Early Stage Larvae Research Articles

In vitro levamisole selection pressure on larval stages of Haemonchus contortus over nine generations gives rise to drug resistance and target site gene expression changes specific to the early larval stages only

There is some evidence that resistance to levamisole and pyrantel in trichostrongylid nematodes is due to changes in the composition of nicotinic acetylcholine receptors (nAChRs) which represent the drug target site. Altered expression patterns of genes coding for nAChR subunits, as well as the presence of truncated versions of several subunits, have been implicated in observed resistances. The studies have mostly compared target sites in worm isolates of very different genetic background, and hence the ability to associate the molecular changes with drug sensitivity alone have been clouded to some extent. The present study aimed to circumvent this issue by following target site gene expression pattern changes as resistance developed in Haemonchus contortus worms under laboratory selection pressure with levamisole. We applied drug selection pressure to early stage larvae in vitro over nine generations, and monitored changes in larval and adult drug sensitivities and target site gene expression patterns. High level resistance developed in larvae, with resistance factors of 94-fold and 1350-fold at the IC50 and IC95, respectively, in larval development assays after nine generations of selection. There was some cross-resistance to bephenium (70-fold increase in IC95). The expression of all the putative subunit components of levamisole-sensitive nAChRs, as well as a number of ancillary protein genes, particularly Hco-unc-29.1 and –ric-3, were significantly decreased (up to 5.5-fold) in the resistant larvae at generation nine compared to the starting population. However, adult worms did not show any resistance to levamisole, and showed an inverse pattern of gene expression changes, with many target site genes showing increased expression compared to the starting population. A comparison of the larval/adult drug sensitivity data with the known relationships for field-derived isolates indicated that the adults of our selected population should have been highly resistant to the drug if the larval/adult sensitivity relationships were in accordance with previous field isolates. Hence, our selected worms showed a life-stage drug sensitivity pattern quite different to that seen in the field. The present study has highlighted an association between drug target site changes and resistance to levamisole in H. contortus larvae. However, it has also highlighted the artificial nature of the larval selection method with levamisole, as the resistance phenotype and the associated molecular changes were only observed in the drug-pressured life stage. The study therefore reinforces the need for caution in extrapolating larval-based laboratory selection outcomes to field resistances.

Do Late‐Instar Drosophila Larvae Experience Functional Oxygen Limitations?

Arthropods gain considerable mass between molts, increasing oxygen demand while parts of the respiratory system are fixed in size. We hypothesized that internal hypoxia could be a cue triggering molting in arthropods and/or be a functional reason that the animal needs to molt. In support of this hypothesis, hypoxic rearing (10 kPa) triggered an ecdysone peak and molting to adulthood at a smaller body size in Drosophila, and hyperoxia induced earlier pupariation (JEB 216:4334). We tested for evidence that late‐third instar Drosophila larvae show signs of functional oxygen‐limitation. The dorsal longitudinal tracheae increased in diameter through the instar, scaling with mass0.38, approximately as predicted to conserve oxygen delivery. Respiratory exchange ratios declined through the instar, indicating that metabolism remains aerobic and shifts away from carbohydrate catabolism. Lactate levels did not increase later in the instar and were unaffected by rearing in hyperoxia. However, hyperoxia (30 kPa) increased late‐instar metabolic rates, suggesting functional oxygen limitation. Late‐instar larvae had greater capacities to generate lactate in response to anoxia, suggesting past selection for coping with late‐instar oxygen limitation. Most late‐ but not early‐stage larvae unregulated HIF signaling. Together these data support the conclusion that Drosophila, and likely other arthropods, experience some functional oxygen limitations later in the instar that trigger HIF signaling, potentially linked to the molting cascade. This research was supported by NSF IOS 1256745.

Response of Test-Organisms to Different Na and Cu Salts

Abstract The scope of this research involves the evaluation of biological impact of different Na and Cu salts (nitrates, sulphates and chlorides) on test-organisms. The toxic impact of Na and Cu salts on seed germination and root growth of Lepidium sativum (garden-cress) as well as mortality, growth and physiological parameters of On-corhynchus mykiss (rainbow trout) in early development stages (embryos and larvae) were determined. Among Na salts, nitrate was the most toxic to both test-organisms. Among tested Cu salts, sulphate caused the strongest toxic impact on L. sativum and nitrate - on embryos and larvae of O. mykiss. The accumulation of all tested anions and cations from the solutions of tested salts was higher in roots than in shoots ofL. sativum. The highest transfer of Na+ and Cu2+ from roots to shoots was determined for plants cultivated in sulphate salt. The transfer of SO42” was the highest among tested anions of sodium salts and the transfer of NO3” was higher among tested anions of copper salts. The rather high correlation was found between root length and amount of Na+, NO3” and SO42” ions in plant roots and rather low correlation coefficient was calculated between root length and the amount of Na+ and Cl” ions in roots.

Acute toxic effects of the herbicide formulation and the active ingredient used in cycloxydim-tolerant maize cultivation on embryos and larvae of the African clawed frog, Xenopus laevis.

Most genetically engineered herbicide-tolerant crops are still awaiting approval in Europe. There is, however, a recent trend for the cultivation of cycloxydim-tolerant maize hybrids for use in maize production. We studied the acute toxic effects of the complementary herbicide Focus(®) Ultra and its active ingredient cycloxydim on embryos and early-stage larvae of the African clawed frog (Xenopus laevis). The results indicate that the herbicide formulation is significantly more toxic than the active ingredient alone. Therefore, it is suggested that the added substances either solely or in a synergistic action with the active ingredient are responsible for adverse effects. The formulation was found to be moderately toxic to embryos but highly toxic to early larvae. Based on calculated teratogenic indices, both cycloxydim and Focus(®) Ultra seem to be non-teratogenic and also the minimum Focus(®) Ultra concentration to inhibit growth in embryos and larvae was close to the LC50 values. The data suggest that tests with the rainbow trout are not in all cases appropriate to assess the risk in aquatically developing anurans. This is demonstrated by 96-h LC50 values, which are for rainbow trout more than 50- to 20-fold higher than for early X. laevis larvae. However, based on worst-case predicted environmental concentrations for surface waters, there is apparently a large safety margin in field use of Focus(®) Ultra if buffer strips between the farm land and the amphibian habitats are regarded.

Caffeine induces high expression of cyp-35A family genes and inhibits the early larval development in Caenorhabditis elegans.

Intake of caffeine during pregnancy can cause retardation of fetal development. Although the significant influence of caffeine on animal development is widely recognized, much remains unknown about its mode of action because of its pleiotropic effects on living organisms. In the present study, by using Caenorhabditis elegans as a model organism, the effects of caffeine on development were examined. Brood size, embryonic lethality, and percent larval development were investigated, and caffeine was found to inhibit the development of C. elegans at most of the stages in a dosage-dependent fashion. Upon treatment with 30 mM caffeine, the majority (86.1 ± 3.4%) of the L1 larvae were irreversibly arrested without further development. In contrast, many of the late-stage larvae survived and grew to adults when exposed to the same 30 mM caffeine. These results suggest that early-stage larvae are more susceptible to caffeine than later-stage larvae. To understand the metabolic responses to caffeine treatment, the levels of expression of cytochrome P450 (cyp) genes were examined with or without caffeine treatment using comparative micro-array, and it was found that the expression of 24 cyp genes was increased by more than 2-fold (p < 0.05). Among them, induction of the cyp-35A gene family was the most prominent. Interestingly, depletion of the cyp-35A family genes one-by-one or in combination through RNA interference resulted in partial rescue from early larval developmental arrest caused by caffeine treatment, suggesting that the high-level induction of cyp-35A family genes can be fatal to the development of early-stage larvae.

Impact of environmental factors on recruitment and hatching patterns of Horse Mackerel (L.) collected in a nearshore rocky reef system

Event Abstract Back to Event Impact of environmental factors on recruitment and hatching patterns of Horse Mackerel (L.) collected in a nearshore rocky reef system Maria Klein1, 2*, Elisabeth Van Beveren1, 3, Diana Rodrigues2, Emanuel J. Gonçalves2, Ester A. Serrão1 and Rita Borges1, 2 1 Centre of Marine Sciences, Portugal 2 MARE - Marine and Environmental Sciences Centre, ISPA – Instituto Universitário, Portugal 3 IFREMER (Institut Français de Recherche pour l’Exploitation de la MER), CRH, Research Unit EME (UMR 212), France Horse mackerel (Trachurus trachurus, Linnaeus, 1758) is a highly exploited fish species, common throughout the North-East Atlantic. As a pelagic-neritic fish it typically occurs over the shelf at 100-200 m depth on sandy bottom and most research has focused on adults or early life stages (eggs and larvae), caught or examined in deeper waters. Nevertheless, larvae and early stages of Trachurus species have been observed in the nearshore environment of a rocky reef system in Portugal. More research is needed in order to understand the importance of nearshore environments for horse mackerel. In addition little is known on how environmental processes might affect early life parameters of this species. In this study we monitored the arrival of early juvenile horse mackerel to the reef environment at a fine time scale, and analyzed the relationship of environmental factors with patterns of recruitment and hatching, revealed by otolith microstructure analysis. In total around 2500 fish were collected with Standard Monitoring Units for the Recruitment of Fish (SMURF) and a distinct depth preference was recorded as 99% of fish were sampled with surface SMURFs. A GAM and GAMM analysis of the recruitment and hatching pattern, respectively, revealed a strong relationship with the lunar cycle and local up-welling. Both recruitment and hatching had a periodic pattern with peaks near the new moon; upwelling had a negative impact. Further, the study indicated that the nearshore environment might be an important nursery area for the post-larval growth of horse mackerel. Keywords: Trachurus trachurus, Lunar pattern, upwelling, juvenile, cohort, generalized additive models Conference: XV European Congress of Ichthyology, Porto, Portugal, 7 Sep - 11 Sep, 2015. Presentation Type: Oral Presentation Topic: Otoliths as a tool to study fish life cycles Citation: Klein M, Van Beveren E, Rodrigues D, Gonçalves EJ, Serrão EA and Borges R (2015). Impact of environmental factors on recruitment and hatching patterns of Horse Mackerel (L.) collected in a nearshore rocky reef system. Front. Mar. Sci. Conference Abstract: XV European Congress of Ichthyology. doi: 10.3389/conf.fmars.2015.03.00066 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 11 Nov 2015; Published Online: 11 Nov 2015. * Correspondence: Ms. Maria Klein, Centre of Marine Sciences, Faro, 8005-139, Portugal, mariaklein55@gmail.com Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Maria Klein Elisabeth Van Beveren Diana Rodrigues Emanuel J Gonçalves Ester A Serrão Rita Borges Google Maria Klein Elisabeth Van Beveren Diana Rodrigues Emanuel J Gonçalves Ester A Serrão Rita Borges Google Scholar Maria Klein Elisabeth Van Beveren Diana Rodrigues Emanuel J Gonçalves Ester A Serrão Rita Borges PubMed Maria Klein Elisabeth Van Beveren Diana Rodrigues Emanuel J Gonçalves Ester A Serrão Rita Borges Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

The ontogeny of larval swimming behavior in the crab Hemigrapsus sanguineus: Implications for larval transport

Many estuarine crab species are exported from this habitat at spawning and are physically transported to coastal waters where they undergo zoeal development. Later, they recruit back to the adult habitat as megalopae. Larval behavior within the context of wind-driven coastal circulation contributes to this process. The present study tested whether the crab Hemigrapsus sanguineus, an invasive species to the mid-Atlantic coast of the United States as well as in Europe, possesses behavioral responses to exogenous cues (gravity and light) and endogenous rhythms that would facilitate this scenario. Throughout larval development, H. sanguineus zoeae were negatively buoyant. In a laboratory test chamber, early stage (Z1) larvae displayed a strong negative geotaxis in darkness which resulted in surface swimming that was not offset by behavioral responses to light exposure. These Z1 stage larvae also possessed an endogenous tidal rhythm in swimming activity that was in phase with ebb tides in the spawning habitat and was independent of light exposure. These behaviors are consistent with export of larvae from estuarine to coastal waters where larval development occurs. Intermediate (Z3) and late (Z5) stage larvae exhibited a predominant negative geotaxis and surface swimming, with some zoeae showing positive geotaxis and/or sinking in the Z5 stage. Visual spectral sensitivity of eyes in Z3 larvae peaked between 450 and 510nm, with a secondary peak evident at short-wavelengths (~370nm). In both the Z3 and Z5 stages, larvae descended in response to light exposure, as expected under a negative feedback model of depth regulation common among crab larvae. Photoresponse thresholds of 5.8×1012 and 1.2×1014 photons m−2s−1 for Z3 and Z5 stage larvae, respectively, predict both stages to be in the lower water column during the day. After molting to megalopae, H. sanguineus display positive geotaxis and/or sinking in darkness and lack a phototactic response, consistent with settlement in the adult benthic habitat. Thus, larvae of the invasive crab H. sanguineus possess endogenous rhythms and behavioral responses to environmental cues that are similar to those observed in successful native species with a similar coastal larval development pattern.

Characteristics of juvenile survivors reveal spatio-temporal differences in early life stage survival of Baltic cod

The spatio-temporal origin of surviving juvenile Baltic cod Gadus morhua was investigated by coupling age information from otolith microstructure analysis and hydrodynamic modeling, which allowed backtracking of drift routes in time and space. The suitability of hydrodynamic modeling for drift simulations of early life stages of Baltic cod up to the pelagic juvenile stage was validated by comparing model simulations with the catch distribution from a survey targeting pelagic juveniles, and mortality rates and hatch date distributions of pelagic and demersal juveniles were estimated. Hatch dates and hatch locations of juvenile survivors showed distinct patterns which did not agree well with the abundance and spatial distribution of eggs, suggesting marked spatio-temporal differences in larval survival. The good agreement of the spatio-temporal origin of survivors from this field investigation with previous modeling studies on the survival chances of early-stage larvae and with general spatio-temporal patterns of larval prey availability suggests that differences in survival are related to food availability during the early larval stage. Results are discussed in relation to the recruitment process of Baltic cod, in particular with respect to the critical period and match-mismatch hypotheses, and to possible implications for the placement of a Marine Protected Area which was established to ensure undisturbed spawning of Baltic cod.

Description of the previously unknown tadpole of &lt;i&gt;Hyalinobatrachium pulveratum&lt;/i&gt; (Anura: Centrolenidae)

Egg clutches of the centrolenid Hyalinobatrachium pulveratum were sampled in four lowland locations of Costa Rica. The ontogenesis of the tadpoles of this species is documented by periodical descriptions of the larval stages. Larvae of H. pulveratum change their shape during development because of the non-equal growth of some body parts. Due to these changes the larvae in early stages of development differ considerably to those from later stages. Young larvae have a nearly circular cross-section, whereas later larval stages change to a typical flat shape. Some further morphological characteristics like width of the interorbital distance and the oral disk width change but not proportional to larvae length. Numerous measurements on different larval sizes help to recognize the larvae of H. pulveratum in all stages. The striking bright red hyobranchial sinus is the conspicuous characteristic feature ventrally of the hyobranchial apparatus. The use of allometric values for taxonomic and ontogenetic studies is discussed.

Bivalves: From individual to population modelling

An individual based population model for bivalves was designed, built and tested in a 0D approach, to simulate the population dynamics of a mussel bed located in an intertidal area. The processes at the individual level were simulated following the dynamic energy budget theory, whereas initial egg mortality, background mortality, food competition, and predation (including cannibalism) were additional population processes. Model properties were studied through the analysis of theoretical scenarios and by simulation of different mortality parameter combinations in a realistic setup, imposing environmental measurements. Realistic criteria were applied to narrow down the possible combination of parameter values. Field observations obtained in the long-term and multi-station monitoring program were compared with the model scenarios. The realistically selected modeling scenarios were able to reproduce reasonably the timing of some peaks in the individual abundances in the mussel bed and its size distribution but the number of individuals was not well predicted. The results suggest that the mortality in the early life stages (egg and larvae) plays an important role in population dynamics, either by initial egg mortality, larvae dispersion, settlement failure or shrimp predation. Future steps include the coupling of the population model with a hydrodynamic and biogeochemical model to improve the simulation of egg/larvae dispersion, settlement probability, food transport and also to simulate the feedback of the organisms' activity on the water column properties, which will result in an improvement of the food quantity and quality characterization.

Expression pattern of the vitellogenin gene in the zhikong scallop, Chlamys farreri, during ontogenesis

Vitellogenin (VTG), the precursor to yolk protein vitellins (Vn), has been widely studied in oviparous animals. However, information about VTG expression during ontogenesis is limited. In this study, we investigate the developmental expression pattern of the zhikong scallop gene, Chlamys farreri vitellogenin (Cf-vtg), using in situ hybridization and real-time RT-PCR techniques. The Cf-vtg mRNA was detected in unfertilized eggs, fertilized eggs, embryos and early-stage larvae, indicating a maternally supplied Cf-vtg. It was located restrictively in D-shaped larvae, and its concentration declined at the gastrula stage and approximated zero from umbo-larva to juveniles of 4–6 mm shell height. However, it was expressed distinctly again in the hepatopancreas of both males and females with shell heights from 7 to 12 mm and in the ovary during the first gonadal development cycle. This report provides experimental evidence of the expression pattern of vtg with the maternal supplication, the hepatopancreas and male expression in C. farreri.

Isolation and characterization of bacteria causing mortality in early stage larvae of captive-bred Japanese eels (Anguilla japonicaTemminck &amp; Schlegel)

Bacteria with lethal effect on eel larvae were isolated from moribund captive-bred eel larvae and their 16S rRNA gene sequences were analysed. Nucleotide sequence of 10 isolates showed highest similarity with Lacinutrix algicola, Crocinitomix catalasitica and Pseudoalteromonas rubra. Age-dependent changes in the susceptibility of eel larvae were observed in response to challenge by a highly lethal isolate. Compared with 10 and 11 days after hatching (DAH), larval susceptibility to the highly lethal isolate was lower at 18 DAH. We found that the bacterial isolates have lethal effect on the captive-bred eel larvae, especially at the early developmental stage. These results will be useful to establish appropriate culture practices for eel larvae that will improve the success of mass production of glass eels for aquaculture.

Eastern Bering Sea pollock recruitment, abundance, distribution and approach to fishery management

Eastern Bering Sea pollock have two distinctly different stable spawning grounds—along the shelf and in the eastern and central Aleutian Islands between 400 and 500 m water columns. Pollock spawning behavior supports the hypothesis that the shelf and deepwater “basin” spawning pollock are completely independent reproductive stocks. Deepwater pollock inhabit the shelf and, once mature at age 5–6 years, migrate from the shelf onto the continental slope into the Zhemchug, Pribilof, and Bering canyons by the end of winter. Bering Sea pollock recruitment and year class abundance have high annual variability, but there are no clear relationships between pollock year class strength and water temperature, ice distribution or survival on early ontogenesis stages (eggs and larvae). Young-of-the-year fish survival varies dramatically during winter supporting the hypothesis that the Bering Sea pollock recruitment and strength of year class have high annual variability depending on young-of-the-year fish survival during winter. The annual change of physical oceanography condition, productivity and species composition of zooplankton community are associated with great differences in pollock seasonal migrations and distribution, reproduction, survival of recruits at early stages of development and finally with abundance of year classes and total biomass. Implementation of ecosystem-based fishery management most important for application of pollock research both of Russian national program and on base of International Agreements.

Horizontal transfer of methoprene by Tribolium castaneum (Herbst) and Tribolium confusum Jacquelin du Val

In food facilities the majority of insect populations typically occur within hidden locations with limited direct exposure to insecticides, but there is potential for dispersing insects to transport insecticides into hidden areas and transfer insecticide to other individuals (i.e., horizontal transfer). In a series of laboratory experiments, the potential for transfer of the insect growth regulator methoprene between treated and untreated Tribolium castaneum (Herbst) and Tribolium confusum (Jacquelin du Val) individuals was evaluated. In the first experiment, late-instar larvae were exposed to methoprene or water treated individuals in flour and their ability to develop successfully was determined. For T. castaneum, survival time for individuals exposed to methoprene treated individuals was shorter than those exposed to control individuals, but the difference was not significant for T. confusum. For both T. castaneum and T. confusum, the number of individuals that were able to successfully survive exposure and complete development without externally visible deformities was significantly reduced for individuals exposed to methoprene treated pupae or larvae relative to controls, but not when exposed to methoprene treated adults. In the second experiment, early-stage larvae, late-stage larvae, and pupae were similar in susceptibility to horizontal transfer of methoprene, even though they were exposed as immatures for different lengths of time. In a third experiment, the potential for sublethal effects due to horizontal transfer of methoprene was evaluated, but no difference in reproduction and oviposition was found for normal appearing adults that developed when exposed to methoprene treated or and control individuals. This is the first report indicating that methoprene can be transferred between stored-product insects and further research is needed to determine the impact this potentially has on pest populations.

Spatio-temporal recruitment variability of naturalized Manila clams (Ruditapes philippinarum) in Willapa Bay, Washington, USA

Manila clam (Ruditapes philippinarum) harvests from Willapa Bay, Washington, USA have increased by an order of magnitude over two decades. This increased yield of a non-native species has been supported by natural recruitment as well as some planting of small clams. Manila clam settlement was recorded over three years in clam spat collectors (mesh bags containing gravel) and occurred in June to October at water temperatures >13°C. At 16 sites in the bay, clam abundance was measured at multiple life stages. Distributions of early-stage larvae during a spawning peak were well-correlated with wild populations of adult clams, with both stages highest in the southwest region having long residence time and little direct freshwater input. In contrast, settlement of these larvae 1–2 weeks later was correlated neither with early-stage larval distributions nor with one year-old recruits a year later; instead, settlement was spread more evenly between southeast and southwest regions, possibly due to mixing during larval development. Therefore, higher natural clam production in west than east may stem from differential post-settlement survival over the first winter, whereas low densities of all life stages in northern regions may be set by larval supply due to water residence time constraints. Despite an extended settlement period of several months, clams were no more abundant after one year than were measured for one week in clam spat collectors, suggesting generally high post-settlement losses in addition to factors that are spatially variable and break down correlations among life stages.

Shallow-water, nearshore current dynamics in Algoa Bay, South Africa, with notes on the implications for larval fish dispersal

Nearshore currents play a vital role in the transport of eggs and larval stages of fish. However, little is known about their complexity and the implications for dispersal of fish larvae. The study describes the complexity of the shallow nearshore environment in eastern Algoa Bay, on the south-east coast of South Africa, and its effect on larval fish ecology. An ADCP was used to assess short-term spatial current variability across the nearshore (4–20 m depth) during intensive one-day-transect profiling surveys. Data showing long-term temporal variability was collected half-hourly from a bottom-moored (15–20 m depth) ADCP over the course of one year (May 2006–May 2007). The short-term profiling revealed complexity in both current speed and direction with largely wind-driven flow patterns identified. The long-term data showed that the currents were aligned approximately west/east with prevailing winds and local shoreline. Modal speeds of 8 cm s–1 near the surface (4 m) and 6 cm s–1 near the bottom (14 m) of the water column are much lower than the average swimming speeds of postflexion larvae known to occur in the area. Mean current speed decreased with depth from ∼30 cm s–1 (4 m) to ∼10 cm s–1 (14 m), suggesting opportunities for depth refuge from current displacement in older larvae. Potential nett displacements were greater during the spring and summer, coinciding with peak fish breeding with passive eggs and early stage larvae travelling distances of up to 475 km near the surface of the water column. These maximum dispersal distances recorded during the present study differ considerably by half that from other calculations made for the area, highlighting a data error in a previous study. These predictions provide preliminary indications of potential transport from a point source and do not factor in anomalous local oceanography, benthic topographic impediments to transport or the complexities of larval fish behaviour.

Survival bottlenecks in the early ontogenesis of Atlantic herring (Clupea harengus, L.) in coastal lagoon spawning areas of the western Baltic Sea

AbstractDominant drivers of larval survival are considered to include oceanographic dispersal, sea temperatures, and food availability in the phase of first-feeding. However, research progress on larval herring survival dynamics indicates that multiple factors might act on differing larval developmental stages. Hypothesizing that in inshore systems of the western Baltic Sea bottlenecks of herring development occur before the point of first-feeding, we analysed an extensive time-series of weekly abundances of early stage larvae in Greifswald Bay, an important spawning area for Western Baltic herring. Additionally, we investigated whether distinct hatching cohorts contribute differently to established survival indices on the level of (i) later larval stages in Greifswald Bay and (ii) 1+ group juveniles in the overall western Baltic Sea. Results revealed that abundances of the earliest larval stage explain 62% of the variability of later stage larvae and 61% of the variability of surviving juveniles, indicating pre-hatching survival bottlenecks. Hatching cohorts occurring later during the spawning season contribute most to the surviving year class. Earlier hatching cohorts were not found to result in significant amounts of growing larvae, indicating a bottleneck phase at the critical period when larvae start feeding.

Niveles de susceptibilidad a temefos en el vector transmisor del dengue en Trujillo, Perú

Objetivo: Determinar los niveles de resistencia a temefos en poblaciones de Aedes aegypti de la provincia de Trujillo. Material y Métodos: Los bioensayos en larvas siguieron la metodología de la Organización Mundial de la Salud. Se empleó larvas del tercer o cuarto estadio temprano de cada población, incluyendo la cepa de referencia Rockefeller. Se usó 5 réplicas de cada concentración del insecticida, produciéndose mortalidades entre 2 y 98 %. Resultados: Se encontró susceptibles a temefos a todas las poblaciones evaluadas, mostrando mayor factor de resistencia la población de Florencia de Mora, con un valor de 3,05 X. Conclusión: Se sugiere realizar monitoreos continuos de resistencia a temefos en poblaciones de A. aegypti para brindar información necesaria que ayude a la toma de decisiones sobre el uso correcto de este insecticida.

The effect of food availability on development and phenotypic plasticity in larvae of the sea cucumber (Apostichopus japonicus)

Three food treatments (low, medium, and high) were used aiming to investigate potential for phenotypic plasticity in the sea cucumber Apostichopus japonicus. On day 5 and 7 after first feeding, the significant delayed development of larvae occurred in 2000 cells mL−1 day−1. Principal component analysis indicated that larvae in the low food group differed morphologically from others mainly due to long lateral maximum and depth on day 5, but individuals from three treatments were not morphologically distinct based on the first two components. The results presumably indicated that early-stage larvae responded to scarce food by development of undulating profiles and long sinuous bands, and thus increased the surface area of ciliated band for feeding at the expense of the delayed development of larvae. No significant difference in larval stages was observed by day 10, but 60% of total larvae in 15,000 cells mL−1 day−1 had greater than two hyaline spheres compared with 20 and 30% in 2000 and 30,000 cells mL−1 day−1. As the presence of hyaline spheres is indicative of metamorphic competence for sea cucumber, it is suggested that A. japonicus larvae in commercial culture should be fed 15,000 cells mL−1 day−1.

Toxicity of native Bacillus thuringiensis isolates on the larval stages of pine processionary moth Thaumetopoea wilkinsoni at different temperatures

Pine processionary moth, Thaumetopoea wilkinsoni Tams, is an important defoliating lepidopteran pest of pine trees. The aim of this study was to determine the required spore-crystal concentration of local Bacillus thuringiensis (Bt) isolates, optimal ambient temperature, and larval stage to control this troublesome forest pest. The susceptibility of T. wilkinsoni larvae decreased with older stage and lower temperatures. The optimum temperature was found to be 15 °C or higher for the control of early larval stages. At the highest spore-crystal concentration (500 µg g^{-1}), the most effective isolate (SY49.1) caused 83% mortality for the second-stage larvae at 5 °C. However, an approximately 4-fold decrease in mortalities was observed in late-stage larvae for all isolates examined at this temperature. Nevertheless, other Bt isolates, excluding SY27.3, caused nearly complete mortality at 25 °C for early-stage larvae. Considering the distribution of seasonal temperature, Bt products should be applied at the highest ambient temperature to earlier stages for efficient control. We propose that local Bt isolates SY27.1, SY49.1, and SY62.1 could be used to develop environmentally safe bioinsecticides to control this important pest species. These results indicate that larval stage and environmental temperature should be taken into consideration for efficient control of T. wilkinsoni using the spore-crystal mixture of Bacillus thuringiensis isolates.