest drivers of ecological change. Typically, control uses chemical agents that often are ineffective, harmful to non-target organisms, and environmentally persistent. Bivalves are frequently high impact IAS, but have proven particularly hard to control due to their valve-closing response when exposed to conventional control agents. Microencapsulation of biocides with edible coatings represents a highly targeted delivery route, bypassing avoidance responses and accumulating in bivalves through their prodigious filter feeding. Uneaten microcapsules degrade and become biologically inactive within hours thus reducing potential impacts on non-target biota. We manufactured two new formulations of microcapsules (BioBullets). Particles were designed to mimic natural food particles (algae) in terms of size (9.5 ± 0.5 to 19.4 ± 1.3 SE µm diameter), buoyancy (near neutral) and shape (spherical). Laboratory exposures demonstrated that two formulations effectively controlled the Gulf wedge clam Rangia cuneata, an IAS currently spreading rapidly through Europe. A single dose of 2-6 mg L-1 of the active ingredient in a static system achieved 90% mortality after 30 days of exposure. Microencapsulation offers an effective and targeted management tool for rapid responses following the early detection of both Gulf wedge clams and many other filter-feeding IAS, and may be especially effective in closed systems or where populations remain very localised.