Larvicidal activity of oak <Emphasis Type="Italic">Quercus infectoria</Emphasis> Oliv. (Fagaceae) gall extracts against <Emphasis Type="Italic">Anopheles stephensi</Emphasis> Liston

There is a growing interest in the use of botanical insecticides to reduce the use of synthetic pesticides in order to avoid environmental side effects. Anopheles stephensi is the primary vector of urban malaria, an endemic disease in India. So, an effort to assay An. stephensi larvae with gall extracts of Quercus infectoria was made under laboratory conditions at Mysore. Ethyl-acetate extract was found to be the most effective of all the five extracts tested for larvicidal activity against the fourth instar larvae, with LC₅₀ of 116.92 ppm followed by gallotannin, n-butanol, acetone, and methanol with LC₅₀ values of 124.62, 174.76, 299.26, and 364.61 ppm, respectively. The efficacy in killing mosquito larvae may make this plant promising for the development of new botanical larvicide.     

Larvicidal and oviposition activity of <Emphasis Type="Italic">Cassia obtusifolia</Emphasis> Linn (Family: Leguminosae) leaf extract against malarial vector, <Emphasis Type="Italic">Anopheles stephensi</Emphasis> Liston (Diptera: Culicidae)

The ethanolic leaf extract of Cassia obtusifolia was investigated for their larvicidal and oviposition deterrence effects against Anopheles stephensi. Concentrations ranging from 25 to 125 mg/l were assessed at 24 h post-treatment against late third instar larvae. The leaf extract had significant larvicidal effect with LC(50) and LC(90) values were 52.2 and 108.7 mg/l, respectively. In oviposition behaviour study, four different concentrations ranging from 100 to 400 mg/l were studied against gravid female mosquitoes. The results of oviposition study indicated that the leaf extract showed concentration dependent oviposition deterrent activity. At higher concentration (400 mg/l) showed 92.5% effective repellency against oviposition, followed by 300, 200 and 100 mg/l showed 87.2%, 83.0% and 75.5%, respectively. The larvicidal and oviposition deterrent effect of C. obtusifolia against A. stephensi make this plant product promising as an alternative to synthetic insecticide in mosquito control programs.     

Larvicidal activity of silver nanoparticles synthesized using <Emphasis Type="Italic">Plumeria rubra</Emphasis> plant latex against <Emphasis Type="Italic">Aedes aegypti</Emphasis> and <Emphasis Type="Italic">Anopheles stephensi</Emphasis>

In the present study activity of silver nanoparticles (AgNPs) synthesized using Plumeria rubra plant latex against second and fourth larval instar of Aedes aegypti and Anopheles stephensi was determined. Range of concentrations of synthesized AgNps (10, 5, 2.5, 1.25, 0.625, 0.3125 ppm) and aqueous crude latex (1,000, 500, 250, 125, 62.50, 31.25 ppm) were tested against larvae of A. aegypti and A. Stephensi. The synthesized AgNps from P. rubra latex were highly toxic than crude latex extract in both mosquito species. The LC₅₀ values for second and fourth larval instars after 24 h of crude latex exposure were 1.49, 1.82 ppm against A. aegypti and 1.10, 1.74 ppm against A. stephensi respectively. These figures were 181.67, 287.49 ppm against A. aegypti and 143.69, 170.58 ppm against A. stephensi respectively for crude latex extract. The mortality rates were positively correlated with the concentration of AgNPs. The characterization studies of synthesized AgNPs by UV–Vis spectrophotometry, transmission electron microscopy (TEM), Particle size analysis (PSA) and zeta potential confirmed the spherical shape and size (32–200 nm) of silver nanoparticles alongwith stability. Toxicity studies carried out against non-target fish species Poecilia reticulata, the most common organism in the habitats of A. aegypti and A. stephensi showed no toxicity at LC₅₀ and LC₉₀ doses of the AgNPs. This is the first report on mosquito larvicidal activity of latex synthesized nanoparticles.     

<Emphasis Type="Italic">Amaranthus oleracea</Emphasis> and <Emphasis Type="Italic">Euphorbia hirta</Emphasis>: natural potential larvicidal agents against the urban Indian malaria vector, <Emphasis Type="Italic">Anopheles stephensi</Emphasis> Liston (Diptera: Culicidae)

Malaria control in developing countries is based largely on vector eradication by the use of mosquito larvicides which is an ideal method for controlling mosquito and the related epidemics. On account of ecohazardous nature, nontarget specificity of chemical insecticides and evidences of developing resistance against them in the exposed species, currently, importance of secondary plant metabolites has been acknowledged. Insecticides of plant origin are environmentally safe, degradable, and target specific. In view of this fact, the present work highlights the larvicidal property of extracts of Amaranthus oleracea and Euphorbia hirta against the third instar larvae of Anopheles stephensi, the urban malaria vector. LC₅₀ values for the carbon tetrachloride fraction of A. oleracea against larvae are 17,768.00 and 13,780.00 ppm after 24 and 48 h of exposure accordingly. For the methanol extract of the same, LC₅₀ values are 15,541.00 and 10,174.00 ppm after 24 and 48 h of exposure. In the case of petroleum ether extract, LC₅₀ values after 24 and 48 h of exposure are 848.75 and 311.50 ppm. LC₅₀ values for carbon tetrachloride extracts of E. hirta against the larvae are 11,063.00 and 10,922.00 ppm after 24 and 48 h of exposure, respectively. For methanol extract of the same extract, the LC₅₀ values are 19,280.00 and 18,476.00 ppm after 24 and 48 h of exposure. In the case of petroleum ether extract, LC₅₀ values after a 24- and 48-h exposure period are 9,693.90 and 7,752.80 ppm. The results obtained for petroleum extracts of A. oleracea are encouraging and there are probabilities that the active principle contained in this extract may be more effective than its crude form and may serve as ecofriendly mosquito larvicide.     

Effect of bioactive fractions of <Emphasis Type="Italic">Citrullus vulgaris</Emphasis> Schrad. leaf extract against <Emphasis Type="Italic">Anopheles stephensi</Emphasis> and <Emphasis Type="Italic">Aedes aegypti</Emphasis>

The benzene extract of Citrullus vulgaris was tested against Anopheles stephensi and Aedes aegypti for the larvicidal activity and ovicidal properties. The crude benzene extract was found to be more effective against A. stephensi than A. aegypti. The LC₅₀ values were 18.56 and 42.76 ppm respectively. The LC₅₀ values for silica gel fractions (bioactive fractions I, II, III and IV) were 11.32, 14.12, 14.53 and 16.02 ppm respectively. The mean per cent hatchability of the egg rafts were observed after 48 h post treatment. The crude extract of benzene exerted 100% mortality at 250 ppm against A. stephensi and at 300 ppm against A. aegypti. The silica gel fractions I and II afforded 100% mortality at 100 ppm and III and IV exerted the hatchability rate of 4.9 and 5.3% at the same concentration against A. stephensi.     

Mediation of oviposition responses in the malaria mosquito <Emphasis Type="Italic">Anopheles stephensi</Emphasis> Liston by certain fatty acid esters

The chemical factors involved in oviposition site selection by mosquitoes have become the focus of interest in recent years, and considerable attention is paid to the chemical cues influencing mosquito oviposition. Studies on synthetic oviposition attractants/repellents of long-chain fatty acid esters against Anopheles stephensi are limited. Screening and identification of chemicals which potentially attract/repel the gravid females to/or from oviposition site could be exploited for eco-friendly mosquito management strategies. The ester compounds demonstrated their ability to repel and attract the gravid A. stephensi females in the treated substrates. Significant level of concentration-dependent negative oviposition response of mosquitoes to octadecyl propanoate, heptadecyl butanoate, hexadecyl pentanoate, and tetradecyl heptanoate were observed. In contrast, decyl undecanoate, nonyl dodecanoate, pentyl hexadecanoate, and propyl octadecanoate elicited concentration-dependent positive oviposition responses from the gravid mosquitoes. Forcing a female to retain her eggs due to unavailability of a suitable oviposition site and attracting them to lay the eggs in a baited ovitraps shall ensure effective control of mosquito breeding and population buildup because the oviposition bioassay target the most susceptible stage of an insect life cycle. Treating relatively smaller natural breeding sites with an effective repellent and placing ovitraps containing an attractant in combination with insect-growth regulator (IGR)/insecticide would be a promising method of mosquito management.     

The efficacy of inhibitors involved in spermidine metabolism in<Emphasis Type="Italic"> Plasmodium falciparum</Emphasis>,<Emphasis Type="Italic"> Anopheles stephensi</Emphasis> and<Emphasis Type="Italic"> Trypanosoma evansi</Emphasis>

In the present study, we have tested the effect of different polyamine inhibitors of the spermidine metabolizing enzymes deoxyhypusine synthase and homospermidine synthase in different chloroquine resistant Plasmodium falciparum strains, in the mosquito Anopheles stephensi (Diptera: Culicidae) and in a Trypanosoma evansi clone I from strain STIB 806 K China. Recent experiments have shown that agmatine is a growth inhibitor of the malaria parasite P. falciparum (Kaiser et al. 2001) in vitro. A comparison of agmatine efficacy with the new antimalarials artemisinin, triclosan and conventional chloroquine showed similar or even better results on the basis of growth inhibition and the reduction of developmental forms. However, no effect of triclosan or agmatine was observed at the ribonucleic acid level. In a second set of experiments, we tested the effect of 1,7-diaminoheptane and agmatine on oocyst formation in A. stephensi after infection with Plasmodium yoelii. Agmatine had an antisporozoite effect since 1,000 M led to a 59.5% inhibition of oocysts. A much weaker inhibitor of oocyst formation was 1,7-diaminoheptane. The most effective in in vitro inhibition of T. evansi was dicyclohexylamine, an inhibitor of spermidine biosynthesis with an IC₅₀ value of 47.44 M and the deoxyhypusine inhibitor 1,7-diaminoheptane with an IC₅₀ value of 47.80 M. However, both drugs were ineffective in in vivo experiments in a Trypanosoma mouse model. Two different spermidine analogues, 1,8-diaminooctane and 1,3-diaminopropane with IC₅₀ values of 171 M and 181.37 M, respectively, were moderate inhibitors in vitro and ineffective in vivo.     

Larvicidal efficacy of <Emphasis Type="Italic">Jatropha curcas</Emphasis> and bacterial insecticide, <Emphasis Type="Italic">Bacillus thuringiensis</Emphasis>, against lymphatic filarial vector<Emphasis Type="Italic">, Culex quinquefasciatus</Emphasis> Say (Diptera: Culicidae)

The present study explored the effects of Jatropha curcas leaf extract and Bacillus thuringiensis israelensis larvicidal activity against the lymphatic filarial vector, Culex quinquefasciatus. Wights were selected for investigating the larvicidal potential against the first to fourth instar larvae of the laboratory-reared mosquito species, C. quinquefasciatus Say, in which the major lymphatic filariasis was used. The medicinal plants were collected from the area around Bharathiar University, Coimbatore. The dried plant materials were powdered by an electric blender. From the powder, 100 g of the plant materials was extracted with 300 ml of organic solvents of methanol for 8 h, using a Soxhlet apparatus, and filtered. The crude plant extracts were evaporated to dryness in a rotary vacuum evaporator. The plant extract showed larvicidal effects after 24 h of exposure; however, the highest larval mortality was found in the leaf extract of methanol J. curcas against the first to fourth instar larvae of values LC₅₀ = 1.200%, 1.290%, 1.358%, and 1.448% and LC₉₀ = 2.094%, 2.323%, 2.444%, and 2.544% and B. thuringiensis israelensis against the first to fourth instar larvae of values LC₅₀ = 9.332%, 9.832%, 10.212%, 10.622% and LC₉₀ = 15.225%, 15.508%, 15.887%, and 15.986% larvae of C. quinquefasciatus, respectively. No mortality was observed in the control. These results suggest methanol extracts of J. curcas and B. thuringiensis israelensis have potential to be used as an ideal eco-friendly approach for the control of the major lymphatic filarial vector, C. quinquefasciatus.     

Efficacy of medicinal plant extracts against malarial vector, <Emphasis Type="Italic">Anopheles subpictus</Emphasis> Grassi

Insecticides of botanical origin may serve as suitable alternative biocontrol techniques in the future. The aim of this study was to evaluate the adulticidal activity and adult emergence inhibition (EI) of leaf hexane, chloroform, ethyl acetate, acetone, and methanol extracts of Aegle marmelos (Linn.) Correa ex Roxb, Andrographis lineata Wallich ex Nees., Andrographis paniculata (Burm.f.) Wall. ex Nees., Cocculus hirsutus L. Diels, Eclipta prostrata L., and Tagetes erecta L. tested against malarial vector, Anopheles subpictus Grassi (Diptera: Culicidae). All plant extracts showed moderate adulticidal activity and EI effects after 24 h of exposure at 1,000 ppm; however, the highest adulticidal activity was observed in ethyl acetate extract of A.lineata, chloroform extract of A.paniculata, acetone extract of C.hirsutus, and methanol extract of T.erecta (LD₅₀ = 126.92, 95.82, 109.40, and 89.83 ppm; LD₉₀ = 542.95, 720.82, 459.03, and 607.85 ppm); and effective EI was found in leaf acetone extract of the A. marmelos, ethyl acetate extract of A.lineata, methanol extracts of C. hirsutus, and T.erecta, (EI₅₀ = 128.14, 79.39, 143.97, and 92.82 ppm; EI₉₀ = 713.53, 293.70, 682.72, and 582.59 ppm), respectively, against A. subpictus. These results suggest that the leaf methanol extract of C. hirsutus and T.erecta have the potential to be used as an ideal eco-friendly approach for the control of A. subpictus. Therefore, this study provides first report on the mosquito adulticidal activity and EI of plant extracts against malaria vector.     

Larvicidal activity of fatty acid methyl esters of <Emphasis Type="Italic">Vitex</Emphasis> species against <Emphasis Type="Italic">Culex quinquefasciatus</Emphasis>

The larvicidal activity of fatty acid methyl ester (FAME) extracts of Vitex altissima, Vitex negundo and Vitex trifolia was studied against early fourth-instar larvae of Culex quinquefasciatus. The fatty composition was analysed by gas chromatography. The highest percentage of lauric acid, palmitic acid, stearic acid, oleic acid and linolenic acid were recorded in V. negundo. The highest percentage of linolenic acid was recorded in V. trifolia. The FAME extract of V. trifolia showed the highest larvicidal activity with an LC50 value of 9.25 ppm followed by V. altissima (14.82 ppm) and V. negundo (18.64 ppm).     

Redescription of <Emphasis Type="Italic">Lemuricola</Emphasis> (<Emphasis Type="Italic">Madoxyuris</Emphasis>) <Emphasis Type="Italic">bauchoti</Emphasis> (Nematoda,Oxyuridae) from <Emphasis Type="Italic">Lemur catta</Emphasis> in Madagascar

Lemuricola (Madoxyuris) bauchoti Chabaud, Brygoo et Petter, 1965 is redescribed from material collected from the ring-tailed lemur, Lemur catta, from the Beza Mahafaly Special Reserve in Madagascar using the scanning electron microscope. This is a new host record and the first oxyurid reported from the ring-tailed lemur. Previously, records of each species of the subgenus Madoxyuris have been restricted to a single host species, but the close relationship between these nematodes and their Strepsirrhini hosts will only be proven when additional records fill in the gaps in their distribution.     

Crossing experiment of <Emphasis Type="Italic">Anopheles maculatus</Emphasis> form K and <Emphasis Type="Italic">Anopheles willmori</Emphasis> (James) (Diptera: Culicidae)

We recently reported crossing experiments between Anopheles maculatus form K and five members of the Maculatus group to support the specific status of form K. In the present study, we performed further crosses between form K and a sixth species of the Maculatus group, Anopheles willmori (James). Low viability was observed in hybrid males and females. All hybrid males were sterile with atrophied testes, or partially sterile with abnormal spermatozoa. The hybrid females showed normal ovaries. The ovarian nurse cell polytene chromosomes of the F₁ hybrid females displayed complete asynapsis. Backcrossing showed low viability. All males were sterile with atrophied testes or partially sterile with abnormal spermatozoa, and the females showed varying degrees of atrophied ovaries. The results provide clear evidence that form K is not conspecific to A. willmori supporting previous studies that form K represents another species of the Maculatus group.     

Cysteine proteinases from promastigotes of <Emphasis Type="Italic">Leishmania</Emphasis> (<Emphasis Type="Italic">Viannia</Emphasis>) <Emphasis Type="Italic">braziliensis</Emphasis>

Leishmania (Viannia) braziliensis is the major causative agent of American tegumentary leishmaniasis, a disease that has a wide geographical distribution and is a severe public health problem. The cysteine proteinase B (CPB) from Leishmania spp. represents an important virulence factor. In this study, we characterized and localized cysteine proteinases in L. (V.) braziliensis promastigotes. By a combination of triton X-114 extraction, concanavalin A-affinity, and ion exchange chromatographies, we obtained an enriched fraction of hydrophobic proteins rich in mannose residues. This fraction contained two proteinases of 63 and 43 kDa, which were recognized by a CPB antiserum, and were partially sensitive to E-64 in enzymatic assays with the peptide Glu-Phe-Leu. In confocal microscopy, the CPB homologues localized in the peripheral region of the parasite. This data together with direct agglutination and flow cytometry assays suggest a surface localization of the CPB homologues. The incubation of intact promastigotes with phospholipase C reduced the number of CPB-positive cells, while anti-cross-reacting determinant and anti-CPB antisera recognized two polypeptides (63 and 43 kDa) derived from phospholipase C treatment, suggesting that some CPB isoforms may be glycosylphosphatidylinositol-anchored. Collectively, our results suggest the presence of CPB homologues in L. braziliensis surface and highlight the need for further studies on L. braziliensis cysteine proteinases, which require enrichment methods for enzymatic detection.     

<Emphasis Type="Italic">Leishmania</Emphasis> (<Emphasis Type="Italic">Viannia</Emphasis>) <Emphasis Type="Italic">shawi</Emphasis> purified antigens confer protection against murine cutaneous leishmaniasis

Objective  

Leishmania (Viannia) shawi was characterized only recently, and few studies concerning the immunogenic and protective properties of its antigens have been performed. The present study aimed to evaluate the protective potential of the five antigenic fractions isolated from L. (V.) shawi promastigotes in experimental cutaneous leishmaniasis.     

Evaluation of larvicidal and nymphicidal potential of plant extracts against <Emphasis Type="Italic">Anopheles subpictus</Emphasis> Grassi, <Emphasis Type="Italic">Culex tritaeniorhynchus</Emphasis> Giles and <Emphasis Type="Italic">Aphis gossypii</Emphasis> Glover

The acetone, chloroform, ethyl acetate, hexane and methanol extracts of peel and leaf extracts of Citrus sinensis, Ocimum canum, Ocimum sanctum and Rhinacanthus nasutus were tested against fourth instar larvae of malaria vector, Anopheles subpictus Grassi, Japanese encephalitis vector, Culex tritaeniorhynchus Giles (Diptera: Culicidae) and feeding deterrence to nymphs of cotton pest, Aphis gossypii Glover (Homoptera: Aphididae). The larval and nymph mortality were observed after 24 h of exposure. All extracts showed moderate larvicidal and nymphicidal effects; however, the highest mortality was found in peel chloroform extract of C. sinensis, leaf ethyl acetate extracts of O. canum and O. sanctum and leaf chloroform extract of R. nasutus against the larvae of A. subpictus (LC₅₀ = 58.25, 88.15, 21.67 and 40.46 ppm; LC₉₀ = 298.31, 528.70, 98.34 and 267.20 ppm), peel methanol extract of C. sinensis, leaf methanol extract of O. canum, ethyl acetate extracts of O. sanctum and R. nasutus against the larvae of C. tritaeniorhynchus (LC₅₀ = 38.15, 72.40, 109.12 and 39.32 ppm; LC₉₀ = 184.67, 268.93, 646.62 and 176.39 ppm), peel hexane extract of C. sinensis, leaf methanol extracts of O. canum and R. nasutus and leaf ethyl acetate extract of O. sanctum against the nymph of A. gossypii (LC₅₀ = 162.89, 80.99, 73.27 and 130.19 ppm; LC₉₀ = 595.40, 293.33, 338.74 and 450.90 ppm), respectively. These results suggest that the peel methanol extracts of C. sinensis and O. canum, ethyl acetate leaf extract of O. sanctum and leaf chloroform and ethyl acetate extract of R. nasutus have the potential to be used as an ideal eco-friendly approach for the control of the A. subpictus, C. tritaeniorhynchus and A. gossypii.     

Larvicidal activity of <Emphasis Type="Italic">Saraca indica,Nyctanthes arbor-tristis</Emphasis>, and <Emphasis Type="Italic">Clitoria ternatea</Emphasis> extracts against three mosquito vector species

Screening of natural products for mosquito larvicidal activity against three major mosquito vectors Aedes aegypti, Culex quinquefasciatus, and Anopheles stephensi resulted in the identification of three potential plant extracts viz., Saraca indica/asoca, Nyctanthes arbor-tristis, and Clitoria ternatea for mosquito larval control. In the case of S. indica/asoca, the petroleum ether extract of the leaves and the chloroform extract of the bark were effective against the larvae of C. quinquefasciatus with respective LC₅₀ values 228.9 and 291.5 ppm. The LC₅₀ values of chloroform extract of N. arbor-tristis leaves were 303.2, 518.2, and 420.2 ppm against A. aegypti, A. stephensi, and C. quinquefasciatus, respectively. The methanol and chloroform extracts of flowers of N. arbor-tristis showed larvicidal activity against larvae of A. stephensi with the respective LC₅₀ values of 244.4 and 747.7 ppm. Among the methanol extracts of C. ternatea leaves, roots, flowers, and seeds, the seed extract was effective against the larvae of all the three species with LC₅₀ values 65.2, 154.5, and 54.4 ppm, respectively, for A. stephensi, A. aegypti, and C. quinquefasciatus. Among the three plant species studied for mosquito larvicidal activity, C. ternatea was showing the most promising mosquito larvicidal activity. The phytochemical analysis of the promising methanolic extract of the seed extract was positive for carbohydrates, saponins, terpenoids, tannins, and proteins. In conclusion, bioassay-guided fractionation of effective extracts may result in identification of a useful molecule for the control of mosquito vectors.     

<Emphasis Type="Italic">Trypanosoma</Emphasis> (<Emphasis Type="Italic">Herpetosoma</Emphasis>) <Emphasis Type="Italic">kuseli</Emphasis> sp. n. (Protozoa: Kinetoplastida) in Siberian flying squirrels (<Emphasis Type="Italic">Pteromys volans</Emphasis>)

All trypanosome species classified in the subgenus Herpetosoma in sciurid hosts have been recorded from ground and tree squirrels to date, but not from any flying squirrels. We describe in this paper a novel trypanosome species, Trypanosoma (Herpetosoma) kuseli sp. n., from Siberian flying squirrels (Pteromys volans) imported from China, and compare it with T. (H.) otospermophili in Richardson's ground squirrels (Spermophilus richardsonii) and Columbian ground squirrels (Spermophilus columbianus) from the USA. Due to a short free flagellum, the new species appeared stumpy compared with T. otospermophili (length of free flagellum 7.0 +/- 0.8 microm, total length 32.1 +/- 0.8 microm, n = 13 and length of free flagellum 15.5 +/- 1.6 microm, total length 35.9 +/- 1.0 microm, n = 13, respectively). Another conspicuous morphological feature of the new species was an anteriorly positioned kinetoplast, found approximately at the midpoint between the nucleus and the posterior end. These characters have not been recorded from any squirrel Herpetosoma trypanosome species. Comparison of the nucleotide sequences of the small and large subunit rRNA genes indicated that T. kuseli sp. n. was more homologous to T. otospermophili than murid Herpetosoma species, such as T. grosi, T. lewisi, T. musculi, T. microti and T. evotomys.     

Antiviral biflavonoids from <Emphasis Type="Italic">Radix Wikstroemiae</Emphasis> (<Emphasis Type="Italic">Liaogewanggen</Emphasis>)

Background  

Radix Wikstroemiae is a common Chinese herbal medicine. The ethyl acetate fraction of the ethanolic extract of W. indica possesses potent in vitro antiviral activity against respiratory syncytial virus (RSV). This study aims to identify the antiviral components of the active fraction.     

Cercarial shedding from <Emphasis Type="Italic">Galba</Emphasis><Emphasis Type="Italic">truncatula</Emphasis> infected with <Emphasis Type="Italic">Fasciola</Emphasis><Emphasis Type="Italic">gigantica</Emphasis> of distinct geographic origins

Galba truncatula snails were experimentally infected with either of two different isolates of Fasciola gigantica, originating from Egypt or China, to determine the influence of these isolates on the characteristics of snail infections. The survival rates of G. truncatula on day 30 post-exposure were 90.0% and 60.2% in the Egyptian and Chinese groups, respectively. The frequency of cercaria-shedding snails within the Egyptian group was 79.8%, whereas in the Chinese group it was 22.4%. The parasite origin had a significant effect on the durations of the prepatent and patent periods. The mean number of cercariae shed from the Egyptian group was significantly greater than that shed from the Chinese group (a mean of 275.5 per cercaria-shedding snail compared with 29.0). These results could be explained by the fact that G. truncatula might be a natural intermediate host for F. gigantica in Egypt, and the greater adaptability of the Egyptian miracidia of F. gigantica to unusual snail hosts. These results demonstrate the influence of the geographic origin of the parasite on the success of trematodes infecting snails.