Feeding deterrence of Azolla in relation to deoxyanthocyanin and fatty acid composition

Ecotoxicology is the science responsible for the study of the adverse effects of chemicals on ecosystems considering biotic and abiotic components. Several invertebrate groups have long been used to evaluate the aquatic toxicity of chemical compounds. Among these organisms, the microcrustaceans are the most recommended in Brazilian and international protocols (e.g. Daphnia sp. and Ceriodaphnia sp.). Until the beginning of the 1990s, the use of mollusks with ecotoxicological purposes was non-existent, except for the species tested as target of molluscicides in public health studies. Since the second half of this same decade the tests with mollusks have begun to be disseminated in several countries, valuing endemic species and especially the scarcity of test species in benthic habitats. In the early 2000s, with the disclosure of the harmful effects of pollutants with endocrine disrupting properties, gastropods have begun to be used not to evaluate lethal effects, but rather to observe physiological ...

Bioassays with freshwater snails Biomphalaria sp.: from control of hosts in public health to alternative tools in ecotoxicology

Applied aspects of Azolla-Anabaena symbiosis

In this study, the most effective agent was Difenoconazole (Score) followed by Asparagus densiflours then Oreopanax guatemalensis plants against Biomphalaria alexandrina snails. The high concentrations of the three tested agents caused a remarkable reduction in hatchability percent of B. alexandrina eggs than the low concentrations. The sublethal concentrations (LC10 and LC25) of both A. densiflorus and Score have more destructive effect on the survival, growth and reproductive rates of the juvenile snails than the corresponding concentrations of O. guatemalensis plant. Different sublethal concentrations (LCo and LC5) of the three agents caused a remarkable elevation in the activity of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) enzymes of the snails after the 1 st week of the exposure. The sublethal concentration LC5 of the three tested agents caused pronounced effect on the alkaline phosphatase (ALP) and acid phosphatase (ACP) activities after the 2 nd weeks of the exposure. Total protein, albumin, globulin and albumin/ globulin (A/G) ratio in hemolymph of snails exposed to sublethal concentration LCo of the three tested agents, are differently affected after the 1 st and 2 nd week of the exposure. The histological examinations demonstrated a severe damage in both secretory cells and digestive cells especially in case of Asparagus densiflours and Score.

Impact of Asparagus densiflours and Oreopanax Guatemalensis plants and Difenoconazole Fungicide on Biochemical Parameters of Biomphalaria Alexandrina Snails

Effect of the dry leaves powder water suspension of the plant Furcraea selloa marginata, belonging to family Agavaceae and Bacillus thuringiensis kurstaki (Dipel-2x) was evaluated against non-infected and Schistosoma mansoni-infected Biomphalaria alexandrina snails as well as their efficacy against the free larval stages of S. mansoni. The obtained results indicated that the LC50 and LC90 values after 24 hrs exposure were 53.66 & 84.35 ppm for F. selloa marginata and 392.3 & 483.64 ppm for B. thuringiensis kurstaki against adult B. alexandrina snails, respectively. The plant F. selloa marginata and B. thuringiensis kurstaki have a larvicidal activity against S. mansoni larvae (miracidia and cercariae), the plant F. selloa marginata was more toxic against larvae than B. thuringiensis kurstaki, the miracidia were more sensitive towards the toxic action of the tested agents than cercariae and the mortality percent of miracidia and cercariae is directly proportional to the time and the tested concentrations. The results revealed that the tested sub-lethal concentrations (LCo, LC10 and LC25) reduced the survival, growth rates and egg laying capacity of both non-infected and S. mansoni-infected snails during 12 weeks of exposure in comparison with their control group. The hatchability percent of B. alexandrina eggs of one, three and six days old exposed to LCo, LC10, LC25, LC50 & LC90 concentrations of F. selloa marginata and B. thuringinesis kurstaki, significantly decreased by increasing their age and the tested concentrations. Exposing B. alexandrina snails to sub-lethal concentrations of the tested agents for 24 hours either pre-, during or post exposure of snails to S. mansoni miracidia caused a marked reduction in the infection rate and decreased the mean total number of shedding cercariae/snail. Also, elongated their prepatent period (cercarial incubation period) and shortened the duration of cercarial shedding in comparison with their control group. Under semi-field conditions the more time of exposure to the concentration (LC90= 84.35 ppm) of the plant F. selloa marginata the more mortality among snails. The mortality rates of the snails were 0%, 2%, 18% and 30% at 3, 6, 12 and 24 hrs post exposure, respectively.

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Biological studies on Biomphalaria alexandrina snails treated with Furcraea selloa marginata plant (family: Agavaceae) and Bacillus thuringiensis kurstaki (Dipel-2x)

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

A. M. Abdel-Hafez

Papers

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