Mosquito control potential of secondary metabolites isolated from Aspergillus flavus and Aspergillus fumigatus

Novel report on soil infection with Metarhizium rileyi against soil-dwelling life stages of insect pests

Entomopathogenic fungi are the most effective control remedy against a wide range of medical and agricultural important pests. The present study aimed to isolate, identify, and assess the virulence of Metarhizium rileyi against Spodoptera litura and Spodoptera frugiperda pupae under soil conditions. The biotechnological methods were used to identify the isolate as M. rileyi. The fungal conidial pathogenicity (2.0 × 107, 2.0 × 108, 2.0 × 109, 2.0 × 1010, and 2.0 × 1011 conidia/mL-1) was tested against prepupae of S. litura and S. frugiperda at 3, 6, 9, and 12 days after treatments. Additionally, the artificial soil-conidial assay was performed on a nontarget species earthworm Eudrilus eugeniae, using M. rileyi conidia. The present results showed that the M. rileyi caused significant mortality rates in S. litura pupae (61-90%), and S. litura pupae were more susceptible than S. frugiperda pupae (46%-73%) at 12 day posttreatment. The LC50 and LC90 of M. rileyi against S. litura, were 3.4 × 1014-9.9 × 1017 conidia/mL-1 and 6.6 × 105-4.6 × 1014 conidia/mL-1 in S. frugiperda, respectively. The conidia of M. rileyi did not exhibit any sublethal effect on the adult stage of E. eugeniae, and Artemia salina following a 12-day treatment period. Moreover, in the histopathological evaluation no discernible harm was observed in the gut tissues of E. eugeniae, including the lumen and epithelial cells, as well as the muscles, setae, nucleus, mitochondria, and coelom. The present findings provide clear evidence that M. rileyi fungal conidia can be used as the foundation for the development of effective bio-insecticides to combat the pupae of S. litura and S. frugiperda agricultural pests.

Study on the virulence of Metarhizium anisopliae against Spodoptera frugiperda (J. E. Smith, 1797)

This study examined the impact of Metarhizium anisopliae (Hypocreales: Clavicipitaceae) conidia on the eggs, larvae, pupae, and adults of Spodoptera frugiperda. The results showed that eggs, larvae, pupae, and adults exhibited mortality rates that were dependent on the dose. An increased amount of conidia (1.5 × 109 conidia/mL) was found to be toxic to larvae, pupae, and adults after 9 days of treatment, resulting in a 100% mortality rate in eggs, 98% in larvae, 76% in pupae, and 85% in adults. A study using earthworms as bioindicators found that after 3 days of exposure, M. anisopliae conidia did not cause any harmful effects on the earthworms. In contrast, the chemical treatment (positive control) resulted in 100% mortality at a concentration of 40 ppm. Histopathological studies showed that earthworm gut tissues treated with fungal conidia did not show significant differences compared with those of the negative control. The gut tissues of earthworms treated with monocrotophos exhibited significant damage, and notable differences were observed in the chemical treatment. The treatments with 70 and 100 µg/mL solutions of Eudrilus eugeniae epidermal mucus showed no fungal growth. An analysis of the enzymes at a biochemical level revealed a decrease in the levels of acetylcholinesterase, α-carboxylesterase, and β-carboxylesterase in S. frugiperda larvae after exposure to fungal conidia. This study found that M. anisopliae is effective against S. frugiperda, highlighting the potential of this entomopathogenic fungus in controlling this agricultural insect pest.

Pathogenicity of Metarhizium rileyi (Hypocreales: Clavicipitaceae) against Tenebrio molitor (Coleoptera: Tenebrionidae)

Tenebrio molitor L., also known as the mealworm, is a polyphagous insect pest that infests various stored grains worldwide. Both the adult and larval stages can cause significant damage to stored grains. The present study focused on isolating entomopathogenic fungi from an infected larval cadaver under environmental conditions. Fungal pathogenicity was tested on T. molitor larvae and pupae for 12 days. Entomopathogenic fungi were identified using biotechnological methods based on their morphology and the sequence of their nuclear ribosomal internal transcribed spacer (ITS). The results of the insecticidal activity indicate that the virulence of fungi varies between the larval and pupal stages. In comparison to the larval stage, the pupal stage is highly susceptible to Metarhizium rileyi, exhibiting 100% mortality rates after 12 days (lethal concentration 50 [LC50] = 7.8 × 106 and lethal concentration 90 (LC90) = 2.1 × 1013 conidia/mL), whereas larvae showed 92% mortality rates at 12 days posttreatment (LC50 = 1.0 × 106 and LC90 = 3.0 × 109 conidia/mL). The enzymatic analyses revealed a significant increase in the levels of the insect enzymes superoxide dismutase (4.76-10.5 mg-1) and glutathione S-transferase (0.46-6.53 mg-1) 3 days after exposure to M. rileyi conidia (1.5 × 105 conidia/mL) compared to the control group. The findings clearly show that M. rileyi is an environmentally friendly and effective microbial agent for controlling the larvae and pupae of T. molitor.

Biocontrol efficacy of cajeput oil against Anopheles stephensi L. mosquito and its effect on non-target species

Chemical insecticides are effective at controlling mosquito populations, but their excessive use can pollute the environment and harm non-target organisms. Mosquitoes can also develop resistance to these chemicals over time, which makes long-term mosquito control efforts challenging. In this study, we assessed the phytochemical, biochemical, and insecticidal properties of the chemical constituents of cajeput oil. Results show that Melaleuca cajuputi essential oil may exhibit mosquito larvicidal properties against Anopheles stephensi larvae (second-fourth instar) at 24 h post-treatment. At 24 h post-exposure, the essential oil resulted in a significant decrease in detoxifying enzymes. All of these findings indicate that cajeput oil infects An. stephensi larvae directly affect the immune system, leading to decreased immune function. Cajeput oil significantly affects the second, third, and fourth instar larvae of An. stephensi, according to the bioassay results. Cajeput oil does not induce toxicity in non-target Eudrilus eugeniae earthworm species, as indicated by a histological study of earthworms. Phytochemical screening and GC-MS analysis of the essential oil revealed the presence of several major phytochemicals that contribute to mosquito larvicidal activity. The importance of cajeput oil as an effective candidate for biological control of the malarial vector An. stephensi is supported by this study.

Biocontrol effects of chemical molecules derived from Beauveria bassiana against larvae of Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae)

In this study, we conducted tests on the isolation, identification, characterization, and extraction of chemical molecules from Beauveria bassiana against Tuta absoluta larvae. The enzyme responses of T. absoluta to the crude extract were examined 24 h after treatment, and the number of dead larvae was calculated 24 and 48 h after treatment. Molecular docking studies were conducted to assess the interaction of important molecules with the acetylcholinesterase enzyme. The larvicidal activity of crude chemicals from fungi was high 24 h after treatment, with LC50 and LC90 values of 25.937 and 33.559 μg/mL, respectively. For a period of 48 h, the LC50 and LC90 values were 52.254 and 60.450 μg/mL, respectively. The levels of acetylcholinesterase, α-carboxylesterase, and β-carboxylesterase enzymes were lower in the treatment group after 24 h compared to the control group. The GC-MS test revealed that the crude extract consisted mainly of 9,10-octadecadienoic acid, which was the primary compound. Docking results indicated that 9,10-octadecadienoic acid showed a strong interaction with acetylcholinesterase (AChE). Our findings suggest that the chemical molecule 9,10-octadecadienoic acid derived from the entomopathogenic fungus B. bassiana is more toxic to T. absoluta larvae. We plan to conduct studies to test its effectiveness in semi-field conditions and to evaluate its stability in field conditions. We believe that this 9,10-octadecadienoic acid molecule could be used to control T. absoluta larvae in the near future without causing environmental pollution.

Entomopathogenic fungi based microbial insecticides and their physiological and biochemical effects on Spodoptera frugiperda (J.E. Smith)

Background

'The fall armyworm, Spodoptera frugiperda', represents a significant threat to maize production, a major staple crop in Asian countries.

Methods

In pursuit of more effective control of this insect pest, our study assessed the physiological and biochemical effects of the entomopathogenic fungus Metarhizium anisopliae against the larvae of S. frugiperda.

Results

Results revealed that, following nine days of treatment, a high concentration of conidia (1.5x107 conidia/mL-1) was toxic to all stages of larvae (second to fifth instar), resulting in 97% mortality of the second instar, 89% mortality of the third instar, 77% mortality of the fourth instar, and 72% mortality of fifth instar. All larval instars were found to have dose-dependent mortality effects. Treated S. frugiperda larvae further displayed significant physiological, morphological, and behavioral changes. Here, treated larvae displayed significantly lower levels of acetylcholinesterase, α-carboxylesterase, and β-carboxylesterase enzyme activity when compared to control groups. Treated larvae underwent an outward morphological change as the result of a decrease in the exterior cuticle of the anal papillae and a demelanization of the interior cuticle. Treated larvae also exhibited abnormal feeding behaviors as a consequence of the negative impact of conidia treatment on the neuromuscular system. Investigation into the effect of M. anisopliae on the non-target organism, the earthworm Eudrilus eugeniae, revealed that M. anisopliae conidia did not produce significant pathogenicity following three days of treatment. Furthermore, histological analysis revealed no significant effect of the entomopathogenic fungi on the gut tissue of the non-target organism.

Conclusion

This study highlights the potential of M. anisopliae in the control of S. frugiperda.

Biocontrol effect of entomopathogenic fungi Metarhizium anisopliae ethyl acetate-derived chemical molecules: An eco-friendly anti-malarial drug and insecticide

Insect pests represent a major threat to human health and agricultural production. With a current over-dependence on chemical insecticides in the control of insect pests, leading to increased chemical resistance in target organisms, as well as side effects on nontarget organisms, the wider environment, and human health, finding alternative solutions is paramount. The employment of entomopathogenic fungi is one such potential avenue in the pursuit of greener, more target-specific methods of insect pest control. To this end, the present study tested the chemical constituents of Metarhizium anisopliae fungi against the unicellular protozoan malaria parasite Plasmodium falciparum, the insect pests Anopheles stephensi Listen, Spodoptera litura Fabricius, and Tenebrio molitor Linnaeus, as well as the nontarget bioindicator species, Eudrilus eugeniae Kinberg. Fungal crude chemical molecules caused a noticeable anti-plasmodial effect against P. falciparum, with IC50 and IC90 values of 11.53 and 7.65 µg/mL, respectively. The crude chemical molecules caused significant larvicidal activity against insect pests, with LC50 and LC90 values of 49.228-71.846 µg/mL in A. stephensi, 32.542-76.510 µg/mL in S. litura, and 38.503-88.826 µg/mL in T. molitor at 24 h posttreatment. Based on the results of the nontarget bioassay, it was revealed that the fungal-derived crude extract exhibited no histopathological sublethal effects on the earthworm E. eugeniae. LC-MS analysis of M. anisopliae-derived crude metabolites revealed the presence of 10 chemical constituents. Of these chemicals, three major chemical constituents, namely, camphor (15.91%), caprolactam (13.27%), and monobutyl phthalate (19.65%), were highlighted for potential insecticidal and anti-malarial activity. The entomopathogenic fungal-derived crude extracts thus represent promising tools in the control of insect pests and malarial parasites.

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.

Insecticidal Efficacy of Metarhizium anisopliae Derived Chemical Constituents against Disease-Vector Mosquitoes

Insecticides can cause significant harm to both terrestrial and aquatic environments. The new insecticides derived from microbial sources are a good option with no environmental consequences. Metarhizium anisopliae (mycelia) ethyl acetate extracts were tested on larvae, pupae, and adult of Anopheles stephensi (Liston, 1901), Aedes aegypti (Meigen, 1818), and Culex quinquefasciatus (Say, 1823), as well as non-target species Eudrilus eugeniae (Kinberg, 1867) and Artemia nauplii (Linnaeus, 1758) at 24 h post treatment under laboratory condition. In bioassays, Metarhizium anisopliae extracts had remarkable toxicity on all mosquito species with LC₅₀ values, 29.631 in Ae. aegypti, 32.578 in An. stephensi and 48.003 in Cx. quinquefasciatus disease-causing mosquitoes, in A. nauplii shows (5.33–18.33 %) mortality were produced by the M. anisopliae derived crude extract. The LC₅₀ and LC₉₀ values were, 620.481; 6893.990 μg/mL. No behavioral changes were observed. A low lethal effect was observed in E. eugeniae treated with the fungi metabolites shows a 14.0 % mortality. The earthworm E. eugeniae mid-gut histology revealed that M. anisopliae extracts had no more harmful effects on the epidermis, circular muscle, setae, mitochondrion, and intestinal lumen tissues than chemical pesticides. By Liquid chromatography mass spectrometry (LC-MS) analysis, camphor (25.4 %), caprolactam (20.68 %), and monobutyl phthalate (19.0 %) were identified as significant components of M. anisopliae metabolites. Fourier transform infrared (FT-IR) spectral investigations revealed the presence of carboxylic acid, amides, and phenol groups, all of which could be involved in mosquito toxicity. The M. anisopliae derived chemical constituents are effective on targeted pests, pollution-free, target-specific, and are an alternative chemical insecticide.

Larvicidal activity against Aedes aegypti and molecular docking studies of compounds extracted from the endophytic fungus Aspergillus sp. isolated from Bertholletia excelsa Humn. & Bonpl

Endophytic fungi are microorganisms capable of colonizing the interior of plant tissues without causing damage to them. The study of the secondary metabolites produced by their vast biodiversity fungal is relevant for the discovery of new products for biotechnological and agrochemical applications. In addition, extract of the endophytic fungus Aspergillus sp., isolated from the almonds of Bertholletia excelsa Humn & Bonlp collected in the Brazilian Amazon, oviposition deterrent, and larvicidal activity of against Aedes aegypti. In the oviposition deterrence test was observed that females able to lay eggs preferred the control oviposition sites (46.6%). Furthermore, the extract showed larvicidal activity with LC50 26.86 µg/mL at 24 h and 18.75 µg/mL at 48 h. Molecular docking studies showed the compound Aspergillol B a potent larvicide by to inhibit the acetylcholinesterase enzyme (- 7.74 kcal/mol). These results indicate that compounds from secondary metabolites of Aspergillus sp., isolated from almonds of B. excelsa, are useful biological potential against vectors A. aegypti.

Pathogenic fungi infection attributes of malarial vectors Anopheles maculipennis and Anopheles superpictus in central Iran

BACKGROUND

Due to the effect of synthetic and commercial insecticides on non-target organisms and the resistance of mosquitoes, non-chemical and environmentally friendly methods have become prevalent in recent years. The present study was to isolate entomopathogenic fungi with toxic effects on mosquitoes in natural larval habitats.

METHODS

Larvae of mosquitoes were collected from Central, Qamsar, Niasar, and Barzok Districts in Kashan County, Central Iran by standard dipping method, from April to late December 2019. Dead larvae, live larvae showing signs of infection, and larvae and pupae with a white coating of fungal mycelium on the outer surface of their bodies were isolated from the rest of the larvae and sterilized with 10% sodium hypochlorite for 2 min, then washed twice with distilled water and transferred to potato-dextrose-agar (PDA) and water-agar (WA) media and incubated at 25 ± 2 °C for 3-4 days. Larvae and fungi were identified morphologically based on identification keys.

RESULTS

A total of 9789 larvae were collected from urban and rural areas in Kashan County. Thirteen species were identified which were recognized to belong to three genera, including Anopheles (7.89%), Culiseta (17.42%) and Culex (74.69%). A total of 105 larvae, including Anopheles superpictus sensu lato (s.l), Anopheles maculipennis s.l., Culex deserticola, Culex perexiguus, and Culiseta longiareolata were found to be infected by Nattrassia mangiferae, Aspergillus niger, Aspergillus fumigatus, Trichoderma spp., and Penicillium spp. Of these, Penicillium spp. was the most abundant fungus isolated and identified from the larval habitats, while An. superpictus s.l. was the most infected mosquito species.

CONCLUSIONS

Based on the observations and results obtained of the study, isolated fungi had the potential efficacy for pathogenicity on mosquito larvae. It is suggested that their effects on mosquito larvae should be investigated in the laboratory. The most important point, however, is the proper way of exploiting these biocontrol agents to maximize their effect on reducing the population of vector mosquito larvae without any negative effect on non-target organisms.