Americanus Larvae Research Articles

Determining the prevalence of Oesophagostomum bifurcum and Necator americanus infections using specific PCR amplification of DNA from faecal samples.

Until recently infection of humans with Oesophagostomum bifurcum was regarded as a rare zoonosis. But in northern Togo and Ghana its prevalence is 50% or more in certain villages. Diagnosis is hampered by the fact that the eggs of O. bifurcum are morphologically identical to those of the hookworm Necator americanus. Stools have to be cultured for 7 days to allow eggs to hatch to the characteristic third-stage (L3) larvae. We evaluated the applicability of specific polymerase chain reactions (PCRs) to amplify DNA from faecal samples as an alternative method for the differential diagnosis of the two infections. Oesophagostomum bifurcum-PCR was positive in 57 of 61 faecal samples known to contain O. bifurcum L3 larvae in coproculture. Necator americanus PCR was positive in 137 of 146 faecal samples known to contain N. americanus L3 larvae in coproculture. PCR also detected 26 additional O. bifurcum cases in 72 samples from O. bifurcum endemic villages in which no O. bifurcum larvae were found and 45 N. americanus cases in 78 samples in which no N. americanus larvae were found in coproculture. No O. bifurcum DNA was detected in 91 stool samples from individuals from two non-endemic villages. These results prove the usefulness of specific PCR assays as epidemiological tools to estimate the prevalence of O. bifurcum and N. americanus infections in human populations.

High survival of neustonic zoea I larvae of American lobster Homarus americanus following short-term exposure to ultraviolet radiation (280 to 400 nm)

Ultraviolet radiation (UV-B = 280 to 320 nm; UV-A = 320 to 400 nm) is harmful to the planktonic early life stages of some marine organisms. In the Gulf of St. Lawrence, Canada, measurements of the diffuse attenuation coefficients have indicated that the maximum depth to which 10% of the surface energy penetrates at 310 nm is 3 m. Thus, organisms residing in this surface layer are exposed to UV radiation. During the summer spawning season (May to September), the first zoeal larval stages of the American lobster Homarus americanus are present in the first 2 m of the water column during the day. Thus, H. americanus larvae are exposed to UV radiation. We incubated stage I larvae of H. americanus under an artificial light source that simulated the irradiance conditions measured at a depth of 1 m in the Gulf of St. Lawrence waters near solar noon. Three spectral exposure treatments were used: (1) UV-B+UV-A+PAR; (2) UV-A+PAR; (3) PAR only. Larvae were irradiated for 4 d (2 h d -1 ) and maintained thereafter under a natural photoperiod (fluorescent lamps) until first molt. Mortality was monitored daily throughout the experiment. There were no differences in mortality amongst the 3 spectral treatments. Larvae began dying at the same time and at the same rate independently of the spectral irradiation that they received. Thus, lobster larvae appear to be tolerant of short (2 h) exposures to UV radiation.

The Lethality of Salmosan (Azamethiphos) to American Lobster (Homarus americanus) Larvae, Postlarvae, and Adults

The pesticide formulation Salmosan (47.5% w/w azamethiphos) is currently registered for use, in Canada, to treat salmonids for infestations of the copepod parasites, Lepeophtheirus salmonis and Caligus elongatus (sea lice). Determination was made of the acute lethality of this product to the three larval stages, the first postlarval stage, and the adult of the American lobster (Homarus americanus), a species of significant economic importance in Eastern Canada. The 48-h LC50 (as azamethiphos) is 3.57 μg/liter for Stage I, 1.03 μg/liter for Stage II, 2.29 μg/liter for Stage III, 2.12μg/liter for Stage IV (the first postlarval stage), and 1.39 μg/liter for adults. These concentrations are not significantly different from each other, although the variability in response is greater in the larval stages than in the postlarvae or adults. These data when interpreted in conjunction with known physical oceanographic data and chemical dispersion studies indicate that single anti-louse treatments are unlikely to result in mortality among lobsters in the vicinity of salmon farms. However, the sublethal effects of this product and the effects of repeated exposures have yet to be determined.

Epidemiological evidence for a differential effect of hookworm species, Ancylostoma duodenale or Necator americanus, on iron status of children.

The hookworms, Ancylostoma duodenale and Necator americanus, cause significant gastrointestinal blood loss. In clinical studies, greater blood losses have been reported with A. duodenale. However, there has been no evidence that endemic A. duodenale infection has greater impact than N. americanus infection on the iron status of populations. In a sample of 525 school children in Pemba Island, Tanzania, we compared the degree of anaemia and iron deficiency associated with the two hookworm species at the individual and community (i.e. school) levels. Multiple regression was used to control for infection intensities and other child characteristics. In the 492 children with hookworm positive faecal cultures, haemoglobin and ferritin concentrations decreased with increasing proportions of A. duodenale. Among children with only N. americanus larvae, the prevalence of anaemia was 60.5 % and the prevalence of ferritin <12 microg/l was 33.1%, while in children with > or =50% A. duodenale larvae, the respective prevalences were 80.6% and 58.9%. When children were grouped by the prevalence of A. duodenale at the school level, children from high prevalence (> or =20%) schools had significantly worse iron deficiency and anaemia than children from low prevalence schools. The species of hookworm being transmitted in a community influences the burden of iron deficiency anaemia in the community, and should be considered in prioritizing and planning programmes for hookworm and anaemia control.

Effect of chemical synergy and larval stage on the toxicity of atrazine and alachlor to amphibian larvae

AbstractWe determined the acute toxicity of field‐grade formulations of atrazine, alachlor, and a 50:50 mixture of the chemicals to early and late larval stages of northern leopard frogs (Rana pipiens) and American toads (Bufo americanus). We conducted identical tests with rainbow trout (Onchorhynchus mykiss) and channel catfish (Ictalurus punctatus) to compare their sensitivity as bioindicators. The acute toxicity (96‐h median lethal concentrations [LC50s]) of herbicides to amphibian larvae ranged from 47.6 mg/L for early‐stageR. pipiensexposed to atrazine to 3.3 mg/L for late‐stageB. americanusexposed to alachlor. The toxicity of a 50:50 mixture of atrazine and alachlor after a 96‐h exposure was greater than additive (chemical synergy present) for most species and life stages tested, with 96‐h LC50s as low as 1.5 mg/L for late‐stageB. americanuslarvae. Older amphibian larvae appeared to be more sensitive than younger larvae for both species and chemicals tested. Overall, rainbow trout and channel catfish appeared to be less sensitive than amphibian larvae. The 96‐h LC50s ranged from 23.8 mg/L for channel catfish exposed to atrazine to 9.1 mg/L for rainbow trout exposed to alachlor. A noteworthy sublethal effect observed in amphibian larvae exposed to atrazine was edema, probably caused by renal disfunction. Chronic predicted no‐observed‐effect concentrations (PNOECs) for lethality after a 30‐d exposure were estimated from mortality data at 3, 6, 24, 48, 72, and 96 h and found to be approximately 10‐ to 20‐fold lower than 96‐h LC50s. The calculated PNOECs are close enough to concentrations actually found in the environment to warrant concern and further tests. Additional research on environmental concentrations, chronic effects, and the effects of chemical synergy is needed before definitive conclusions can be drawn. Chemical synergy and life‐stage sensitivity should be addressed to properly assess the toxicity of herbicides to nontarget organisms.

Increment formation in otoliths of slow-growing winter flounder (Pleuronectes americanus) larvae in cold water

Known-age winter flounder (Pleuronectes americanus) larvae were reared in large outdoor mesocosms where the temperatures were &lt;5°C for the first 40 days and increased slowly after this and in field enclosures where the temperature ranged between 12.3 and 19.6°C. In the cold-water group, somatic and otolith growth were suppressed at the low initial temperatures and no increments were visible. After temperatures increased, somatic growth was evident and a variable number of initial narrow increments (0.2-0.6 µm) was observed. As larvae emerged from this initial period of slow growth, they began to develop rapidly and otolith increment widths increased to 1.0-3.0 µm. In contrast, larvae reared at the warmer temperature grew rapidly and laid down daily increments beginning 5 days after hatching.

Temperature affects selectivity of Chaoborus larvae-eating Daphnia

In ponds, a chemical produced by predaceous Chaoborus (Insecta, Diptera) larvae changes the development of juvenile Daphnia pulex (Crustacea, Branchiopoda) so the juveniles grow spines (neckteeth) on the back of their head. It is generally assumed that the spined phenotype is (or is an indicator of) a morphological predator defense. The research reported here tests the hypothesis that the induced neckteeth do in fact increase Daphnia survivorship, over a range of temperatures. Predation experiments were conducted over a range of temperatures from 6 to 22 °C using fourth instar Chaoborus americanus larvae as the predator. The prey were a mixture of spined (induced “necktooth” phenotype) and unspined (uninduced) juvenile Daphnia pulex. At 6 and 11 °C, Chaoborus selected the unspined phenotype over the spined phenotype, as expected. However, at 22 °C, the selectivity was reversed: significantly fewer on the spined survived compared to the unspined phenotype. These results suggest that the spined phenotype may either increase or decrease Daphnia pulex survival, depending on temperature and clone.

Influence of body size and alternate prey abundance on the risk of predation to fish larvae

We investigated the effects of variations in the abundance of microzooplankton (Artemia sp. nauplii) and the size of larval fish on the latter's vulnerability to predation by a vertebrate, the threesplne stickleback Gasterosteus aculeatus. We used capelin Mallotus villosus, cod Gadus morhua and winter flounder Pleuronectes americanus larvae as our prey species. Analysis of covariance indicated a highly significant effect on mortality rates due to predation caused by the presence of alternate prey = 10.8, p < 0.001), but a close examination of the results indicates that only levels of alternate prey exceeding 250 nauplii 1-' caused a reduction in the impact of sticklebacks on larval fish. Furthermore. the size of the fish larvae also had a significant impact on mortality rates (Fl,148 = 6.9, p c 0.001) in a comparison among species, however, this relationship was not apparent within species. Overall, as the size of larvae increased, mortality rates increased. As the slze of the larvae decreased, the Ingestion rate of larvae by the predator at low levels of alternate prey (525 nauplii 1-l) showed a substantial increase relative to the ingestion rate of larvae at high levels of alternate prey (250 nauplii I-'). Results indicate that as the size of larvae approaches the size of the more abundant alternate prey, the likelihood of an attack may decrease due to the presence of alternate prey. Whether the impact of increased microplankton abundance in the field would be greater through enhanced feeding of the larvae or reduced impact of the predator is unclear.

Differential Predation by Chaoborus americanus on Males and Females of Two Species of Diaptomus

Feeding experiments were performed to determine relative feeding rates of fourth-instar Chaoborus americanus larvae (Diptera) on both sexes of two calanoid copepod species, Diaptomus leptopus and D. minutus. Feeding rates, using a single prey type, showed that predation rates by Chaoborus on female D. minutus were highest, followed by male D. minutus, male D. leptopus, and female D. leptopus, respectively, when exposed to Chaoborus individually. Selectivity experiments with the four prey types made available simultaneously confirmed this pattern. Prey sizes and swimming speeds were determined, and both strike efficiency and handling time of Chaoborus were measured. Data suggested that selection between prey species was determined primarily by prey size whereas selection between sexes was determined primarily by differential swimming speed.

Resumption of Feeding In vitro by Hookworm Third-Stage Larvae: A Comparative Study

Third-stage infective larvae of the canine hookworm Ancylostoma caninum resume feeding in vitro in response to several stimuli. Experiments were conducted to characterize the in vitro feeding behavior of several hookworm species. Reduced glutathione and, to a lesser extent, canine and human serum stimulated third-stage larvae of Ancylostoma duodenale to resume feeding. Glutathione-induced feeding reached a maximum by 16 hr and was concentration-dependent between 0- and 15-mM glutathione. Oxidized glutathione and the reducing agents dithiothreitol and L-cysteine failed to induce feeding, suggesting that reducing conditions alone were not stimulatory. Serum incubated with glutathione was the most efficient stimulus for Ancylostoma ceylanicum, Ancylostoma braziliense, and Ancylostoma tubaeforme larvae, whereas Uncinaria stenocephala larvae responded best to canine serum alone. Necator americanus larvae did not resume feeding in response to glutathione, serum, glutathione plus serum, or linoleic acid (0.1-10 mM). These differences in feeding behavior suggest that generalizations concerning hookworm biology must be interpreted cautiously.

Estimation of live standard length for winter flounder Pleuronectes americanus larvae from formalin-preserved, ethanol-preserved and frozen specimens

Estimation of live standard length for winter flounder Pleuronectes americanus larvae from formalin-preserved, ethanol-preserved and frozen specimens

Potential impact of a toxic dinoflagellate (Alexandrium excavatum) bloom on survival of fish and crustacean larvae

We investigated the impact of neurotoxins produced by the dinoflagellateAlexandrium excavatum on survival of Atlantic mackerel (Scomber scombrus) and American lobster (Homarus americanus) larvae, respectively reared from eggs and from female lobster, collected in 1988 from the southern Gulf of St. Lawrence, Canada. Sensitivity to the toxins was first verified by exposing larvae of both species to various concentrations of toxicA. excavatum (treatment) and non-toxicA. tamarense (control). Daily mortality rates ranged from 65 to 96% among mackerel larvae directly fed upon toxic cells and reached 36% in postlarvae exposed to toxic microzooplankton. Lobster larvae were apparently immune to the toxins, which they concentrated up to five times relative to vector toxicities. Bioassays conducted on mackerel larvae by exposure to natural plankton samples collected in situ during a bloom of toxicA. excavatum confirmed that exposure to the toxins could also have lethal effects in natural ecosystems. We conclude that the current proliferation of toxic dinoflagellates threatens early survival of finfish larvae and their recruitment to adult populations.

Bacteriological Character in the Culture Water of Penaeid, Homarid and Palinurid Larvae.

Growth and development of crustacean larvae were affected by microflora associated with microalgae in water. The microflora in the culture water for larvae of penaeid, homarid and palinurid was compared. Penaeus japonicus larvae were cultured at 24.5-28°C, being fed on diatoms, Nannochloropsis sp., Tetraselmis sp., artificial micro-diet and Artemia nauplii. Homarus americanus larvae were cultured at about 20°C, being fed on Artemia. Jasus edwardsii phyllosomas were cultured at about 20°C, being fed on Artemia nauplii and Mytilus edulis. The total viable count in the culture water of penaeid and homarid larvae were higher than those of phyllosomas. Bacteria which produce pale white and white pigments were predominated in the culture water of homarid and palinurid. In addition to these bacteria, yellow, orange and swarming colonies forming bacteria were detected in the penaeid culture water in particularly. Feeding behaviour of phyllosomas became less active and mortality occurred, when swarming bacteria were detected. The phyllosomas were more sensitive to the presence of bacteria than the penaeid and homarid larvae.

Experimental Aquatic Food Webs: Interactions between Two Predators and Two Prey

We performed four replicates of all 16 combinations of the presence and absence of two predators (larvae of the dragonfly Anax junius and adult salamanders Notophthalmus viridescens) and two anuran prey (Bufo americanus and Rana palustris larvae) in an array of artificial temporary ponds. The two species of anurans were introduced at densities high enough to cause density-dependent reductions in survival and body size at metamorphosis and to increase larval period. The two species were in competition when raised together. Notophthalmus reduced the density of Bufo and caused the survivors to metamorphose early and at a small size. Anax caused an even greater reduction in survival but not as strong an acceleration of metamorphosis. Newts also reduced the density of Rana, but survivors benefited by growing rapidly. The effects of Anax were even stronger; the only Rana tadpoles that were able to metamorphose in the 2 mo of the experiment were from ponds in which Anax reduced densities enough to permit rapid g...

Experience-Independent Attraction To Slave-Maker Ant Larvae in Host-Species Ant Workers (Leptothorax Longispinosus; Hymenoptera: Formicidae)

Newly eclosed workers of the frequently enslaved ant species Leptothorax longispinosus were either exposed to conspecific larvae, exposed to larvae of the slave-making parasite Harpagoxenus americanus, or reared in social isolation. In all conditions, the L. longispinosus workers later accepted H. americanus larvae preferentially. This finding indicates that H. americanus larvae are highly attractive to Leptothorax workers and demonstrates that early learning need not to be invoked to account for the acceptance of Harpagoxenus brood by enslaved Leptothorax workers.

Predator driven changes in community structure.

The zooplankton community of a small pond changed markedly with temporal variation in predation pressure. Long term changes in zooplankton community structure occurred following the replacement of planktivorous fish by phantom midge (Chaoborus americanus) larvae as the predominant predator of zooplankton. The interannual changes following the establishment of Chaoborus included the apparent or near extinction, of species ill adapted to the new predation pressure and the successful colonization of well adapted species. Seasonal changes in the species composition and size distribution of the zooplankton community correlate with temporal variation in predation intensity associated with temperature-activity patterns of the predator or changes in the stage structure of the predator population.

Life History and Laboratory Rearing of Nepa apiculata (Heteroptera: Nepidae), with Descriptions of Immature Stages1

The life history of Nepa apiculata Uhler was studied in southern Illinois, and immature stages were described. The bug was reared from egg to adult in the laboratory. Adults of this univoltine species overwintered under the water in mud and detritus near the shoreline and became active in late March. The few eggs found were deposited singly in mud away from the shoreline between early May and mid-June. First instars appeared in mid-May, after which there was marked overlapping of the three subsequent instars. This insect is one of only a few heteropterans with four instars. Active adults were last observed during mid-October. Individuals were reared on Chaoborus americanus (Johannsen) larvae under a 16:8 (L:D) photoperiod at 26.7± 1.5°C. The incubation period averaged 14.1 d. Durations of the four subsequent stadia averaged 9.1, 8.8, 10.5, and 17.3 d respectively. Total developmental time averaged 59.8 d.

Ecology and coexistence of two species of Brachycentrus (Trichoptera) in a Rocky Mountain river

Life-cycle dynamics, growth rates, and relative abundance of Brachycentrus occidentalis and Brachycentrus americanus were studied over a 3-year period in the Flathead River, Montana. Brachycentrus occidentalis appeared as early instar larvae in mid to late summer, grew rapidly during autumn, and reached fourth and fifth instars prior to winter conditions. Most larvae remained active until mid-spring and the onset of spring runoff. Individuals pupated during late April through May and adults emerged after peak runoff in mid-June. Brachycentrus americanus larvae appeared as first instar larvae in autumn and overwintered as early instars. Larvae grew rapidly during spring as temperatures began to rise, but growth was discontinued during spring runoff. Larvae completed growth during summer after the runoff period and emerged in late August and early September. Growth patterns and emergence of both species occurred primarily during fall or spring and late summer, with little growth during winter or spring freshet. Thus growth was associated with quantitatively similar but temporally different periods of organic seston, temperature, and moderate flow.

Preference for unfamiliar siblings over familiar non-siblings in American toad ( Bufo americanus) tadpoles

Kin recognition may involve comparisons between conspecifics' traits and one's own or those of known genetic relatives. In American toad ( Bufo americanus) larvae, association patterns appear to reflect this ‘phenotype matching’, based, in part, upon traits of familiar conspecifics. To examine whether socially-reared tadpoles might additionally use their own traits in making such discriminations, individuals were tested in a Y-maze apparatus for their tendencies to discriminate between waterborne cues released by their unfamiliar siblings and by familiar non-siblings. Six of seven test groups spent more time oriented toward their unfamiliar siblings than toward familiar non-siblings, but the difference was significant for only two of these groups. Overall, 84 subjects oriented toward siblings and 51 toward non-siblings. Thus, in some circumstances, toad tadpoles appear to recognize siblings based on shared recognition traits rather than on prior social experience with conspecifics.

Feeding ecology of American sand lance Ammodytes americanus larvae from Long Island Sound

Sand lance larvae consumed phytoplankton and various developmental stages of the copepods Ternora longicornis, Acartia hudsonica and Pseudocalanus sp. Their diet changed with ontogeny: small larvae consumed phytoplankton and larger larvae ate copepods of increasingly older developmental stages. Samples taken during daylight indicated that the larvae have a gut capacity of approximately 0.56 % of their body dry weight. Laboratory studles conducted with live larvae indicated non-selective feeding on copepod n a u p h , but in the field, Ivlev indlces indicated selection for T 1ong1corni.s nauplii and against A. hudsonjca n a u p h . Larger larvae selected for T longicornjs copepodites and against A. hudsonica copepodites and females, but as they approach metan~orphosis, they began to select for A. hudsonica females. The feeding behavior of small larvae is passive, but becomes more aggressive as the larvae mature. Biomass consumed Increased with Increased prey density and water temperature. Clearance rates for larvae at 7OC In the laboratory were 0.02, 0.05, 0.48 and 3.2 1 d' for 4.5 to 5.0, 6 to 7.0, 10 to 11.0, and 21 mm ldrvae, respectively. Calculations of the predatory impact of sand lance larvae on copepod nauplii ind~calu that they are lnslgnificant consumers taking a maximum of 13.4 % of the copepod production per ddy.