Larval Mortality Research Articles

Microencapsulation of Bacillus thuringiensis strains for the control of Aedes aegypti

In this study, we investigated the microencapsulation of two strains of the entomopathogenic bacteria Bacillus thuringiensis (B. thuringiensis) (BtMA-750 and BtMA-1114), which are biopesticides of high toxicity for the mosquito vector Aedes aegypti. The encapsulation of different concentrations of microorganisms in starch microparticles was evaluated, and the inverse suspension polymerization technique was explored. It was possible to observe that the higher amounts of the biopesticide caused a slight decrease in the diameter of the particles; however, even when encapsulated, the biopesticide still presents an average diameter that is able to be consumed by the larvae of Aedes aegypti. Furthermore, it was noticed that the presence of both of the B. thuringiensis strains did not affect the thermal stability of the particles. The microencapsulated bacterial strains presented a high number of viable spores and preserved the expression of proteins with molecular masses corresponding to the insecticidal toxins Cry and Cyt, indicating that the encapsulation process was conducted satisfactorily. Finally, the encapsulated strains were tested against Ae. aegypti larvae and maintained 100% larval mortality even after 35 days. Therefore, microencapsulation of B. thuringiensis not only guarantees the bacterial activity, but also prolongs the action of the biopesticide. Collectively, such findings highlight the great potential of the new biopesticides, which may help to reduce the population indices of the mosquito vector Ae. aegypti via a sustainable and environment-friendly route.

Comparison on mortality, pupation, and emergence of Plodia interpunctella (hübner) treated by 2, 4, 6, and 8% carbon dioxide mixed with 2 and 4% oxygen at three temperatures

Low concentration CO2 (e.g., 2–8%) mixed with 2–4% O2 balanced by N2 is more economically feasible than applying 99.99% N2 alone. Mortality, pupation, and emergence of the fifth instar larvae of Plodia interpunctella (Lepidoptera: Pyralidae) were tested in 2 or 4% O2 mixed with 2, 4, 6, or 8% CO2 balanced by N2 at 28, 23, and 18 °C. Mortality of eggs, second instar larvae, and pupae was tested in the mixture of 2% O2, 4% CO2, and 94% N2 at the three temperatures. When fifth instar larvae were exposed in 2% O2 mixed with 0, 2, 4, 6, and 8% CO2 or increasing temperature, the LT50, LT99 value, and time reaching 100% mortality was decreased significantly. Exposing in 4% O2 mixed with 0, 2, 4, 6, and 8% CO2, the pupation and emergence of the surviving fifth instar larvae were also decreased significantly, and reduced more in higher temperatures. This study found 2, 4, 6, and 8% CO2 had additive effect to low O2 on insect mortality, pupation, and emergence at any tested temperature, and higher CO2 concentration or temperature resulted in a higher additive percentage. The fifth instar was the most tolerant stage to the gas mixtures followed by second instar larvae, pupae, and egg; and increasing temperature would sufficiently decrease the lethal exposure time.

Evaluation of Brown and red seaweeds-extracts as a novel larvicidal agent against the deadly human diseases-vectors, Anopheles stephensi, Aedes aegypti and Culex quinquefasciatus

Infectious diseases such as malaria, dengue, and yellow fever are predominantly transmitted by insect vectors like Anopheles stephensi, Aedes aegypti, and Culex quinquefasciatus in tropical regions like India and Africa. In this study, we assessed the larvicidal activity of commonly found seaweeds, including Padina gymnospora, P. pavonica, Gracilaria crassa, Amphiroa fragilissima, and Spatoglossum marginatum, against these mosquito vectors. Our findings indicate that extracts from P. gymnospora Ethyl Acetate (PgEA), P. pavonica Hexane (PpH), and A. fragilissima Ethyl Acetate (AfEA) displayed the highest larval mortality rates for A. stephensi, with LC50 values of 10.51, 12.43, and 6.43 μg/mL, respectively. Additionally, the PgEA extract from P. gymnospora exhibited the highest mortality rate for A. aegypti, with an LC50 of 27.0 μg/mL, while the PgH extract from the same seaweed showed the highest mortality rate for C. quinquefasciatus, with an LC50 of 9.26 μg/mL. Phytochemical analysis of the seaweed extracts revealed the presence of 71 compounds in the solvent extracts. Fourier-transform infrared spectra of the selected seaweeds indicated the presence of functional groups such as alkanes, alcohols, and phenols. Gas chromatography–mass spectrometry analysis of the seaweeds identified major compounds, including hexadecanoic acid in PgEA, tetradecene (e)- in PpEA, octadecanoic acid in GcEA, and 7-hexadecene, (z)-, and trans-7-pentadecene in SmEA.

Effects of Arabika Coffee (Coffea arabica L.) Pulp Extracts on Anopheles sp. Larva Mortality

Malaria is one of the main public health problems in Indonesia. Anopheles sp. mosquito larvae is vector of malaria that must be treated before it develops into a mosquito. Control of larvae by using larvicides containing hazardous chemicals causes side effects on the environment and resistance. This study aimed to determine the effect of giving the Arabika Coffee (Coffea arabica L.) pulp extracts on the mortality of Anopheles sp. larvae. Arabika coffee pulp extracts was fractionated with polar, semi-polar and non-polar. This study used ten larvae of Anopheles sp. Observations of larval mortality were carried 24 hours with five concentration series (0, 125, 250, 500, and 1000 ppm). The results of the mortality test showed that non-polar fraction of Arabika coffee pulp extracts had the highest larvicidal activity with values of LC50 and LC90, 278 ppm and 22950 ppm. In semi-polar and polar fractions, the LC50 and LC90, 1718 and 92683 ppm, 34085 and 40862 ppm were obtained. The results of compound analysis obtained 16 active compounds from non-polar extract of arabika coffee pulp with the five highest compounds, namely Hexadecanoic acid, 9,12-Octadecadienoic 15-Octadecenoic acid, Octadecanoic acid and 3-Furanacetic acid. Non-polar fraction of arabika coffee pulp extracts had larvicidal activity against Anopheles sp.

Antimicrobial and Cytotoxic Activities of Water-Soluble Isoxazole-Linked 1,3,4-Oxadiazole with Delocalized Charge: In Vitro and In Vivo Results.

The distinct structure of cationic organic compounds plays a pivotal role in enhancing their water solubility, which in turn influences their bioavailability. A representative of these compounds, which contains a delocalized charge, is 5-amino-2-(5-amino-3-methyl-1,2-oxazol-4-yl)-3-methyl-2,3-dihydro-1,3,4-oxadiazol-2-ylium bromide (ED). The high-water solubility of ED obviates the need for potentially harmful solvents during in vitro testing. The antibacterial and antifungal activities of the ED compound were assessed in vitro using the microtiter plate method and a biocellulose-based biofilm model. Additionally, its cytotoxic effects on wound bed fibroblasts and keratinocytes were examined. The antistaphylococcal activity of ED was also evaluated using an in vivo larvae model of Galleria mellonella. Results indicated that ED was more effective against Gram-positive bacteria than Gram-negative ones, exhibiting bactericidal properties. Furthermore, ED demonstrated greater efficacy against biofilms formed by Gram-positive bacteria. At bactericidal concentrations, ED was non-cytotoxic to fibroblasts and keratinocytes. In in vivo tests, ED was non-toxic to the larvae. When co-injected with a high load of S. aureus, it reduced the average larval mortality by approximately 40%. These findings suggest that ED holds promise for further evaluation as a potential treatment for biofilm-based wound infections, especially those caused by Gram-positive pathogens like S. aureus.

Experimental Infection and Treatment of Vibrio alginolyticus and Vibrio splendidus in Captive Bred Spotted Seahorse, Hippocampus kuda Larvae

Due to their distinctive look, seahorses are famous in the aquarium trade and traded worldwide for their alleged therapeutic benefits. The present study was conducted to identify the causative agents for larval mortality of Hippocampus kuda and to find a treatment to reduce larval mortality at an ornamental fish hatchery in Sri Lanka. Bacteria causing vibriosis in H. kuda larvae were isolated and identified using morphological and biochemical tests. The disc diffusion method was used with 30 μg of chloramphenicol, streptomycin, tetracycline and ampicillin to evaluate antibiotic susceptibility of isolated bacteria. As pathogenic vibrios were more sensitive to tetracycline, the experimentally infected H. kuda larvae were exposed to 20-50 μg/L tetracycline for 30 days. V. alginolyticus, Vibrio splendidus, V. parahaemolyticus, V. mimicus, Aeromonas hydrophila and Plesiomonas shigelloides were found in H. kuda larvae, while V. alginolyticus and V. splendidus were encountered repeatedly. V. alginolyticus, V. mimicus, V. fluvialis, Aeromonas sp., Micrococcus spp., M. leteus and Bacillus circulans were identified from the larval culture water. V. alginolyticus was sensitive to chloramphenicol and tetracycline, while V. splendidus was sensitive to tetracycline. Tetracycline, 30 mg/L as a bath treatment, effectively treats vibriosis in larval rearing tanks of H. kuda.

Crude extract and effective fractions from Andrographis paniculata for immature Aedes aegypti and Culex quinquefasciatus mosquito

In the quest for environmentally friendly alternatives to combat the challenges of resistance development and environmental toxicity associated with synthetic insecticides in mosquito control, the aim of this study is to explore the potential of fractions derived from Andrographis paniculata as environmentally friendly alternatives for controlling Aedes aegypti and Culex quinquefasciatus mosquitoes, with a focus on assessing their larvicidal, pupicidal, and ovicidal activities. Initially, crude extracts of hexane, chloroform, and methanol from A. paniculata leaves were evaluated for their efficacy against Ae. aegypti and Cx. quinquefasciatus mosquitoes, with the methanol extract showing promising activity. Subsequently, a comprehensive methanol extraction of A. paniculata leaves was conducted, followed by fractionation via column chromatography using various eluents, including chloroform, ethyl acetate, methanol, and their combinations. This process yielded 80 fractions, which were consolidated into 10 fractions based on thin-layer chromatography (TLC) profiles. Each fraction was assessed for ovicidal, larvicidal, and pupicidal activity across concentrations of 2.5, 5.0, 7.5, and 10 ppm. Among these fractions, ‘F-4’ exhibited exceptional efficacy against the larvae, pupae, and eggs of both mosquito species. At a concentration of 10 ppm, ‘F-4’ achieved 100% larval mortality, with LC50 values of 7.2 ppm for Ae. aegypti and 5.0 ppm for Cx. quinquefasciatus. Additionally, ‘F-4’ demonstrated substantial pupicidal activity, with LC50 values of 7.6 ppm for Ae. aegypti and 5.7 ppm for Cx. quinquefasciatus. Furthermore, ‘F-4’ exhibited ovicidal activity, with efficacy ranging between 77% and 78%. These results highlight ‘F-4’ from A. paniculata shows promise as an eco-friendly biocontrol agent against Ae. aegypti and Cx. quinquefasciatus mosquitoes, warranting further investigation for sustainable mosquito control.

Pathogenicity of microsclerotia from Metarhizium robertsii against Aedes aegypti larvae and antimicrobial peptides expression by mosquitoes during fungal-host interaction

Aedes aegypti is a vector of various disease-causing arboviruses. Chemical insecticide-based methods for mosquito control have increased resistance in different parts of the world. Thus, alternative control agents such as the entomopathogenic fungi are excellent candidates to control mosquitoes as part of an ecofriendly strategy. There is evidence of the potential of entomopathogenic fungal conidia and blastospores for biological control of eggs, larval and adult stages, as well as the pathogenicity of fungal microsclerotia against adults and eggs. However, there are no studies on the pathogenicity of microsclerotia against either aquatic insects or insects that develop part of their life cycle in the water, such as the A. aegypti larvae. In this study, we assayed the production of microsclerotia and their pathogenicity against A. aegypti larvae of two isolates of Metarhizium robertsii, i.e., CEP 423 isolated in La Plata, Argentina, and the model ARSEF 2575. Both isolates significantly reduced the survival of A. aegypti exposed to their microsclerotia. The fungus-larva interaction resulted in a delayed response in the host. This was evidenced by the expression of some humoral immune system genes such as defensins and cecropin on the 9th day post-infection, when the fungal infection was consolidated as a successful process that culminates in larvae mortality. In conclusion, M. robertsii microsclerotia are promising propagules to be applied as biological control agents against mosquitoes since they produce pathogenic conidia against A. aegypti larvae.

Survival potential and assessment of deformities in embryo and larvae of Chinese carps (Hypophthalmichthys molitrix and Ctenopharyngodon idella) under acute exposure of cadmium and nickel

ABSTRACT The effects of cadmium (Cd) and nickel (Ni) toxicity on embryonic and larval development of Hypophthalmichthys molitrix and Ctenopharyngodon idella was determined. Different concentrations (0.1, 0.3, and 0.5 mg/l) of Cd and Ni were administered in separate trials to the fish after spawning to 168 h post-hatching (hph) period. Cd was more toxic to the embryos of both fish, as highest embryonic mortality (%) of H. molitrix and C. idella was observed. However, Ni was found to be more toxic to the larvae of H. molitrix and C. Idella with highest larval mortality at 168 hph. However, Ni was found to be more toxic to the larvae of H. molitrix and C. idella with highest larval mortality at 168 hph. The study found a significant effect of heavy metal and metal concentration for causing deformities in H. molitrix. However, in C. idella only the effect of metal concentration on fish deformities was significant. Furthermore, Ni was found to cause more deformities as compared to Cd in H. molitrix. While Cd was found to cause more deformities as compared to Ni in C. idella. In conclusion, the study suggests that Cd and Ni may cause serious deformities in fish.

Comparison of the accumulation and effects of copper pyrithione and copper sulphate on rainbow trout larvae

Copper pyrithione (CuPT) is used as a co-biocide in new antifouling paints but its toxicity remains little known. To compare the toxicity of copper-based compounds, rainbow trout (Oncorhynchus mykiss) larvae were exposed for 8-day to CuPT and CuSO4 at equivalent copper concentrations. CuPT exposure led to the greatest accumulation of Cu in larvae. Exposure to 10 µg.L−1 CuPT induced 99% larval mortality but only 4% for CuSO4-exposed larvae. The larval development and growth were affected by CuPT (from 0.5 µg.L−1 Cu) but not by CuSO4. Lipid peroxidation was not induced by either contaminant. The expression of genes involved in oxidative stress defence, detoxification and copper transport was induced in larvae exposed to CuSO4 and CuPT but at higher concentrations for CuPT. This study highlights the marked toxicity of CuPT for early life stages of fish and raises the question of the possible environmental risks of this antifouling compound.

Infection Causes Trade-Offs between Development and Growth in Larval Amphibians.

AbstractTrade-offs between life history traits are context dependent; they vary depending on environment and life stage. Negative associations between development and growth often characterize larval life stages. Both growth and development consume large parts of the energy budget of young animals. The metabolic rate of animals should reflect differences in growth and developmental rates. Growth and development can also have negative associations with immune function because of their costs. We investigated how intraspecific variation in growth and development affected the metabolism of larval amphibians and whether intraspecific variation in growth, development, and metabolic rate could predict mortality and viral load in larvae infected with ranavirus. We also compared the relationship between growth and development before and after infection with ranavirus. We hypothesized that growth and development would affect metabolism and predicted that each would have a positive correlation with metabolic rate. We further hypothesized that allocation toward growth and development would increase ranavirus susceptibility and therefore predicted that larvae with faster growth, faster development, and higher metabolic rates would be more likely to die from ranavirus and have higher viral loads. Finally, we predicted that growth rate and developmental rate would have a negative association. Intraspecific variation in growth rate and developmental rate did not affect metabolism. Growth rate, developmental rate, and metabolism did not predict mortality from ranavirus or viral load. Larvae infected with ranavirus exhibited a trade-off between developmental rate and growth rate that was absent in uninfected larvae. Our results indicate a cost of ranavirus infection that is potentially due to both the infection-induced anorexia and the cost of infection altering priority rules for resource allocation.

Microplastic pollution differentially affects development of disease-vectoring Aedes and Culex mosquitoes

Plastic in the form of microplastic particles (MPs) is now recognized as a major pollutant of unknown consequences in aquatic habitats. Mosquitoes, with aquatic eggs, larvae, and pupae, are likely to encounter microplastic, particularly those species that are abundant in close proximity to human development, including those that vector human and animal disease. We examined the effects of polyethylene MPs, the most common microplastic documented in environmental samples, on the development and survival of the mosquitoes Aedes albopictus and Culex quinquefasciatus. In laboratory egg-laying and larval development container environments similar to those used by both species in the field, a mix of 1–53 µm MPs at concentrations of 60, 600, and 6000 MP ml−1 increased early instar larval mortality in both species relative to control treatments. A significant difference was found in the response of each species to microplastic at the lowest microplastic concentration tested, with Cx. quinquefasciatus survival equivalent to that in control conditions but with Ae. albopictus larvae mortality elevated to 37% within 48 h. These results differ from those of previous studies in which larvae were only exposed to MPs during the last aquatic instar stage and from which it was concluded that microplastic was ontogenically transferred without negatively affecting development. Increasing plastic pollutant concentrations could therefore act as selective pressures on aquatic larvae and ultimately influence outcomes of ecological interactions among mosquito vector populations.

Assessing effective mechanical and chemical strategies for managing Eucosma giganteana (Lepidoptera: Tortricidae) in the perennial oilseed crop, Silphium integrifolium (Asteraceae: Heliantheae).

Eucosma giganteana (Riley) is a native specialist pest of silflower, Silphium integrifolium Michx., which is currently being domesticated as a perennial oilseeds crop. The larvae of this moth attack silflower capitula and root crowns, causing both seed damage and long-term degradation of plants. To determine methods to manage E. giganteana in silflower crop fields, we conducted a laboratory bioassay and 3 field experiments to assess the effects of a suite of organic, conventional, and mechanical treatments on E. giganteana mortality and colonization of flower heads. Pyrethroids (permethrin, cyfluthrin), chlorantraniliprole, and methoxyfenozide each had significant insecticidal effects on E. giganteana in at least 2 of the experiments conducted. Nematodes marginally increased larva mortality in the laboratory bioassay and could be further investigated as a soil-applied biological control. In 2 separate field experiments, trimming the top 15% of silflower plants to delay flowering did not alone reduce E. giganteana colonization of flower heads throughout the growing season. However, when trimming was paired with a single chlorantraniliprole application, colonization of capitula was reduced by 83% over untreated control plants. Collectively, these experiments provide evidence for several treatments that could be further tested and incorporated into an integrated pest management strategy for E. giganteana.

Comparative metaproteomics reveal co-contribution of onion maggot and its gut microbiota to phoxim resistance

Pesticide resistance inflicts significant economic losses on a global scale each year. To address this pressing issue, substantial efforts have been dedicated to unraveling the resistance mechanisms, particularly the newly discovered microbiota-derived pesticide resistance in recent decades. Previous research has predominantly focused on investigating microbiota-derived pesticide resistance from the perspective of the pest host, associated microbes, and their interactions. However, a gap remains in the quantification of the contribution by the pest host and associated microbes to this resistance. In this study, we investigated the toxicity of phoxim by examining one resistant and one sensitive Delia antiqua strain. We also explored the critical role of associated microbiota and host in conferring phoxim resistance. In addition, we used metaproteomics to compare the proteomic profile of the two D. antiqua strains. Lastly, we investigated the activity of detoxification enzymes in D. antiqua larvae and phoxim-degrading gut microbes, and assessed their respective contributions to phoxim resistance in D. antiqua. The results revealed contributions by D. antiqua and its gut bacteria to phoxim resistance. Metaproteomics showed that the two D. antiqua strains expressed different protein profiles. Detoxifying enzymes including Glutathione S-transferases, carboxylesterases, Superoxide Dismutase, Glutathione Peroxidase, and esterase B1 were overexpressed in the resistant strain and dominated in differentially expressed insect proteins. In addition, organophosphorus hydrolases combined with a group of ABC type transporters were overexpressed in the gut microbiota of resistant D. antiqua compared to the sensitive strain. 85.2% variation of the larval mortality resulting from phoxim treatment could be attributed to the combined effects of proteins from both from gut bacteria and D. antiqua, while the individual contribution of proteins from gut bacteria or D. antiqua alone accounted for less than 10% of the variation in larval mortality caused by phoxim. The activity of the overexpressed insect enzymes and the phoxim-degrading activity of gut bacteria in resistant D. antiqua larvae were further confirmed. This work enhances our understanding of microbiota-derived pesticide resistance and illuminates new strategies for controlling pesticide resistance in the context of insect-microbe mutualism.

Effects of the mycotoxins aflatoxin B1, deoxynivalenol and zearalenone on survival, biomass and toxin accumulation in Musca domestica larvae

Abstract Insects are receiving increasing attention as a possible ingredient for feed and/or food production. When used efficiently, insects can provide a sustainable and economically favourable contribution to global food security. Housefly larvae (HFL) can grow on a variety of organic side streams and upgrade them by partial conversion into high-quality protein. Organic side streams may be chemically contaminated by naturally occurring toxins, e.g. mycotoxins, therefore, effects on insect survival and biomass as well as other feed and/or food safety issues should be investigated. In this study, the HFL were exposed to a feed substrate spiked with aflatoxin B1 (AFB1), deoxynivalenol (DON) or zearalenone (ZEN) at concentrations of either 1 or 10 times the maximum levels or guidance values set for feed materials by the European Commission. Mortality and biomass of HFL were recorded over five days of exposure. LC-MS/MS analysis was used to determine the concentration of the mycotoxins in the substrate offered, the larvae and the residual feed material. A molar mass balance was calculated to estimate how much of the spiked mycotoxins (and several metabolites), was recovered in the larval body and the residual material. Exposure to either of the three mycotoxins did not affect larval mortality and biomass, and accumulation in the larval body did not take place. Metabolism does seem to occur for AFB1 and ZEN as the molar mass balance revealed an unrecovered fraction of ca. 40-50%. Little DON metabolism occurred as most of the initially present DON was found back unchanged. The results of this study support the potential for safe use of HFL as food- and/or feed when reared on mycotoxin contaminated side-streams, as accumulation of the tested mycotoxins did not take place in HFL. Further research is needed to identify the fate of the unrecovered fractions of AFB1 and ZEN.

Rolling circle transcription: A new system to produce RNA microspheres for improving RNAi efficiency in an agriculturally important lepidopteran pest (Mythimna separate)

We applied a new RNA interference (RNAi) system using rolling circle transcription (RCT) technology to generate RNA microspheres (RMS) for targeting two key chitin synthetic pathway genes [chitin synthase A (CHSA), chitin synthase B (CHSB)] in the larvae of the oriental armyworm (Mythimna separate), a RNAi-unsusceptible agriculturally important lepidopteran pest. Feeding the third-instar larvae with the RMS-CHSA- or RMS-CHSB-treated corn leaf discs suppressed the expression of CHSA by 81.7% or CHSB by 88.1%, respectively, at 72 h. The silencing of CHSA consequently affected the larval development, including the reduced body weight (54.0%) and length (41.3%), as evaluated on the 7th day, and caused significant larval mortalities (51.1%) as evaluated on the 14th day. Similar results were obtained with the larvae fed RMS-CHSB. We also compared RNAi efficiencies among different strategies: 1) two multi-target RMS [i.e., RMS-(CHSA + CHSB), RMS-CHSA + RMS-CHSB], and 2) multi-target RMS and single-target RMS (i.e., either RMS-CHSA or RMS-CHSB) and found no significant differences in RNAi efficiency. By using Cy3-labeled RMS, we confirmed that RMS can be rapidly internalized into Sf9 cells (<6 h). The rapid cellular uptake of RMS accompanied with significant RNAi efficiency through larval feeding suggests that the RCT-based RNAi system can be readily applied to study the gene functions and further developed as bio-pesticides for insect pest management. Additionally, our new RNAi system takes the advantage of the microRNA (miRNA)-mediated RNAi pathway using miRNA duplexes generated in vivo from the RMS by the target insect. The system can be used for RNAi in a wide range of insect species, including lepidopteran insects which often exhibit extremely low RNAi efficiency using other RNAi approaches.

Efficacy of local essential oils against Amblyomma variegatum tick from Burkina Faso

The native tick Amblyomma variegatum remains one of the most important tick species affecting cattle in West Africa. This hinders animal production by negatively impacting the health and reproduction of animals infested with the tick. Given the negative consequences on production quality and environmental health, the use of chemical products for tick control is increasingly being discouraged. Therefore, this study aimed to assess the acaricidal activity of essential oils such as Ageratum conyzoïdes, Cymbopogon citratus, Cymbopogon giganteus, Lippia multiflora and Ocimum gratissimum against specimens of A. variegatum from Burkina Faso. A larval immersion test was performed to investigate the larvicidal activities of these essential oils. Gas chromatography-mass spectrometry was used to determine the chemical compositions of essential oils. The chemical composition was predominantly oxygenated monoterpenes in A. conyzoïdes (48.71 %), C. citratus (99.9 %) and C. giganteus (73.63 %), while hydrocarbon monoterpenes were the most abundant in O. gratissimum (63.7 %) and hydrocarbon sesquiterpenes in L. multiflora (71.719 %). The recorded larvicidal activity, varied according to the species of plants and the dose applied. At a dose of 12.5 mg/mL, all essential oils studied, except L. multiflora (7.54 %), induced 100 % larval mortality. In this study, we highlight the promising larvicidal effects of local essential oils against A. variegatum. These essential oils can be used as bio-acaricides, which are effective and environmentally-friendly alternatives to chemical products. However, further investigations are required to determine the mechanisms of action of these essential oils for in vivo experimentation and their practical application in the control of A. variegatum ticks.

Local scale population risk determines the adaptive responses of larval salamanders to predator kairomones

Abstract Organisms can exhibit plasticity in phenotypic responses to environmental stimuli but the response can vary based on the evolutionary history of a population. Numerous studies have found that prey will express adaptive responses when subjected to various predators in experimental settings. For species with a large distribution, such as Ambystoma maculatum (spotted salamander), it is not surprising that phenotypic variance can be high across their range. This variance has been hypothesized to be because of different predator regimes of populations. While A. maculatum preferentially oviposit eggs in low-risk ponds (temporary fishless) to decrease egg and larval mortality, Missouri populations still use high-risk ponds (permanent with fish) for reproduction. Using a series of experiments, we investigated how A. maculatum population risk influenced adaptive responses to both native and novel predator kairomones. For natural predators, we used larval A. opacum (marbled salamanders) and Lepomis macrochirus (bluegill) and for novel predators we used Siren intermedia (lesser siren). We found that larval salamanders generally responded with no differences in morphological traits to all three predators. However, head width was larger for low-risk populations. One hypothesized benefit of larger heads (increased foraging efficiency) was not fully supported. All larval salamanders also increased refuge use with predators but this decreased over time. Our results suggest that predation risk of a population may influence the degree of phenotypic expression in response to larval predators. Overall, local adaptation may dictate the ability of prey to respond to environmental conditions within a life stage.

Sporothrix brasiliensis Infection Modulates Antimicrobial Peptides and Stress Management Gene Expression in the Invertebrate Biomodel Galleria mellonella.

Sporothrix brasiliensis is the most pathogenic species, responsible for the Brazilian cat-transmitted sporotrichosis hyperendemic. In this scenario, an investigation of the pathogen-host interaction can provide relevant information for future treatment strategies. To this end, the invertebrate Galleria mellonella has proven to be a suitable alternative for evaluating the virulence of pathogenic fungi, since the insect immune system is similar to the mammalian innate immune response. The aim of this work was to investigate phenotypic and molecular aspects of the immune response of G. mellonella throughout the S. brasiliensis infection. Hemocyte density and the evolution of the fungal load were evaluated. In parallel, RT-qPCR expression analysis of genes encoding antimicrobial peptides (Gallerimycin and Galiomycin) and stress management genes (C7 Contig 15362 and C8 Contig 19101) was conducted. The fungal load and hemocyte densities increased simultaneously and proportionally to the deleterious morphological events and larvae mortality. Gallerimycin, C7 Contig 15362 and C8 Contig 19101 genes were positively regulated (p < 0.05) at distinct moments of S. brasiliensis infection, characterizing a time-dependent and alternately modulated profile. Galiomycin gene expression remained unchanged. Our results contribute to the future proposal of potential alternative pathways for treating and consequently controlling S. brasiliensis zoonosis, a major public health issue in Latin America.

The Toxicity Differences of Fluralaner against the Red Imported Fire Ant (Solenopsis invicta) at Different Developmental Stages.

The red imported fire ant (RIFA), Solenopsis invicta, is an invasive pest that causes damage to agricultural and ecological environments worldwide. Fluralaner is a new isoxazoline pesticide with the potential to become a control agent against RIFA. However, it is not clear whether S. invicta responds the same way to fluralaner at different reproductive stages. The present study firstly evaluated the toxicity of fluralaner to S. invicta at different developmental stages, finding that fourth instar larvae (LD50, 1744.23 mg/kg) and worker ants (LD50, 8.62 mg/kg) were differently susceptible to fluralaner, while the mortality rate of fourth instar larvae was significantly lower at the same concentration of 10 mg/L (5.56 ± 3.14%) than that of worker ants (62.22 ± 3.14%), demonstrating a greater tolerance to fluralaner. Subsequently, the metabolic responses of worker and larval ants to fluralaner stress (10 mg/L) were investigated using non-targeted metabolomics, which indicated that the amount of differential metabolites and the KEGG metabolic pathways enriched were different between workers and larvae when exposed to the same dose (10 mg/L) of fluralaner. Differential metabolites of larvae and worker ants under fluralaner stress were mainly concentrated in organic acids and their derivatives, lipids and lipid-like molecules, nucleosides, nucleotides, and analogues, combined with the enriched metabolic pathways, revealed that the differential metabolic responses of larvae and worker ants were mainly in energy metabolism, detoxification metabolism, and neurotransmitter ligands. Workers consumed more substrates in the arginine synthesis pathway (l-glutamic acid, l-aspartic acid, and fumaric acid) to provide energy for the detoxification (glutathione) of pesticides when exposed to fluralaner stress, and the high accumulation of l-aspartic acid induced excitotoxicity in the worker ants. Larval ants consumed more arachidonic acid to synthesize PG D2, and changes in the metabolism of antioxidants such as catechins, hesperidin, and l-ascorbic acid suggested that larvae were more capable of scavenging the ROS response than worker ants. The results of non-targeted metabolomics successfully revealed differences in the sensitivity of larvae and workers to fluralaner agents, providing insights into the fluralaner control of Solenopsis invicta.