Larval Movement Research Articles

Accurate assessment of marine protected area success depends on metric and spatiotemporal scale of monitoring

Marine protected areas are being monitored to determine whether they increase abundance of fished populations, with responses often expected within a few years. Evaluations typically compare abundance inside versus outside or after versus before implementation, but the temporal and spatial scales over which these measures can reflect marine protected area success are untested. We modeled the response of fished populations for a range of marine protected area sizes, fishing intensities, larval dispersal distances, and adult movement ranges. Our results, which can inform experimental design and interpretation of monitoring, show that the spatial and temporal scale of population responses to marine protected areas will be determined by simple relationships between marine protected area size, larval and adult movement distances, and generation time, in addition to the effects of exploitation rate. The largest effects of marine pro- tected areas should be expected with 'outside' samples located at least 2 dispersal units from the edge, and after 2 generations have passed since establishment. In general, monitoring studies over time (after versus before) should provide better assessment of marine protected area success than monitoring over space (inside versus outside), but understanding of the limitations of each type of measurement is key. Because it may take many years for marine protected area effects to be fully realized, we strongly caution against judgment of marine protected area effectiveness at inappropriately short time frames.

Modelling larval fish navigation: the way forward

Abstract Recent advances in high-resolution ocean circulation models, coupled with a greater understanding of larval behaviour, have increased the sophistication of individual-based, biophysical models used to study the dispersal of larvae in the sea. Fish larvae, in particular, have the ability to swim directionally and increasingly fast during ontogeny, indicating that they may not only disperse, but also migrate using environmental signals. How and when larvae use local and large-scale cues remains a mystery. Including three-dimensional swimming schemes into biophysical models is becoming essential to address these questions. Here, we highlight state-of-the-art modelling of vertical and horizontal migrations of fish larvae, as well as current challenges in moving towards more realistic larval movements in response to cues. Improved understanding of causes for orientation will provide insight into the evolutionary drivers of dispersal strategies for fish and marine organisms in general.

Resistance and behavioural response of Plutella xylostella (Lepidoptera: Plutellidae) populations to Bacillus thuringiensis formulations

Insecticide resistance is probably the major cause of control failure of Plutella xylostella (L.) in Brazil. In most production regions, the use of chemicals has been the prevalent method of control, with reduced efficacy through cropping seasons, even for the most recent use of products based on Bacillus thuringiensis (Bt). The current status of the resistance to these products was assessed, as well as the behavioural response of P. xylostella populations to Bt sprays. Most populations of P. xylostella were resistant to Bt products, particularly to Xentari®WDG (2-54-fold). Differences in walking characteristics of larvae were variable for most populations, for both Dipel®WP and Xentari®WDG, but not associated with resistance. Most females preferred to lay eggs on untreated surfaces and showed a reduced proportion of oviposition on treated surfaces that only correlated with resistance to Dipel®WP (r = -0.74, P = 0.02). Broad and indiscriminate use of Bt-based products has selected Brazilian P. xylostella populations to resistance. Larval movement appears to be a resistance-independent mechanism. Most populations of P. xylostella preferred to lay eggs on Bt-free surfaces, which might be a result of growers' practice of spraying the cabbage head. Reduced oviposition on treated surfaces correlated with physiological resistance, suggesting a behavioural response among the Bt-resistant colonies to Dipel®WP.

Integrating field data into individual-based models of the migration of European eel larvae

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 487:135-149 (2013) - DOI: https://doi.org/10.3354/meps10368 Integrating field data into individual-based models of the migration of European eel larvae Paco Melià1,*, Marcello Schiavina1, Marino Gatto1, Luca Bonaventura2, Simona Masina3,4, Renato Casagrandi1 1Dipartimento di Elettronica e Informazione, Politecnico di Milano, Via Ponzio 34/5, 20133 Milano, Italy 2MOX, Dipartimento di Matematica ‘F. Brioschi’, Politecnico di Milano, Piazza Leonardo da Vinci 32, 20133 Milano, Italy 3Centro Euro-Mediterraneo sui Cambiamenti Climatici, Viale Aldo Moro 44, 40127 Bologna, Italy 4Istituto Nazionale di Geofisica e Vulcanologia, Viale Aldo Moro 44, 40127 Bologna, Italy *Email: paco.melia@polimi.it ABSTRACT: Lagrangian simulations based on coupled physical-biological models can help determine the mechanisms that affect fish recruitment, but only if the key biological and environmental drivers are accurately described. However, it is difficult to obtain experimental measurements for some vital traits, such as mortality and/or movement patterns. The different hypotheses about these traits can be contrasted by comparing simulation outputs with experimental data that can be collected in the field, such as body size distribution at selected transects. We used this approach to study the oceanic migration of European eel larvae. Despite considerable research effort (involving both field surveys and simulation studies), it is still uncertain whether this migration is a purely passive process or the result of the interaction between transport by currents and an active larval movement. Based on present knowledge of eel larvae and predictions of metabolic ecology, we developed a parameterized model that provided a simple, yet biologically reasonable description of the species’ key life history traits (body growth, mortality and movement). We contrasted different model settings and identified the most plausible migration scenario by comparing simulation results against experimental data. The best-performing scenario was not purely passive but included an active larval propulsion proportional to body size. The corresponding migration duration was about 3 yr. Our modelling study succeeded in assimilating experimental data within a conceptual framework that is consistent with that sketched out, almost a century ago, by Danish biologist Johannes Schmidt. KEY WORDS: Anguilla anguilla · Lagrangian simulations · Larval dispersal · Physical-biological coupling · Movement ecology · Life history traits · Data assimilation Full text in pdf format Supplementary material PreviousNextCite this article as: Melià P, Schiavina M, Gatto M, Bonaventura L, Masina S, Casagrandi R (2013) Integrating field data into individual-based models of the migration of European eel larvae. Mar Ecol Prog Ser 487:135-149. https://doi.org/10.3354/meps10368 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 487. Online publication date: July 30, 2013 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2013 Inter-Research.

Theoretical and empirical assessment of a seed mix refuge in corn for southwestern corn borer

Larval movement in seed mixes of Bt and non-Bt corn (Zea mays L.) can potentially increase the rate at which resistance evolves compared to a structured refuge. Pyramided Bt crops with multiple efficacious Bt toxins make it less likely that interplant larval movement will be successful within a seed mix field but high levels of larval movement may decrease refuge value as larvae moving from non-Bt plants die on neighboring Bt plants. Estimates of refuge productivity obtained from multi-site field studies evaluating larval movement and survival of the southwestern corn borer (SWCB), Diatraea grandiosella Dyar, in MON 89034 seed mix refuge fields were compared to predictions from model simulations of larval movement within a seed mix refuge. Results from field studies and modeling simulations of interplant movement show that seed mix refuge was a productive source of susceptible SWCB and that successful interplant movement by larvae within a seed mix refuge was unlikely to occur at frequency that would increase the fitness of resistant heterozygotes or low level resistance mechanisms. Combined, these results indicate that MON 89034 with a 5% seed mix refuge is a durable IRM tactic for SWCB across a range of larval movement and refuge assumptions and show that a 5% seed mix refuge can delay resistance longer than a similar-sized structured refuge given the nature of grower compliance with refuge requirements.

Recruitment constraints in Singapore's fluted giant clam (Tridacna squamosa) population--a dispersal model approach.

Recruitment constraints on Singapore's dwindling fluted giant clam, Tridacna squamosa, population were studied by modelling fertilisation, larval transport, and settlement using real-time hydrodynamic forcing combined with knowledge of spawning characteristics, larval development, behaviour, and settlement cues. Larval transport was simulated using a finite-volume advection-diffusion model coupled to a three-dimensional hydrodynamic model. Three recruitment constraint hypotheses were tested: 1) there is limited connectivity between Singapore's reefs and other reefs in the region, 2) there is limited exchange within Singapore's Southern Islands, and 3) there exist low-density constraints to fertilisation efficacy (component Allee effects). Results showed that connectivity among giant clam populations was primarily determined by residual hydrodynamic flows and spawning time, with greatest chances of successful settlement occurring when spawning and subsequent larval dispersal coincided with the period of lowest residual flow. Simulations suggested poor larval transport from reefs located along the Peninsular Malaysia to Singapore, probably due to strong surface currents between the Andaman Sea and South China Sea combined with a major land barrier disrupting larval movement among reefs. The model, however, predicted offshore coral reefs to the southeast of Singapore (Bintan and Batam) may represent a significant source of larvae. Larval exchange within Singapore's Southern Islands varied substantially depending on the locations of source and sink reefs as well as spawning time; but all simulations resulted in low settler densities (2.1–68.6 settled individuals per 10,000 m2). Poor fertilisation rates predicted by the model indicate that the low density and scattered distribution of the remaining T. squamosa in Singapore are likely to significantly inhibit any natural recovery of local stocks.

Spinal Efference Copy Signaling and Gaze Stabilization during Locomotion in JuvenileXenopusFrogs

In swimming Xenopus laevis tadpoles, gaze stabilization is achieved by efference copies of spinal locomotory CPG output that produce rhythmic extraocular motor activity appropriate for minimizing motion-derived visual disturbances. During metamorphosis, Xenopus switches its locomotory mechanism from larval tail-based undulatory movements to bilaterally synchronous hindlimb kick propulsion in the adult. The change in locomotory mode leads to body motion dynamics that no longer require conjugate left-right eye rotations for effective retinal image stabilization. Using in vivo kinematic analyses, in vitro electrophysiological recordings and specific CNS lesions, we have investigated spino-extraocular motor coupling in the juvenile frog and the underlying neural pathways to understand how gaze control processes are altered in accordance with the animal's change in body plan and locomotor strategy. Recordings of extraocular and limb motor nerves during spontaneous "fictive" swimming in isolated CNS preparations revealed that there is indeed a corresponding change in spinal efference copy control of extraocular motor output. In contrast to fictive larval swimming where alternating bursts occur in bilateral antagonistic horizontal extraocular nerves, during adult fictive limb-kicking, these motor nerves are synchronously active in accordance with the production of convergent eye movements during the linear head accelerations resulting from forward propulsion. Correspondingly, the neural pathways mediating spino-extraocular coupling have switched from contralateral to strictly ipsilateral ascending influences that ensure a coactivation of bilateral extraocular motoneurons with synchronous left-right limb extensions. Thus, adaptive developmental plasticity during metamorphosis enables spinal CPG-driven extraocular motor activity to match the changing requirements for eye movement control during self-motion.

Occurrence and larval movement of Diatraea saccharalis (Lepidoptera: Crambidae) in seed mixes of non-Bt and Bt pyramid corn

Larval movement of target pest populations among Bt and non-Bt plants is a major concern in the use of a seed mixture refuge strategy for Bt resistance management. In this study, occurrence and larval movement of the sugarcane borer, Diatraea saccharalis (F.), were evaluated in four planting patterns of non-Bt and Bt plants containing Genuity® SmartStax(TM) traits in 2009-2011. The four planting patterns were: (1) a pure stand of 27 Bt plants; (2) one non-Bt plant in the center, surrounded by 26 Bt plants; (3) a pure stand of 27 non-Bt plants; (4) one Bt plant in the center, surrounded by 26 non-Bt plants. Studies were conducted under four conditions: (1) open field with natural infestation; (2) greenhouse with artificial infestations; open field with artificial infestations (3) on the center plants only and (4) on every plant. The major objective of this study was to determine whether refuge plants in a seed mixture strategy could provide a comparable refuge population of D. saccharalis to a 'structured refuge' planting. Larvae of D. saccharalis showed the ability to move from infested plants to at least four plants away, as well as to adjacent rows, but the majority remained within the infested row. However, the number of larvae found on the non-Bt plants in the mixture plantings was not significantly reduced compared with the pure stand of non-Bt corn. The results of this study show that refuge plants in a seed mixture may be able to provide a comparable refuge population of D. saccharalis to a structured refuge planting.

Validation of the Zebrafish Pentylenetetrazol Seizure Model: Locomotor versus Electrographic Responses to Antiepileptic Drugs

Zebrafish have recently emerged as an attractive in vivo model for epilepsy. Seven-day-old zebrafish larvae exposed to the GABAA antagonist pentylenetetrazol (PTZ) exhibit increased locomotor activity, seizure-like behavior, and epileptiform electrographic activity. A previous study showed that 12 out of 13 antiepileptic drugs (AEDs) suppressed PTZ-mediated increases in larval movement, indicating the potential utility of zebrafish as a high-throughput in vivo model for AED discovery. However, a question remained as to whether an AED-induced decrease in locomotion is truly indicative of anticonvulsant activity, as some drugs may impair larval movement through other mechanisms such as general toxicity or sedation. We therefore carried out a study in PTZ-treated zebrafish larvae, to directly compare the ability of AEDs to inhibit seizure-like behavioral manifestations with their capacity to suppress epileptiform electrographic activity. We re-tested the 13 AEDs of which 12 were previously reported to inhibit convulsions in the larval movement tracking assay, administering concentrations that did not, on their own, impair locomotion. In parallel, we carried out open-field recordings on larval brains after treatment with each AED. For the majority of AEDs we obtained the same response in both the behavioral and electrographic assays. Overall our data correlate well with those reported in the literature for acute rodent PTZ tests, indicating that the larval zebrafish brain is more discriminatory than previously thought in its response to AEDs with different modes of action. Our results underscore the validity of using the zebrafish larval locomotor assay as a rapid first-pass screening tool in assessing the anticonvulsant and/or proconvulsant activity of compounds, but also highlight the importance of performing adequate validation when using in vivo models.

Population genetic structures of three congeneric species of coastal pelagic fishes (Arripis: Arripidae) with extensive larval, post-settlement and adult movements

The population genetic structures of three congeneric coastal pelagic marine fishes (Arripis trutta, A. truttaceus and A. georgianus) were investigated to determine whether these structures were consistent with the apparently high gene flow life histories of these species. This investigation used fragment length polymorphisms at two to four nDNA intron loci (amplified by EPIC-PCR) in samples of each species collected from across their entire Australian distributions. The results revealed no evidence of genetic subdivision in any species based on an analysis of variation either across samples (with multilocus FST values ranging from effectively zero to 0.005), or between pairs of samples. These findings, when considered in combination with other available evidence, are consistent with the view that each of these species represents a rare example of a coastal fish species that is genetically homogeneous over a vast area, including the entire geographic range (A. truttaceus and A. georgianus) or Australian distribution (A. trutta).

Western Corn Rootworm Larval Movement in SmartStax Seed Blend Scenarios

Insect resistance management (IRM) can extend the lifetime of management options, but depends on extensive knowledge of the biology of the pest species involved for an optimal plan. Recently, the Environmental Protection Agency (EPA) registered seed blends refuge for two of the transgenic Bacillus thuringiensis (Bt) corn products targeting the western corn rootworm, Diabrotica virgifera virgifera LeConte. Larval movement between Bt and isoline plants can be detrimental to resistance management for high dose Bt products because the larger larvae can be more tolerant of the Bt toxins. We assessed movement of western corn rootworm larvae among four spatial arrangements of SmartStax corn (expressing both the Cry34/35Ab1 and Cry3Bb1 proteins) and isoline plants by infesting specific plants with wild type western corn rootworm eggs. Significantly fewer western corn rootworm larvae, on average, were recovered from infested SmartStax plants than infested isoline plants, and the SmartStax plants were significantly less damaged than corresponding isoline plants. However, when two infested isoline plants surrounded a SmartStax plant, a significant number of larvae moved onto the SmartStax plant late in the season. These larvae caused significant damage both years and produced significantly more beetles than any other plant configuration in the study (including isoline plants) in the first year of the study. This plant configuration would occur rarely in a 5% seed blend refuge and may produce beetles of a susceptible genotype because much of their initial larval development was on isoline plants. Results are discussed in terms of their potential effects on resistance management.

An In Vivo Platform for Rapid High-Throughput Antitubercular Drug Discovery

Treatment of tuberculosis, like other infectious diseases, is increasingly hindered by the emergence of drug resistance. Drug discovery efforts would be facilitated by facile screening tools that incorporate the complexities of human disease. Mycobacterium marinum-infected zebrafish larvae recapitulate key aspects of tuberculosis pathogenesis and drug treatment. Here, we develop a model for rapid in vivo drug screening using fluorescence-based methods for serial quantitative assessment of drug efficacy and toxicity. We provide proof-of-concept that both traditional bacterial-targeting antitubercular drugs and newly identified host-targeting drugs would be discovered through the use of this model. We demonstrate the model's utility for the identification of synergistic combinations of antibacterial drugs and demonstrate synergy between bacterial- and host-targeting compounds. Thus, the platform can be used to identify new antibacterial agents and entirely new classes of drugs that thwart infection by targeting host pathways. The methods developed here should be widely applicable to small-molecule screens for other infectious and noninfectious diseases.

Preimaginal development of the parasitoid Minotetrastichus frontalis (Nees) (Hymenoptera, Eulophidae)

The paper presents the first detailed description of preimaginal development of the parasitic wasp Minotetrastichus frontalis, an ectoparasitoid of the larvae and pupae of the lime leaf miner Phyllonorycter issikii, developing on Tilia cordata. Prior to the parasitization of the host, the female wasp induces permanent paralysis and then lays 1–7 eggs, depending on the host stage. The eggs are oval, smooth, and have no attachment structures. The species develops with 4 larval instars. The larval body consists of the head and 13 somatic segments. Papilliform processes facilitating larval movement are present on thoracic segments I–III and abdominal segments V, VII, IX, and XI; similar processes on segments XII and XIII are underdeveloped. The cephalic sensory system consists of 3 pairs of sensory setae situated near the mouth. The tracheal system includes 8 pairs of spiracles on thoracic segments II and III and abdominal segments V–X. The pupa has weakly sclerotized integument and a specific filament used for fixation inside the mine. The entire preimaginal development lasts for 12–14 days.

Muga silkworm (Antheraea assamensis helfer) indoor rearing by integrated “leaf freshness technology”- A new technology

Integrated Muga silkworm indoor rearing technology includes “leaf freshness technology” (LFT), “Nutrient Supplemented Phago-stimulant” and bacterial disease control by streptomycin sulfate. All these techniques were applied in complete indoor conditions up to cocoon formation and, very high positive significant results were achieved in respect of larval survivability, larval biomass growth and error (ERR) percent in comparison to outdoor conventional rearing. Muga silkworm, being wild in nature, is very difficult to rear in indoor condition. Moreover, the detached food plant leafs goes on wilting within few hours. LFT made it possible to rear Muga silkworm completely in indoor conditions and minimized early stage loss of larvae from nature’s vagaries, like pest and predators, souring temperature, hailstorm, wind, etc. The use of Nutrient Supplemented Phago-stimulant resulted to increased leaf nutrient quality, arrestancy of larval movement and increased feeding rate which reflected in the higher biomass growth in comparison to treatment without it use. Spraying of 0.5% streptomycin sulfate solution in the indoor reared Muga silkworm, minimized the bacterial infection thereby contributing to larval survivability. Normal cocoon qualities such as silk ratio, denier, sex ratio of male and female cocoon, were not affected by the use of Nutrient Supplemented Phago-stimulant, chemically treated host plant leafs used in LFT and spray of streptomycin sulfate solution. This new integrated LFT may help in adopting indoor rearing of naturally wild Muga silkworm for more production of Muga silk yean. Key words: Leaf freshness, phago-stimulant, nutrient, biomass, denier, integrated, streptomycin sulfate, indoor.

Deceptive vibratory communication: pupae of a beetle exploit the freeze response of larvae to protect themselves

It is argued that animal signals may have evolved so as to manipulate the response of receivers in a way that increases the fitness of the signallers. In deceptive communication, receivers incur costs by responding to false signals. Recently, we reported that pupae of the soil-inhabiting Japanese rhinoceros beetle Trypoxylus dichotoma produce vibratory signals to deter burrowing larvae, thereby protecting themselves. In the present study, monitoring of vibrations associated with larval movement revealed that T. dichotoma larvae remained motionless for ca 10 min when pupal vibratory signals were played back transiently (freeze response). Furthermore, pupal signals of T. dichotoma elicited a freeze response in three other scarabaeid species, whose pupae do not produce vibratory signals. This indicates that the freeze response to certain types of vibration evolved before the divergence of these species and has been evolutionarily conserved, presumably because of the fitness advantage in avoiding predators. Pupae of T. dichotoma have probably exploited pre-existing anti-predator responses of conspecific larvae to protect themselves by emitting deceptive vibratory signals.

When and where a seed mix refuge makes sense for managing insect resistance to Bt plants

Planting of a separate structured refuge for Bt crops as part of an insect resistance management (IRM) strategy to delay resistance evolution is the most common method of refuge deployment but this strategy depends on growers planting a refuge. A seed mix refuge interspersed with a pyramided Bt product is an alternative strategy that addresses the risk of growers not planting a refuge. However, concerns exist regarding how larval movement between Bt and non-Bt plants might influence resistance evolution in a seed mix field. To understand when seed mixes are an appropriate IRM strategy, a deterministic model run probabilistically was used to examine the evolution of Bt resistance in seed mix and structured refuges under varying levels of Bt efficacy, pest fitness, refuge size, larval movement, movement penalty and grower compliance. Results from modeling simulations show that the addition of a second and third Bt toxin can delay resistance evolution longer than a single toxin, making a seed mix refuge strategy a viable option where refuge compliance is a concern. In seed mixes, resistance was shown to evolve faster compared to a responsibly implemented structured refuge and evolved fastest in seed mixes when larval movement rates were high. However, when mortality from larval movement was included in model simulations, the selection pressure from Bt was reduced and two or three Bt-pyramids with a 5% seed mix refuge were at least as durable as the same products with a 5% structured refuge, depending upon refuge compliance. These simulations show that, across a range of conditions, seed mix refugia provide an effective alternative IRM tactic for delaying resistance evolution. Under some conditions use of seed mix refugia may be a superior IRM tactic leading to longer delays to resistance, and greater durability, compared to structured refugia and is a risk adverse tactic in situations when no refuge is planted.

Kauri seeds and larval somersaults: The larval trunk of the seed mining basal moth Agathiphaga vitensis (lepidoptera: Agathiphagidae)

The trunk morphology of the larvae of the kauri pine (Agathis) seed infesting moth Agathiphaga is described using conventional, polarization, and scanning electron microscopy. The pine seed chamber formed by the larva is also described and commented on. The simple larval chaetotaxy includes more of the minute posture sensing setae, proprioceptors, than expected from the lepidopteran larval ground plan. The excess of proprioceptors is suggested to be necessary for sensory input concerning the larval posture within the seed chamber. The trunk musculature includes an autapomorphic radial ventral musculature made up of unique multisegmental muscles. The combined presence of additional proprioceptors and the unique ventral musculature is proposed to be related to the larval movement within the confined space of the seed chamber, especially to a proposed somersault movement that allows the larva to orientate itself within the chamber.

Setting tools for the early assessment of the quality of thawed Pacific oyster (Crassostrea gigas) D-larvae

Parameters used to assess the survival of larvae after cryopreservation generally misestimate the damages that prevent larval development. The objectives of the present study were to 1) define the reliability of the survival rate, assessed at 2 and 7 days post fertilization, to estimate Pacific oyster larval quality after thawing, and 2) select complementary tools allowing an early and reliable estimation of their quality. Oyster larvae were reared for 25 h after fertilization at 19 °C and cryopreserved at early D-stage. Then, thawed larvae were incubated in 2-L beakers. At 2 days post fertilization, the survival rate of thawed Pacific oyster larvae was lower than that of fresh larvae for only one experiment (Experiment 3) among the four identical experiments carried out in this work (Experiments 1–4). By contrast, the survival of thawed larvae, as assessed 7 days after fertilization, was lower than that of fresh larvae for the four experiments. These results confirm that the quality of thawed larvae is lower than that of fresh larvae and that the survival rate, estimated 2 days post fertilization, is not adapted to a reliable estimation of the subsequent development ability of thawed larvae. Then, complementary parameters were tested at 2 days: the movement characteristics (Experiments 1 and 2) and the morphologic features (Experiments 3 and 4) of thawed larvae. Compared to values observed on fresh larvae, the percentage of thawed motile larvae was different for only one experiment (Experiment 2) of the two. Compared to control, a reduced Average Path Velocity (VAP) of larvae (determined at the D-larval stage using a CASA-Computer Assisted Sperm Analysis-system) was observed after thawing for both experiments (Experiments 1 and 2), suggesting the ability of larval movement velocity to assess the decrease of the quality of thawed oyster larvae. Using an ASMA (Automated Sperm Morphology Analysis) device, a lower area of thawed larvae was observed, compared to control and for the two experiments (Experiments 3 and 4). By contrast, the Crofton perimeter of thawed larvae was lower than that of control larvae for only one experiment (Experiment 3) and no significant difference of circularity between fresh and thawed larvae was recorded for Experiments 3 and 4. In conclusion, changes in the movement velocity (assessed by CASA) and in the area (measured by ASMA) of D-larvae allow an early and reliable estimation of the quality of thawed Pacific oyster larvae.

Modeling the Impact of Cross-pollination and Low Toxin Expression in Corn Kernels on Adaptation of European Corn Borer (Lepidoptera: Crambidae) to Transgenic Insecticidal Corn

We used a mathematical model with processes reflecting larval mortality resulting from feeding on cross-pollinated ears or Bt ears of corn to analyze the risk of evolution of Cry-toxin resistance in Ostrinia nubilalis (Hübner). In the simulations, evolution of resistance was delayed equally well by both seed mixtures and blocks with the same proportion of refuge. Our results showed that Bt-pollen drift has little impact on the evolution of Bt resistance in O. nubilalis. However, low-toxin expression in ears of transgenic corn can reduce the durability of transgenic corn expressing single toxin, whereas durability of pyramided corn hybrids is not significantly reduced. The toxin-survival rate of heterozygous larvae in Bt-corn ears expressing one or two proteins has more impact on evolution of Bt resistance in O. nubilalis than the parameters related to larval movement to Bt ears or the toxin-survival rate of the homozygous susceptible larvae in Bt ears. Bt resistance evolves slower when toxin mortality is distributed across the first two larval stadia than when only the first instars are susceptible to Bt toxins. We suggest that stakeholders examine toxin-survival rates for insect pests and take into account that instars may feed on different parts of Bt corn.

Low-concentration copper solution jeopardizes larval movement and ability to survive predation: New insight into malaria eradication via vector control

Low-concentration copper solution jeopardizes larval movement and ability to survive predation: New insight into malaria eradication via vector control