Essential oils from Acacia nilotica (Fabales: Fabaceae) seeds: May have insecticidal effects?

Fungal communities are more sensitive to mildew than bacterial communities during tobacco storage processes

Mildew poses a significant threat to tobacco production; however, there is limited information on the structure of the abundant and rare microbial subcommunities in moldy tobacco leaves. In this study, we employed high-throughput sequencing technology to discern the disparities in the composition, diversity, and co-occurrence patterns of abundant and rare fungal and bacterial subcommunities between moldy and normal tobacco leaves collected from Guizhou, Shanghai, and Jilin provinces, China. Furthermore, we explored the correlation between microorganisms and metabolites by integrating the metabolic profiles of moldy and normal tobacco leaves. The results showed that the fungi are more sensitive to mildew than bacteria, and that the fungal abundant taxa exhibit greater resistance and environmental adaptability than the rare taxa. The loss of rare taxa results in irreversible changes in the diversity, richness, and composition of the fungal community. Moreover, rare fungal taxa and abundant bacterial taxa played crucial roles in maintaining the stability and functionality of the tobacco microecosystem. In moldy tobacco, however, the disappearance of rare taxa as key nodes resulted in reduced connectivity and stability within the fungal network. In addition, metabolomic analysis showed that the contents of indoles, pyridines, polyketones, phenols, and peptides were significantly enriched in the moldy tobacco leaves, while the contents of amino acids, carbohydrates, lipids, and other compounds were significantly reduced in these leaves. Most metabolites showed negative correlations with Dothideomycetes, Alphaproteobacteria, and Gammaproteobacteria, but showed positive correlations with Eurotiales and Bacilli. This study has demonstrated that abundant fungal taxa are the predominant biological agents responsible for tobacco mildew, while bacteria may indirectly contribute to this process through the production and degradation of metabolites. KEY POINTS: • Fungi exhibited greater sensitivity to mildew of tobacco leaf compared to bacteria • Rare fungal taxa underwent significant damage during the mildew process • Mildew may damage the defense system of the tobacco leaf microecosystem.

Insecticidal activity of two organic extracts from Libidibia coriaria (Jacq.) Schltdl. fruits against Spodoptera frugiperda J. E. Smith

This study describes the chemical characterisation of two extracts (ethyl acetate, EtOAc-E and hexanic, Hx-E) from Libidibia coriaria fruits and their insecticidal properties on Spodoptera frugiperda. The HPLC analysis in EtOAct-E revealed the presence of ellagic acid and phenolic compounds. The CG-MS analysis in Hx-E revealed the presence of Hexadecanoic acid, 11-Methylheptacosane, Dodecanoic acid and Nonacosane as major compounds. The application of both extracts was performed on the dorsal part of each larva via aspersion. The larval mortality, relative growth and emergence percentage of adults were evaluated. The Hx-E caused a 93.33% mortality at 100 mg/mL at 24 h post-application. A minor relative growth with both EtOAc-E (12.64 mg) and Hx-E (7.90 mg) was observed compared with their respective negative controls (methanol = 25.05 mg and tween20 = 24.53 mg). The lowest emergence percentage of adults with the Hx-E (25%) at 50 mg/mL was observed. Libidibia coriaria fruits exhibit insecticidal properties against S. frugiperda.

Evaluation of five medicinal plants for the management of Sitophilus oryzae in stored rice and identification of insecticidal compound

Sitophilus oryzae is a kind of stored grain pest. This is controlled by using natural pesticides, which are more reliable, cost-effective, biodegradable, and eco-friendly than synthetic pesticides. Several plants show different insecticidal activities against various pests on their different parts (leaves, seeds, etc.). In this study, methanolic extracts of Lantana camara (leaves), Carica papaya (seeds), Ricinus communis (leaves), Calotropis gigantea (flowers), and Gliciridia sepium (leaves) were used to identify the best insecticidal activity against the rice weevil by doing mortality tests for one week with four replications under laboratory conditions. Gliciridia sepium leaves showed the highest insecticidal activity (100 ± 0) after seven days, and its extract was fractionated by using column chromatography and yielded 12 fractions. A contact bioassay of each fraction was performed, and fraction-11 showed the highest insecticidal activity against Sitophilus oryzae with a 100 % mortality after four days. Fraction-11 was analyzed by using GC-MS and FT-IR. Results revealed that the major constituent identified in fraction-11 was 4-C-methyl-myo-inositol. Therefore, 4-C-methyl-myo-inositol acts as a natural insecticide against rice weevils.

Toxicity, biochemical and molecular docking studies of Acacia nilotica L., essential oils against insect pests

Botanical essential oils are natural insecticides derived from plants, offering eco-friendly alternatives to synthetic chemicals for pest control. In this study, the essential oils were extracted from Acacia nilotica seed cotyledons, and their toxicity was tested against insect pests. Furthermore, the chemical components of the essential oils were identified through gas chromatography-mass spectrometry (GC-MS) analysis. The essential oil extracted from A. nilotica seeds exhibited the highest mortality rates of 60% and 98% in Culex quinquefasciatus, and 60% and 96.66% mortality in Plutella xylostella at 24 and 48 h after treatment, respectively. The essential oils resulted in a lower LC50 of 159.263 ppm/mL, and LC90 of 320.930 ppm/mL within 24 h. In 48 h, the LC50 was 52.070 ppm/mL and the LC90 was 195.123 ppm/mL for C. quinquefasciatus. In the essential oil treatment of P. xylostella, the lower LC50 was 165.900 ppm/mL, and the LC90 was 343.840 ppm/mL 24 h after the treatment. At 48 h post-treatment, the LC50 decreased to 62.965 ppm/mL, and the LC90 decreased to 236.795 ppm/mL in P. xylostella. The study investigated the impact of essential oils on insect enzymes 24 h after treatment. The study revealed significant changes in the levels of insect enzymes, including a decrease in acetylcholinesterase enzymes and an increase in glutathione S-transferase compared to the control group. Essential oils had minimal effects, resulting in mortality rates of 30.66% and 46% at 24 and 48 h after treatment on Artemia salina. After 48 h, minimal toxic effects of essential oils were observed on E. eugeniae, with a mortality rate of 11.33%. The GC-MS analysis of A. nilotica seed-derived essential oils revealed ten major chemical constituents, including 6-hydroxymellein, phthalic acid, trichloroacetic acid, hexadecane, acetamide, heptacosane, eicosane, pentadecane, 1,3,4-eugenol, and chrodrimanin B. Among these constituents, Heptacosane is the major chemical component, and this molecule has a high potential for involvement in insecticidal activity.

Efficacy of maturase K and rpL20 protein extracted from C. procera leaves on Anophelesstephensi

The present work is carried out to protein isolation, purification, and characterization from leaves, stem, and seed of C. procera and to evaluate the larvicidal potential on Anopheles stephensi. The whole protein was isolated using protein extraction buffer and precipitated by ammonium sulphate and larvicidal active protein was purified by the column chromatography. The homogeneity of larvicidal protein was confirmed by the SDS-PAGE. The identification of protein was done by the HPLC and LC-MS/ESI-MS. The crude protein from leaves showed 100% mortality of 3rd instar larvae of An. stephensi at the concentration of 5.5 mg/ml after 24 h of exposure. The crude protein from stem showed 25% mortality and no mortality observed was observed in seed protein. The leaves crude protein was further purified by ion exchange chromatography and eluted fractions were tested for larvicidal potential. The purified single protein fractions L2 and L3 from C. procera leaves showed 100% mortality at concentration of 0.06 mg/ml. The homogeneity of purified protein was confirmed by SDS-PAGE and two bands of 26 kDa and 15 kDa protein were observed. The peptide sequence "R.SQMLENSFLIENVMKR.L" was identified in the trypsin digested homogenous protein fraction L2 and "R.DRGSQKR.N" peptide sequence in L3 fraction by LC-MS/ESI-MS. The CprL2 peptide showed the sequence similarity with the protein maturase K and CprL3 peptide showed the sequence similarity with ribosomal protein L20 of C. procera. The conserved functional domain was also identified in both the CprL2 and CprL3 peptide. The identified proteins showed strong larvicidal efficacy at very low concentration. The identified proteins are novel and natural larvicidal agents against An. stephensi and hence can be used to control the malaria.

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.

Anti-Culex pipiens activity of different pomegranate cultivars and determination of their bioactive compounds using LC-MS profiling

INTRODUCTION

Pomegranate (Punica granatum L.) peels are rich in various bioactive compounds. Characterization of these compounds is crucial for the utilization of peel waste in industrial processing.

OBJECTIVE

The study aimed (1) to establish and compare the metabolic profiles of the peel of seven pomegranate cultivars and (2) to identify bioactive compounds contributing to the larvicidal activity against the third instar larvae of Culex pipiens.

MATERIALS AND METHODS

UPLC-ESI-MS/MS was utilized to analyze peel methanol extracts of different pomegranate cultivars. The larvicidal activity was determined by calculating the larval mortality among the third instar larvae of C. pipiens. Multivariate data analysis was conducted to identify the metabolites that exhibited a larvicidal effect.

RESULTS

A total of 24 metabolites, including hydrolyzable tannins, flavonoids, and alkaloids, were tentatively identified in both negative and positive ionization modes. The extract of cultivar 'Black' exhibited the most potent larvicidal effect with LC50 values of 185.15, 156.84, and 138.12 ppm/mL after 24, 48, and 72 h of treatment, respectively. By applying chemometric techniques, the larvicidal activity could be directly correlated to the bioactive compounds punicalagin, quercetin-O-rhamnoside, quercetin-O-pentoside, and galloyl-HHDP-glucose.

CONCLUSION

The present study implemented UPLC-ESI-MS/MS and chemometric techniques as potential tools for metabolomics analysis and differentiation between peels of different pomegranate cultivars. In addition, cultivar 'Black' extract could be a promising natural insecticide against mosquitoes since it is rich in bioactive compounds with larvicidal activity.

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.