Wild Larvae Research Articles

Stably inherited transfer of the bacterial symbiont Candidatus Erwinia dacicola from wild olive fruit flies Bactrocera oleae to a laboratory strain

The olive fruit fly, Bactrocera oleae, the most serious pest of olives, requires the endosymbiotic bacteria Candidatus Erwinia dacicola in order to complete its development in unripe green olives. Hence a better understanding of the symbiosis of Ca. E. dacicola and its insect host may lead to new strategies for reduction of B. oleae and thus minimize its economic impact on olive production. Studies of this symbiosis are hampered as the bacterium cannot be grown in vitro and the established B. oleae laboratory populations, raised on artificial diets, are devoid of this bacterium. Here, we sought to develop a method to transfer the bacteria from wild samples to laboratory populations. We tested several strategies. Cohabitation of flies from the field with the laboratory line did not result in a stable transfer of bacteria. We provided the bacteria directly to the egg and also in the food of the larvae but neither approach was successful. However, a robust method for transfer of Ca. E. dacicola from wild larvae or adults to uninfected flies by transplantation to females was established. Single female lines were set up and the bacteria were successfully transmitted for at least three generations. These results open up the possibilities to study the interaction between the symbiont and the host under controlled conditions, in view of both understanding the molecular underpinnings of an exciting, unique in nature symbiotic relationship, as well as developing novel, innovative control approaches.

Utilising mixotrophically cultured “designer algae” as blue mussel larval feed

The production of blue mussels is currently reliant upon supply of wild larvae, which is a limiting factor to upscaling production. A potential solution to address this limiting factor is to develop a larval hatchery; however, costs associated with microalgal cultivation to feed the larvae account for around 30% of total costs. Microalgae are classically considered to be photoautotrophic and are cultured under light, in seawater with additional nitrate and phosphate. Many microalgae can be cultured mixotrophically, or heterotrophically, on an organic carbon source which results in an enhanced cell density and altered biochemical profile. Over the course of two feeding trials this study compares larval growth and survival employing current “industry standard” and mixotrophic “designer” microalgal feeds as diets. The “designer” feed employed proved to be as effective as the standard feed and subsequent optimisation demonstrated that a diet tailored towards the development of the larvae performs the most effectively in terms of larval growth. A sequential diet of mixotrophically cultured microalgae, where the primary component of the diet changed as the larvae increased in size, resulted in the greatest larval growth (174.35 μm) and total fatty acid content (7.20% dry weight). First-order modelling indicates that approximately ten times lower volume of mixotrophically cultivated microalgae was required to produce sufficient larval feed. Thus, mixotrophic culture has the potential to reduce the costs of microalgal cultivation and increase the profitability of a mussel larval hatchery.

Morpho-Molecular Mechanisms Study of Photodynamic Therapy and Curcumin Larvicide Action on Wild Mosquitoes Larvae of Genus <i>Aedes<i></i></i>

Morpho-Molecular Mechanisms Study of Photodynamic Therapy and Curcumin Larvicide Action on Wild Mosquitoes Larvae of Genus <i>Aedes<i></i></i>

Laboratory evaluation of spinosad as a potential larvicide against immature forms of Aedes aegypti

Background and Objectives: Aedes mosquito has been recognized as a global emerging threat with its potential to transmit fatal diseases of international public health importance such as dengue, chikungunya, and yellow fever. Prior attempts to manage the vector with various synthetic larvicides have resulted in emergence of resistance, thus necessitating search for a safer and effective alternative. The study was an experimental laboratory-based study to screen the recent World Health Organization (WHO)-approved insecticide spinosad for larvicidal activity and compare the efficacy of the same with other currently used larvicides, namely temephos and Bacillus thuringiensis var. israelensis (Bti). Methodology: An experimental setup was done as per the WHO Pesticide Evaluation Scheme to assess the larvicidal activity of the spinosad at varying concentrations along with a positive and negative control. A preliminary screening to assess the larvicidal property of the spinosad was undertaken with 0.5 ppm concentration as recommended by the WHO. The mortality was checked after 24 h and results were statistically analyzed and LC50 and LC90 values were calculated. Results: Spinosad brought about 100% larval mortality at the recommended dosage (0.5 ppm) as well as at a lower dosage of 0.1 ppm. The comparison with the other two commonly used larvicides, namely temephos and Bti, reveals 100% and 90% mortality, respectively, in wild Aedes larvae. Conclusion: The study concludes that spinosad is a promising larvicide that can be used in rotation with temephos against Aedes aegypti in potable water and may be used at a lower dosage of 0.1 ppm. However, large-scale field trials are required to ascertain the effectiveness of the larvicide in field conditions.

The life cycle of Orthemis ferruginea (Fabricius, 1775) (Odonata: Libellulidae)

The complete life cycle of O. ferruginea is described for the first time, represent the first complete life cycle described for an odonate in Mexico. The 17 larval instars obtained are described and illustrated in detail, from prolarva through F-0. Two egg batches of different females were obtained in the field and were subsequently reared in the laboratory. Eggs and larvae of the batches were raised under 26°C controlled temperature conditions until they reached instars F-6 and F-5. An extra collection of wild organisms was made in order to complete the life cycle from F-5. Only four of the wild larvae managed to complete the last five missing larval instars at 30°C. Larvae of the youngest instars (F-15 to F-8) were fed nauplii of Artemia franciscana, while F-7 to F-0 were fed larvae of Culicidae and Chironomidae. Larval life cycle from F-0 to F-16 lasted average of 186 days.

Bay Scallop Growth Rates as Measured by Citizen-Scientist Partners During Restoration Efforts in Florida

Local bay scallop Argopecten irradians populations are threatened or depleted in southwest Florida estuaries (Pinellas through Lee Counties) and in the Panhandle (Bay through Escambia Counties), and community-driven restoration efforts have been ongoing for many years. To obtain juvenile scallops for use in restoration, wild larvae (spat) were allowed to settle on suitable surfaces (settlement traps) at sites known to still have high larval supply. Traps used to harvest spat were constructed with enhanced surface area relative to routine monitoring traps. Enhanced traps resulted in 142 ± 317.1 (mean ± SD) spat per trap and a maximum of 2,321 spat on a single trap, whereas the routine traps resulted in 67 ± 146.7 spat per trap and a maximum of 726. Spat were harvested each winter (2008–2012) from either St. Andrew Bay or Tampa Bay and delivered to restoration sites where citizen-scientists or collaborators measured the growth (shell heights) and mortality (live count) of 25–50 scallops within 3–25 cages each month. Most cages were hung from their own dock or the dock of a partner organization. Scientists from the lead agency also measured growth of caged scallops. Thus, simultaneous sampling occurred across a large geographical range with varied organizations and skill levels. In the shortest trials, survival remained very high, and in most years involving prolonged efforts, some of the planted scallops survived long enough to reach a size where spawning likely occurred. A maximum survival period of 559 days and the greatest mean shell height (65.18 ± 2.48 mm) of caged scallops were observed in Sarasota Bay in 2012. The observed growth in restoration cages fit previously described patterns for Florida Bay scallops, reaching maximum sizes between 60 and 70 mm shell height in 1 y. Mean daily growth rates (mm/day ± SD) increased as latitude decreased: St. Andrew Bay, 0.15 ± 0.096 y; Tampa Bay, 0.21 ± 0.124; Sarasota Bay, 0.22 ± 0.134; Charlotte Harbor, 0.28 ± 0.112; and Pine Island Sound, 0.29 ± 0.086). Temperature, scallop shell height, and the number of days in captivity (a proxy for age) generally had only minor or no effect on growth rates. When combined, the process of collecting wild spat and growing those scallops in cages using volunteer networks offers the advantages of community engagement, relatively low costs, minimal technical skill requirements, and reduced threat of loss of genetic diversity.

Disease Vector Relative Spatio-Temporal Abundances to Water Bodies and Thermal Fitness Across Malaria Endemic Semi-Arid Areas.

The biophysical environment plays an important role in the spatio-temporal abundance and distribution of mosquitoes. This has implications for the spread of vectors and diseases they cause across diverse landscapes. Here, we assessed vector mosquito abundances in relation to large water bodies, from three malaria districts in a semi-arid environment. Furthermore, we explored thermal limits to activity of the dominant and most medically important malaria vector across malaria-endemic areas. Mosquitoes were trapped near permanent water bodies across different districts. Critical thermal limits (critical thermal-maxima and -minima) to activity of wild adults and 4th instar larvae Anopheles arabiensis (Diptera: Culicidae) were assessed. Our results showed that Anopheles spp. dominate mosquito communities across all three districts, but that their numbers were far greater in Okavango than in other regions. At the Okavango sites, the numbers of Anopheles spp. decreased with distance from main water source. Anopheles spp. sampled in this region comprised Anopheles gambiae (Giles,1902) and Anopheles funestus (Giles, 1900) species complexes, with the former dominating in numbers. Thermal activity assays showed An. arabiensis females had wider thermal tolerance windows than males while larval thermal activity limits differed significantly across space. These results confirm that the Okavango district should be prioritized for vector control measures. Moreover, intervention strategies should consider recommendations for proximity effects to large water bodies, given the differential risk associated with distance from water. The wider thermal window on female vectors has implications for possible future malaria transmission and diverse habitat utilization under changing environments.

Fruit host-dependent fungal communities in the microbiome of wild Queensland fruit fly larvae

Bactrocera tryoni (Froggatt), the Queensland fruit fly (Qfly), is a highly polyphagous tephritid fly that is widespread in Eastern Australia. Qfly physiology is closely linked with its fungal associates, with particular relationship between Qfly nutrition and yeast or yeast-like fungi. Despite animal-associated fungi typically occurring in multi-species communities, Qfly studies have predominately involved the culture and characterisation of single fungal isolates. Further, only two studies have investigated the fungal communities associated with Qfly, and both have used culture-dependant techniques that overlook non-culturable fungi and hence under-represent, and provide a biased interpretation of, the overall fungal community. In order to explore a potentially hidden fungal diversity and complexity within the Qfly mycobiome, we used culture-independent, high-throughput Illumina sequencing techniques to comprehensively, and holistically characterized the fungal community of Qfly larvae and overcome the culture bias. We collected larvae from a range of fruit hosts along the east coast of Australia, and all had a mycobiome dominated by ascomycetes. The most abundant fungal taxa belonged to the genera Pichia (43%), Candida (20%), Hanseniaspora (10%), Zygosaccharomyces (11%) and Penicillium (7%). We also characterized the fungal communities of fruit hosts, and found a strong degree of overlap between larvae and fruit host communities, suggesting that these communities are intimately inter-connected. Our data suggests that larval fungal communities are acquired from surrounding fruit flesh. It is likely that the physiological benefits of Qfly exposure to fungal communities is primarily due to consumption of these fungi, not through syntrophy/symbiosis between fungi and insect ‘host’.

World Travelers: DNA Barcoding Unmasks the Origin of Cloning Asteroid Larvae from the Caribbean.

AbstractThe identity of wild cloning sea star larvae has been a mystery since they were first documented in the Caribbean. The most commonly collected cloning species was thought to belong to the Oreasteridae, on the basis of similarity with sequences from Oreaster reticulatus and Oreaster clavatus. This larval form has recently been linked to a rare benthic juvenile. As part of two larger DNA barcoding projects, we collected cloning asteroid larvae from the Caribbean coast of Panama and compared them to a large reference database of tropical echinoderms. Morphological and DNA barcode data from the cytochrome c oxidase subunit I gene demonstrated that Panamanian larvae belonged to the same operational taxonomic unit as those recovered in previous studies of cloning larvae from the Caribbean. Much to our surprise, sequences from these larvae clearly identified them as belonging to Valvaster striatus, a species typically considered to be endemic to the Indo-West Pacific. A lineage of Mithrodia clavigera that occurs in both the Caribbean and the Indo-West Pacific also has cloning larvae, suggesting that this unusual life history has allowed larvae to pass around the Cape of Good Hope and the Benguela upwelling region, which is a barrier to dispersal for most tropical marine invertebrates.

Functional redundancy of structural proteins of the peritrophic membrane in Trichoplusia ni

The peritrophic membrane (or peritrophic matrix) (PM) in insects is formed by binding of PM proteins with multiple chitin binding domains (CBDs) to chitin fibrils. Multi-CBD chitin binding proteins (CBPs) and the insect intestinal mucin (IIM) are major PM structural proteins. To understand the biochemical and physiological role of IIM in structural formation and physiological function of the PM, Trichoplusia ni mutant strains lacking IIM were generated by CRISPR/Cas9 mutagenesis. The mutant T. ni larvae were confirmed to lack IIM, but PM formation was observed as in wild type larvae and lacking IIM in the PM did not result in changes of protease activities in the larval midgut. Larval growth and development of the mutant strains were similar to the wild type strain on artificial diet and cabbage leaves, but had a decreased survival in the 5th instar. The larvae of the mutant strains with the PM formed without IIM did not have a change of susceptibility to the infection of the baculovirus AcMNPV and the Bacillus thuringiensis (Bt) formulation Dipel, to the toxicity of the Bt toxins Cry1Ac and Cry2Ab and the chemical insecticide sodium aluminofluoride. Treatment of the mutant T. ni larvae with Calcofluor reduced the larval susceptibility to the toxicity of Bt Cry1Ac, as similarly observed in the wild type larvae. Overall, in the mutant T. ni larvae, the PM was formed without IIM and the lacking of IIM in the PM did not drastically impact the performance of larvae on diet or cabbage leaves under the laboratory conditions.

The phytotoxic air-pollutant O3 enhances the emission of herbivore-induced volatile organic compounds (VOCs) and affects the susceptibility of black mustard plants to pest attack

Stress-induced changes to plant biochemistry and physiology can influence plant nutritional quality and subsequent interactions with herbivorous pests. However, the effects of stress combinations are unpredictable and differ to the effects of individual stressors. Here we studied the effects of exposure to the phytotoxic air-pollutant ozone (O3), feeding by larvae of the large cabbage white butterfly (Pieris brassicae), and a combination of the two stresses, on the emission of volatile organic compounds (VOCs) by black mustard plants (Brassica nigra) under field and laboratory conditions. Field-grown B. nigra plants were also measured for carbon-nitrogen (C–N) content, net photosynthetic activity (Pn), stomatal conductance (gs) and biomass. The effects of O3 on interactions between plants and a herbivorous pest were addressed by monitoring the abundance of wild diamondback moth larvae (Plutella xylostella) and feeding-damage to B. nigra plants in an O3-free air concentration enrichment (O3-FACE) field site. Herbivore-feeding induced the emission of VOCs that were not emitted by undamaged plants, both under field and laboratory conditions. The combination of O3 and herbivore-feeding stresses resulted in enhanced emission rates of several VOCs from field-grown plants. Short-term O3 exposure (of 10 days) and P. brassicae-feeding did not affect C–N content, but chronic O3 exposure (of 34 and 47 days) and P. brassicae-feeding exacerbated suppression of Pn. Ozone exposure also caused visible injury and decreased the plant biomass. Field-grown B. nigra under elevated O3 were infested with fewer P. xylostella larvae and received significantly less feeding damage. Our results suggest that plants growing in a moderately polluted environment may be of reduced quality and less attractive to foraging herbivores.

The role of the Glucocorticoid Receptor in the Regulation of Diel Rhythmicity

Virtually all organisms have adapted to the earth's day-night cycles by the evolution of endogenous rhythms that regulate most biological processes. Recent research has highlighted the role of glucocorticoids and the Glucocorticoid receptor (GR) in coordinating clock function across various levels of biological organisation. In the present study, we have explored the role of the GR in the rhythmicity of the biological clock, by comparing 5 day old wildtype zebrafish larvae (gr+) with mutant larvae with a non-functional GR (grs357). The mutants display a weaker rhythmicity in locomotor activity in wildtypes than in mutants, while the rhythmicity of the angular velocity was higher for wildtypes. The melatonin production of the mutants showed a weaker rhythmicity, but surprisingly, there were no differences in the rhythmicity of clock-related gene expression between genotypes that could explain a mechanism for GR functionality at the transcriptional level. Furthermore, our results show that grs357 larvae have a more erratic swimming path, and cover more distance during locomotor activity than wild type larvae, in line with previously described behaviour of this mutant. Therefore, these results suggest that GR affects the diel rhythmicity of zebrafish larvae at the behavioural and endocrine level, but that these effects are not mediated by changes in the expression of clock-related genes.

Sequencing of a npc1L1 mutation in larval zebrafish

NPC1L1 transport protein is located in the lumen of the intestines and is critical for cholesterol absorption. The reason why we study NPC1L1 is because cholesterol absorption in the intestines affect obesity and diabetes which is still under investigation. Our goal is to investigate the mechanism by which the protein NPC1L1 absorbs cholesterol we are creating an npc1l1 -/- (knockout) line of zebrafish. We hypothesize that the npc1l1 -/- larval zebrafish will show reduced intestinal cholesterol absorption when feed a high fat diet compared to wild type zebrafish larvae. We are screening two zebrafish lines that carry mutations within the NPC1L1 sequence. These zebrafish lines were obtained from the Zebrafish International Resource Center. Parent fish carrying the mutation are identified by fin clipping, DNA extraction, and DNA sequencing of the potential mutant locus within NPC1L1.After identifying the mutation we will amplify the DNA fragments. The DNA fragments will then be sent off to Marshall Genomics Core for sequencing. The mutation sequence will be compared to a wild type sequence. Then the zebrafish that has been confirmed a carrier will be outcrossed with a wild type to eliminate background mutations and then intercrossed to make a homozygous carrier. This work was supported by NIH Grant P20GM103434 to the West Virginia IDeA Network for Biomedical Research Excellence and NIH Grant P20GM103434 awarded to Bluefield State College.

Thyroid disruption and developmental toxicity caused by Cd2+ in Schizopygopsis younghusbandi larvae

In recent years, the adverse effects of cadmium (Cd2+) on aquatic systems have attracted much attention because Cd2+ can induce endocrine disorders and toxicity in aquatic organisms at low levels. However, its effects on the thyroid system in native fish in Lhasa are still unclear. In the present study, Schizopygopsis younghusbandi larvae were exposed to Cd2+ (0.25, 2.5, 25 or 250 μg/L) for 7 or 14 days to determine its toxic effects on thyroid function. The results showed that whole-body total T4 and T3 levels were significantly decreased, which was accompanied by the significant upregulation of the expression of the dio1 and dio2 genes after exposure to Cd2+ for 7 or 14 days. Genes related to thyroid hormone synthesis (crh and tshβ) were upregulated after both 7 and 14 days of Cd2+ exposure, possibly due to the negative feedback regulation of the hypothalamic-pituitary-thyroid (HPT) axis caused by a decrease in thyroid hormone. In addition, survival rates and body lengths were reduced after treatment with Cd2+. This suggests that Cd2+ caused developmental toxicity in Schizopygopsis younghusbandi larvae. An integrated assessment of biomarker response (IBR) showed that there were dose-dependent and time-dependent effects of Cd2+ exposure on Schizopygopsis younghusbandi larvae. Schizopygopsis younghusbandi larvae were sensitive to Cd2+, which caused adverse effects at a concentration as low as 2.5 μg/L. In summary, the results indicated that Cd2+ causes thyroid disruption and developmental toxicity in Schizopygopsis younghusbandi larvae and that wild Schizopygopsis younghusbandi larvae living in the Lhasa River are at potential ecological risk.

Sox9a, not sox9b is required for normal cartilage development in zebrafish

Sox9 is a multifunctional gene and plays crucial roles in vertebrate development including chondrogensis. In teleost, due to the genome duplication event, there are two co-orthologs sox9a and sox9b. In this study, CRISPR/Cas9 technology was performed to disrupt the function of either sox9a or sox9b. All sox9a mutants (sox9aΔ10 and sox9aΔ67) and sox9b mutants (sox9bΔ11 and sox9bΔ20) lost HMG domain and Q/S domain, however, only sox9a mutant larvae had mis-shaped pectoral fins and lacked the scapulocoracoid cartilage. sox9b mutant larvae showed normal cartilages similar to wild type larvae. The results suggested that sox9a, not sox9b was required for cartilage development in zebrafish, which was different from the sox9b-mutant phenotype induced by N-ethyl-N-nitrosourea (ENU) treatment, gamma radiation treatment or morpholino injection. This study confirmed that ancestral sox9 gene functions partitioned between the two paralogs in zebrafish.

Domestication process modifies digestion ability in larvae of Eurasian perch (Perca fluviatilis), a freshwater Teleostei

To date, a comparative analysis of larval performance and digestion abilities between wild and domesticated Eurasian perch has not yet been performed. Eurasian perch larvae from wild and domesticated spawners were reared in the same conditions and at different development stages, growth performance variables, the expression of genes encoding digestive enzymes and specific enzymatic activity were analysed. No significant differences in hatching rate, deformity rate or swim bladder inflation effectiveness between wild and domesticated larvae were found. Specific growth rate, final total length and wet body weight were significantly lower in wild larvae, whereas higher mortality in wild larvae was observed compared to domesticated larvae. The data obtained in this study clearly indicate that during domestication, significant modification of digestion ability occurs at the very beginning of ontogeny, where domesticated fish are characterised by lower enzymatic activity and lower expression of genes encoding digestive enzymes. This probably results from the low diversity of the food offered in culture conditions, which significantly modified digestion capability. The obtained data provide an understanding of how domestication affects fish in aquaculture and may improve the planning of selective breeding programs of Eurasian perch and other freshwater Teleosts.

Oyster larvae as a potential first feed for small-mouthed ornamental larval fish

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 11:657-669 (2019) - DOI: https://doi.org/10.3354/aei00338 Oyster larvae as a potential first feed for small-mouthed ornamental larval fish Alexander J. Basford*, Benjamin Mos, Tomoki Mishina, Symon A. Dworjanyn National Marine Science Centre, Southern Cross University, Coffs Harbour, NSW 2450, Australia *Corresponding author: alex.basford@scu.edu.au ABSTRACT: Aquaculture of ornamental marine fish for the aquarium trade is a possible solution to the negative environmental impacts of wild collection. An impasse to the culture of many marine fish species is high larval mortality due to unsuitable live feeds. Common live feeds can be too large for ornamental species, which often have larvae with small mouths. We tested wild oyster larvae as an alternative live feed for first-feeding blue tang Paracanthurus hepatus. P. hepatus readily consumed oyster larvae but did not consume rotifers. Survival and growth of P. hepatus fed oyster larvae was similar to unfed controls, likely due to the oyster trochophores developing into indigestible veligers. Restricting the diet of P. hepatus to only oyster trochophores improved survival and eye development, but survival rates remained low. Oyster trochophores were conditioned in pH 4.8 seawater to compromise their aragonite shells, and P. hepatus fed these had higher survival at 5 d post-hatch (dph) compared to those fed untreated trochophores and were the only fish surviving to 10 dph. The high consumption rates of oyster larvae by P. hepatus highlight the potential for bivalve larvae to be used as live feeds for first-feeding larval fish. Further research into improving the nutritional value of oyster larvae for larval fish may improve their viability as first feeds. KEY WORDS: Acidification · Blue tang · Paracanthurus hepatus · Fatty acids · Live feeds · Larval rearing Full text in pdf format Supplementary material Corrections to supplement PreviousNextCite this article as: Basford AJ, Mos B, Mishina T, Dworjanyn SA (2019) Oyster larvae as a potential first feed for small-mouthed ornamental larval fish. Aquacult Environ Interact 11:657-669. https://doi.org/10.3354/aei00338 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 11. Online publication date: December 05, 2019 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2019 Inter-Research.

Gut Microbiota of Migrating Wild Rabbit Fish (Siganus guttatus) Larvae Have Low Spatial and Temporal Variability.

We investigated the gut microbiota of rabbit fish larvae at three locations in Vietnam (ThuanAn-northern, QuangNam-intermediate, BinhDinh-southern sampling site) over a three-year period. In the wild, the first food for rabbit fish larvae remains unknown, while the juveniles and adults are herbivores, forming schools near the coasts, lagoons, and river mouths, and feeding mainly on filamentous algae. This is the first study on the gut microbiota of the wild fish larvae and with a large number of individuals analyzed spatially and temporally. The Clostridiales order was the most predominant in the gut, and location-by-location alpha diversity showed significant differences in Chao-1, Hill number 1, and evenness. Analysis of beta diversity indicated that the location, not year, had an effect on the composition of the microbiota. In 2014, the gut microbiota of fish from QuangNam was different from that in BinhDinh; in 2015, the gut microbiota was different for all locations; and, in 2016, the gut microbiota in ThuanAn was different from that in the other locations. There was a time-dependent trend in the north-south axis for the gut microbiota, which is considered to be tentative awaiting larger datasets. We found limited variation in the gut microbiota geographically and in time and strong indications for a core microbiome. Five and fifteen OTUs were found in 100 and 99% of the individuals, respectively. This suggests that at this life stage the gut microbiota is under strong selection due to a combination of fish-microbe and microbe-microbe interactions.

Chemical composition and larvicidal activity of the essential oil of <i>Cymbopogon nardus</i> (L.) Rendle on <i>Anopheles gambiae</i>

The increasing resistance toward a number of insecticides of synthetic origin developed by Anopheles gambiae (the main vector of malaria in Benin) has prompted us to seek new pesticide formulations in the fight against malaria. In this study, we tested the insecticidal potential of the essential oil of Cymbopogon nardus on Anopheles gambiae larvae for two genotypes: the sensitive strain Kisumu of Kenyan origin and the wild strain from stagnant water in Cotonou. The essential oil of this plant obtained by steam distillation with a yield of 1.3 ± 0.11% was analyzed by chromatographic method (GC / MS). The main oil compounds were citronellal (37.87%), nerol (19.88%), citronellol (9.11%), elemol (7.40%) and gamma murollene (4.65%). Sensitivity tests performed on Anopheles gambiae larvae 3rd instar revealed the larvicidal properties of the oil tested. The lethal concentrations (LC50) figures obtained were respectively 36.83 ppm and 97.33 ppm for the Kisumu strain and the local wild population respectively. The LC90 adopted the same trend with 55.72 ppm and 147.9 ppm respectively for sensitive and wild larvae. The essential oil of Cymbopogon nardus constitutes thus a bioactive substance for a preventive strategy against malaria vectors by means of green chemistry. Keywords: Anopheles gambiae, Cymbopogon nardus, Essential oil, Larvicidal activity.

Observation of Aneurobracon philippinensis (Hymenoptera: Braconidae) Immatures Shows How Koinobiont Offspring Flexibly Adjust Their Development to Host Growth

AbstractKoinobionts are parasitoids that allow their hosts to grow after infection, and they finally kill their host individuals at parasitoid-specific host stages. Since fatal accidents of host organisms directly result in the deaths of parasitizing koinobionts, a longer parasitization period in vulnerable hosts is likely to increase the mortality of the koinobionts. However, for hosts inhabiting concealed environments in their later developmental stages, koinobionts should begin parasitization in early-stage hosts to make use of the grown hosts. A koinobiont parasitoid, Aneurobracon philippinensis (Muesebeck), mainly uses a leaf-mining moth, Acrocercops transecta Meyrick (Lepidoptera: Gracillariidae) as a host. Due to the three-dimensional structure of the mines constructed by later instars of A. transecta, females of A. philippinensis seldomly oviposit into later instar hosts, whereas feeding on final instar hosts is essential for A. philippinensis larvae. This implies that oviposition targets in the wild are shifted to early instars, though the final instar is the ideal target to shorten the parasitization period. The dissection of wild host larvae demonstrated that no eggs were observed in the final instar, supporting the above expectation. Laboratory parasitization experiments revealed that A. philippinensis eggs hatched approximately 80 h after oviposition, and hatched larvae stayed in the first instar until the host larvae completed making cocoons. These results suggest that the first-instar period of the parasitoid larvae functions as an adjusting period to synchronize the parasitoid and host developmental stages and that koinobiosis plays an important role in utilizing the final instar of A. transecta as a resource.