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PubMed2006

Bumblebees can be used in combination with juvenile hormone analogues and ecdysone agonists.

This study examined the lethal and sublethal effects on the beneficial insect Bombus terrestris by two classes of insect growth regulators (IGRs) that are commercially used in agriculture to control pest insects. Three juvenile hormones analogues (JHAs) (pyriproxyfen, fenoxycarb and kinoprene) and two ecdysone agonists or moulting accelerating compounds (MACs) (tebufenozide and methoxyfenozide) were tested. The bumblebee workers were exposed to the insecticides via three different routes of exposure: dermally by topical contact, and orally via the drinking sugar water or the pollen. In the first series of experiments the IGRs were applied at their respective maximum field recommended concentration (MFRC). These risk hazard tests showed that the tested IGRs caused no acute toxicity on the workers, and any compound had an adverse effect on reproduction (production of males). In addition, larval development was followed in the treated nests compared with the controls. After application of the two MACs and the JHA fenoxycarb no adverse effects were observed on larval development. However, in the nests where the workers were exposed to the JHAs pyriproxyfen and kinoprene higher numbers of dead larvae were scored. These larvae were third and fourth instars, implying a lethal blockage of development before metamorphosis. In a second test, a series of dilutions was made for kinoprene, and these results revealed that only the MFRC caused a toxic effect on the larval development. On the other hand, kinoprene at lower concentrations (0.0650 mg ai/l) had a stimulatory effect on brood production. It was remarkable that ovaries of such treated dominant workers were longer and contained more eggs than in the controls. In a last experiment, the cuticular uptake was determined for a JHA and MAC to evaluate to what extent worker bees accumulate these classes of IGRs. Cuticular uptake ranged from 34 to 83% at 24 h after topical application. Overall, the obtained results indicate that the tested IGRs at their recommended concentration are safe to be used in combination with B. terrestris.

Animals↗
PubMed1995

Bafilolides, potent inhibitors of the motility and development of the free-living stages of parasitic nematodes.

Three Streptomyces isolates were identified as producing macrolide antibiotics of the bafilomycin or leucanicidin types during an evaluation of Australian actinomyces for the production of inhibitors of larval development in the parasitic nematode, Haemonchus contortus. Bafilomycins A1, B1, C1, and D were obtained from culture A239 and the 2-O-methyl-L-rhamnosyl derivative of bafilomycin A1, leucanicidin, from cultures A223 and A240. All these 'bafilolides' gave similar patterns of inhibition typified by an initial paralysis of newly hatched L1 larvae and a lethal toxicity within 24 h. LD50 values for inhibition of larval development of McMaster H. contortus ranged from 0.23 micrograms ml-1 for leucanicidin to 2.5 micrograms ml-1 for bafilomycin D. The bafilolides had broad spectrum nematocidal activity, being equi-potent as inhibitors of H. contortus, Trichostrongylus colubriformis and Ostertagia circumcincta larval development. Further, all bafilolides caused some inhibition of H. contortus L3 motility, with the semi-synthetic analogue, bafilomycin B2, the most potent inhibitor (LP50 against McMaster H. contortus 1.9 microgram ml-1). Nematode strains resistant to the known benzimidazole, levamisole and avermectin anthelmintics showed no cross resistance to the bafilolides, supporting the hypothesis that the bafilolides act by an independent mechanism.

Animals↗
PubMed2004

Evaluation of the developmental and reproductive toxicity of methoxychlor using an anuran (Xenopus tropicalis) chronic exposure model.

The chronic toxicity of methoxychlor to the South African clawed frog, Xenopus (Silurana) tropicalis, was evaluated using a life cycle approach. The chronic exposure period ranged from mid-cell blastula stage [NF (Nieuwkoop and Faber, 1994) stage 8] to 90 days of exposure, during which time the organisms generally completed metamorphosis and emerged as juvenile frogs. Methoxychlor concentrations ranged from 1 to 100 micrograms/l. Methoxychlor concentrations >10 micrograms/l caused delayed development. Organisms exposed to 10 micrograms/l methoxychlor for 30 days showed enlarged thyroid glands with follicular hyperplasia. No increase in mortality or external malformation was observed at any of the test concentrations during early embryo-larval development (NF stage 8 to NF stage 46; ca. 2 days exposure). A concentration-dependent increase in external malformations and internal abnormalities of the liver and gonads were noted after 90 days of exposure, however. Skewing of the sex ratio toward the female gender decreased ovary weight and number of oocytes, and increased oocyte immaturity and necrosis were noted at methoxychlor concentrations of 100 micrograms/l. Reductions in testis weight and sperm cell count were also detected at 100 micrograms/l methoxychlor. Results from these studies suggested that methoxychlor was capable of altering the rate of larval development, but did not adversely affect early embryo-larval development (2 days of exposure) as manifested in external malformations. Internal malformations, increases in the ratio of phenotypic females, were induced by chronic methoxychlor exposure. In addition, reproductive endpoints, most notably in the female specimens, were adversely affected by methoxychlor exposure. These studies add to the standardization and validation of a useful amphibian test methods capable of evaluating both reproductive and developmental effects of potential endocrine disrupting chemicals over a life cycle exposure.

Animals↗
PubMed2006

Ovicidal and larvicidal activity of Melia azedarach extracts on Haemonchus contortus.

Haemonchus contortus is responsible for severe economic losses in sheep and goat breeding in the Northeast of Brazil. However, the effectiveness of control is compromised due to anthelmintic resistance and misuse. In the search for natural anthelmintics, Melia azedarach L., a plant indigenous to India but now distributed throughout Brazil, was selected due to the reported anthelmintic properties of its seeds. The aim of this study was to evaluate the anthelmintic activity of the seed and leaf extracts of the Brazilian adapted plant and investigate the type of organic chemical compounds present in the most active extracts. The ovicidal and larvicidal activity of M. azedarach extracts on H. contortus was evaluated through egg hatching and larval development tests. Hexane and ethanol extracts of seeds and chloroform and ethanol extracts of leaves of M. azedarach were used in the tests. To perform the larval development test, feces of an animal free from parasites were mixed with third instar H. contortus larvae and extracts in several concentrations. The coprocultures were incubated for 7 days at 30 degrees C, then the larvae were recovered and counted. LC50 was calculated by probits using the SPSS 8.0 program. The seed ethanol extract was the most active on eggs (LC50=0.36mgmL(-1)) and the leaf ethanol extract showed the best inhibition of larval development (LC50=9.18mgmL(-1)). Phytochemical analysis of the most active extracts revealed the presence of condensed tannins, triterpenes and alkaloids.

Animals↗
PubMed1998

A divergent multi-domain cyclophilin is highly conserved between parasitic and free-living nematode species and is important in larval muscle development.

A divergent multi-domain cyclophilin from the filarial nematodes Brugia malayi, Onchocerca volvulus and Dirofilaria immitis has a highly conserved orthologue in the free-living nematodes Caenorhabditis elegans and C. briggsae. Cyclophilins are the receptors for the immunosuppressive and anti-parasitic agent cyclosporin A and additionally these ubiquitously expressed proteins have protein folding capabilities, and exhibit proline isomerase activity. These divergent nematode cyclophilins (CYP-4 isoforms) are three domain proteins, which share 63-88% identity and have highly conserved differences present in their functionally important cyclosporin A binding and proline isomerase domains. This unusual class of nematode cyclophilins has been studied in the model nematode C. elegans, revealing a unique temporal and spatial expression pattern. The cyp-4 transcript is most abundantly expressed in the early larval stages and is expressed exclusively in the body-wall striated muscle cells. An important functional role was established for this divergent enzyme, as specific double-stranded RNA interference experiments resulted in progeny with a phenotypically lumpy appearance. This morphological defect was predominantly expressed in the early larval stages and is consistent with an effect on body-wall muscle cell development. This study has established that this highly conserved family of nematode cyclophilins has a tissue-specific, functional role in early larval development and supports the use of C. elegans as a model for the study of orthologues in the experimentally less amenable parasitic nematodes.

Amino Acid Sequence↗
PubMed2003

Expression of Drosophila FOXO regulates growth and can phenocopy starvation.

BACKGROUND: Components of the insulin signaling pathway are important regulators of growth. The FOXO (forkhead box, sub-group "O") transcription factors regulate cellular processes under conditions of low levels of insulin signaling. Studies in mammalian cell culture show that activation of FOXO transcription factors causes cell death or cell cycle arrest. The Caenorhabditis elegans homologue of FOXO, Daf-16, is required for the formation of dauer larvae in response to nutritional stress. In addition, FOXO factors have been implicated in stress resistance and longevity. RESULTS: We have identified the Drosophila melanogaster homologue of FOXO (dFOXO), which is conserved in amino acid sequence compared with the mammalian FOXO homologues and Daf-16. Expression of dFOXO during early larval development causes inhibition of larval growth and alterations in feeding behavior. Inhibition of larval growth is reversible upon discontinuation of dFOXO expression. Expression of dFOXO during the third larval instar or at low levels during development leads to the generation of adults that are reduced in size. Analysis of the wings and eyes of these small flies indicates that the reduction in size is due to decreases in cell size and cell number. Overexpression of dFOXO in the developing eye leads to a characteristic phenotype with reductions in cell size and cell number. This phenotype can be rescued by co-expression of upstream insulin signaling components, dPI3K and dAkt, however, this rescue is not seen when FOXO is mutated to a constitutively active form. CONCLUSIONS: dFOXO is conserved in both sequence and regulatory mechanisms when compared with other FOXO homologues. The establishment of Drosophila as a model for the study of FOXO transcription factors should prove beneficial to determining the biological role of these signaling molecules. The alterations in larval development seen upon overexpression of dFOXO closely mimic the phenotypic effects of starvation, suggesting a role for dFOXO in the response to nutritional adversity. This work has implications in the understanding of cancer and insulin related disorders, such as diabetes and obesity.

Amino Acid Sequence↗
PubMed1989

Postembryonic development of Wohlfahrtia magnifica (Schiner, 1862) (Diptera: Sarcophagidae).

A description of the larval development of Wohlfahrtia magnifica (Schiner, 1862) is given. An interpretation of the morphological development correlated with functional and adaptive aspects of myiasis-causing flies is also included. A detailed analysis of morphological changes that occurred in W. magnifica larvae during postembryonic development is carried out. These changes happen in 2 larval interinstars, I-II and II-III, in which several structures such as anterior and posterior peritremes and cephalopharyngeal skeleton play an important role. The possible functions of these structures are considered. We also describe the first instar in W. magnifica to differentiate it from that belonging to Sarcophaga species, paying special attention to disposition of the cephalopharyngeal skeleton, anterior peritremes, and spinulation on the last 3 segments. Several structures, not described previously in Sarcophagidae, were observed: modified spines of the buccal and peritremal cavities, peritremal tubercles, and modified spines on the ventral surface. Changes occurring in these structures during larval development are described. Their probable role in the taxonomy of the genus Wohlfahrtia and their application to Nearctic species belonging to this genus, Wohlfahrtia vigil and Wohlfahrtia opaca, are also discussed.

Animals↗
PubMed2006

Bionomics of larvae of Parelaphostrongylus odocoilei (Nematoda: Protostrongylidae) in experimentally infected gastropod intermediate hosts.

Parelaphostrongylus odocoilei is a protostrongylid parasite that has recently been recognized at several locations in sub-Arctic, but not Arctic, North America. We investigated factors that may determine the distribution of P. odocoilei, including suitable gastropod intermediate hosts, temperature requirements for larval development in gastropods, and larval emergence facilitating overwinter transmission. We collected and experimentally infected gastropods from a site in the sub-Arctic where P. odocoilei is at the northern limit of its distribution. Deroceras laeve, Catinella sp., and Euconulus cf fulvus, but not members of the Pupillidae, were suitable intermediate hosts. We describe bionomics of larvae of P. odocoilei in D. laeve and Catinella sp. Infective larvae emerged from all slugs (D. laeve) and 60% of Catinella sp. snails, and emergence from D. laeve was intensity dependent. Emerged infective larvae survived up to 6 mo under conditions approximating that of the subnivean environment. In D. laeve, there was a direct relationship between temperature and development rate of larvae of P. odocoilei. Larvae of P. odocoilei did not develop to infective stage below the theoretical threshold (8.5 C), and required a minimum of 163 degree days to complete development. These developmental parameters can be incorporated into a model to predict larval development in the field. Knowledge of the factors influencing larval bionomics provides the foundation for predicting temporal and spatial patterns of parasite distribution, abundance, and transmission.

Animals↗
PubMed2004

Gene expression during early ascidian metamorphosis requires signalling by Hemps, an EGF-like protein.

Hemps, a novel epidermal growth factor (EGF)-like protein, is expressed during larval development and early metamorphosis in the ascidian Herdmania curvata and plays a direct role in triggering metamorphosis. In order to identify downstream genes in the Hemps pathway we used a gene expression profiling approach, in which we compared post-larvae undergoing normal metamorphosis with larval metamorphosis blocked with an anti-Hemps antibody. Molecular profiling revealed that there are dynamic changes in gene expression within the first 30 minutes of normal metamorphosis with a significant portion of the genome (approximately 49%) being activated or repressed. A more detailed analysis of the expression of 15 of these differentially expressed genes through embryogenesis, larval development and metamorphosis revealed that while there is a diversity of temporal expression patterns, a number of genes are transiently expressed during larval development and metamorphosis. These and other differentially expressed genes were localised to a range of specific cell and tissue types in Herdmania larvae and post-larvae. The expression of approximately 24% of the genes that were differentially expressed during early metamorphosis was affected in larvae treated with the anti-Hemps antibody. Knockdown of Hemps activity affected the expression of a range of genes within 30 minutes of induction, suggesting that the Hemps pathway directly regulates early response genes at metamorphosis. In most cases, it appears that the Hemps pathway contributes to the modulation of gene expression, rather than initial gene activation or repression. A total of 151 genes that displayed the greatest alterations in expression in response to anti-Hemps antibody were sequenced. These genes were implicated in a range of developmental and physiological roles, including innate immunity, signal transduction and in the regulation of gene transcription. These results suggest that there is significant gene activity during the very early stages of H. curvata metamorphosis and that the Hemps pathway plays a key role in regulating the expression of many of these genes.

Animals↗
PubMed1983

Caste-specific maturation of the endocrine system in the female honey bee larva.

The endocrine system of female honey bee larvae has been studied through postembryonic development with histological and autoradiographic techniques. During larval development, brain and retrocerebral complex proceed from immature cells to an active endocrine system. Caste-specific retardation occurs in the worker during this process. In the developing queen, the differentiation of the neurosecretory cells (NSC) and the outgrowth of their axons occurs from the second instar onward and is nearly completed in the fourth, whereas in the worker larva these processes are delayed by more than one instar. In the queen, RNA synthesis starts in the NSC at the end of the third instar and in the worker at the fifth instar. Stainable neurosecretory material is present only in fifth instar queen larvae. The queen's corpora cardiaca become active at the end of the fourth, those of the worker in the fifth instar. In the corpora allata (CA), nuclei undergo several phases of endomitosis. These phases of polyploidization end at the beginning (queen) or at the end (worker) of the fifth instar respectively. CA volume in the queen is twice that of a worker at its height at the end of larval development. these data demonstrate a caste-specific maturation of the endocrine organs which results in differences in hormone titres.

Animals↗
PubMed1991

Connectivity of identified central synapses in the cricket is normal following regeneration and blockade of presynaptic activity.

Cercal sensory neurons in the cricket innervate interneurons in the central nervous system (CNS) and provide a model system for studying the formation of central synapses. When axons of the sensory neurons were transected during larval development, the cell bodies and the soma-bearing portion of axons, which are located within the cercus, survived but lost their excitability for 9-10 days. During this period, the sensory neurons grew new axons and reinnervated the terminal abdominal ganglion. Physiological recordings showed that sensory neurons of known identity reestablished monosynaptic contacts with their normal postsynaptic interneuron. Moreover, each synapse exhibited a characteristic strength indistinguishable from the intact synapse in an unoperated cricket. Since this selective connectivity was apparent immediately after the excitability of the axotomized sensory neurons was restored, action potentials in the sensory neurons appear to be unnecessary for normal synaptic regeneration to occur. Consistent with this, the reinnervation process was unaffected even when action potentials in the sensory neurons were blocked by tetrodotoxin (TTX) immediately following axotomy until just before testing. During the normal course of development, the characteristic strength of individual synapses changes systematically, resulting in the developmental rearrangement of these synapses (Chiba et al., 1988). This synaptic rearrangement was also unaffected when action potentials in the sensory neurons were blocked by TTX for the last 30% of larval development. Therefore, in the cricket cercal sensory system, both regeneration of the central synapses following axotomy of the presynaptic sensory neurons and the normal rearrangement of connectivity during larval development appear not to require axonal action potentials.

Action Potentials↗
PubMed2003

Effects of four synthetic musks on the life cycle of the harpacticoid copepod Nitocra spinipes.

A full life-cycle (</=26 days exposure) toxicity test with the harpacticoid copepod Nitocra spinipes was used to study the effects of one nitro musk (musk ketone) as well as three polycyclic musks (Tonalide, Celestolide and Galaxolide). A subchronic individual life-table endpoint, the larval development rate, was recorded after 7-8 days exposure of juveniles and was significantly decreased in copepods exposed to sublethal concentrations of musk ketone, Celestolide and Galaxolide. However, none of the Tonalide concentrations had any effect on larval development. The lowest Galaxolide concentration (0.02 mg/l), which affected juvenile development, was about 100 times below the adult 96-h-LC(50)-value of 1.9 mg/l (95% confidence interval: 1.4-2.7 mg/l). However, none of the four musks had any agonistic or antagonistic activity in the ecdysteroid-sensitive Drosophila melanogaster B(II)-cell line. This indicates that the decrease in larval development rate was due to pharmacological effects rather than steroid receptor-mediated endocrine disruption. A modified Euler-Lotka equation was used to calculate a population-level endpoint, the intrinsic rate of natural increase (r(m)), from individual life-table endpoints, i.e. mortality rate, time of release of first brood, sex ratio, the fraction of ovigerous females among all females as well as the number of nauplii per ovigerous female. The second highest musk ketone concentration (0.1 mg/l) was the only treatment, which significantly affected r(m) (***P<0.001). At the highest musk ketone (0.3 mg/l) and Celestolide (0.3 mg/l) concentrations, all copepods were dead at the end of the exposures. This shows that a sensitive individual life-table endpoint is protective over the population-level endpoint r(m). Though we think that it is necessary to obtain population-level endpoints from standardised toxicity test, for ecologically successful risk characterisation of synthetic musks as well as other chemicals. The results from the present study show that it is possible to obtain population-level data from the full life-cycle test with N. spinipes. However, there seems to be little risk that synthetic musks are harmful to copepods at present environmental concentrations.

Animals↗
PubMedDate not supplied

[A 35-kDa polypeptide of the crystalline lens in the common frog: its biochemical properties, tissue specificity and appearance in the developmental process].

The vertebrate lens contains so-called taxon-specific water-soluble proteins. One of them is p-crystallin with a molecular weight of 35 kDa characteristic of Ranidae family. We have identified a polypeptide with a molecular weight of 35 kDa in the eye lens of Rana temporaria which: (1) can be extracted from the lens by aqueous salt solutions, (2) has a molecular mass of 36.1 +/- 0.4 kDa (by SDS-electrophoresis) and 37 kDa (by gel filtration), (3) is heterogeneous in terms of isoelectric point (pI 6.5-8.0), (4) binds to heparin-agarose, (5) denatures in response to freezing-thawing, lyophilization and in solutions with low ionic strength. Thus, major biochemical parameters of this polypeptide differ from that of amphibian alpha, beta- and gamma-crystallins. In addition to lens, 35 kDa polypeptide was detected by immunoelectroblotting in retina, testes, liver, kidney, spleen, stomach, intestine and lungs. Its level (as percentage of water-soluble protein) is 1.1 +/- 1.4% in the lens, 1.6 +/- 0.7% in retina. 0.05% in testes and liver and 0.01% or less in other organs. Thus, despite its wide tissue distribution, 53 kDa polypeptide is expressed predominantly in lens and retina. We studied the time-course of appearance and accumulation of this polypeptide in tissues where it is expressed at high or low levels. 35 kDa polypeptide was detected for the first time during larval development: (1) in the lens (some time after the mouth opening; stages 33-34 according to Dabagian and Sleptsova, 1975), (2) in the retina (by the time of anus opening; stages 36-37), (3) in the liver (at the stage of elongated hind limb bud; stages 40-41). Definitive expression level of this protein was achieved in the lens by the beginning of metamorphosis and in the retina and liver during first months of development. Hence, during the whole period of larval development 35 kDa polypeptide content of the lens exceeds that of retina or liver. A more substantial evidence is required to confirm the identity of studied polypeptide with rho-crystallin.

Animals↗
PubMed1999

Pathogenicity of cyathostome infection.

Cyathostomes are now the principle parasitic pathogen of the horse: a remarkable transformation during the last 25 years from virtual obscurity to focus of attention in equine parasitology. This rise to prominence coincides with the marked decrease in prevalence of large strongyle infections as a result of widespread use of modern anthelmintic compounds. On the basis that strongyle-associated diseases continue to commonly occur in the absence of these large strongyle species, clinical attention has turned to the pathogenicity of cyathostomes. Although many horses harbour burdens of tens of thousands of cyathostomes without developing detectable illness, these parasites can result in an inflammatory enteropathy affecting the caecum and colon. Although the principle clinical effect of cyathostomosis is weight loss, affected individuals may exhibit other signs including diarrhoea and/or subcutaneous oedema and/or pyrexia. Clinical cyathostomosis occurs more commonly in young horses in late winter/early spring but there is lifelong susceptibility to cyathostomes and they can cause clinical disease in any age of horse during any season. Animals with cyathostomosis often develop hypoalbuminaemia and/or neutrophilia but there are no clinicopathological features specific for the disease. Experimental infections with cyathostomes have resulted in both clinical and pathological features similar to those of naturally-occuring cyathostomosis cases. From the experimental infection studies, it is evident that cyathostomes are pathogenic at times of both penetration into and emergence from the large intestinal mucosa. An unusual feature of cyathostome biology is the propensity for arrested larval development within the large intestinal mucosa for more than 2 years. From limited studies it appears that this arrested larval development is favoured by: feedback from luminal to mucosal worms; larger size of challenge dose of larvae and trickle (versus single bolus) infection. During arrested larval development cyathostomes have minimal susceptibility to all anthelmintic compounds, thus, limiting the effectiveness of therapeutic and/or control strategies. Although, the relative importance of individual cyathostomes is not known, the development of species-specific DNA methods for identification of cyathostomes provides a means by which the pathogenicity of different species might be established.

Animals↗
PubMed1987

Mode of growth of retinal axons within the tectum of Xenopus tadpoles, and implications in the ordered neuronal connection between the retina and the tectum.

Retinal axons of Xenopus tadpoles at various stages of larval development were filled with horseradish peroxidase (HRP), and their trajectories and the patterns of branching within the tectum were analyzed in wholemount preparations. To clarify temporal and spatial modes of growth of retinal axons during larval development, special attention was directed to labeling a restricted regional population of retinal axons with HRP, following reported procedures (H. Fujisawa, K. Watanabe, N. Tani, and Y. Ibata, Brain Res. 206:9-20, 1981; 206:21-26, 1981; H. Fujisawa, Dev. Growth Differ 26:545-553, 1984). In developing tadpoles, individual retinal axons arrived at the tectum, without clear sprouting. Axonal sprouting first began when growing tips of each retinal axon had arrived at the vicinity of its site of normal innervation within the tectum. Thus, the terminals of the newly added retinal axons were retinotopically aligned within the tectum. The retinotopic alignment of the terminals may be due to an active choice of topographically appropriate tectal regions by growth cones of individual retinal axons. The stereotyped alignment of the newly added retinal axons was followed by widespread axonal branching and preferential selection of those branches. Each retinal axon was sequentially bifurcated within the tectum, and old branches that had inevitably been left at ectopic parts of the tectum (owing to tectal growth) were retracted or degenerated in the following larval development. The above mode of axonal growth provides an adequate explanation of cellular mechanisms of terminal shifting of retinal axons within the tectum during development of retinotectal projection. Selection of appropriate branches may also lead to a reduction in the size of terminal arborization of retinal axons, resulting in a refinement in targeting.

Animals↗
PubMed2003

Ovicidal and larvicidal activity in vitro of Spigelia anthelmia Linn. extracts on Haemonchus contortus.

The rapid development of anthelmintic resistance, associated with the high cost of the available anthelmintic drugs, had limited the success of gastrointestinal nematodiasis control in sheep and goats and thus awakened interest in the study of medicinal plants as alternative sources of anthelmintics. Spigelia anthelmia extracts obtained with hexane, chloroform, ethyl acetate or methanol, were tested on Haemonchus contortus eggs and larvae via egg hatch and larval development tests. The extracts were evaluated at five concentrations: 3.1, 6.2, 12.5, 25.0 and 50.0 mg ml(-1). At 50.0 mg ml(-1), the ethyl acetate extract inhibited 100% of the egg hatching and 81.2% of the larval development. In a similar way the methanolic extract inhibited 97.4% of the egg hatching and 84.4% of larval development. These results suggest that utilization of S. anthelmia extracts may be useful in the control of sheep and goats gastrointestinal nematodes.

Animals↗
PubMed1993

Strongyloides stercoralis: an initial autoinfective burst amplifies primary infection.

Compartmental analysis of Strongloides stercoralis burdens in experimentally infected, serially necropsied dogs was used to test an autoinfective burst hypothesis. The hypothesis states that in well-established, active infections and in chronic infections as well, the rate of larval development is down-regulated so that most larvae do not attain infectivity internally. The majority pass in the feces as preinfective, rhabditiform larvae, but a few (those with the most rapid developmental rate) attain infectivity internally, and therefore are positioned for autoinfectivity. In contrast, in immunologically naive hosts, larval development proceeds without host hindrance and many larvae, proceeding at the most rapid rate of a spectrum of normal intrinsic developmental rates, attain infectivity internally. For a brief period, hyperinfection occurs, during which the adult worm population increases sharply. Gut-level resistance soon occurs, larval development is retarded, and an increasing proportion of larvae are discharged as preinfective rhabditiform larvae. With fewer larvae developing to infectivity internally, recruitment into the adult population decreases, with an attendant increase in the mean age and a gradual decrease in the size of the adult population. The data and the attendant model strongly support this autoinfective burst hypothesis.

Animals↗
PubMed1987

Development and survival of free-living stages of equine strongyles under laboratory conditions.

In a series of laboratory studies the optimum conditions for the development and survival of the free-living stages of strongyle parasites occurring in horses in tropical north Queensland were determined. No differences in behaviour were noted between the strongyle species. Development to the infective stage occurred only between 10 and 35 degrees C. The rate was affected by temperature, taking 15-24 days and 3 days, respectively, at the lowest and highest temperatures for the developing stages to reach the infective third stage. Yields of infective larvae were very low outside the range 20-33 degrees C, and were highest at 28 degrees C. Survival of infective larvae was good between 20 and 33 degrees C, and large numbers were recovered after 3 months in faeces incubated at 20-28 degrees C. At 33 and 37 degrees C larval survival was affected by the moisture content of the faeces, with infective larvae surviving better in dry than in moist faeces; even a residual moisture level of 40% significantly reduced the number of larvae recovered from faeces incubated at 37 degrees C for 1 month. Moisture also affected larval development, especially at the higher temperatures of 25-39 degrees C. When faecal moisture content fell to less than or equal to 20% by 3 days, larvae which had not yet reached the infective stage were still pre-infective at 7 days, while all larvae in faeces with adequate moisture had reached the infective third stage. It was not possible to determine the critical faecal moisture level below which larval development ceased, however, 28 degrees C (range 25-33 degrees C) was found to be the optimum temperature. Larval development was very rapid and yields of infective larvae highest at this temperature.

Animals↗