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PubMed2001

The difference in efficacy of ivermectin oral, moxidectin oral and moxidectin injectable formulations against an ivermectin-resistant strain of Trichostrongylus colubriformis in sheep.

AIM: To evaluate the efficacy of ivermectin oral, moxidectin oral and moxidectin injectable formulations against an ivermectin-resistant strain of Trichostrongylus colubriformis in sheep. METHODS: Twenty-four mixed breed lambs were infected with 15,000 infective third-stage larvae of an ivermectin-resistant strain of T. colubriformis which had originally been isolated from a goat farm in Northland in 1997. Twenty-six days post infection, the lambs were divided into 3 treatment groups and a control group (n=6 lambs/group). Treatment consisted of either ivermectin oral formulation (0.2 mg/kg), moxidectin oral formulation (0.2 mg/kg), or moxidectin injectable formulation (0.2 mg/kg). Faecal egg counts (FECs) were determined at 0, 3, 5, 7 and 10 days after treatment. All animals were necropsied 12 days after treatment and worm counts were performed. Larval development assays were conducted 24 days post infection. A further 3 lambs were infected with 15,000 infective third-stage larvae of a fully susceptible strain of T. colubriformis for comparative purposes in the larval development assay. The efficacy of the moxidectin injectable formulation was also confirmed in these 3 lambs. RESULTS: The FEC reduction test at day 10 after treatment revealed 62%, 100% and 0% reductions in arithmetic-mean FECs for ivermectin oral, moxidectin oral and moxidectin injectable groups, respectively. The ivermectin oral, moxidectin oral and moxidectin injectable formulations achieved 62%, 98% and 4% reductions in arithmetic-mean worm burdens, respectively. Larval development assays showed resistance ratios for ivermectin of 4:1, avermectin B2 of 2.7:1, ivermectin aglycone of 37:1, moxidectin of 1.4:1, thiabendazole of 14.6:1 and levamisole of 1.8:1. CONCLUSIONS: The moxidectin oral formulation provided a high degree of control against ivermectin-resistant T. colubriformis whereas the moxidectin injectable formulation had very low efficacy. Ivermectin aglycone was the analogue of choice for diagnosis of ivermectin resistance in T. colubriformis in the larval development assay.

Journal Article↗
PubMed2006

Life history of Spodoptera exigua (Lepidoptera: Noctuidae) on various host plants.

The incubation period of Spodoptera exigua (Hübner) was not influenced by the host plant, whereas larval development time and pupal period were affected. Larval development time was longest on shallot and lady's finger, followed by cabbage and long bean. Larvae did not develop beyond the first instar when fed on chilli. The pupal period was longer on lady's finger than on cabbage, shallot and long bean. Overall, adult longevity was not influenced by the host plant but there was a difference between female and male longevity among the host plants. Survival of S. exigua was affected by the host plant at the larval stage. The number of larval instars varied between 5 and 8 within and between the studied host plants. Long bean was found to be the most suitable host plant and provide the best food quality for S. exigua compared to the other host plants, as it allowed faster development, fewer larval instars and a higher survival rate.

Abelmoschus↗
PubMed1994

Late-generated cells in the lateral motor columns of developing frog spinal cord.

Spinal motor neurons of larval frogs continue to be generated for the lateral motor columns (LMCs) even after their peak numbers have been reached and during the major period of normal neuronal loss. This study elucidates the extent to which relatively late generated motor neurons survive to the end of larval development. Bromodeoxyuridine was injected into Rana pipiens tadpoles at mid-larval stages twice a day for 5 days in order to label LMC neurons arising during the period of greatest neuron loss. Counts of labeled neurons visualized by immunocytochemical methods revealed that substantial numbers of late generated motor neurons survive to the end of larval development and may be retained in greater proportion than early generated motor neurons (prior to the onset of normally occurring neuron loss). Tadpoles that had been exposed to exogenous thyroxine so as to increase proliferative activity and thereby label more motor neurons during the injection period, exhibited an increase in labeled LMC cells although the total number of neurons remained comparable to controls. Protracted neurogenesis concurrent with cell loss during the later phases of development is a major determinant of the final population of the LMC.

Animals↗
PubMed2005

Microflora species and their volatile compounds affecting development of an alcohol dehydrogenase homozygous strain (Adh-I) of Bactrocera (Dacus) oleae (Diptera: Tephritidae).

Microflora species and volatiles emitted from artificial diets were examined from the larvae of three homozygous alcohol dehydrogenase (Adh) strains of the olive fruit fly, Bactrocera (Dacus) oleae (Gmelin), reared under identical conditions. Differences in volatile composition were detected when Adh-I homozygous larvae developed in a diet lacking the preservative p-hydroxybenzoic acid methyl ester (nipagin). Larval development of the Adh-I strain in the preservative-free diet was reduced by 50%, whereas pupal emergence was completely inhibited. The larval development and pupal emergence of Adh-F and Adh-S strains were not affected. Unique microorganisms with characteristic volatile profiles were isolated from the preservative-free diet of the Adh-I strain that were different from those, isolated from Adh-S, Adh-F, laboratory colony, and wild insect populations. Our results indicated that the variations in volatile composition of the artificial diets, and the inhibition of larval development and pupal emergence in Adh-I strain were related to changes in the microflora that developed in the diets of the Adh-I strain.

Alcohol Dehydrogenase↗
PubMed1989

Developmental regulation of energy metabolism in Caenorhabditis elegans.

Changes in energy metabolism during larval development in Caenorhabditis elegans have been investigated using phosphorus nuclear magnetic resonance (31P NMR). The relative concentrations of ATP, ADP, AMP, sugar phosphates, and other metabolites were observed to change during larval development, producing stage-specific spectra. These spectra are consistent with enzyme assays for isocitrate dehydrogenase and isocitrate lyase, indicating that high activity of the glyoxylate pathway during embryonic development decreases during the first larval (L1) stage, and respiration during the L2, L3, and L4 stages occurs preferentially through the TCA cycle. Metabolic strategies were further studied using mutants that are predisposed to enter the dauer stage, a developmentally arrested third-stage larva formed under conditions of overcrowding and limited food. After the L1 molt, energy metabolism in animals destined to become dauer larvae diverges from that of animals committed to growth. Relative to the L1, the L2 larvae committed to growth exhibit increased isocitrate dehydrogenase activity as well as increases in ATP and other high-energy phosphates, but predauer (L2d) larvae exhibit declining enzyme activities and declining levels of high-energy phosphates. The predominant phosphorus NMR signal in dauer larva extracts corresponds to inorganic phosphate. We conclude that metabolism is regulated during C. elegans larval development, with a major transition apparent after the L1 stage. This transition does not occur in larvae destined to form dauer larvae.

Adenine Nucleotides↗
PubMed2005

Edysteroid receptor (EcR) shows marked differences in temporal patterns between tissues during larval-adult development in Rhodnius prolixus: correlations with haemolymph ecdysteroid titres.

The presence of ecdysteroid receptor (EcR) in various tissues was studied throughout larval-adult development of the blood-sucking bug, Rhodnius prolixus, using an antibody to EcR that recognizes all isoforms. On Western blots, the antibody recognizes three peptides of approximate molecular masses of 70, 68 and 64 kDa, from epidermis and fat body of developing larvae, which contain high levels of haemolymph ecdysteroids. These peptides are absent from both unfed larvae and adults, which are devoid of ecdysteroids. In vitro treatment of epidermis and fat body from unfed larvae with 20E induces the appearance of all three EcR immunoreactive peptides. The stage-specific appearance and 20E inducibility of the peptides implies that they represent the native EcR(s) of Rhodnius. Confocal fluorescence analysis using this antibody revealed a great diversity of temporal profiles of EcR in various tissues during development. Developmental profiles of EcR were examined in abdominal epidermis, fat body, spermatocytes, brain (including the medial neurosecretory cells), prothoracic glands (PGs), rectal epithelium and Malpighian tubules. EcR fluorescence was confined to the nuclei in close association with chromatin. EcR was absent from tissues of unfed larvae or adults, supporting the results from Western blots. Different tissues develop EcR at different developmental times and in the presence of radically different concentrations of haemolymph ecdysteroids, retain EcR for different lengths of time and lose EcR at different concentrations of ecdysteroids. These results suggest that each tissue possesses a distinctive response mechanism to ecdysteroids. An exception to this, are the PGs, which exhibited no EcR fluorescence at any time during development.

Animals↗
PubMed2003

Genetic polymorphism and trade-offs in the early life-history strategy of the Pacific oyster, Crassostrea gigas (Thunberg, 1795): a quantitative genetic study.

We investigated genetic variability and genetic correlations in early life-history traits of Crassostrea gigas. Larval survival, larval development rate, size at settlement and metamorphosis success were found to be substantially heritable, whereas larval growth rate and juvenile traits were not. We identified a strong positive genetic correlation between larval development rate and size at settlement, and argue that selection could optimize both age and size at settlement. However, trade-offs, resulting in costs of metamorphosing early and large, were suggested by negative genetic correlations or covariances between larval development rate/size at settlement and both metamorphosis success and juvenile survival. Moreover, size advantage at settlement disappeared with time during the juvenile stage. Finally, we observed no genetic correlations between larval and juvenile stages, implying genetic independence of life-history traits between life-stages. We suggest two possible scenarios for the maintenance of genetic polymorphism in the early life-history strategy of C. gigas.

Animals↗
PubMed2006

Digestive enzymes during development of Ceratitis capitata (Diptera:Tephritidae) and effects of SBTI on its digestive serine proteinase targets.

The digestive system of Ceratitis capitata was characterized during its larval development and in the insect stage. Disaccharidases against maltose and sucrose were more evident in the 2nd and 3rd day of larval development and in the adult stage, respectively. Glycosil-hydrolyses with higher specific alpha-galactosidasic and beta-galactosidasic activities were detected in the 2nd and 3rd day of the larval stage, respectively. Specific proteolytic activities against azocasein showed an increase in the 4th and 5th day of the larval stage and in the adult stage. Specific hemoglobin activities were constant between 2nd and 6th day of the larval stage. The larvae used mainly serine proteinases, such as trypsin/chymotrypsin, and the adult insects only chymotrypsin-like enzymes in their digestive process. Two serine proteinases were separated from zymogram between the 4th and 5th day of larval development and in the adult stage. Effect of soybean trypsin inhibitor (SBTI, a serine proteinase inhibitor) on development of C. capitata was examined by bioassay. C. capitata was susceptible to SBTI which affected larval mass at ED50 3.01%.

Animals↗
PubMed1983

Ecdysone 20-monooxygenase activity during larval-pupal development of Manduca sexta.

Profiles of ecdysone 20-monooxygenase (E-20-M) activity in the fat body and midgut of Manduca sexta were determined during larval-pupal development. The E-20-M activities for both tissues were found to exhibit a single major fluctuation during this 10-day period of development: fat body, a 10-fold fluctuation with peak activity on day 4; midgut, a 60-fold fluctuation with peak activity on day 5. Substrate kinetics revealed that the apparent Km values of fat body and midgut monooxygenases for ecdysone were fairly constant during the instar, 2.42 X 10(-7) M and 4.67 X 10(-7) M, respectively. By contrast, the monooxygenase Vmax values in each tissue fluctuated in a manner both quantitatively and temporally coincident with the fluctuations in enzyme activity. These findings suggest that changes in E-20-M activity are a function of changes in the titer of the enzyme. The possible developmental significance of the fluctuations in E-20-M activity are discussed.

Animals↗
PubMed1990

Expression of MHC class II antigens during Xenopus development.

Larval and adult forms of the amphibian Xenopus differ in their MHC class II expression. In tadpoles, class II epitopes can be detected by monoclonal antibodies only on B cells, macrophages (whatever their location), spleen reticulum, thymus epithelium, and the pharyngobuccal cavity. In contrast, all adult T cells express class II on their surface. The transitions in class II expression occur at metamorphosis and are accompanied by other changes. The skin is invaded by class II positive dendritic cells, and the skin glands differentiate and also express class II. The gut, which expressed class II in discrete areas of the embryonic tissue, becomes invaded with B cells, and its epithelium also becomes class II positive.

Animals↗
PubMed1993

Ultrastructure of prothoracic glands during larval-pupal development of the tobacco hornworm, Manduca sexta: a reappraisal.

The structure of Manduca sexta prothoracic glands was investigated using a protocol that preserves membranes. During the last larval stadium, prothoracic gland cells increase in diameter, volume, protein content, and perhaps number, enhancing their capacity to produce ecdysteroids. The glands' strand-of-cells morphology, their in situ location, the presence of gap junctions between cells, and junctional foot-like structures within cells support previous findings that prothoracicotropic hormone stimulates ecdysteroidogenesis via Ca(2+)-induced Ca2+ release. A different method of tissue fixation from that previously used to investigate the ultrastructure of Manduca sexta prothoracic glands has revealed a significantly different ultrastructure. These new findings begin to define roles for endoplasmic reticulum and mitochondria in ecdysteroid synthesis and support the hypothesis that the glands secrete the steroid hormone via exocytosis. The structural dynamics of the glands are discussed in the context of the glands' function during Manduca sexta larval-pupal development.

Animals↗
PubMed1998

Comparison of sensitivity to methyl methanesulphonate among tadpole developmental stages using the alkaline single-cell gel electrophoresis (comet) assay.

In a previous study, we demonstrated that tadpoles are suitable organisms for monitoring small bodies of water (e.g., creeks, ponds, and drainage ditches) for genotoxicity using the alkaline single-cell gel DNA electrophoresis (SCG) or "comet" assay [Ralph and Petras, 1997]. This approach involves detection, under alkaline conditions, of cell DNA fragments which on electrophoresis migrate from the nuclear core, resulting in a "comet with tail" formation. In this initial study, most of the tadpoles collected were in the early stages of larval development, but this is not always possible. The present study evaluated the sensitivity of tadpoles, at different stages of larval development, to a range of concentrations of the genotoxicant methyl methane-sulphonate (MMS). Four specific phases of Rana clamitans (green frog) larval development were examined: first-year limbless tadpoles (Stage I as defined by Taylor and Kollros [1946]), second-year limbless tadpoles (Stages II-III), second-year tadpoles with only hindlimbs (Stages X-XVIII), and second-year tadpoles with all four limbs evident and a tail undergoing resorption (Stages XXII-XXIII). Twenty-four hour exposures to MMS of tadpoles in the three earliest phases produced a significant (P < 0.01) added variance component among tadpoles for DNA damage and there were significant increases (P < 0.05) in the length:width ratios of the DNA patterns at concentrations as low as 1.56 mg/I. However, tadpoles in the last phase studied (both pairs of limbs present) showed no significant (P > 0.05) added variance component and no significant increases (P> 0.05) in DNA damage upon exposure to any of the MMS doses tested. A nested ANOVA indicated that, for each of the tested concentrations of MMS, but not the dechlorinated water control, there was significant heterogeneity (P < 0.05) in DNA damage when tadpoles of all four phases studied were compared. However, when tadpoles of the lost phase of development were removed from the comparison, there was no significant heterogeneity (P > 0.05) among tadpoles of the remaining three phases. Possible reasons for this insensitivity to MMS as animals enter the metamorphic climax were considered. The results indicate that pooling of the early tadpole phases of R. clamitans for SCG environmental genotoxicity biomonitoring is acceptable.

Animals↗
PubMed1999

Energy metabolism during embryonic development and larval growth of an Antarctic sea urchin.

Developmental energetics of an Antarctic sea urchin, Sterechinus neumayeri, were quantified to describe the physiological bases underlying ontogenetic changes in metabolic rate at extreme cold temperatures (-1.5 degrees C). Rates of development from a four-arm to a six-arm larval stage were not affected by food availability. The respiratory cost of development to the six-arm larval stage (day 60) was 14.0 mJ for fed larvae and 8.2 mJ for unfed larvae. We observed three phases of metabolic regulation during development. During embryogenesis (day 0-22), increasing metabolic rates were proportional to increases in cell numbers. During early larval development (day 22-47), the differences in respiratory rate between fed and unfed larvae were not accounted for by cell number, but by cell-specific metabolic rate (respiratory rate normalized to DNA content). Once an advanced larval stage had been reached (day 47-60), cell-specific respiratory rate and mitochondrial densities (citrate synthase activity normalized to DNA content) were more equivalent between fed and unfed larvae, suggesting that size-specific metabolic rates were determined at a level of physiological regulation that was independent of cell numbers or feeding history.

Animals↗
PubMed1992

Developmental arrest and ecdysteroid deficiency resulting from mutations at the dre4 locus of Drosophila.

Loss-of-function mutations of the dre4 gene of Drosophila melanogaster caused stage-specific developmental arrest, the stages of arrest coinciding with periods of ecdysteroid (molting hormone) regulated development. Nonconditional mutations resulted in the arrest of larval development in the first instar; embryogenesis was not impaired, and mutant larvae were behaviorally normal and long-lived. At 31 degrees the temperature-sensitive dre4e55 allele caused the arrest of larval development in the first or second instars. When upshifted to 31 degrees at various times during development, dre4e55 mutants exhibited nonpupariation of third-instar larvae, failure of pupal head eversion, failure of adult differentiation, or noneclosion of pharate adults. Under some temperature regimens second-instar larvae pupariated precociously without entering the normally intervening third-instar. Nonpupariation and defects in metamorphosis were associated with the reduction or elimination of ecdysteroid peaks normally associated with late-larval, prepupal, pupal and pharate adult development. Ecdysteroid production by larval ring glands from dre4e55 hemizygous larvae was suppressed after 2 hr of incubation in vitro at 31 degrees, indicating autonomous expression of the dre4 gene in the ring gland. We postulate that the dre4 gene is required for ecdysteroid production at multiple stages of Drosophila development and that the pathologies observed in dre4 mutants reflect developmental consequences of ecdysteroid deficiency.

Animals↗
PubMed2002

Infection of its lepidopteran host by the Helicoverpa armigera stunt virus (Tetraviridae).

Techniques of microscopy and histopathology were employed to study the positive-sense, single-stranded RNA virus, the Helicoverpa armigera stunt virus (HaSV; omegatetravirus, Tetraviridae) infecting its caterpillar host. Infection of the virus per os during the first three instars of larval development is virulent and leads to rapid stunting and mortality. In contrast, no detectable symptoms occur in later larval development, signifying a high degree of developmental resistance. A quantitative study of cell populations in the host midgut during this time showed that increased cell numbers during development alone could not account for the increase in resistance. HaSV infection was restricted to the midgut and three of its four cell types. In younger larvae, the virus initiated its infection in closely situated foci that appeared to expand to link with others to cover larger areas of the midgut. The midgut cells of the infected larvae responded with an increased rate of sloughing to an extent rendering the midgut incapable of maintenance or recovery of normal function. In contrast, infection of older larvae by HaSV did not lead to overt pathology although foci of HaSV infection were detected in their midguts. However, the foci were more sparsely situated, failed to expand, and eventually disappeared, presumably due to cell sloughing. These observations indicate that cell sloughing is an immune response existing throughout larval development but midguts of older larvae have an additional mechanism to account for the increased resistance. This second mechanism results in midgut cells becoming more refractory to infection and, combined with cell sloughing, allows the midguts of older larvae to recover more readily from HaSV infection. These two mechanisms are similar to those seen with host responses to baculoviruses, which display developmental resistance to a lesser degree against more general infections. HaSV remaining in the midgut appears to amplify the degree of developmental resistance.

Animals↗
PubMed2003

Macroevolutionary consequences of developmental mode in temnopleurid echinoids from the Tertiary of southern Australia.

Taxonomic revision and cladistic analysis of a morphological dataset for Australian Tertiary temnopleurids resolve the phylogeny of the group and allow the testing of a series of hypotheses about the evolution of larval development and consequences of changes in development. Australian Tertiary temnopleurids encompass all three major developmental types found in marine invertebrates (planktotrophy, lecithotrophy, and brooding). Planktotrophy is plesiomorphic for this clade, and nonplanktotrophic larval development evolved independently at least three times during the Tertiary. The change to a nonplanktotrophic mode of larval development is unidirectional with no evidence of reversal. In addition, there is no evidence of an ordered transformation series from planktotrophy through planktonic lecithotrophy to brooding. In common with previous studies of other invertebrate groups, analysis of the raw data suggests that nonplanktotrophic taxa within this clade have significantly shorter species longevities, more restricted geographic ranges and higher speciation rates than taxa with planktotrophic development. However, analysis using phylogenetically independent contrasts is unable to confirm that the stratigraphic and geographic patterns are unbiased by the phylogenetic relationships of the included taxa.

Animals↗
PubMed2006

The effect of temperature on the development of Angiostrongylus cantonensis (Chen 1935) in Pomacea canaliculata (Lamarck 1822).

Angiostrongyliasis cantonensis, clinically presented as eosinophilic meningitis, is a snail-borne parasitic disease. We studied the effects of different temperatures on the larval development of Angiostrongylus cantonensis in the freshwater snail Pomacea canaliculata. Six groups of snails were infected and each group was cultured under different temperature conditions. At predefined intervals, four snails from each group were dissected to examine the larval development. The development-time curve of each group was drawn according to the fraction of third-stage larvae present. The developmental time was defined as the time needed until 50% of the first-stage larvae developed into third-stage larvae. A linear regression model was established based on the time (D; in days) and the corresponding temperature (T; in degrees Celsius): DT = 15.04 x D + 262.53. The threshold temperature for larval development was 15.04 degrees C and the thermal constant was 262.53 degree-days. These parameters could be helpful in estimating the number of parasite generations in a year and the impact of climate change on the distribution of A. cantonensis.

Angiostrongylus cantonensis↗
PubMed2002

Chondrocranial development in larval Rana sylvatica (Anura: Ranidae): morphometric analysis of cranial allometry and ontogenetic shape change.

This study provides baseline quantitative data on the morphological development of the chondrocranium in a larval anuran. Both linear and geometric morphometric methods are used to quantitatively analyze size-related shape change in a complete developmental series of larvae of the wood frog, Rana sylvatica. The null hypothesis of isometry was rejected in all geometric morphometric and most linear morphometric analyses. Reduced major axis regressions of 11 linear chondrocranial measurements on size indicate a mixture of allometric and isometric scaling. Measurements in the otic and oral regions tend to scale with negative allometry and those associated with the palatoquadrate and muscular process scale with isometry or positive allometry. Geometric morphometric analyses, based on a set of 11 chondrocranial landmarks, include linear regression of relative warp scores and multivariate regression of partial warp scores and uniform components on log centroid size. Body size explains about one-quarter to one-third of the total shape variation found in the sample. Areas of regional shape transformation (e.g., palatoquadrate, otic region, trabecular horns) are identified by thin-plate spline deformation grids and are concordant with linear morphometric results. Thus, the anuran chondrocranium is not a static structure during premetamorphic stages and allometric patterns generally follow scaling predictions for tetrapod cranial development. Potential implications regarding larval functional morphology, cranial development, and chondrocranial evolution in anurans are discussed.

Animals↗