Rhamnolipids inhibit aflatoxins production in Aspergillus flavus by causing structural damages in the fungal hyphae and down-regulating the expression of their biosynthetic genes

Aflatoxins are hepatotoxic and carcinogenic fungal secondary metabolites that usually contaminate crops and represent a serious health hazard for humans and animals worldwide. In this work, the effect of rhamnolipids (RLs) produced by Pseudomonas aeruginosa #112 on the growth and aflatoxins production by Aspergillus flavus MUM 17.14 was studied in vitro. At concentrations between 45 and 1500 mg/L, RLs reduced the mycelial growth of A. flavus by 23-40% and the production of aflatoxins by 93.9-99.5%. Purified mono-RLs and di-RLs exhibited a similar inhibitory activity on fungal growth. However, the RL mixture had a stronger inhibitory effect on aflatoxins production at concentrations up to 190 mg/L, probably due to a synergistic effect resulting from the combination of both congeners. Using transmission electron microscopy, it was demonstrated that RLs damaged the cell wall and the cytoplasmic membrane of the fungus, leading to the loss of intracellular content. This disruptive phenomenon explains the growth inhibition observed. Furthermore, RLs down-regulated the expression of genes aflC, aflE, aflP and aflQ involved in the aflatoxins biosynthetic pathway (6.4, 44.3, 38.1 and 2.0-fold, respectively), which is in agreement with the almost complete inhibition of aflatoxins production. Overall, the results herein gathered demonstrate for the first time that RLs could be used against aflatoxigenic fungi to attenuate the production of aflatoxins, and unraveled some of their mechanisms of action.

Efficacy of Ocimum tenuiflorum essential oil as grain protectant against coleopteran beetle, infesting stored pulses

In the present investigation, essential oil (EO) of Ocimum tenuiflorum and its principal constituent (eugenol) was evaluated for its toxicity and mode of action against Callosobruchus maculatus. Furthermore, fumigant toxicity and germination studies on the application of O. tenuiflorum EO and eugenol against C. maculatus on different pulses was also studied. Fumigant activity studies revealed that EO toxicity was significantly (p < 0.05) influenced by concentration and exposure time. In fumigant toxicity assay without food, O. tenuiflorum EO and eugenol showed LC50 value of 278.6 and 256.5 µL/L air, respectively, at one hour exposure. Further, O. tenuiflorum EO displayed fumigant toxicity via inhibiting acetylcholinesterase activity. Pulses treated with O. tenuiflorum EO showed 70% of C. maculatus mortality at 250 µL/L air concentration after 24 h. Furthermore, these treatments didn't affect the seed viability of the pulses tested. Hence, the application of O. tenuiflorum EO has potential scope as a botanical insecticide.

Comparing the efficacy of nutmeg essential oil and a chemical pesticide against Musca domestica and Chrysomya albiceps for selecting a new insecticide agent against synantropic vectors

The insecticidal activity of Myristica fragrans (Houtt) essential seed oil, (Nutmeg) was evaluated against Musca domestica (Linnaeus) and Chrysomya albiceps (Wiedemann); both important infectious pathogenic disease vectors. The oil was extracted by distillation, and 21 components were identified during chemical analysis; principally β-pinene (26%), α-pinene (10.5%), Sabinene (9.1%) and γ-terpinen (8.5%). Insecticidal properties were identified through larvicide and adulticide tests. Using the immersion method, the oil at 5% was found to be very effective (90 ± 1%) against M. domestica larvae. The results for adulticide activity varied by fly species, dosage, time, and method of exposure. Topical application (on the insect thorax) was more toxic to C. albiceps, where the lethal concentration at 50% (LC₅₀) was 2.02 ± 0.56, and 8.57 ± 2.41 for the common flies. When the insects were exposed to oil impregnated paper, the results were similar for M. domestica and C. albiceps adults with respective LC₅₀ values of 2.74 ± 0.24, and 3.65 ± 0.48. Thus, the results demonstrated that M. fragrans oil presents insecticidal activity and can be used for control of Musca domestica and Chrysomya albiceps.

Karanjin

Karanjin [IUPAC: 3-methoxy-2-phenylfuro-(2,3-h-chrome-4-ol)], a bioactive furanoflavonoid and a potent biomolecule, was first isolated from Pongamia pinnata (L.). The crude extracts from root, leaf and seed having active constituent karanjin is highly valued in both traditional and modern knowledge systems. This review highlights, critically assesses, and presents the probable biosynthetic pathways of karanjin and its isolation methodologies with a view to actualizing its full potential. Karanjin exhibits multiple health benefits and applications, with evident anti-diabetic, anti-cancer, anti-inflammatory, anti-hyperglycemic, antioxidant, anti-colitis, anti-ulcer, and anti-Alzheimer properties. Consequently, the physiochemical properties and biological effects of karanjin have been detailed and analyzed. The efficacy of karanjin has been attenuated by toxicological studies that have proven karanjin to be non-toxic at physiological conditions as substantiated by in vitro and in vivo studies. In addition, the multiple insect repellent/insecticidal properties of karanjin and its availability as an acaricide/bio-insecticide have been reviewed. This review article underscores and endorses the immense potential for novel drug leads in various medicinal and industrial applications, suggesting a deeper insight into its metabolic fate, bioavailability, and cellular effects that await further investigations.

Multifaceted interactions between the pseudomonads and insects: mechanisms and prospects

Insects and bacteria are the most widespread groups of organisms found in nearly all habitats on earth, establishing diverse interactions that encompass the entire range of possible symbiotic associations from strict parasitism to obligate mutualism. The complexity of their interactions is instrumental in shaping the roles of insects in the environment, meanwhile ensuring the survival and persistence of the associated bacteria. This review aims to provide detailed insight on the multifaceted symbiosis between one of the most versatile bacterial genera, Pseudomonas (Gammaproteobacteria: Pseudomonadaceae) and a diverse group of insect species. The Pseudomonas engages with varied interactions with insects, being either a pathogen or beneficial endosymbiont, as well as using insects as vectors. In addition, this review also provides updates on existing and potential applications of Pseudomonas and their numerous insecticidal metabolites as biocontrol agents against pest insects for the improvement of integrated pest management strategies. Here, we have summarized several known modes of action and the virulence factors of entomopathogenic Pseudomonas strains essential for their pathogenicity against insects. Meanwhile, the beneficial interactions between pseudomonads and insects are currently limited to a few known insect taxa, despite numerous studies reporting identification of pseudomonads in the guts and haemocoel of various insect species. The vector-symbiont association between pseudomonads and insects can be diverse from strict phoresy to a role switch from commensalism to parasitism following a dose-dependent response. Overall, the pseudomonads appeared to have evolved independently to be either exclusively pathogenic or beneficial towards insects.

Differential insecticidal properties of Spodoptera frugiperda multiple nucleopolyhedrovirus isolates against corn-strain and rice-strain fall armyworm, and genomic analysis of three isolates

The fall armyworm, Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae) is a destructive crop pest native to North, Central, and South America that recently has spread to Africa and Asia. Isolates of Spodoptera frugiperda multiple nucleopolyhedrovirus (SfMNPV) have the potential to be developed as low-risk biopesticides for management of fall armyworm, and a commercially available formulation has been developed for control of fall armyworm in North and South America. In this study, the virulence (LC₅₀ and LT₅₀) of several SfMNPV isolates towards larvae of both corn-strain and rice-strain fall armyworm was assessed. Bioassays with corn-strain larvae revealed that the isolates could be organized into fast-killing (LT₅₀ < 56 h post-infection) and slow-killing (LT₅₀ > 68 h post-infection) groups. Rice-strain larvae exhibited narrower ranges of susceptibility to baculovirus infection and of survival times in bioassays with different isolates. Two SfMNPV isolates with rapid speeds of kill (SfMNPV-459 from Colombia and SfMNPV-1197 from Georgia, USA) along with an isolate that killed corn-strain at relatively low concentrations (SfMNPV-281 from Georgia) were selected for the complete determination of their genome sequences. The SfMNPV-1197 genome sequence shared high sequence identity with genomes of a Nicaraguan isolate, while SfMNPV-281 formed a separate clade with a USA and a Brazilian isolate in phylogenetic trees. The SfMNPV-459 sequence was more divergent with the lowest genome sequence identities in pairwise alignments with other sequenced SfMNPV genomes, and was not grouped reliably with either the 1197 clade or the 281 clade. SfMNPV-459 contained homologs of two ORFs that were unique to another Colombian isolate, but these isolates were not placed in the same clade in phylogenetic trees. This study identifies isolates with superior properties for control of fall armyworm and adds to our knowledge of the genetics of SfMNPV.

On-Farm Trials Reveal Significant but Uncertain Control of Botrytis cinerea by Aureobasidium pullulans and Potassium Bicarbonate in Organic Grapevines

Botrytis cinerea, a fungal pathogen that causes gray mold on grapes, can decrease yield, substantially reduce wine quality, and therefore cause significant economic losses. In a context of increasing awareness of environmental and human health, biopesticides are a potential alternative to synthetic chemical treatments to produce grapes and wine in compliance with high food standards. However, the effectiveness of biopesticides is not well known and more research is needed to help winegrowers assess their ability to control wine diseases. Our study aims to assess the efficacy of two commercial biopesticides, based on potassium bicarbonate and Aureobasidium pullulans, in reducing the incidence of gray mold (i.e., the proportion of grape bunches that are diseased). We use data from an on-farm trial network managed over 3 years (from 2014 to 2016) in a major wine producing region located in Southwestern France, and fit Bayesian generalized linear multilevel models able to take the variability of treatment effect across trials into account. The fitted models were then used to estimate the efficacy on incidence as a function of the severity (i.e., the proportion of diseased grape berries in a bunch) in an untreated plot in order to determine if the effectiveness of the treatments depends on the disease pressure. At average disease severity (i.e., 3%), the efficacy on disease incidence at the network level was equal to 20% [95% CI = (-0.1; 37.3)] and 13% [95% CI = (0.2; 24.7)] for potassium bicarbonate and A. pullulans, respectively. For both biopesticides, the efficacy on incidence for a new site-year is highly uncertain, but potassium bicarbonate had a lower uncertainty and a lower application cost compared to A. pullulans. Our results confirm that potassium bicarbonate is an interesting biopesticide under farming conditions in organic vineyards in southwestern France, but the amount of uncertainty points to the need for further research.

Evaluation of spray applications of Metarhizium anisopliae, Metarhizium brunneum and Beauveria bassiana against larval winter ticks, Dermacentor albipictus

Dermacentor albipictus (Acari: Ixodidae), the winter tick, is a one-host tick that parasitizes large ungulates. They can dramatically affect moose, Alces alces (Artiodactyla: Cervidae), causing significant physiological and metabolic stress and mortality among heavily parasitized individuals. Entomopathogenic fungi in the genera Metarhizium (Hypocreales: Clavicipitaceae) and Beauveria (Hypocreales: Cordycipitaceae) are promising tick biological control agents. We examined the pathogenicity of experimental and commercially formulated isolates of M. anisopliae, M. brunneum and B. bassiana sprayed at concentrations of 10⁶, 10⁷ and 10⁸ conidia/mL against the larval stage of D. albipictus and assessed the efficacy of spraying the commercial product Met52®EC, containing M. brunneum, strain F52, under laboratory conditions. Results showed larval D. albipictus mortality was significantly higher and occurred earlier when treated with M. anisopliae and M. brunneum isolates compared to B. bassiana at 10⁶, 10⁷ and 10⁸ conidia/mL. Mortality was observed as early as 3 days in the M. anisopliae and M. brunneum treatments and after 6 days in the B. bassiana treatments. After 21 days, larval mortality ranged from 74-99% when ticks were treated with M. anisopliae and M. brunneum isolates at 10⁶, 10⁷ and 10⁸ and conidia/mL. In contrast, mortality of ticks treated with B. bassiana ranged from 30 to 64%. When larvae were treated with the commercial product Met52, mortality was ~ 45% after 3 days and ~ 96% after 9 days. These results demonstrate the effectiveness of M. anisopliae and M. brunneum against D. albipictus.

Inhibitory mechanism of 6-Pentyl-2H-pyran-2-one secreted by Trichoderma atroviride T2 against Cylindrocarpon destructans

Root rot caused by Cylindrocarpon destructans is one of the most devastating diseases of Panax notoginseng, and Trichoderma species are potential agents for the biocontrol of fungal diseases. Thus, we screened a total of 10 Trichoderma isolates against C. destructans and selected Trichoderma atroviride T2 as an antagonistic strain for further research. 6-Pentyl-2H-pyran-2-one (6PP) was identified as an important active metabolite in the fermentation broth of the strain and exhibited antifungal activity against C. destructans. Transcriptome and metabolome analyses showed that 6PP significantly disturbed the metabolic homeostasis of C. destructans, particularly the metabolism of amino acids. By constructing a gene coexpression network, ECHS1 was identified as the hub gene correlated with 6PP stress. 6PP significantly downregulated the expression of ECHS1 at the transcriptional level and combined with the ECHS1 protein. Autophagy occurred in C. destructans cells under 6PP stress. In conclusion, 6PP may induce autophagy in C. destructans by downregulating ECHS1 at the transcriptional level and inhibiting ECHS1 protein activity. 6PP is a potential candidate for the development of new fungicides against C. destructans.

Combining insect pathogenic fungi and a pheromone trap for sustainable management of the fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae)

Fall armyworm, Spodoptera frugiperda (Lepidoptera: Noctuidae), is a key invasive pest of maize and other crops in Africa. Entomopathogenic fungi play an important role in regulating the immature stages of this invasive pest as opposed to synthetic pesticides that are hazardous to human, environment and biodiversity. To tackle the adult stage of the pest (the moth) and to improve on the application strategy of the fungal-based biopesticides, this study evaluated the effect of various entomopathogenic fungi isolates on S. frugiperda moths. Twenty-two isolates (16 Metarhizium anisopliae and 6 Beauveria bassiana) were screened in the laboratory to assess their pathogenicity and virulence against S. frugiperda moths. The compatibility of the most pathogenic isolates with S. frugiperda pheromone FALLTRACT lure, the horizontal transmission of the inoculum among S. frugiperda moths, and the effect on oviposition were also determined under laboratory conditions. All 22 fungal isolates screened were pathogenic to the moths, but the mortality varied significantly among the isolates (P < 0.0001) seven days post-treatment. Beauveria bassiana ICIPE 621 and M. anisopliae ICIPE 7 outperformed all the other isolates by causing 100% mortality of the moths with the lowest LT₅₀ values of 3.6 ± 0.1 and 3.9 ± 0.0 days, respectively. Both isolates were also found compatible with FALLTRACT lure, as the lure had no effect on the conidial germination in the laboratory. Male and female moths were able to horizontally transmit conidia of both fungal isolates to untreated moths, causing high mortality of S. frugiperda in 'donor' and 'recipient' groups. In addition, the oviposition, hatchability of eggs and longevity of larvae were significantly affected on the fungal infected females. Although single moths still retained high conidial numbers 72 h post-inoculation, the number of conidia decreased with time. These results suggest that ICIPE 7 and ICIPE 621 could be used in combination with S. frugiperda pheromone in an autodissemination approach to suppress S. frugiperda population.

Recovery and resiliency of skin microbial communities on the southern leopard frog (Lithobates sphenocephalus) following two biotic disturbances

BACKGROUND

Microorganisms have intimate functional relationships with invertebrate and vertebrate taxa, with the potential to drastically impact health outcomes. Perturbations that affect microbial communities residing on animals can lead to dysbiosis, a change in the functional relationship, often associated with disease. Batrachochytrium dendrobatidis (Bd), a fungal pathogen of amphibians, has been responsible for catastrophic amphibian population declines around the globe. Amphibians harbor a diverse cutaneous microbiome, including some members which are known to be antagonistic to Bd (anti-Bd). Anti-Bd microorganisms facilitate the ability of some frog populations to persist in the presence of Bd, where other populations that lack anti-Bd microorganisms have declined. Research suggests disease-antagonistic properties of the microbiome may be a function of microbial community interactions, rather than individual bacterial species. Conservation efforts have identified amphibian-associated bacteria that exhibit anti-fungal properties for use as 'probiotics' on susceptible amphibian populations. Probiotic application, usually with a single bacterial species, may benefit from a greater understanding of amphibian species-specific microbiome responses to disturbances (e.g. dysbiosis vs. recovery). We assessed microbiome responses to two microbial disturbance events over multiple time points.

RESULTS

Exposing Lithobates sphenocephalus (southern leopard frog) adults to the biopesticidal bacteria Bacillus thuringiensis, followed by exposure to the fungal pathogen Bd, did not have long term impacts on the microbiome. After initial shifts, microbial communities recovered and returned to a state that resembled pre-disturbance.

CONCLUSIONS

Our results indicate microbial communities on L. sphenocephalus are robust and resistant to permanent shifts from some disturbances. This resiliency of microbial communities may explain why L. sphenocephalus is not experiencing the population declines from Bd that impacts many other species. Conservation efforts may benefit from studies outlining amphibian species-specific microbiome responses to disturbances (e.g. dysbiosis vs. recovery). If microbial communities on a threatened amphibian species are unlikely to recover following a disturbance, additional measures may be implemented to ameliorate the impacts of physical and chemical stressors on host-associated microbial communities.

Side effects of chlorantraniliprole, phosalone and spinosad on the egg parasitoid, Trichogramma brassicae

The combined use of chemicals and biological control is not always a successful strategy owing to the potential side effects on biocontrol agents. Lethal and sublethal effects of three commonly used insecticides were assessed on adult and immature stages of the egg parasitoid Trichogramma brassicae Bezdenko (Hymenoptera: Trichogrammatidae). Recommended field concentrations of chlorantraniliprole, phosalone and spinosad caused mortality on preimaginal stages by 24, 87, and 98%, respectively. Lethal effects on parasitoid adults exposed to the insecticide dry residues were estimated as median lethal concentrations (LC₅₀) that were 13.28, 0.25, and 0.03 µg a.i. ml^-1 for chlorantraniliprole, phosalone, and spinosad, respectively. The effect of a low lethal concentration (LC₃₀) of the compounds was evaluated on various adult biological traits, such as longevity, fecundity, emergence rate and other life table parameters. All compounds caused detrimental effects on all the estimated demographical indexes. Chlorantraniliprole affected the net reproductive rate, mean generation time and doubling time in comparison to the control; while, phosalone and spinosad adversely affected all assessed parameters. Phosalone and spinosad significantly reduced gross reproductive rate, net reproductive rate, intrinsic rate of increase, finite rate of increase, mean generation time and doubling time and reduced longevity, fecundity, emergence rate related to other biological parameters in comparison with control. The results suggest that all compounds are not fully compatible with the activity of T. brassicae, and that the inclusion of chlorantraniprole, spinosad and phosalone into Integrated Pest Management (IPM) involving this parasitoid has to be avoided. Nevertheless, further studies in open field conditions and on a multiple generation scale are necessary for providing a more definitive conclusion on the IPM suitability of the three tested insectcides.

Combined thermal and insecticidal stresses on the generalist predator Macrolophus pygmaeus

Ecotoxicological risk assessments of pesticides on non-target arthropods are often carried out under constant and optimal temperature regimes. However, living organisms rarely experience these conditions in real field situations. Understanding the impact of pesticides on non-target beneficial arthropods under temperature stresses is especially important in terms of global warming. We assessed the lethal and sublethal effects of four modern insecticides (chlorantraniliprole, cyantraniliprole, spinetoram, spinosad), on the generalist predator Macrolophus pygmaeus (Hemiptera: Miridae) under a range of temperatures (from 10 to 40°C) frequently experienced in a real field scenario. A reduction coefficient (E_x) was calculated by summarizing the mortality and predator reproductive capacity and, the chemicals were classified according to the International Organization for Biological Control (IOBC) toxicity classes. The insecticides showed a marked synergistic effect with temperature, as the predator mortality and reproductive outputs were significantly correlated with increasing temperatures. Spinosyns interacted significantly with temperature causing the highest mortality and lowest fertility rates. Anthranilic diamides showed a safer ecotoxicological profile compared to spinosyns, with cyantraniliprole being more harmful than chlorantraniliprole. These results suggest that temperature should be taken into account in pesticide ecotoxicology studies within the framework of integrated pest management and the recent climate changes.

Bacillus thuringiensis endotoxin production: a systematic review of the past 10 years

Bacillus thuringiensis (Bt) is one of the most promising biological control agents used commercially. Its products can contribute to reducing ecological and environmental problems associated with the use of chemical pesticides. Among the limiting factors of using Bt as bioinsecticide are the costs and ensuring its biological activity, which may vary according to the strain and culture conditions. This systematic review aimed to collect state-of-the-art information on the production of Bt endotoxins and to score the methodological feasibility of the data obtained, thus highlighting possible incoherencies. In order to consolidate recent findings and guide future studies, a total of 47 original articles from the last 10 years was analysed, with special attention being given to corroborating data, identifying inconsistencies and suggesting future adjustments so as to increase data reliability. With a maximum score of 8 points, three production parameters were classified on the following scale: preferable (score: 2), adequate (score: 1) and inadequate (score: 0), and another two parameter were classified as adequate (score: 1) or inadequate (score: 0). No article scored more than 6 out of the maximum of 8, thus reflecting the need for more detailed studies regarding Bt endotoxin production. The lack of standardization of methods and units of measurement also have made a comparison of results and an overall analysis difficult. Standards are suggested in the present study. The inclusion of bioassays and quantifying toxin via alkaline dilution are strongly recommended for studies of this nature, along with LC50 expressed in mg/L. Sixteen articles (34%) did not use either of these suggested methods, which indicates the need for further supporting studies. These findings reinforce the need for robust studies in this area, which could include the development of more affordable and effective bioinsecticides, thus increasing their competitiveness against insecticides derived from unsustainable sources.

Nematicidal Efficacy of Milbemectin against Root-Knot Nematodes

The nematicidal efficacy of milbemectin and its commercial formulate Milbeknock^® on (i) egg hatching, (ii) juvenile motility and (iii) infective capacity of root-knot nematodes was evaluated in vitro and in planta assays. Serial dilutions of pure milbemectin were tested against nematode eggs and juveniles and lethal concentrations LC50 and LC90 calculated. Exposure of egg masses to milbemectin at a concentration of 30 μg/mL for 72 h reduced egg hatching by 52%. The increase in exposure time to 240 h did not increase the egg hatching inhibition at the highest concentration 30 μg/mL (53%) but reduced egg hatching at 15 and 7 μg/mL by 35 and 24%, respectively, when compared to untreated controls. The inhibitory effect of milbemectin on juvenile motility ranged from 41 to 87% depending on its concentration, and this effect was persistent after rinsing the juveniles in water. The probabilistic dose–response model indicated that lethal concentrations of milbemectin for juvenile motility were LC50: 7.4 μg/mL and LC90: 29.9 μg/mL. The pre-plant application of Milbeknock^® to soils infested with the nematode reduced its infective capacity by 98–99% compared to untreated soils in pot experiments. Milbeknock^® reduced nematode soil population densities by 50–60% in natural infestations under field conditions. Milbemectin shows a high level of efficacy against root-knot nematodes as it reduces egg hatching, persistently immobilizes nematode juveniles, and reduces tomato root infection.

Synergistic effect of aromatic plant essential oils on the ant Acromyrmex balzani (Hymenoptera: Formicidae) and antifungal activity on its symbiotic fungus Leucoagaricus gongylophorus (Agaricales: Agaricaceae)

Leaf-cutting ants have great potential for damage to agricultural and forest crops. Although chemical control is the most used method for the management of this pest, more friendly alternative methods have been investigated. Thus, this study aimed to evaluate the insecticidal and antifungal potential of essential oils obtained from Aristolochia trilobata, as well as the potential of two chemotypes of Myrcia lundiana and their major compounds (isopulegol and citral) on Acromyrmex balzani and its symbiotic fungus Leucoagaricus gongylophorus. Toxicity and synergism and/or antagonism tests were performed using essential oils and their major compounds on A. balzani ants. The antifungal activity of these compounds was tested on the fungus L. gongylophorus. The essential oils and their major compounds were toxic to A. balzani. The mixture of essential oils of A. trilobata with those of M. lundiana had higher toxicity to the ants. This synergistic effect is mainly due to the interactions between the citral compound and the major compounds present in A. trilobata essential oil. The essential oils of M. lundiana chemotypes showed antifungal properties against L. gongylophorus, and the citral compound proved to have fungicidal activity. These results show that the use of M. lundiana and A. trilobata essential oils and their major compounds is a potential alternative for the management of leaf-cutting ants A. balzani, as they have a toxic effect on worker ants and antifungal activity on their symbiotic fungus.

Adding value to home compost: Biopesticide properties through Bacillus thuringiensis inoculation

Home and community composting are considered potential tools for the self-management of organic waste. The production of added value products from biowaste is an encouraging step further to valorise this waste stream. To increase the profits of homemade compost, this paper presents a strategy to produce enriched home compost with biopesticide properties through a simple and low-cost process. Bacillus thuringiensis (Bt) was inoculated in a home composter bin through a solid inoculum previously prepared using the same waste as substrate. The process was monitored and compared with a home composting control process without inoculation. Final composts were analysed and compared in terms of physicochemical and microbiological properties, respiration and germination indices, indicating the suitability of both to be used as organic amendments. Also, a standardized toxicity test proved that Bt-enriched compost can be safely applied to the soil. Microbiological analysis revealed highly diverse communities in both cases, with limited differences at phylum taxonomic level, but dissimilar relative abundances of species within phylum. Bacteroidetes and Proteobacteria were dominant, with the presence of species able to transform organic matter from vegetal origin, but not usually related to compost. Bt-cristal toxin was clearly present in Bt-enriched compost, indicating the coexistence of Bt with the different microbial populations till the end of the composting process. Although Bt has been widely investigated due to its biopesticide properties, the incorporation of this microorganism to home composting level has not been previously reported.

Ecologically controlling insect and mite pests of tea plants with microbial pesticides: a review

Insect and mite pests are damaging stressors that are threatening the cultivation of tea plants, which result in enormous crop loss. Over the years, the effectiveness of synthetic pesticides has allowed for its prominent application as a control strategy. However, the adverse effects of synthetic pesticides in terms of pesticide residue, environmental contamination and insect pest resistance have necessitated the need for alternative strategies. Meanwhile, microbial pesticides have been applied to tackle the damaging activities of the insect and mite pests of tea plants, and their performances were scientifically adjudged appreciable and environmental friendly. Herein, entomopathogenic microbes that were effective against tea geometrid (Ectropis obliqua Prout), tea green leafhopper (Empoasca onukii Matsuda), paraguay tea ampul (Gyropsylla spegazziniana), tea mosquito bug (Helopeltis theivora Waterhouse) and red spider mite (Oligonychus coffea Nietner) have been reviewed. The current findings revealed that microbial pesticides were effective and showed promising performances against these pests. Overall, this review has provided the basic and integrative information on the integrated pest management (IPM) tool(s) that can be utilized towards successful control of the aforementioned insect and mite pests.

Members of the nitronate monooxygenase gene family from Metarhizium brunneum are induced during the process of infection to Plutella xylostella

Metarhizium species are the most abundant fungi that can be isolated from soil, with a well-known biopesticide capacity. Metarhizium recognizes their hosts when the conidium interacts with insects, where the fungi are in contact with the hydrocarbons of the outermost lipid layer cuticle. These cuticular hydrocarbons comprise a mixture of n-alkanes, n-alkenes, and methyl-branched chains. Metarhizium can degrade insect hydrocarbons and use these hydrocarbons for energy production and the biosynthesis of cellular components. The metabolism of nitroalkanes involves nitronate monooxygenase activity. In this work, we isolated a family of six genes with potential nitronate monooxygenase activity from Metarhizium brunneum. The six genes were expressed in Escherichia coli, and the nitronate monooxygenase activity was verified in the recombinant proteins. Additionally, when the conidia of M. brunneum were grown in medium with nitroalkanes, virulence against Plutella xylostella increased. Furthermore, we analyzed the expression of the six Npd genes during the infection to this insect, which showed differential expression of the six Npd genes during infection.

Biological control of tomato bacterial wilt by oxydifficidin and difficidin-producing Bacillus methylotrophicus DR-08

Bacillus methylotrophicus DR-08 exhibited strong antibacterial activity against Ralstonia solanacearum, a causal agent of tomato bacterial wilt. This study aimed to identify the antibacterial metabolites and evaluate the efficacy of the strain as a biocontrol agent for tomato bacterial wilt. A butanol extract of the DR-08 broth culture completely inhibited the growth of 14 phytopathogenic bacteria with minimum inhibitory concentration (MIC) values of 1.95-500 μg/mL. R. solanacearum was highly sensitive to the DR-08 extract, with an MIC value of 12.62 μg/mL. Two antibacterial metabolites were isolated and identified as difficidin and oxydifficidin derivatives through bioassay-guided fractionation and instrumental analyses. Both metabolite derivatives inhibited the growth of most of the phytopathogenic bacteria tested and the oxydifficidin derivatives generally presented a stronger antibacterial activity than the difficidin derivatives. A 30% suspension concentrate of DR-08, at a 500-fold dilution, effectively suppressed the development of tomato bacterial wilt in pot and field experiments. It also effectively reduced the development of bacterial leaf spot symptoms on peach and red pepper. The results of this study suggests that B. methylotrophicus DR-08 can be utilized as a biocontrol agent for various bacterial plant diseases including tomato bacterial wilt.

Antifungal activity of endophytic Bacillus safensis B21 and its potential application as a biopesticide to control rice blast

Endophytic bacteria are potential biocontrol agents for the control of fungal diseases. Here, an endophyte strain, B21, was isolated from Osmanthus fragrans Lour. fruits and identified as Bacillus safensis by analysis of its 16S rDNA gene sequence and its biochemical and physiological characteristics. The culture filtrate showed antifungal activity against Magnaporthe oryzae, which causes rice blast disease, and the IC₅₀ of the methanol extract was 15.56 μg/mL, which was significantly lower than that of carbendazim (25.16 μg/mL). The antifungal activity of the methanol extract was stable at a wide range of pH values (1-9) and temperatures (40-100 °C). Two antifungal compounds were isolated by organic extraction, silica gel column chromatography and high-performance liquid chromatography (HPLC). Based on electrospray ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance spectrometry (NMR) analyses, the structures of the antifungal compounds were identified as iturin A2 and iturin A6. Additionally, the hyphae treated with iturin (iturin A2 or iturin A6) could be stained with the fluorescent dye propidium iodide (PI), indicating that these two compounds inhibited the growth of hyphae by changing the hyphal membrane permeability. In field experiments, spray treatment with fermentation broth resulted in a lower disease index than treatment with carbendazim, as did the culture filtrate. The results suggest that strain B21 and its bioactive compounds have the potential to be developed into a biopesticide for the biocontrol of rice blast.

A Bacillus thuringiensis kurstaki Biopesticide Does Not Reduce Hatching Success or Tadpole Survival at Environmentally Relevant Concentrations in Southern Leopard Frogs (Lithobates sphenocephalus)

Amphibians are in global decline, and anthropogenic activities are known leading causes of their demise. Thus the interaction between agriculture and amphibian health has been examined for decades. Many facets of amphibian physiology and ecology place them at high risk among the nontarget organisms affected by agricultural byproducts. Research has shown that many chemicals and fertilizers affect amphibian growth, reproduction, and survival. The impacts differ based on the type of agricultural byproduct (e.g., chemical pesticide or nutrient-heavy fertilizer) and amphibian species, but the effects are usually negative. However, minimal research exists on how organic biopesticides interact with amphibian populations. Biopesticides utilize insecticidal bacteria as the active ingredient in lieu of synthetic chemicals. The inert ingredients present in biopesticide commercial products are considered safe to nontarget organisms. The present study tested the impacts of a commercial biopesticide on the survival of amphibian embryos and larvae. We found that expected environmental concentrations of the microbial biopesticide Monterrey B.t. did not significantly reduce survival in embryos or larvae. However, the higher doses used to assess threshold toxicity levels caused significant mortality. Our data suggest that biopesticides are not directly harmful to amphibian embryos or larvae in concentrations regularly applied for pest control. Environ Toxicol Chem 2019;39:155-161. © 2019 SETAC.

Outstanding insecticidal activity and sublethal effects of Carlina acaulis root essential oil on the housefly, Musca domestica, with insights on its toxicity on human cells

Carlina acaulis (Compositae) is traditionally used for food and medicinal purposes in central and southern Europe. Its root essential oil (EO), mainly composed by carlina oxide, is included in the BELFRIT botanical list of food supplements. It is also recognized as a potent mosquito larvicide. It is matter of concern whether this EO could be endowed with intrinsic toxicity to limit its use on a food level. Focusing on the insecticidal activity of this EO, we investigated the acute toxicity and sublethal effects on Musca domestica. In topical assays, the EO was extremely effective (LD₅₀ = 2.74 and 5.96 μg fly^-1, on males and females, respectively). The exposure to a sublethal dose (LD₃₀) led to significant reductions of female longevity (LT₅₀ = 6.7-9.0 days vs. control LT₅₀ = 12.9-13.7 days). Treated females laid 2.5 times fewer eggs over control ones. F₁ vitality decreased: F₁ larvae and pupae showed high mortality, 2-4-fold higher over the control. The EO also showed high cytotoxicity on normal human fibroblasts (NHF-A12, IC₅₀ = 9.4-14.2 μg mL^-1 after 6-48 h). Overall, our findings support the employ of this EO for developing botanical insecticides. At the same time, they encourage food safety authorities to perform a full toxicological assessment for possible restrictions at food level.

Production of Bacillus thuringiensis based biopesticide formulation using starch industry wastewater (SIW) as substrate: A techno-economic evaluation

In this study, cost simulation was made to produce Bacillus thuriengiensis based biopesticide formulation using starch industry wastewater (SIW) as substrate. The results obtained at pilot plant (2000L capacity fermenter) were used for cost simulation of the process. The unit production cost for annual production of 5 million L of formulated biopesticide (20.2 Billion International Units (BIU)/L) was estimated to be $ 2.54/L, which is competitive to chemical pesticides. The techno-economic evaluation revealed that the profitability of the biopesticide manufacturing process was sensitive to the plant capacity and selling price of the biopesticide. The manufacturer should target 5 million L annual plant capacity and selling price of $ 15/L for payback period to be less than 5 years. The process serves many advantages (1) alternate disposal or bio-valorisation of industry wastewater and (2) use of industry wastewater as inexpensive carbon source reducing cost of raw materials for fermentation.

The comet assay in Ceraeochrysa claveri (Neuroptera: Chrysopidae): A suitable approach for detecting somatic and germ cell genotoxicity induced by agrochemicals

Some agrochemicals are genotoxic to several organisms. Nevertheless, few protocols are currently available for measuring the toxicogenetic effects of these compounds in target and non-target field-collected species of insects important to agriculture. Herein, we used the species Ceraeochrysa claveri (Neuroptera: Chrysopidae), a non-target predator insect, to investigate the ability of an azadirachtin-based biopesticide (Azamax™) to induce DNA damage. The alkaline version of the comet assay was standardized to evaluate genetic instability caused by the toxicant in somatic (gut) and germ (nurse cells and oocytes) cells of C. claveri. For this, C. claveri larvae were distributed into three groups (10/each) and treated with Azamax™ at 0, 0.3% or 0.5% throughout the larval stage. DNA damage (tail intensity) was measured in adult insects, four days after emerged. The data showed that both doses of Azamax™ (0.3% and 0.5%) were able to significantly (p < 0.05) increase DNA damage in somatic and germ cells of C. claveri. In conclusion, C. claveri (intestinal and ovarian cells) was a sensitive bioindicator for identifying Azamax™ genotoxic potential, whereas the comet assay was a useful tool for detecting the genotoxic hazard of the pesticide in the field-collected insect species. Given that estimation of adverse effects of pollutants on ecosystems is an essential component of environmental risk assessment, the approach used can be recommended to estimate the ecotoxicity of agricultural chemicals.