Good Biocontrol Agent Research Articles

Ladybird predators in natural and agricultural landscapes in Mexico: diversity and parasitism

Ladybirds (Coleoptera: Coccinellidae) are a significant predator group that plays a role in agricultural contexts. They serve as important biocontrol agents against several agricultural pests. However, there is limited information available about how ladybirds’ populations are regulated by their natural enemies and habitat perturbation. In this study, we evaluated ladybird communities associated with natural and managed areas during the agricultural cycle of 2018 (June–September). We identified seven ladybird species; the most abundant species were Hippodamia convergens (70% individuals) and Cycloneda sanguinea (20% individuals), followed by the exotic species Harmonia axyridis (3.33% individuals), while Paranaemia vittigera, Coleomegilla maculata, Brachiacantha sp., and Olla v-nigrum represented less than 3% each. Ladybirds were more abundant in agricultural fields than in natural habitats. We identified several natural enemies associated with the collected ladybirds, including parasitoids (Dinocampus coccinellae, Hymenoptera: Braconidae), ectoparasitic Acari (Coccipolipus sp., Podapolipidae), and nematodes (Mermithidae). However, none of the natural enemies affected more than 10% of the ladybirds, so natural enemies do not appear to be exerting substantial control over their populations. Our results corroborated that ladybirds can efficiently thrive in anthropogenic habitats in Mexico and therefore may represent good biocontrol agents for agriculture. It is important to consider the ecology of agriculturally important ladybirds in programs for integrated pest management. This includes factors contributing to the mortality of ladybirds, including their natural enemies.

Diversity of Wasp (Hymenoptera) in Obafemi Awolowo University, Ile-Ife, Osun State, Nigeria

The inventory of wasp species and distribution within Obafemi Awolowo University (O. A. U.), Ile-Ife campus was investigated with the view of updating the checklist of the insect species found in the habitats. The research was carried out between the month of May 2021 and April 2022. Wasp’s species were collected from six selected habitats on the campus using active/direct method of collection which involves the use of sweep net and indirect/passive method of setting of traps with baits. The collected wasp specimens were pinned, dried in an automated oven at the Museum of Natural History, O. A. U., Ile-Ife then stored in insect boxes containing naphthalene flakes (camphor). Identification was made using identification keys for Afrotropical Hymenoptera. Data collected were analyzed using descriptive (tables) and inferential statistics. Paleontological Statistics (PAST) (version 16) was used for analysis of wasps Diversity Indices with level of significant (p=0.05). Twenty eight species of wasps were collected which belongs to six Families from the selected habitats, comprising of Families Crabronidae, Evaniidae, Ichneumonidae, Pompilidae, Sphecidae, Vespidae. Opa Reservoir habitats have the most diverse of the species with eleven (11) species (Shannon index of 1.464) while the hills have the least (1) (Shannon index of 0). The Family Vespidae has the highest numbers of genera (13) while the genus Belonogaster has the highest numbers of species (3). There are many more wasp species yet to be discovered in Nigeria as some wasp species are predatory in nature; some are pollinator of flowers, some do lay their eggs in the nest of other wasps, while most of the solitary wasps are parasitic in nature and feed on almost every pest, an attribute qualifying them as good bio-control agents (O’Neill and Kevin. 2001).

Arthospira platensis and Bacillus subtilis Synergies for Sustainable Agriculture

The aim of this study is to analyze the biofertilizer value of B. subtilis by estimating its phosphate solubilizing potential and its antagonistic activity against pathogenic strains of E. coli and Bacillus cereus. Prolonged use of chemical fertilizers have adverse effects on the soil and through food chain they cause hazards to organisms including humans. Moreover pests and pathogenic microbes are becoming immune to the chemical pesticides and herbicides. Hence the need of biofertilizers that are ecofriendly and good biocontrol agents are gaining importance. Use of biofertilizers leads us towards the path of sustainable agriculture yielding better productivity without compromising the fertility of agricultural fields. Bacillus subtilis is a PGPR (Plant growth promoting rhizobacteria) capable of phosphate and zinc solubilizing and it increases the bioavailability of nutrients to the plants. Due to its antagonistic nature, B. subtilis can be utilized in biocontrol management practices. Arthospira platensis is a well explored microalgal species that is rich in micronutrients and a wide array of amino acids that has immense biofertilizer value. The methodology involves UV spectrometric estimation of bioavailable phosphate in Pikovskaya’s broth at 690nm and percentage of inhibition of B. subtilis against E. coli and Bacillus cereus using OD600values. Evidences for utilizing mixed culture of A. platensis and B. subtilis as biofertilizer are explored from literature. B. subtilis strain AMLA5 isolated from oil contaminated soil from Coimbatore had phosphate solubilizing potential of 1.3ppm and showed good antagonistic effects against E. coli and B. cereus. The NCBI genebank accession number of the strain SUB13179211 AMLA5 is OQ874086 that showed 99.77% sequence identical to Bacillus subtilis. This strain was a surfactin producer that utilized A. platensis as its economical substrate. A. platensis & B. subtilis are GRAS level organisms that can be utilized in agriculture as biofertilizer as mixed culture. The synergism existing between these two organisms can be exploited in multiple sectors

Evaluation of the application of <i>Wickerhamomyces anomalus</i> supernatant for the control of relevant spoilage yeasts in wines

SO2 is traditionally used to limit or nullify the proliferation of spoilage yeasts in must/wine, but its use has become controversial due to its negative effects on human health. An alternative strategy for the control of spoilage yeasts is the use of biocontrol yeasts. Wickerhamomyces anomalus is an outstanding biocontroller yeast that has been examined by our group and that is a good biocontrol agent against Brettanomyces bruxellensis and Zygosaccharomyces rouxii. The challenge regarding the application of the results of microbial biocontrol studies lies in exploring technologically simple and economical ways to make use of microbial biocontrol activity. The introduction of foreign microbiota adds complexity to the fermentation medium and can cause technological difficulties and have oenological consequences inherent to the implementation of mixed cultures. Therefore, the objective of this study was to characterise the concentrated culture supernatant of W. anomalus and evaluate its biocontrol action in liquid medium on two main wine spoilage yeasts. W. anomalus BWa156 supernatant demonstrated inhibitory killer protein characteristics. The production of the inhibitory supernatant by the biocontroller yeast was independent of the presence or absence of the spoilage yeast. Supernatant can be produced faster under aerobic conditions than in traditional fermentation (i.e., with around 24 h), thus increasing its potential for technological development. The treatment with the supernatant of BWa156 was effective against the two spoilage populations Zygosaccharomyces rouxii and Brettanomyces bruxellensis, which are considered problematic for the wine industry. The supernatant of the biocontrol yeast can be considered to be a relevant additional stress factor for the spoilage population, which together with other factors such as ethanol, competition for nutrients, oxygen and pH, contributes to the elimination of the polluting population. This technology would allow a simple future application, through its production in a bioreactor parallel to the fermentation and subsequent inoculation in the must/wine.

BIODIVERSITY OF ICHNEUMONID FLIES (HYMENOPTERA : ICHNEUMONIDAE) FROM WESTERN GHATS, MAHARASHTRA

Ichneumonids (Hymenoptera : Ichneumonidae) are very good biocontrol agents offorest insect pests. Therefore, as part of conservation and protection of flora of Western Ghats,biodiversity of Ichneumonid flies has been studied from Western Ghats, Maharashtra. In all, 35species belonging to genera Diadegma, Isotima, Goryphus, Charops, Campoletis, Enicospilus, Pimpla,Xanthopimpla, Eriborus, Netelia and Ecthromorpha have been reported parasitizing lepidopterouspests of forest trees

Desirable traits for a good biocontrol agent against fire blight disease

This study aimed to improve the screening strategy for the selection of biocontrol agents with high biocontrol efficacy against fire blight disease. A two-step screening procedure consisting of in-vitro laboratory tests and an ex-vivo test system using detached pear leaves was applied to 43 Bacillus strains originated from the rhizosphere and the aerial parts of apple and pear plants. The grouping of the studied strains and the tested traits based on the principal component analysis and the two-way hierarchical cluster analysis showed that siderophore production and biofilm formation are the most desirable traits in a Bacillus biocontrol agent to control fire blight disease and that rhizospheric originating strains are the most effective. In contrast to the previous screening strategies that are often insufficient to select the most suitable microorganisms, this study reported an improved strategy based on the microbial competition traits to select potential Bacillus biocontrol agents with high biocontrol efficacy against fire blight disease.

Isolation and characterization of a high-efficacy Beauveria bassiana strain from the European tent caterpillar, Malacosoma neustria Linnaeus (Lepidoptera: Lasiocampidae).

The European tent caterpillar, Malacosoma neustria Linnaeus (Lepidoptera: Lasiocampidae), is a worldwide known pest that causes significant losses by feeding on many woody and shrub-like plants during the larval period. In this study, a Beauveria bassiana strain isolated from M. neustria larvae and characterized according to its morphological and molecular properties. Its insecticidal activity was tested on M. neustria larvae. Sequence results of partial ITS (ITS1-5.8S-ITS2) gene region identified the isolate (named as Mn1) as a B. bassiana strain. Phylogenetic analysis showed that Mn1 strain displays close similarity to B. bassiana ARSEF 1848 and ARSEF 751 isolates. According to the concentration-responce tests performed using 1 × 103-1 × 109 conidia per mL concentrations, LC50 value of the new strain was calculated as 1 × 105 conidia per mL within 7days against the larvae of M. neustria in the laboratory conditions. B. bassiana Mn1 strain, characterized in this study, is recorded as the first entomopathogenic fungus isolated from M. neustria, and the results showed that new strain of B. bassiana has a serious potential to be utilized as a good biocontrol agent against M. neustria.

Efficacy of Biocontrol Agent (BCA) Trichoderma spp. Against Black Scurf Disease (Rhizoctonia solani) of Potato

The current study was designed to determine the efficacy of Trichoderma against soil borne pathogen Rhizoctonia solani causing Black scurf disease in potato. Five various species of Trichoderma (Trichoderma herzianum, Trichoderma asperellum, Trichoderma viride, Trichoderma hamatum and Trichoderma helicum) were screened in vitro against Rhizoctonia solani via Dual culture technique. Amongst the antagonists Trichoderma herzianum, Trichoderma viride and Trichoderma helicum was found to be more potent in inhibiting the mycelial growth of Rhizoctonia solani. The results indicate that Trichoderma helicum and Trichoderma viride showed significant growth in suppressing the mycelial growth of Rhizoctonia solani thus a highest inhibition percentage 71.8% was attained however, the Trichoderma herzianum, Trichoderma asperellum and Trichoderma hamatum showed mycelial percentage of 71.45%, 68.2% and 64.5% respectively. It is therefore concluded that an insignificant inhibition percentage 64.5% was shown by Trichoderma hamatum and found to be least effective in reducing mycelial growth as well as sclerotia formation of the test pathogen Rhizoctonia solani. However Trichoderma is good biocontrol agent and therefore can be used against Black scurf disease of potato.

Influence of hot water and UV radiation on host infectivity of entomopathogenic nematode Steinernema glaseri (Glaser, 1932)

Entomopathogenic nematodes act as good bio-control agents to manage lepidopteron and coleopteran pests. Steinernematidae and Heterorhabditae are considered important families in entomopathogenic nematodes. An in-vitro experiment was conducted to enhance the efficacy of Steinernema glaseri using hot water and UV radiation on final instar larvae of Corcyra Cephalonia. The results showed that the highest number of larvae were infected at 35 °C and 45 °C of hot water immersion. Among the UV-exposed larvae, the highest number of larvae infected was obtained by UV exposure for 10 minutes.

Tachinids as good biocontrol agents of agricultural pests

Tachinids as good biocontrol agents of agricultural pests

Yeasts as a Potential Biological Agent in Plant Disease Protection and Yield Improvement—A Short Review

The role of biocontrol products is expected to increase worldwide consumer demand and facilitate the implementation of sustainable agricultural policies. New biocontrol agents must allow for an effective crop-protection strategy in sustainable agriculture. Yeasts are microorganisms living in various niches of the environment that can be antagonists of many plant pathogens. Yeasts rapidly colonize plant surfaces, use nutrients from many sources, survive in a relatively wide temperature range, produce no harmful metabolites and have no deleterious effects on the final food products. Hence, they can be a good biocontrol agent. In this paper, the biological characteristics and potential of yeast are summarized. Additionally, the mechanisms of yeasts as plant-protection agents are presented. This includes the production of volatile organic compounds, production of killer toxins, competition for space and nutrient compounds, production of lytic enzymes, induction of plant immunity and mycoparasitism. The mechanisms of yeast interaction with plant hosts are also described, and examples of yeasts used for pre- and postharvest biocontrol are provided. Commercially available yeast-based products are listed and challenges for yeast-based products are described.

Zelus renardii Roaming in Southern Italy.

Simple SummaryThe leafhopper assassin bug Zelus renardii (Hemiptera: Reduviidae) first entered Europe in 2012 and has since acclimatised. Z. renardii is now a common insect predator in agroecosystems and urban and peri-urban areas. We performed a metadata analysis of 165 years of Z. renardii literature. Moreover, we provide laboratory tests of Z. renardii predation. The latter indicates Z. renardii interplay with relevant insect targets, such as Philaenus spumarius, Neophilaenus campestris, Bactrocera oleae, Kermes vermilio, Nidularia pulvinata, Harmonia axyridis, Apis mellifera, Aleurocanthus spiniferus, Aleurothrixus floccosus, Macrohomotoma gladiata, Drosophila suzukii, Drosophila melanogaster, Megaselia scalaris, Pseudococcidae, Miridae, and Issidae. Furthermore, predation on Aphrophoridae and other olive pests brands Z. renardii as a good mass-rearing candidate for inundative biocontrol programs of Xylella fastidiosa pauca ST53 infections and could also reduce damage caused by other olive pests. Overall, this reduviid is harmless to humans and beneficial insects.This study collects data from the literature and updates our Zelus renardii Kolenati, 1856 (Leafhopper Assassin Bug, LAB) prey knowledge. The literature consists of ca. 170 entries encompassing the years 1856 to 2021. This reduviid originated in the Nearctic region, but has entered and acclimatised in many Mediterranean countries. Our quantitative predation experiments—in the laboratory on caged plants plus field or environmental observations—confirm that LAB prefers a selected array of prey. Laboratory predation tests on living targets (Hemiptera, Coleoptera, Diptera, and Hymenoptera) agree with the literature. Zelus renardii prefers comparatively large, highly mobile, and readily available prey. LAB preferences on available hemipterans targets suggest that Zelus renardii is a good inundative biocontrol agent for Xylella fastidiosa pauca ST53 infections. LAB also prey on other important olive pests, such as Bactrocera oleae. Therefore, Zelus renardii is a major integrated pest management (IPM) component to limit Xylella fastidiosa pandemics and other pest invasions.

Draft genome sequence of a lipopeptide-producing Bacillus amyloliquefaciens strain isolated from wheat field soil with antagonistic activity against azole-resistant Fusarium graminearum

Lipopeptides have been revealed as good potential biocontrol agents against various pathogenic microbes. In the present work, we report the draft genome sequence of a lipopeptide-producing strain of Bacillus amyloliquefaciens (7D3) that showed good antifungal activity against the azole-resistant pathogenic fungus Fusarium graminearum. Whole-genome sequencing of strain 7D3 was performed on an Illumina MiSeq 300 platform. Raw data were cleaned using Trim Galore v.0.4.0 and were checked for quality using FastQC. De novo assembly was performed using the SOAPdenovo2 package. Genes responsible for the biosynthesis of secondary metabolites were identified using antiSMASH. Bacillus amyloliquefaciens 7D3 genome assembly resulted in a total genome size of 3 913 220 bp with a G+C content of 46.13%. There were 3998 predicted genes with 72 tRNAs and 9 rRNAs. A total of ten gene clusters were found to be related to secondary metabolite biosynthesis, of which five were identified as lipopeptide synthesis clusters. This study presents the genome sequence of B. amyloliquefaciens 7D3, which exhibited intense antagonistic activity against azole-resistant fungi. The whole genome sequence will help in the search for novel antifungal peptides against drug-resistant pathogens.

Streptomyces eurocidicus promotes soybean growth and protects it from fungal infections

The aim of this work was to analyze Streptomyces eurocidicus as growth promoter for soybean (Glycine max (L.) Merr.) plants and to study the role of antifungal polyene eurocidin produced by this strain on the biocontrol over two soybean phytopathogenic fungi, Macrophomina phaseolina and Diaporthe aspalathi, which are generally controlled by environmentally harmful chemical antifungals and genetic resistance, respectively. In vitro studies confirmed that the eurocidin producer S. eurocidicus inhibited these pathogens as well as several other important phytopathogenic fungi, while non-antagonistic effect on Bradyrhizobium japonicum was observed. Phenotypic characterization of S. eurocidicus strain showed its potential as growth promoter agent, a property probably related with its ability to produce siderophores and 3-indolacetic acid and also to solubilize tricalcium phosphate. Moreover, the results obtained demonstrate that seeds treatment with S. eurocidicus promotes soybean plants growth and development, either alone or in combination with B. japonicum in vegetative stage and also, enhances seeds produced per plant at crop maturity under greenhouse conditions. Biocontrol experiments using soybean-M. phaseolina and soybean-D. aspalathi pathosystems showed that the polyene-producer S. eurocidicus and a eurocidin non-producer mutant strain protect soybean plants reducing the severity of both diseases. These results suggested that there is/are another mechanism/s for soybean plants protection independent of the polyene antifungal per se. Altogether these results demonstrate that S. eurocidicus is a good biocontrol agent and also a growth and development promoter; and strongly support further research on this field in order to pursue their use to sustainably manage crop diseases while stimulating plant growth.

Genome mining and In‐silico determination of secondary metabolites of bacteria against Fusarium oxysporum f. sp. Lycopersici

AbstractFusarium wilt caused by Fusarium oxysporum f. sp. lycopersici (FOL) is a devastating global plant fungal disease particularly in tomatoes leading to serious economic losses. The aim of this study was to determine an in silico effective antifungal metabolite against two important FOL proteins. An in silico ligand–protein interaction was carried out by genome mining and molecular docking of the best ligand‐producing strains of bacteria using AutoDock and antiSMASH tools. The secondary metabolites obtained from different bacteria selected for biocontrol agents (BCA) were docked against SIX and TOM proteins. The selected compounds were docked in the active site of both proteins while random starting positions, torsion angles were established for all ligands. Based on the protein–ligand interactions, the best inhibitor of SIX and TOM protein was xanthobaccine A from Lysobacter sp. strain SB‐K88. On the other hand, the best BCAs compound was heat‐stable antifungal factor obtained from L. enzymogenes, viginiafactin (Pseudomonas sp. QS1027), massetolide A (P. fluorescenss 5101), bicorlnutin A1 and A2 (Xenorhabdus budapestensis) which showed similarity scores viz., 1.25 (with domain NRP, Polyketide), 1.09 (NRP domain), 1.06(NRP domain), 1.00 (NRP domain). The results of our findings suggest Lysobacter sp. as a good biocontrol agent with active biosynthetic gene clusters and as a suitable substitute for agrochemicals. The output of this study will be useful in future management of F. oxysporum f. sp. lycopersici with other plant pathogen and help in crop improvement.

Mycofumigation with the endophytic fungi Fusarium proliferatum (Matsushima) Nirenberg and Diaporthe sp. for the control of banana and mango anthracnose

Banana and mango are the top commodities in the Philippines that are traded worldwide however, fungal diseases such as anthracnose affect their yield and quality. Environmentally sound control strategies have been explored and one of these is mycofumigation using fungal endophytes. This alternative approach is understudied in the Philippines, hence, the study aimed to evaluate the mycofumigation potential of fungal endophytes collected from Mt. Makiling, Luzon, Philippines and their pathogenicity to banana and mango fruits. In vitro and in vivo mycofumigation assays were conducted with a completely randomized design layout with triplicates per treatment under laboratory conditions. The fungal endophytes used as mycofumigants, Diaporthe sp. and Fusarium proliferatum, were comparatively effective in controlling the anthracnose of banana and mango. The mycelial growth for in vitro assay of Colletotrichum musae and Colletotrichum gloeosporioides were significantly reduced compared to the control when exposed to volatile organic compounds produced by the fungal endophytes. In addition, the results of the in vivo mycofumigation assay against C. musae showed Diaporthe sp. had a significantly higher inhibition rate (93%) than F. proliferatum (67%) when grown on potato dextrose agar plates. The bioefficacy of the Diaporthe sp. and F. proliferatum was improved when grown on peanut and corn seed substrates with a reduction of banana and mango anthracnose severity ranging from 82 to 100%. Cultures grown on corn substrate performed better than those grown on peanut. Pathogenicity tests also revealed that these endophytic fungi did not cause disease in the banana or mango fruits indicating their potential as good biocontrol agents against C. musae and C. gloeosporioides.

Characterization and Food Application of the Novel Lytic Phage BECP10: Specifically Recognizes the O-polysaccharide of Escherichia coli O157:H7.

Escherichia coli O157:H7 is a global concern that causes serious diseases, such as hemolytic uremic syndrome and bloody diarrhea. To control E. coli O157:H7 in food, a novel siphophage, BECP10, that targets the O157 serotype was isolated and characterized. Unlike other E. coli phages, BECP10 can only infect E. coli O157 strains, and thus, did not infect other strains. The 48 kbp genome of BECP10 contained 76 open reading frames (ORFs), including 33 putative functional ORFs. The phage did not contain lysogeny-related modules or toxin-associated genes, suggesting that the phage might be strictly lytic. The tail spike protein (TSP) sequence had very low homology with the reported T1-like phages, indicating that TSP might be related to this unique host spectrum. The specific O-antigen residue of E. coli O157:H7 may be a key factor for phage infection by adsorption and receptor identification. The phage exhibited strong antibacterial activity against E. coli O157:H7 over a broad pH range and showed little development of phage-insensitive mutants. The phage sustained viability on the burger patties and reduced E. coli O157:H7 to a non-detectable level without the emergence of resistant cells at low temperatures for five days. Therefore, phage BECP10 might be a good biocontrol agent for E. coli O157:H7-contaminated food matrices.

Understanding the Transcriptional Changes During Infection of Meloidogyne incognita Eggs by the Egg-Parasitic Fungus Purpureocillium lilacinum.

The egg-pathogenic fungus Purpureocillium lilacinum parasitizes on nematode eggs, and thus, it is used as a good biocontrol agent against plant root-knot nematodes. However, little is known about the transcriptional response of P. lilacinum while infecting nematode eggs. This study presents the whole transcriptome sequencing of P. lilacinum and transcriptome-wide gene expression analysis of P. lilacinum upon infecting the eggs of Meloidogyne incognita compared to non-infecting controls. A transcriptomic library of P. lilacinum was used as reference gene set and six transcriptomic libraries of the non-infecting control and P. lilacinum infecting M. incognita eggs were constructed, respectively, comprising three biological replicates of each. A total of 1,011 differently expressed genes (DEGs) were identified in the infecting samples, including 553 up-regulated and 458 down-regulated genes compared to the non-infecting control samples. Furthermore, functional enrichment analysis exhibited that these DEGs were primarily involved in oxidative phosphorylation, oxidoreductase activity, and metabolic processes. Fifteen DEGs were randomly selected to verify the RNA sequencing results through quantitative real-time polymerase chain reaction (qPCR). The study focused on P. lilacinum genes that were strongly expressed upon infecting M. incognita eggs. These DEGs were primarily involved in detoxification, parasitic behavior, and nutritional utilization. This study contributes significantly to the understanding of the molecular mechanisms underlying the parasitic action of P. lilacinum on nematode eggs and provides a valuable genetic resource for further research on parasitic behavior of P. lilacinum. Notably, this study examined the transcriptomics of P. lilacinum infecting M. incognita eggs at only one time point. Since there were fungi at different stages of the infection process at that time point, the transcriptional profiles are not precisely examining one specific stage in this process.

Mite pests and their predators on seven vegetable crops (Arachnida: Acari).

During this study the frequency of occurrence and dominance of phytophagous and predatory mites harboring seven vegetable crops in Egypt, namely common bean, cowpea, eggplant, okra, squash, sweet pepper and sweet potato during 2017–2018 were investigated to identify predatory mites that might be useful for the biological control of the phytophagous mites. Three phytophagous and nine predatory mite species were surveyed. The two spotted spider mite Tetranychus urticae Koch of the family Tetranychidae was the dominant pest on these vegetables, while phytoseiids Phytoseiulus persimilis (Athias- Henriot), Typhlodromips swirskii (Athias- Henriot) and Euseius scutalis Chant were the dominant predators. The population of the native or indigenous phytoseiid mite fauna in Egypt such as Phytoseiulus persimilis could be considered as a good biocontrol agent and a part of the Integrated Pest Management (IPM) program in the future. Mite fauna of Egypt especially local populations of Phytoseiulus persimilis can be considered for implementation in future Integrated Pest Management (IPM).

Isolation of bacterial microbiota associated to honey bees and evaluation of potential biocontrol agents of Varroa destructor.

The honey bee parasitic mite Varroa destructor is one of the main causes of depopulation of bee colonies. Bacterial symbionts associated to honey bees are known to produce a variety of bioactive molecules that have been suggested to play a protective role against honey bee pathogens. We hypothesised that among these bacteria, those colonising the external body of honey bees, and therefore able to survive and reproduce in the hive environment outside the insect gut, may be good candidate biocontrol agents to be tested against V. destructor. The aim of this study was to isolate bacterial species from healthy honey bees and dead varroa mites and to evaluate the potential miticidal effect of their spent medium containing both bacterial metabolites and viable cells, with the final objective of finding a long-lasting solution for mite control. 61 bacterial strains belonging to the Firmicutes, Proteobacteria and Actinobacteria phyla were isolated from the surface of foragers, nurse bees and larvae collected in 10 different apiaries. The most common species was Lactobacillus kunkeei (62%). Growth capability of a selection of isolates was observed at 30 and 34 °C with 1% and 20% glucose and fructose. Laboratory bioassays were conducted by spraying mites with six-day-grown bacterial cultures containing 107 cfu/ml of four strains of L. kunkeei, Bacillus thuringiensis, Bifidobacterium asteroides and an Acetobacteraceae bacterium. The effect of each strain on varroa survival was tested independently. The first three caused 95-100% mortality of mites in 3 days, indicating a potential role as natural antagonists towards varroa. The mediation of pH of the bacterial cultures did not appear to be determinant in mite inhibition, suggesting the involvement of other modes of action against varroa. The exploitation of honey bee microbiota for controlling one of the major threats for honey bee health may be a promising approach deserving further investigation.