Potential of Hemianax ephippiger (Odonata-Aeshnidae) nymph as predator of Fasciola intermediate host, Lymnaea natalensis

Objective: To evaluate the predatory capacity of the Odonata, Hemianax ephippiger nymph as a biocontrol agent for the freshwater snail Lymnaea natalensis, intermediate host of Fasciola gigantica. Methods: Observations on the searching, attacking and devouring of the snails with a series of laboratory-based predation experiments, whose aims were to determine daily predation rate, differential predation on small-, medium- and large-sized snails were carried out. Results: Laboratory evaluation revealed that, the Odonata nymph could kill and consume all three sizes of snails. Searching and handling time of the predator differed depending on snail size and predator vulnerability. The predation rate varied also with respect to snail size and density.Conclusions: Our observations suggested that the predator Hemianax ephippiger may be a suitable bio-control agent of Lymnaea natalensis snail population.

Experimental evaluation of Odonata nymph in the biocontrol of schistosomiasis intermediate hosts

Objective:To evaluate the predatory potential of the Odonata nymph on freshwater snails that serve as intermediate hosts for Schistosoma species(Bulinus truncatus and Biomphalaria alexandrina).Methods:Observations on the searching,attacking and devouring of the two snail types with series of laboratory-based predation experiments,whose aims were to determine daily predation rate,differential predation,prey preference considering small-,mediumand large-sized snails were conducted.Results:Laboratory evaluation revealed that,the Odonata nymph could kill and consume the two intermediate hosts.The number of snails consumed differed according to the snail type,size and density.The times taken for searching and handling times were dependent on the snail size,type and satiation of the predator.The predation rate varied also with respect to snail type,size and density.This study also evaluated that Odonata nymphs consumed more Bulinus truncatus than Biomphalaria alexandrina per unit time,and that there may be a preference for smaller than larger snails.Conclusions:According to our observation,the predator,Hemianax ephippiger nymph may be a suitable biocontrol agent in connection with Schistosoma intermediate hosts.

In vitro efficacy of new synthetic benzimidazole-related compounds against Schistosoma mansoni adult worms

Objective:To evaluate the in vitro antischistosomal activity of two new synthetic benzimidazole-related compounds:NBTP-OH and NBTP-F.Methods:Schistosoma adult worms were recovered from mice infected with Schistosoma mansoni cercaria,washed and then incubated in the culture media with different concentrations of compounds NBTP-OH and NBTP-F up to 72 h.Scanning electron microscopy was conducted to report morphological changes.Results:Incubation of adult Schistosoma mansoni with 10 μg/mL of NBTP-OH for 48 h killed 81.25% of worms.The calculated LC50and LC90 72 h post-incubation were 6.8 μg/mL and 9.8 μg/mL,respectively.Exposure of worms to 10 μg/mL of NBTP-F killed89.5% of worms after 48 h,mostly males(83.3%),the LC50 and LC90 after 72 h of incubation were 4.8 μg/mL and 6.9 μg/mL,respectively.Worms incubated for 72 h with these compounds revealed swelling and deformity of oral sucker,disorganization and erosion of the tegument when examined with scanning electron microscopy.Conclusions:NBTP-OH and NBTP-F possess in vitro antischistosomal activities;however,in vivo studies should be conducted to examine their antischistosomal effects..

Molluscicidal effectiveness of Luo-Wei,a novel plant-derived molluscicide,against Oncomelania hupensis,Biomphalaria alexandrina and Bulinus truncatus

Background:Control of snail intermediate hosts has been proved to be a fast and efficient approach for interrupting the transmission of schistosomiasis.Some plant extracts have shown obvious molluscicidal activity,and a new compound Luo-Wei,also named tea-seed distilled saponin(TDS),was developed based on the saponins extracted from Camellia oleifera seeds.We aimed to test the molluscicidal activity of 4%TDS against the intermediate host snails in China and Egypt,and evaluate its environmental safety to non-target organisms.Methods:In the laboratory,Oncomelania hupensis,Biomphalaria alexandrina and Bulinus truncatus were exposed to 4%TDS,and the median lethal concentration(LC5o)was estimated at 24,48 and 72 h.In the field,snail mortalities were assessed 1,2,3 and 7 d post-immersion with 2.5 g/m34%TDS and 1,3,7 and 15 d post-spraying with 5 g/m24%TDS.in addition,the acute toxicity of 4%TDS to Japanese quail(Coturnixjaponica),zebrafish(Brachydanio rerio)and freshwater shrimp(Macrobrachium nipponense)was assessed by estimations of LC5o or median lethal dose(LD5o).Results:In the laboratory,the LC5o values of 4%TDS for O.hupensis were 0.701,0.371 and 0.33 mg/L at 24,48 and 72 h,respectively,and 4%TDS showed a 0.33 mg/L 24 h LC5o against B.alexandrina,and a 1.396 mg/L 24 h LCs0 against B.truncatus.Across all study regions,the pooled mortalities of O.hupensis were 72,86,94 and 98%at 1,2,3 and 7 d,following field immersion of 4%TDS at a dose of 2.5 g/m3,and were 69,77,85 and 88%at 1,3,7 and 15 d,following field spraying at 5 g/m2,respectively.4%TDS had moderate toxicity to Japanese quail(7 d LD5o>60 mg/kg)and to shrimp(96 h LCs0=6.28 mg/L;95%CI:3.53-11.2 mg/L),whereas its toxicity to zebrafish was high(96 h LCso--0.15 mg/L;95%CI:0.14-0.17 mg/L).Conclusions:4%TDS is active against O.hupensis,B.alexandrina and B.truncatus under laboratory and field conditions,and it may be a candidate molluscicide of plant origin.