Larval Mortality Research Articles

Toxicity of Bt Protein on Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) Fed With Corn Leaves in Paraguay

The fall armyworm Spodoptera frugiperda is the most destructive pest in corn cultivation in Paraguay with yield losses of 20 to 70%. The adoption of genetically modified crops (GMO) is a valid technique for managing this pest. The objective of this investigation was to evaluate the toxicity among Bt events used locally; determining mortality and important biological parameters. The S. frugiperda population previously collected from the field was raised under laboratory conditions fed with leaves from events MIR162TM (Vip3A19), VT3ProTM (Cry1A105, Cry2Ab2, Cry3Bb), PowerCoreTM (Cry1A105, Cry1F, Cry2Ab2) and a treatment with non-maize. Bt BR106TM. The mortality of 120 larvae was evaluated for each treatment and the viability until the adult stage of those larvae that managed to survive the different treatments was observed. A high toxicity effect was verified with 100% mortality of neonatal larvae fed with the MIR162TM (Vip3A19) event; as for the other events, 86% and 61% VT3ProTM (Cry1A105, Cry2Ab2, Cry3Bb), and PowerCoreTM (Cry1A105, Cry1F, Cry2Ab2) respectively; with 13% mortality for the non-Bt control variety BR106TM. The oviposition period, viability and number of eggs laid in adults surviving the PowerCoreTM (Cry1A105, Cry1F, Cry2Ab2) and VT3ProTM (Cry1A105, Cry2Ab2, Cry3Bb) events were reduced, affecting the fecundity of the surviving insect population.

Toxicity of Bt Protein on Spodoptera frugiperda (Smith) (Lepidoptera: Noctuidae) Fed With Corn Leaves in Paraguay

The fall armyworm Spodoptera frugiperda is the most destructive pest in corn cultivation in Paraguay with yield losses of 20 to 70%. The adoption of genetically modified crops (GMO) is a valid technique for managing this pest. The objective of this investigation was to evaluate the toxicity among Bt events used locally; determining mortality and important biological parameters. The S. frugiperda population previously collected from the field was raised under laboratory conditions fed with leaves from events MIR162TM (Vip3A19), VT3ProTM (Cry1A105, Cry2Ab2, Cry3Bb), PowerCoreTM (Cry1A105, Cry1F, Cry2Ab2) and a treatment with non-maize. Bt BR106TM. The mortality of 120 larvae was evaluated for each treatment and the viability until the adult stage of those larvae that managed to survive the different treatments was observed. A high toxicity effect was verified with 100% mortality of neonatal larvae fed with the MIR162TM (Vip3A19) event; as for the other events, 86% and 61% VT3ProTM (Cry1A105, Cry2Ab2, Cry3Bb), and PowerCoreTM (Cry1A105, Cry1F, Cry2Ab2) respectively; with 13% mortality for the non-Bt control variety BR106TM. The oviposition period, viability and number of eggs laid in adults surviving the PowerCoreTM (Cry1A105, Cry1F, Cry2Ab2) and VT3ProTM (Cry1A105, Cry2Ab2, Cry3Bb) events were reduced, affecting the fecundity of the surviving insect population.

Evaluation of Reproductive and Growth Performance in New Breeds and Hybrids of Bivoltine Silkworm (Bombyx mori L.)

This study aimed to evaluate the reproductive and growth performance of recently developed bivoltine silkworm parental breeds and their hybrids to improve silk production and ensure the long-term sustainability of sericulture. Utilizing five thermotolerant pure breeds (B1, B2, B4, B6 and B8) and four popular CSR breeds (CSR2, CSR27, CSR6 and CSR26), six foundation crosses and eight double hybrids were developed and evaluated for ten traits. Results showed that B1 exhibited superior performance in fecundity (524.00), hatching percentage (98.67%), dead eggs (1.33%), pupal weight (1.31 g), pupation rate (96.84%) and cumulative survival index (CSI) (93.84%). The foundation cross B1 × B2 excelled in fecundity (553.67), larval mortality (2.67%), pupal weight (1.53 g), ERR (97.33%) and CSI (93.27%) while FC2 performed better in hatching percentage (97.60%), dead eggs percentage (2.40%), fifth instar larval duration (157.21 h), fifth instar larval weight (35.64 g/10 larvae) and pupation rate (96.33%). Among the double hybrids, (B1 × B2) × (FC1) demonstrated superior performance in fecundity (614.33), larval mortality (1.41%), pupal weight (2.06 g), ERR (98.59%) and CSI (97.24%). FC2 × FC1 excelled in larval duration (141.11 h), fifth instar larval weight (51.96 g/10 larvae) and pupation rate (98.94%). Double hybrids showed significant improvements compared to parental breeds and foundation crosses, indicating potential for field testing and further development. These results indicate the potential of using the newly identified breeds and foundation crosses in silkworm breeding, particularly in developing new double hybrids as an alternative to established CSR breeds and hybrids.

Mealworm (Tenebrio molitor) rearing and growth optimization as a sustainable food source using various larval diets under laboratory conditions

AbstractA new approach to supplying foods and feeds that are high in protein has emerged in the form of insect farming. Insect‐farmed food may also serve as part of a sustainable diet for humans. The mealworm Tenebrio molitor L. (Coleoptera: Tenebrionidae) is the most widely consumed insect worldwide. In this study, 10 larval diets were tested in the laboratory to determine their suitability for mass‐feeding mealworms at 28 °C and 60–65% r.h., in a completely randomized design. Various larval diets had a significant impact on the biological features of T. molitor. The larvae, pupae, and adults were greater on diets containing wheat bran alone and wheat bran in combination with maize and porridge. Larval mortality was significantly higher (60.7%) on a diet with porridge alone, compared to a control diet, followed by diets with porridge in combination with barley (55.6%) or maize (50.6%). Sex ratio was also affected by the tested larval diets. Female hatch (65%) was higher than male hatch (35%) on diet containing wheat bran alone as compared to all other diets. The findings contribute to optimizing mealworm rearing practices for sustainable food production and promote the potential use of mealworms as a viable protein source – especially livestock diets based on mealworm reared on wheat bran show promise.

Virulence phenotypes differ between toxigenic Vibrio parahaemolyticus isolated from western coasts of Europe

Vibrio parahaemolyticus is the leading bacterial cause of gastroenteritis associated with seafood consumption worldwide. Not all members of the species are thought to be pathogenic, thus identification of virulent organisms is essential to protect public health and the seafood industry. Correlations of human disease and known genetic markers (e.g. thermostable direct hemolysin (TDH), TDH-related hemolysin (TRH)) appear complex. Some isolates recovered from patients lack these factors, while their presence has become increasingly noted in isolates recovered from the environment. Here, we used whole-genome sequencing in combination with mammalian and insect models of infection to assess the pathogenic potential of V. parahaemolyticus isolated from European Atlantic shellfish production areas. We found environmental V. parahaemolyticus isolates harboured multiple virulence-associated genes, including TDH and/or TRH. However, carriage of these factors did not necessarily reflect virulence in the mammalian intestine, as an isolate containing TDH and the genes coding for a type 3 secretion system (T3SS) 2α virulence determinant, appeared avirulent. Moreover, environmental V. parahaemolyticus lacking TDH or TRH could be assigned to groups causing low and high levels of mortality in insect larvae, with experiments using defined bacterial mutants showing that a functional T3SS1 contributed to larval death. When taken together, our findings highlight the genetic diversity of V. parahaemolyticus isolates found in the environment, their potential to cause disease and the need for a more systematic evaluation of virulence in diverse V. parahaemolyticus to allow better genetic markers.

Keap1 Negatively Regulates Transcription of Three Counter-Defense Genes and Susceptibility to Plant Toxin Gossypol in Helicoverpa armigera

Expressions of a wide range of cytoprotective counter-defense genes are mainly regulated by the Keap1-Nrf2-ARE signaling pathway in response to oxidative stress from xenobiotics. Gossypol is the major antiherbivore secondary metabolite of cotton, but how the polyphagous pest Helicoverpa armigera copes with this phytochemical to utilize its favorite host plant cotton remains largely elusive. In this study, we first suppressed the Keap1 gene in newly hatched larvae of cotton bollworm by feeding them the siRNA diet for 4 days. All of the larvae were subsequently fed the artificial diet supplied with gossypol or the control diet for 5 days. We identified that the knockdown of the Keap1 gene significantly decreased larval mortality and significantly increased the percentages of larval survival, reaching the fourth instar, compared with ncsiRNA when exposed to a diet containing gossypol. Three counter-defense genes CYP9A17, CYP4L11 and UGT41B3, which were related to the induction or metabolism of gossypol according to the report before, were all significantly up-regulated after the knockdown of the Keap1 gene. The Antioxidant Response Elements (AREs) were also detected in the promoter regions of the three counter-defense genes above. These data indicate that the suppression of the Keap1 gene activates the Keap1-Nrf2-ARE signaling pathway, up-regulates the expressions of counter-defense genes involved in the resistance of oxidative stress and finally contributes to reducing the susceptibility of gossypol. Our results provide more knowledge about the transcriptional regulation mechanisms of counter-defense genes that enable the cotton bollworm to adapt to the diversity of host plants including cotton.

In vitro ovicidal and larvicidal activity of a hydroalcoholic extract and its fractions from Cyrtocarpa procera fruits on Haemonchus contortus

This study describes the in vitro anthelmintic effect of a hydroalcoholic extract (HA-E) and its fractions from Cyrtocarpa procera fruits against Haemonchus contortus eggs and infective larvae. The HA-E was subjected to bipartition using ethyl acetate, which resulted in an aqueous fraction (Aq-F) and an organic fraction (EtOAc-F). The HA-E and both fractions were tested using the egg hatching inhibition assay (EHIA) and the larval mortality test (LMT). Fractionation of the EtOAc-F was achieved using different chromatographic processes, i.e., open glass column and HPLC analysis. Fractionation of the EtOAc-F gave 18 subfractions (C1R1-C1R18), and those that showed the highest yields (C1R15, C1R16, C1R17 and C1R18) were subjected to anthelmintic assays. The HA-E and the EtOAc-F displayed 100% egg hatching inhibition at 3 and 1 mg/mL, respectively, whereas Aq-F exhibited 92.57% EHI at 3 mg/mL. All subfractions tested showed ovicidal effect. Regarding the larval mortality test, HA-E and EtOAc-F exhibited a larvicidal effect higher than 50% at 50 and 30 mg/mL, respectively. The subfractions that showed the highest larval mortality against H. contortus were C1R15 and C1R17, with larval mortalities of 53.57% and 60.23% at 10 mg/mL, respectively. Chemical analysis of these bioactive subfractions (C1R15 and C1R17) revealed the presence of gallic acid, protocatechuic acid, and ellagic acid. This study shows evidence about the ovicidal and larvicidal properties of C. procera fruits that could make these plant products to be considered as a natural potential anthelmintic agents for controlling haemonchosis in goats and sheep.

Exposure of Beauveria bassiana from different sites to changes in behaviour and mortality of oil palm beetle larvae: Oryctes rhinoceros

The potential of Beauveria bassiana as a biological control agent for Oryctes rhinoceros is still rarely reported. The objective of the research was to analyse the behaviour and mortality of O. rhinoceros larva due to exposure to several of B. bassiana. The research method used the Completely Randomized Design and analysis with 5% Tukey’s test. The results showed that B. bassiana form different sites had the potential to be developed as an effective biological control product in controlling O. rhinoceros as a part of novelty to explore the biodiversity of native biological control in Indonesia. Larvae of O. rhinoceros that were exposed to and infected with B. bassiana experienced changes in movement activity and decreased appetite as well as differences in cuticle colour, the initially limp body will turn stiff while the cuticle colour will change and the next symptom will be white mycelium growth which was proven by the SEM. The B. bassiana from Jember 1 had the highest mortality rate of 37.5% at 30 days after application even though it had the lowest spore density. These results indicate something new and require further study regarding the toxin content of each B. bassiana from different sites.

GABA attenuates neurotoxicity of zinc oxide nanoparticles due to oxidative stress via DAF-16/FoxO and SKN-1/Nrf2 pathways

Zinc oxide nanoparticles (ZnO-NPs) are one of the most widely used metal oxide nanomaterials. The increased use of ZnO-NPs has exacerbated environmental pollution and raised the risk of neurological disorders in organisms through food chains, and it is urgent to look for detoxification strategies. γ-aminobutyric acid (GABA) is an inhibitory neurotransmitter that has been shown to have anxiolytic, anti-aging and inhibitory effects on nervous system excitability. However, there are few reports on the prevention and control of the toxicity of nano-metal ions by GABA. In zebrafish, ZnO-NPs exposure led to increased mortality and behavioral abnormalities of larva, which could be moderated by GABA intervention. Similar results were investigated in Caenorhabditis elegans, showing lifespan extension, abnormal locomotor frequency and behavior recovery when worms fed with GABA under ZnO-NPs exposure. Moreover, GABA enhanced antioxidant enzyme activities by upregulating the expression of antioxidant-related genes and thus scavenged excessive O2−. In the case of ZnO-NPs exposure, inhibition of nuclear translocation of DAF-16 and SKN-1 was restored by GABA. Meanwhile, the protective effect of GABA was blocked in daf-16 (−) and skn-1 (−) mutant, suggesting that DAF-16/FoxO and SKN-1/Nrf2 pathways is the key targets of GABA. This study provides a new solution for the application of GABA and mitigation of metal nanoparticle neurotoxicity.

Toxicity Test of Red-Shoot Leaves (Syzygium myrtifolium Walp.) Extract as Biolarvicide on Filariasis Vector Mortality

The Control of Culex sp. using synthetic larvicides is harmful to the environment and human health. Biolarvicide from red shoot leaves (Syzygium myrtifolium) is a safe alternative for the environment and human health. This study aims to determine the effect of Syzygium myrtifolium leaves extract with ethanol solvent and water solvent on larval mortality and the LC50 values of these extracts. ANOVA test results (α = 0.05) on the mortality of Culex sp. larvae exposed to the ethanol extract and aqueous extract of S. myrtifolium leaves consecutively showed F-calculated (287)>F-tabulated (3,11) and F-calculated (153)>F-tabulated (3, 11). The treatment of S. myrtifolium leaves extract with ethanol and water solvents had a significant effect on the mortality of Culex sp. larvae. The LC50 value of the ethanol extract and the aqueous extract of S. myrtifolium leaves are 1659 ppm and was 2053.7 ppm. It can be concluded that S. myrtifolium leaves extracts with ethanol solvent and water solvent have an effect on the mortality of Culex sp. larvae, but are not yet effective as biolarvicide

Larvicides Activity of Krokot Extract into Aedes aegypti Mortality

Dengue Hemorrhagic Fever (DHF) is transmitted by Aedes aegypti, one of controlling vectors which is larvicides. Synthetic larvicides cause several problems so that alternative natural larvicides are used. One of which is the krokot (Portulaca oleracea, L.), the content such as flavonoids, tannins, alkaloids, and saponins can be used as larvicides. This study aims to determine the larvicides activity of krokot extract on mortality of Aedes aegypti. The study was conducted using experimental quantitative research. The study was conducted by pouring the ethanol extract on 25 larvae and repeated 3 times, for 24 hours. The result of larvae mortality test at concentrations of 4%, 5% and 6%, namely 39%, 57% dan 72%. LC50 value from krokot extract on the larvae mortality, that is equal to 9.294%. Based on the study, it can be concluded that the krokot ethanol extract is able to kill 50% of the Aedes aegypti larvae population.   Keywords:          krokot, ethanol extract, Aedes aegypti, mortality

Host–pathogen interaction between the African fig fly, Zaprionus indianus, and its external mycobiome under laboratory conditions

AbstractThe African fig fly, Zaprionus indianus Gupta (Diptera: Drosophilidae), is an ecologically diverse pest species that interacts with and feeds on various microbial pathogens including bacteria and yeast found in decomposing fruits. However, the interaction of Z. indianus with its microbial community and microbial pathogens is obscure. To determine the presence of fungal pathogens, we collected wild Z. indianus from the northwestern part of the Indian subcontinent. Based on molecular identification and phylogenetic analysis, Debaryomyces hansenii (Zopf) Lodder & Kreger‐van Rij (isolate ziha1) was the most commonly observed fungus associated with Z. indianus. Furthermore, we identified two more opportunistic fungal pathogens: Aspergillus flavus Link (isolate zias2), and Pichia kudriavzevii Boidin, Pignal & Besson (isolate zibd3). The interaction of isolated fungi with Z. indianus was evaluated in terms of larval mortality, adult emergence, and fecundity. Debaryomyces hansenii ziha1 resulted in 90% emergence rate for adults, and did not cause significant mortality in the larval stage. In contrast, A. flavus zias2 and P. kudriavzevii zibd3 showed a significant reduction in fecundity and caused 99% and 74% larval mortality of Z. indianus, respectively. In the laboratory oviposition preference assay, mated females of Z. indianus preferred D. hansenii ziha1 supplemented food with a positive oviposition index compared to the uninfected control and compared to food infected with P. kudriavzevii zibd3 or A. flavus zias2. These findings underscore Z. indianus' potential to act as a reservoir for both symbiotic and pathogenic fungal species, some of which may be further harnessed for effective fruit fly pest control strategies.

A probabilistic foundation for the study of larval fish feeding, growth, and mortality rates

Survival through the larval phase is predicated on the probabilities of successful feeding, which dictates growth rates, and the probabilities of encountering predators. Here I perform a synthesis of feeding, growth, and mortality rates estimated during several studies from coastal Newfoundland, Canada, to provide a description of the probability distribution that can serve as a foundation of the expected distribution of vital rates. The standardized observations clearly follow that of skewed distributions, appropriately fit to a probability gamma distribution, with feeding demonstrating a stronger degree of skewness than either mortality or growth, possibly because each vital rate integrates prey-predator interactions over different time scales. Commonality in the underlying form of the distribution of vital rates in larval fish, along with clear functional relationships between gamma parameters, represents a probabilistic basis of expectations against which observations from prior or new studies can be contrasted. An example of the use of such expectations demonstrates that they can provide useful contextual information about the contrast among observations and our ability to identify their relationship with environmental drivers.

The combined effects of ocean warming and ocean acidification on Pacific cod (Gadus macrocephalus) early life stages

The eastern North Pacific is simultaneously experiencing ocean warming (OW) and ocean acidification (OA), which may negatively affect fish early life stages. Pacific cod (Gadus macrocephalus) is an economically and ecologically important species with demonstrated sensitivity to OW and OA, but their combined impacts are unknown. Through a ~ 9-week experiment, Pacific cod embryos and larvae were reared at one of six combinations of three temperatures (3, 6, 10 °C) and two CO2 levels (ambient: ~ 360 μatm; high: ~ 1560 μatm) in a factorial design. Both embryonic and larval mortality were highest at the warmest temperature. Embryonic daily mortality rates were lower under elevated CO2 and there was no effect of CO2 level on larval daily mortality rates. Growth rates of young larvae (0 to 11 days post-hatch) were faster at warmer temperatures and at high CO2 levels, but growth during the 11–28 days post-hatch interval increased by temperature alone. The condition of larvae decreased with age, but less markedly under high CO2 levels. However, at 6 °C, fish incubated in ambient CO2 remained in higher condition than fish in the high CO2 treatment throughout the experiment. Overall, temperature had the greater influence on Pacific cod early life stages across each measurement endpoint, while CO2 effects were more modest and inconsistent. Subtle developmental differences in larval Pacific cod could be magnified later in life and important in the context of recruitment. These results show the complexity of stage- and trait-specific responses to and value of investigating the combined effects of co-occurring climatic stressors.

Protective role of DTPA against Hylotrupes bajulus L. infestations by targeting metal ion incorporation in larval mandibles

AbstractThe house longhorn beetle, Hylotrupes bajulus L., is a recognized wood pest with larvae capable of infesting and damaging various wood species. The larvae’s wood-cutting capability is attributed to the metal-reinforced chitin in their mandibles, which provides enhanced mechanical strength. This reinforcement is due to the presence of metal ions such as zinc (Zn) and manganese (Mn) bound to the chitin structure. The present study investigates the potential of diethylenetriaminepentaacetic acid (DTPA), a chelating agent, to sequester these crucial metal ions thereby affecting the larvae’s feeding capability. Wood samples treated with varying doses of DTPA showed significant larval mortality, with a 100% rate at a dose of 6 g/l. Electron microscopic analyses of deceased larvae revealed an absence of Zn in their mandibles, suggesting that DTPA effectively reduces its bioavailability, hindering mandible strengthening. The toxicity profile of DTPA is lower compared to many traditional wood treatments, indicating a potential for reduced environmental impact. However, the full spectrum of DTPA’s preservation capabilities and its interactions with other organisms require further investigation.

Roles of a newly lethal cuticular structural protein, AaCPR100A, and its upstream interaction protein, G12-like, in Aedes aegypti

Mosquitoes form a vital group of vector insects, which can transmit various diseases and filarial worms. The cuticle is a critical structure that protects mosquitoes from adverse environmental conditions and penetration resistance. Thus, cuticle proteins can be used as potential targets for controlling the mosquito population. In the present study, we found that AaCPR100A is a structural protein in the soft cuticle, which has flexibility and elasticity allowing insects to move or fly freely, of Aedes aegypti. RNA interference (RNAi) of AaCPR100A caused high mortality in Aedes aegypti larvae and adults and significantly decreased the egg hatching rate. Transmission electron microscopy (TEM) analysis revealed that the larval microstructure had no recognizable endocuticle in AaCPR100A-deficient mosquitoes. A yeast two-hybrid assay was performed to screen proteins interacting with AaCPR100A. We verified that the G12-like protein had the strongest interaction with AaCPR100A using yeast two-hybrid and GST pull-down assays. Knockdown of G12-like transcription resulted in high mortality in Ae. aegypti larvae, but not in adults. Interestingly, RNAi of G12-like rescued the high mortality of adults caused by decreased AaCPR100A expression. Additionally, adults treated with G12-like dsRNA were found to be sensitive to low temperature, and their eggshell formation and hatching were decreased. Overall, our results demonstrated that G12-like may interacts with AaCPR100A, and both G12-like and AaCPR100A are involved in Ae. aegypti cuticle development and eggshell formation. AaCPR100A and G12-like can thus be considered newly potential targets for controlling the Ae. aegypti mosquito.

Efficacy of entomopathogenic fungi for the management of Trogoderma granarium Everts on wheat grains

AbstractFour species of Trichoderma genius (T. harzianum, T. citrinoviride, T. viride and T. asperellum) and Metarhizium anisopliae were assessed for their effects on larval mortality and progeny production of Trogoderma granarium Everts (Coleoptera: Dermestidae). The fungal strains were tested at 2.0 × 106, 2.0 × 107, 2.0 × 108 and 2.0 × 109 spores/kg. The larval mortality of T. granarium was recorded after 7, 14 and 21 days of treatment. The emerged adults (F1) from treated larvae were counted after 30 days of treatment, while F2 and grain weight loss were examined after 80 days of treatment. In general, increasing of spore concentration of all fungal strains enhanced the larval mortality. After 21 of treatment, all fungal strains induced notable larval mortality particularly at the highest concentration (2.0 × 109 spores/kg) except T. viride (19.4%). The highest larval mortality was observed in treatments with M. anisopliae (82.1%) and T. citrinoviride (69.0%) at 2.0 × 109 spores/kg, respectively. Furthermore, all spore concentrations of tested fungi decreased the emerged adults (F1 and F2) with M. anisopliae, T. citrinoviride and T. harzianum being the most potent, particularly at 2.0 × 109 spores/kg. After 80 days, M. anisopliae and T. citrinoviride at 2.0 × 109 spores/kg induced the highest protection of wheat grains against larvae of T. granarium with weight loss of 0.7 and 1.3%, respectively. The outcomes of the present study indicate that the two fungi, M. anisopliae and T. citrinoviride are highly effective seed protectants against T. granarium and could be applied in the integrated pest management programs (IPM) of khapra beetle as effective biological control agents.

Interactions between Bacillus thuringiensis and selected plant extracts for sustainable management of Phthorimaea absoluta

Phthorimaea absoluta is a global constraint to tomato production and can cause up to 100% yield loss. Farmers heavily rely on synthetic pesticides to manage this pest. However, these pesticides are detrimental to human, animal, and environmental health. Therefore, exploring eco-friendly, sustainable Integrated Pest Management approaches, including biopesticides as potential alternatives, is of paramount importance. In this context, the present study (i) evaluated the efficacy of 10 Bacillus thuringiensis isolates, neem, garlic, and fenugreek; (ii) assessed the interactions between the most potent plant extracts and B. thuringiensis isolates, and (iii) evaluated the gut microbial diversity due to the treatments for the development of novel formulations against P. absoluta. Neem recorded the highest mortality of 93.79 ± 3.12% with an LT50 value of 1.21 ± 0.24 days, Bt HD263 induced 91.3 ± 3.68% mortality with LT50 of 2.63 ± 0.11 days, compared to both Bt 43 and fenugreek that caused < 50% mortality. Larval mortality was further enhanced to 99 ± 1.04% when Bt HD263 and neem were combined. Furthermore, the microbiome analyses showed that Klebsiella, Escherichia and Enterobacter had the highest abundance in all treatments with Klebsiella being the most abundant. In addition, a shift in the abundance of the bacterial genera due to the treatments was observed. Our findings showed that neem, garlic, and Bt HD263 could effectively control P. absoluta and be integrated into IPM programs after validation by field efficacy trials.

Changes in the Biology and Susceptibility of Weevil (Cylas formicarius) to the Insecticide Spinetoram as a Response to Cadmium Contamination.

The sweet potato weevil Cylas formicarius is a notorious underground pest in sweet potato (Ipomoea batatas L.). However, little is known about the effects of cadmium (Cd) stress on weevil biology and resistance to pesticides and biotic agents. Therefore, we fed sweet potato weevils with Cd-contaminated sweet potato and assessed adult food intake and survival and larval developmental duration and mortality rates, as well as resistance to the insecticide spinetoram and susceptibility to the entomopathogenic fungus Beauveria bassiana. With increasing Cd concentration, the number of adult weevil feeding holes, adult survival and life span, and larval developmental duration decreased significantly, whereas larval mortality rates increased significantly. However, at the lowest Cd concentration (30 mg/L), adult feeding was stimulated. Resistance of adult sweet potato weevils to spinetoram increased at low Cd concentration, whereas Cd contamination did not affect sensitivity to B. bassiana. Thus, Cd contamination affected sweet potato weevil biology and resistance, and further studies will investigate weevil Cd accumulation and detoxification mechanisms.

Reproductive and Developmental Effects of Sex-Specific Chronic Exposure to Dietary Arsenic in Zebrafish (Danio rerio).

The present study investigated the reproductive and developmental effects of sex-specific chronic exposure to dietary arsenic in zebrafish. Adult zebrafish (Danio rerio) were exposed to environmentally realistic doses of arsenic via diet [0 (control; no added arsenic), 30 (low), 60 (medium), and 100 (high) μg/g dry weight, as arsenite] for 90 days. Following exposure, arsenic-exposed females from each dietary treatment were mated with control males, and similarly, arsenic-exposed males from each dietary treatment were mated with control females. In females, arsenic exposure resulted in a dose-dependent decrease in reproductive performance (fecundity, fertilization success, and hatching success). Moreover, a dose-dependent increase in developmental toxicity (larval deformities and larval mortality) was observed with maternal exposure to arsenic. In contrast, in males, arsenic exposure also induced similar reproductive and developmental toxicity; however, the adverse effects were mainly evident only in the medium and high dietary arsenic treatment groups. We also examined the sex-specific effects of dietary arsenic exposure on the expression of genes that regulate the hypothalamus-pituitary-gonadal-liver (HPG-L) axis in fish. The gene expression results indicated the downregulation of HPG-L axis genes in females irrespective of the arsenic treatment dose; however, the reduced expression of HPG-L axis genes in males was recorded only in the medium and high arsenic treatment groups. These observations suggest that chronic arsenic exposure in either females or males causes reproductive and developmental toxicity in zebrafish. However, these toxic effects are markedly higher in females than in males. Our results also suggest that arsenic can act as an endocrine disruptor and mediate reproductive and developmental toxicity by disrupting the HPG-L axis in zebrafish.