Aspergillus flavus (Link) toxins reduces the fitness of dengue vector Aedes aegypti (Linn.) and their non-target toxicity against aquatic predator

Toxicity of fungal-derived volatile organic compounds against root-knot nematodes

BACKGROUND

Root-knot nematodes (RKNs), including Meloidogyne species, are among the most destructive plant-parasites worldwide. Recent evidence suggests that entomopathogenic fungi (EPF) can antagonize RKNs. Such antagonistic effects are likely mediated by toxic metabolites, including volatile organic compounds (VOCs), produced by the fungi. However, how widespread these effects are across EPF species, and which VOCs mediate negative interactions between EPF and RKNs needs to be further elucidated.

RESULTS

First, we evaluated the nematicidal effect of VOCs emitted by 46 EPF isolates against Meloidogyne incognita and found variable toxicity depending on the isolate. Second, we measured the nematicidal effect of highly toxic isolates, including species in the genus Talaromyces, Aspergillus, Clonostachys, and Purpureocillium and, third, we analyzed the nematicidal effect of major VOCs, including 2-methyl-1-propanol, 3-methyl-1-butanol, isopropyl alcohol and 2-methyl-3-pentanone. The mortality of M. incognita juveniles (J2s) was generally high (50%) either via airborne or in-solution contact with VOCs. Moreover, the tested VOCs significantly inhibited egg hatching, and repelled J2s away from the VOCs.

CONCLUSION

This study not only provides insights into the ecological function of VOCs in the rhizosphere, but also provides new approaches for developing environmentally friendly control methods of RKNs in agroecosystems. © 2023 Society of Chemical Industry.

Larvicidal and anti-termite activities of microbial biosurfactant produced by Enterobacter cloacae SJ2 isolated from marine sponge Clathria sp

The widespread use of synthetic pesticides has resulted in a number of issues, including a rise in insecticide-resistant organisms, environmental degradation, and a hazard to human health. As a result, new microbial derived insecticides that are safe for human health and the environment are urgently needed. In this study, rhamnolipid biosurfactants produced from Enterobacter cloacae SJ2 was used to evaluate the toxicity towards mosquito larvae (Culex quinquefasciatus) and termites (Odontotermes obesus). Results showed dose dependent mortality rate was observed between the treatments. The 48 h LC50 (median lethal concentration) values of the biosurfactant were determined for termite and mosquito larvae following the non-linear regression curve fit method. Results showed larvicidal activity and anti-termite activity of biosurfactants with 48 h LC50 value (95% confidence interval) of 26.49 mg/L (25.40 to 27.57) and 33.43 mg/L (31.09 to 35.68), respectively. According to a histopathological investigation, the biosurfactant treatment caused substantial tissue damage in cellular organelles of larvae and termites. The findings of this study suggest that the microbial biosurfactant produced by E. cloacae SJ2 is an excellent and potentially effective agent for controlling Cx. quinquefasciatus and O. obesus.

Biotechnological Potential of Microorganisms for Mosquito Population Control and Reduction in Vector Competence

Mosquitoes transmit pathogens that cause human diseases such as malaria, dengue fever, chikungunya, yellow fever, Zika fever, and filariasis. Biotechnological approaches using microorganisms have a significant potential to control mosquito populations and reduce their vector competence, making them alternatives to synthetic insecticides. Ongoing research has identified many microorganisms that can be used effectively to control mosquito populations and disease transmission. However, the successful implementation of these newly proposed approaches requires a thorough understanding of the multipronged microorganism-mosquito-pathogen-environment interactions. Although much has been achieved in discovering new entomopathogenic microorganisms, antipathogen compounds, and their mechanisms of action, only a few have been turned into viable products for mosquito control. There is a discrepancy between the number of microorganisms with the potential for the development of new insecticides and/or antipathogen products and the actual available products, highlighting the need for investments in the intersection of basic research and biotechnology.

A recombinant Aspergillus oryzae fungus transmitted from larvae to adults of Anopheles stephensi mosquitoes inhibits malaria parasite oocyst development

The control of malaria parasite transmission from mosquitoes to humans is hampered by decreasing efficacies of insecticides, development of drug resistance against the last-resort antimalarials, and the absence of effective vaccines. Herein, the anti-plasmodial transmission blocking activity of a recombinant Aspergillus oryzae (A. oryzae-R) fungus strain, which is used in human food industry, was investigated in laboratory-reared Anopheles stephensi mosquitoes. The recombinant fungus strain was genetically modified to secrete two anti-plasmodial effector peptides, MP2 (midgut peptide 2) and EPIP (enolase-plasminogen interaction peptide) peptides. The transstadial transmission of the fungus from larvae to adult mosquitoes was confirmed following inoculation of A. oryzae-R in the water trays used for larval rearing. Secretion of the anti-plasmodial effector peptides inside the mosquito midguts inhibited oocyst formation of P. berghei parasites. These results indicate that A. oryzae can be used as a paratransgenesis model carrying effector proteins to inhibit malaria parasite development in An. stephensi. Further studies are needed to determine if this recombinant fungus can be adapted under natural conditions, with a minimal or no impact on the environment, to target mosquito-borne infectious disease agents inside their vectors.

Recent Advancements in Pathogenic Mechanisms, Applications and Strategies for Entomopathogenic Fungi in Mosquito Biocontrol

Fungal diseases are widespread among insects and play a crucial role in naturally regulating insect populations. Mosquitoes, known as vectors for numerous infectious diseases, pose a significant threat to human health. Entomopathogenic fungi (EPF) have emerged as highly promising alternative agents to chemical mosquitocides for controlling mosquitoes at all stages of their life cycle due to their unique infection pathway through direct contact with the insect's cuticle. In recent years, significant advancements have been made in understanding the infection pathways and pathogenic mechanisms of EPF against mosquitoes. Various strategies involving the use of EPF alone or combinations with other approaches have been employed to target mosquitoes at various developmental stages. Moreover, the application of genetic technologies in fungi has opened up new avenues for enhancing the mosquitocidal efficacy of EPF. This review presents a comprehensive summary of recent advancements in our understanding the pathogenic mechanisms of EPF, their applications in mosquito management, and the combination of EPF with other approaches and employment of transgenic technologies. The biosafety concerns associated with their use and the corresponding approaches are also discussed. The recent progress suggests that EPF have the potential to serve as a future biorational tool for controlling mosquito vectors.

Effect of High Temperature and UV Radiation on the Insecticidal Capacity of a Spodoptera frugiperda Nucleopolyhedrovirus Microencapsulated in a Matrix Based on Oxidized Corn Starch

A multiple nucleopolyhedrovirus native isolate (SfCH32) of Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) was encapsulated by spray-drying in a matrix based on oxidized corn starch without and with a fluorescent brightener. The microcapsules were exposed to UV radiation (365 nm) for 0, 2, 4, and 8 h at 25 °C or temperatures of 35, 40, and 45 °C for 8 h. The data obtained with temperatures 35, 40, and 45 °C were contrasted with those obtained at 25 °C. The microcapsules were evaluated for size, shape, and insecticidal capacity against third instar S. frugiperda larvae under laboratory conditions. The 82-84.2% of the encapsulating matrix, in a dry-weight basis, was recovered as NPV microcapsules of heterogeneous shape and size. The exposure to UV radiation and temperatures reduced significantly the insecticidal capacity of tested viruses; however, such capacity was higher for microencapsulated than for non-microencapsulated viruses. The non-encapsulated virus that had been exposed to 45 °C or maintained at UV radiation for 8 h showed the lowest insecticidal activity at 5th day post-inoculation, with a larvae mortality of 25.3 and 16%, respectively. The fluorescent brightener increased significantly the insecticidal capacity of encapsulated and non-encapsulated viruses, causing a mortality of 100% at that time point, and decreased the median lethal time independently of the incubation temperature and exposure time to radiation. The findings suggested that an encapsulating matrix based on oxidized corn starch might protect the insecticidal capacity of NPV under field conditions.

Characterization and Evaluation of Metarhizium spp. (Metsch.) Sorokin Isolates for Their Temperature Tolerance

A field survey was done in teak (Tectona grandis F.) forests in South India to explore the entomopathogenic effect of Metarhizium anisopliae (Ascomycota: Sordariomycetes) against teak defoliator, Hyblaea puera (Lepidoptera: Hyblaeidae). About 300 soils and infected insect samples were collected during the survey and thirty-six fungal isolates were isolated from soil and insect samples and characterized. The fungi were cultured on PDAY with dodine and antibiotics. Generally, the EPF culture was incubated at 27 °C in darkness for 15 days. Virulence of the Entomopathogenic Fungi (EPF) ability to germinate under cold and heat temperatures was assessed in a culture impregnated with conidia. In the experiment, it was found that for the first time Metarhizium quizhouense, Metarhizium robertsii, and Metarhizium majus species caused significantly higher mortality to hosts. These isolates of M. anisopliae, M. robertsii, M. majus, and M. quizhouense were all considered to be effective virulent and environmentally adaptive. The Metarhizium isolates were recommended as effective bio-control agents through the field investigation of teak defoliator Hyblaea puera from South India forest. This study paves the way to utilize the indigenous isolates of EPF for the control of teak defoliator and to combat the pests thatare resistant to insecticide.

Susceptibility of Demotispa neivai (Coleoptera: Chrysomelidae) to Beauveria bassiana and Metarhizium anisopliae entomopathogenic fungal isolates

BACKGROUND

The potential of Beauveria bassiana and Metarhizium anisopliae isolates obtained from naturally infected oil palm pests was evaluated to control Demotispa neivai as an alternative for organophosphate insecticide use in oil palm crops in Latin America. Two B. bassiana (Bb-0018 and Bb-0025) and two M. anisopliae (Ma-0002 and Ma-0003) isolates were tested against D. neivai adults for hydrophobicity, virulence, survival, adhesion to host cuticle, and mortality in semi-field conditions.

RESULTS

Concentration-mortality bioassays demonstrate that isolates had lethal effect on D. neivai adults with Bb-0025 [median lethal concentration (LC₅₀ ) = 3.45 × 10⁷ conidia mL^-1 ] and Bb-0018 (LC₅₀  = 3.75 × 10⁷ conidia mL^-1 ) being the most effective followed by Ma-0003 (LC₅₀  = 3.38 × 10⁸ conidia mL^-1 ) and Ma-0002 (5.33 × 10⁸ conidia mL^-1 ). Adult survival was 99% without exposure to fungal isolates, decreasing to 21.65% in insects exposed to Ma-0002, 19.41% with Ma-0003, 20.13% with Bb-0018, and 0.17% with Bb-0025. Mortality of D. neivai adults caused by the entomopathogenic fungal isolates was similar in both laboratory and semi-field conditions. Also, vegetative growth of the entomopathogenic fungal isolates was found in infected D. neivai adults in the field.

CONCLUSION

Our data suggest that the tested entomopathogenic fungal isolates are effective against D. neivai with potential to be used as biological control agents contributing to the decrease of the use of chemical insecticides to control this oil palm pest. © 2021 Society of Chemical Industry.

Identification of locally isolated entomopathogenic Fusarium species from the soil of Changa Manga Forest, Pakistan and evaluation of their larvicidal efficacy against Aedes aegypti

Dengue fever vectored by the mosquito Aedes aegypti is one of the most rapidly spreading insect-borne diseases. Current reliance of dengue vector control is mostly on chemical insecticides. Growing insecticide resistance in the primary mosquito vector, Aedes aegypti, limits the effectiveness of vector control through chemical insecticides. These chemical insecticides also have negative environmental impacts on animals, plants and human health. Myco-biocontrol agents are naturally occurring organisms and are found to be less damaging to the environment as compared to chemical insecticides. In the present study, entomopathogenic potential of local strains of fungi isolated from soil was assessed for the control of dengue vector. Local fungal isolates presents better alternative to introducing a foreign biocontrol strain, as they may be better adapted to environmental conditions of the area to survive and may have more entomopathogenic efficacy against target organism. Larvicidal efficacy of Fusarium equiseti and Fusarium proliferatum was evaluated against Aedes aegypti. Local strains of F. equiseti (MK371718) and F. proliferatum (MK371715) were isolated from the soil of Changa Manga Forest, Pakistan by using insect bait method. Larvicidal activity of two Fusarium spp. was tested against forth instar larvae of A. aegypti in the laboratory, using concentrations 105, 106, 107 and 108 conidia /ml. LC50 values for F. equiseti after 24h, 48h, 72h and 96h of exposure were recorded as 3.8x 108, 2.9x107, 2.0x107, and 7.1x106 conidia /ml respectively while LC50 values for F. proliferatum were recorded as 1.21x108, 9.6x107, 4.2x107, 2.6x107 conidia /ml respectively after 24h, 48h, 72h and 96h of exposure. The results indicate that among two fungal strains F. equiseti was found to be more effective in terms of its larvicidal activity than F. proliferatum against larvae of A. aegypti.

Cytochrome P450-mediated mycotoxin metabolism by plant-feeding insects

Mycotoxins are secondary metabolites produced primarily by filamentous fungi that when consumed cause pathological responses in animal hosts or consumers. Defined functionally rather than structurally, mycotoxins derive from numerous primary metabolic pathways. Through opportunistic or mutualistic associations, insect herbivores inflict damage that can predispose plants to infection by mycotoxin-producing phytopathogens, resulting in economically significant contamination. The few cytochrome P450 subfamilies implicated in mycotoxin detoxification by insects, including CYP6 and CYP9, are also known to detoxify phytochemicals. Some insect P450s bioactivate, rather than detoxify, mycotoxins, suggestive of an 'escalation' in arms-race interactions between these herbivores and fungi. Characterizing insect P450s that detoxify mycotoxins can be useful for developing biological remediation technologies and for ensuring the safety of insects reared for human or livestock consumption.

Target Activity of Isaria tenuipes (Hypocreales: Clavicipitaceae) Fungal Strains against Dengue Vector Aedes aegypti (Linn.) and Its Non-Target Activity Against Aquatic Predators

The present investigation aimed to determine the fungal toxicity of Isaria tenuipes (My-It) against the dengue mosquito vector Aedes aegypti L. and its non-target impact against the aquatic predator Toxorhynchitessplendens. Lethal concentrations (LC₅₀ and LC₉₀) of My-It were observed in 2.27 and 2.93 log ppm dosages, respectively. The sub-lethal dosage (My-It-1 × 10⁴ conidia/mL) displayed a significant oviposition deterrence index and also blocked the fecundity rate of dengue mosquitos in a dose-dependent manner. The level of major detoxifying enzymes, such as carboxylesterase (α-and β-) and SOD, significantly declined in both third and fourth instar larvae at the maximum dosage of My-It 1 × 10⁵ conidia/mL. However, the level of glutathione S-transferase (GST) and cytochrome P-450 (CYP450) declined steadily when the sub-lethal dosage was increased and attained maximum reduction in the enzyme level at the dosage of My-It (1 × 10⁵ conidia/mL). Correspondingly, the gut-histology and photomicrography results made evident that My-It (1 × 10⁵ conidia/mL) heavily damaged the internal gut cells and external physiology of the dengue larvae compared to the control. Moreover, the non-target toxicity against the beneficial predator revealed that My-It at the maximum dosage (1 × 10²⁰ conidia/mL) was found to be less toxic with <45% larval toxicity against Tx.splendens. Thus, the present toxicological research on Isaria tenuipes showed that it is target-specific and a potential agent for managing medically threatening arthropods.

Efficacy of Andrographis paniculata supplements induce a non-specific immune system against the pathogenicity of Aeromonas hydrophila infection in Indian major carp (Labeo rohita)

Aeromonas hydrophila, an opportunistic fish pathogen, which causes several major diseases including skin ulcer and haemorrhagic septicemia, contributes considerably to the lethality in aquaculture. Chemical and antibiotic treatment employed against A. hydrophila for disease management are expensive and consequently prompted the advent of drug resistance among the pathogens. To overcome these draw backs, alternative aquatic disease control methods using conventional plant-based medicines are focussed. Our present study aimed to augment the fish non-specific immune system with the implementation of methanolic crude extracts of Andrographis paniculata to Labeo rohita, for evaluating their efficacy against A. hydrophila. Histology of major organs of A. hydrophila-infected fish such as the gills and liver displayed severe tissue damage. A. paniculata extracts exhibited the strong antibacterial activity against A. hydrophila even at lower concentrations (50 μl). The extracts also altered the haematological profile of treated infected fishes by increasing the levels of haemoglobin and total erythrocyte-leucocyte counts, along with the phagocytic index. The extracts also had a significant impact on modifying the anatomy and swimming pattern of infected fish, post treatment with the extracts. Also, A. paniculata treated infected fishes in all the plant extract administration methods, viz. injection, oral feeding and diffusion, and reduced the cumulative mortality rate to less than 30%. Even lower concentrations of A. paniculata extracts (50 μl) resulted in maximum relative percentage survival of treated fishes. Therefore, our findings suggest that A. paniculata was effective against A. hydrophila infection in aquaculture, thereby maintaining a healthy status of these fishes in aquaculture.

Toxicological screening of marine red algae Champia parvula (C. Agardh) against the dengue mosquito vector Aedes aegypti (Linn.) and its non-toxicity against three beneficial aquatic predators

Larval toxicity of ethanolic extract of C. parvula (Ex-Cp) was prominent in the second and the third instars at the maximum lethal dosage of 100 ppm with 98 and 97 % mortality rate respectively. The LC₅₀ and LC₉₀ was displayed at 43 ppm and 88 ppm dosage respectively. Correspondingly, the sub-lethal dosage (65 ppm) of Ex-Cp significantly alters the carboxylesterase (α and β), GST and CYP450 enzyme level in both III and IV instar larvae in dose-dependent manner. Similarly, the Ex-Cp displayed significant repellent activity (97 %) with a maximum level of protection time (210 min). Photomicrography assay of Ex-Cp (65 ppm) were toxic to dengue larvae as compared to control. The non-target toxicity of Ex-Cp against the beneficial mosquito predators displayed less toxicity at the maximum dosage of 600 ppm as compared to Temephos. Thus the present research delivers the target and non-target toxicity of red algae C. parvula against the dengue mosquito vector.

A Review of Resistance Mechanisms of Synthetic Insecticides and Botanicals, Phytochemicals, and Essential Oils as Alternative Larvicidal Agents Against Mosquitoes

Mosquitoes are a serious threat to the society, acting as vector to several dreadful diseases. Mosquito management programes profoundly depend on the routine of chemical insecticides that subsequently lead to the expansion of resistance midst the vectors, along with other problems such as environmental pollution, bio magnification, and adversely affecting the quality of public and animal health, worldwide. The worldwide risk of insect vector transmitted diseases, with their associated illness and mortality, emphasizes the need for effective mosquitocides. Hence there is an immediate necessity to develop new eco-friendly pesticides. As a result, numerous investigators have worked on the development of eco-friendly effective mosquitocidal compounds of plant origin. These products have a cumulative advantage of being cost-effective, environmentally benign, biodegradable, and safe to non-target organisms. This review aims at describing the current state of research on behavioral, physiological, and biochemical effects of plant derived compounds with larvicidal effects on mosquitoes. The mode of physiological and biochemical action of known compounds derived from various plant families as well as the potential of plant secondary metabolites, plant extracts, and also the essential oils (EO), as mosquitocidal agents are discussed. This review clearly indicates that the application of vegetal-based compounds as mosquito control proxies can serve as alternative biocontrol methods in mosquito management programes.

Comparative efficacy of two mycotoxins against Spodoptera litura Fab. And their non-target activity against Eudrilus eugeniae Kinb

Entomopathogenic fungi are feasible and effective against the agricultural pest. In the current research we investigated the bioactive comparison of two widely accepted entmopathogens (Beauveria bassiana (Bals.) Vuill. and Metarhizium anisopliae, (basionym)) against the Spodoptera litura (Fab.) through the assessment of larval tolerance and regulation of antioxidants and non-target impact on the earth worm, E. eugeniae, along with commercial pesticides. The entomopathogenic fungus exposure resulted in the modification of the levels of detoxification enzymes as well as significant increases in catalase and superoxide dismutase activity after exposure to the entomopathogenic fungus. Bioassay results showed that B. bassiana and M. anisopliae displayed larval mortality against third and fourth instars. Correspondingly, sub-lethal concentrations of B. bassiana showed development impairment as compared to M. anisopliae. Gut-histology revealed that mycotoxins dosage (4 × 10⁵) showed significant changes in the midgut tissues as compared to control larvae. The non-target screening through artificial soil assay on the earth worm E. eugeniae, with mycotoxins B. bassiana (5 × 10⁸ conidia/ml/kg) and M. anisopliae (5 × 10⁸ conidia/ml/kg) showed less toxicity as compared to Monocrotophos (10 ppm/kg). Current results suggest that the fungal mycotoxins of M. anisopliae and B. bassiana significantly reduce the development of lepidopteran pests, while having only lesser impact on beneficial earthworms.