Laboratory evaluation of a native strain of Beauveria bassiana for controlling Dermanyssus gallinae (De Geer, 1778) (Acari: Dermanyssidae)

Evaluation of acaricidal activity in entomopathogenic fungi for poultry red mite (Dermanyssus gallinae) control

The poultry red mite (PRM), Dermanyssus gallinae, significantly impacts the health of egg-laying hens. Mites feed on the blood of infested chickens and have a great economic impact on the poultry industry. Chemical treatment of mites raises concerns about their resistance to miticides and residues in eggs and poultry. Biocontrol using entomopathogenic fungi is expected to be a chemical-free strategy for reducing PRM infestations. Therefore, the present study aimed to investigate the effects of various entomopathogenic fungal species collected in South Korea on the inhibition of PRM. Seventeen strains of six fungal species collected from various sources were used to evaluate acaricidal activity against PRM. The results showed that 16/17 strains had acaricidal properties against PRM, of which strains of Metarhizium anisopliae had the highest acaricidal activity. Mites treated with M. anisopliae CBNU 4-2 showed 100 % mortality 5 d after inoculation, followed by M. flavoviride var. pemphigi. The M. flavoviride var. pemphigi CBNU 1-1-1 showed 97.78 % mortality after 10 d of exposure to fungi. The mortality rate of PRM treated with other strains slowly increased and reached its highest value on the 14th day of inoculation. The results of this study provide information on the acaricidal activity of different entomopathogenic fungi against PRM. This information is important for the selection of fungal species for developing biocontrol methods for PRM treatment. These strains could be used for further evaluation of PRM treatment on chicken farms, or in combination with other methods, to increase PRM treatment efficiency.

Entomopathogenic fungi with biological control potential against poultry red mite (Dermanyssus gallinae, Arachnida: Dermanyssidae)

The poultry red mite, Dermanyssus gallinae (Arachnida: Dermanyssidae) is a pest that causes significant economic loss in laying hens for which control methods are limited. In this study, the effects of 20 indigenous fungal strains on poultry red mites in chicken farms were investigated. All experiments were conducted under laboratory condition at 28 ± 1 °C and 80 ± 5% humidity. A screening test showed that Metharizium flavoviride strain As-2 and Beauveria bassiana strain Pa4 had the greatest measured effect on D. gallinae at 1 × 107 conidia/ml 7 days after application. In a subsequent does-response experiment, these strains also caused 92.7% mortality at 1 × 109 conidia/ml within the same period. The LC50 of these strains was 5.5 × 104 (95% CI: 0.8-37.5) conidia/ml for As-2 and 3.2 × 104 (95% CI: 0.4-26.0) conidia/ml for Pa4, and their LT50 were 1.94 and 1.57 days, respectively. The commercial Metarhizium anisopliae bioinsecticide Bio-Storm 1.15% WP, used as a comparator, had LC50 and LT50 1 × 105 (95% CI: 0.1-7.9) conidia/ml and 3.03 (95% CI: 2.4-3.8) days, respectively. It is suggested that mycoacaricides could be developed using the best two fungal strains found in this study (As-2 and Pa4), providing potential for biological control of poultry red mites.

Computational Applications: Beauvericin from a Mycotoxin into a Humanized Drug

Drug discovery was initially attributed to coincidence or experimental research. Historically, the traditional approaches were complex, lengthy, and expensive, entailing costly random screening of synthesized compounds or natural products coupled with in vivo validation largely depending on the availability of appropriate animal models. Currently, in silico modeling has become a vital tool for drug discovery and repurposing. Molecular docking and dynamic simulations are being used to find the best match between a ligand and a molecule, an approach that could help predict the biomolecular interactions between the drug and the target host. Beauvericin (BEA) is an emerging mycotoxin produced by the entomopathogenic fungus Beauveria bassiana, being originally studied for its potential use as a pesticide. BEA is now considered a molecule of interest for its possible use in diverse biotechnological applications in the pharmaceutical industry and medicine. In this manuscript, we provide an overview of the repurposing of BEA as a potential therapeutic agent for multiple diseases. Furthermore, considerable emphasis is given to the fundamental role of in silico techniques to (i) further investigate the activity spectrum of BEA, a secondary metabolite, and (ii) elucidate its mode of action.

Materials Engineering to Help Pest Control: A Narrative Overview of Biopolymer-Based Entomopathogenic Fungi Formulations

Biopolymer-based formulations show great promise in enhancing the effectiveness of entomopathogenic fungi as bioinsecticides. Chitosan and starch, among other biopolymers, have been utilized to improve spore delivery, persistence, and adherence to target insects. These formulations offer advantages such as target specificity, eco-friendliness, and sustainability. However, challenges related to production costs, stability, and shelf life need to be addressed. Recently, biomimetic lure and kill approaches based on biopolymers offer cost-effective solutions by leveraging natural attractants. Further research is needed to optimize these formulations and overcome challenges. Biopolymer-based formulations have the potential to revolutionize pest control practices, providing environmentally friendly and sustainable solutions for agriculture.

Characterization and transcriptomic analysis of a native fungal pathogen against the rice pest Nilaparvata lugens

The brown planthopper (BPH), Nilaparvata lugens, is one of the most destructive pests of rice. Given the threats posed by insecticide resistance to its control, eco-friendly strategies based on microbial pathogens emerged as a promising biocontrol alternative. In the present study, we isolated a native fungal pathogen against BPH from infected BPH cadavers and preliminarily identified as a strain of Aspergillus fumigatus based on morphological and molecular methods. Laboratory bioassay revealed that this fungal strain was highly virulent to BPH both at nymphal and adult stages, with the median lethal times (LT₅₀) of 7.5 and 5.8 days under high conidial concentration of 1 × 10⁹ conidia mL^-1. A genome-wide view of gene expressions in BPH against fungal attack was analyzed by transcriptomic sequencing and consequently a large number of differentially expressed genes that mainly involved in host immune defense and cell detoxification were found. RNAi-mediated knockdown of an upregulated gene encoding a serine protease (NlSPN) could cause a significant decrease in BPH survival. Combination of dsRNA injection and fungal infection showed an additive effect on BPH mortality, which provided clues to develop new pest management strategies against BPH.

Management of the poultry red mite Dermanyssus gallinae with physical control methods by inorganic material and future perspectives

Poultry red mite (PRM), the ectoparasitic mite Dermanyssus gallinae found in laying hen farms, is a significant threat to poultry production and human health worldwide. It is a suspected disease vector and attacks hosts' other than chickens, including humans, and its economic importance has increased greatly. Different strategies to control PRM have been widely tested and investigated. In principle, several synthetic pesticides have been applied to control PRM. However, recent alternative control methods to avoid the side effects of pesticides have been introduced, although many remain in the early stage of commercialization. In particular, advances in material science have made various materials more affordable as alternatives for controlling PRM through physical interactions between PRM. This review provides a summary of PRM infestation, and then includes a discussion and comparison of different conventional approaches: 1) organic substances, 2) biological approaches, and 3) physical inorganic material treatment. The advantages of inorganic materials are discussed in detail, including the classification of materials, as well as the physical mechanism-induced effect on PRM. In this review, we also consider the perspective of using several synthetic inorganic materials to suggest novel strategies for improved monitoring and better information regarding treatment interventions.

Pathogenesis and defense mechanism while Beauveria bassiana JEF-410 infects poultry red mite, Dermanyssus gallinae

The poultry red mite, Dermanyssus gallinae (Mesostigmata: Dermanyssidae), is a major pest that causes great damage to chicken egg production. In one of our previous studies, the management of red mites using entomopathogenic fungi was evaluated, and the acaricidal fungus Beauveria bassiana JEF-410 was selected for further research. In this study, we tried to elucidate the pathogenesis of B. bassiana JEF-410 and the defense mechanisms of red mites at a transcriptome level. Red mites collected from a chicken farm were treated with B. bassiana JEF-410. When the mortality of infected red mites reached 50%, transcriptome analyses were performed to determine the interaction between B. bassiana JEF-410 and red mites. Uninfected red mites and non-infecting fungus served as controls. In B. bassiana JEF-410, up-regulated gene expression was observed in tryptophan metabolism and secondary metabolite biosynthesis pathways. Genes related to acetyl-CoA synthesis were up-regulated in tryptophan metabolism, suggesting that energy metabolism and stress management were strongly activated. Secondary metabolites associated with fungal up-regulated DEGs were related to the production of substances toxic to insects such as beauvericin and beauveriolide, efflux pump of metabolites, energy production, and resistance to stress. In red mites, physical and immune responses that strengthen the cuticle against fungal infection were highly up-regulated. From these gene expression analyses, we identified essential factors for fungal infection and subsequent defenses of red mites. These results will serve as a strong platform for explaining the interaction between B. bassiana JEF-410 and red mites in the stage of active infection.

Proof of Concept of Biopolymer Based Hydrogels as Biomimetic Oviposition Substrate to Develop Tiger Mosquitoes (Aedes albopictus) Cost-Effective Lure and Kill Ovitraps

Pest management is looking for green and cost-effective innovative solutions to control tiger mosquitoes and other pests. By using biomimetic principles and biocompatible/biodegradable biopolymers, it could be possible to develop a new approach based on substrates that selectively attract insects by reproducing specific natural environmental conditions and then kill them by hosting and delivering a natural biopesticide or through mechanical action (biomimetic lure and kill approach, BL&K). Such an approach can be theoretically specialized against tiger mosquitoes (BL&K-TM) by designing hydrogels to imitate the natural oviposition site’s conditions to employ them inside a lure and kill ovitraps as a biomimetic oviposition substrate. In this work, the hydrogels have been prepared to prove the concept. The study compares lab/on-field oviposition between standard substrates (absorbing paper/masonite) and a physical and chemically crosslinked hydrogel composition panel. Then the best performing is characterized to evaluate a correlation between the hydrogel’s properties and oviposition. Tests identify a 2-Hydroxyethylcellulose (HEC)-based physical hydrogel preparation as five times more attractive than the control in a lab oviposition assay. When employed on the field in a low-cost cardboard trap, the same substrate is seven times more capturing than a standard masonite ovitrap, with a duration four times longer.

Entomopathogenic Fungi and Bacteria in a Veterinary Perspective

Simple Summary

Several fungal species are well suited to control arthropods, being able to cause epizootic infection among them and most of them infect their host by direct penetration through the arthropod’s tegument. Most of organisms are related to the biological control of crop pests, but, more recently, have been applied to combat some livestock ectoparasites. Among the entomopathogenic bacteria, Bacillus thuringiensis, innocuous for humans, animals, and plants and isolated from different environments, showed the most relevant activity against arthropods. Its entomopathogenic property is related to the production of highly biodegradable proteins. Entomopathogenic fungi and bacteria are usually employed against agricultural pests, and some studies have focused on their use to control animal arthropods. However, risks of infections in animals and humans are possible; thus, further studies about their activity are necessary.

Abstract

The present study aimed to review the papers dealing with the biological activity of fungi and bacteria against some mites and ticks of veterinary interest. In particular, the attention was turned to the research regarding acarid species, Dermanyssus gallinae and Psoroptes sp., which are the cause of severe threat in farm animals and, regarding ticks, also pets. Their impact on animal and human health has been stressed, examining the weaknesses and strengths of conventional treatments. Bacillus thuringiensis, Beauveria bassiana and Metarhizium anisopliae are the most widely employed agents. Their activities have been reviewed, considering the feasibility of an in-field application and the effectiveness of the administration alone or combined with conventional and alternative drugs is reported.

Molecular insight into the endophytic growth of Beauveria bassiana within Phaseolus vulgaris in the presence or absence of Tetranychus urticae

Entomopathogenic fungi are an important factor in the natural regulation of arthropod populations. Moreover, some can exist as an endophyte in many plant species and establish a mutualistic relationship. In this study, we have investigated the endophytic growth of Beauveria bassiana within different tissues of Phaseolus vulgaris in the presence and absence of Tetranuychus urticae. After the colonization of the B. bassiana within the internal tissues of P. vulgaris. The susceptibility of T. urticae appeared to depend on the life stage where high, moderate, and low mortalities were recorded among adults, nymphs, and eggs, respectively. In addition, this study provided, for the first time, molecular insight into the endophytic growth of B. bassiana by analyzing the expression of several genes involved in the development of the entomopathogenic fungi at 0-, 2-, and 7- days post-inoculation. B. bassiana displayed preferential tissue colonization within P. vulgaris that can be put into the following order based on the detection rate: leaf > stem > root. After analyzing the development-implicated genes (degrading enzymes, sugar transporter, hydrophobins, cell wall synthesis, secondary metabolites, stress management), the most remarkable finding is the detection of behavioral change between parasitic and endophytic Beauveria during post-penetration events. This study elucidates the tri-trophic interaction between fungus-plant-herbivore.

Fumigant activity of essential oils from Cinnamomum and Citrus spp. and pure compounds against Dermanyssus gallinae (De Geer) (Acari: Dermanyssidae) and toxicity toward the nontarget organism Beauveria bassiana (Vuill.)

Dermanyssus gallinae(De Geer) (Acari: Dermanyssidae) is the main ectoparasite associated with laying poultry. This mite is commonly controlled by the application of synthetic chemical insecticides, wich lead to the selection of resistant populations and formation of residues in eggs. Thus, new molecules must be developed to control D. gallinae. This work evaluated the toxicity of essential oils (EOs) from Cinnamomum cassia, Cinnamomum camphora, Cinnamomum camphora var. linalooliferum, Citrus aurantium, Citrus aurantium var. bergamia, Citrus aurantifolia and Citrus reticulata var. tangerine against D. gallinae. Additionally, the chemical profiles of the most bioactive EOs were analyzed by gas chromatography coupled with mass spectrometry (GC-MS) and the major compounds were subjected to new tests using D. gallinae. The most toxic EOs against D. gallinae were evaluated for the nontarget entomopathogenic fungus Beauveria bassiana (Unioeste 88). The EOs from C. cassia (LC₅₀ = 25.43 ± 1.0423 μg/cm³) and C. camphora var. linalooliferum (LC₅₀ = 39.84 ± 1.9635 μg/cm³) were the most active in the fumigant bioassay and caused mortality rates of 96 and 61%, respectively. The GC-MS analysis revealed that the major constituents of EOs from C. cassia and C. camphora var. linalooliferum were trans-cinnamaldehyde and linalool, respectively. The pure compounds, trans-cinnamaldehyde (LC₅₀ = 68.89 ± 3.1391 μg/cm³) and linalool (LC₅₀ = 51.45 ± 1.1967 μg/cm³), were tested on D. gallinae and showed lower toxicity than the EOs. Thus, the compounds were not the only active substances produced by C. cassia and C. camphora var. linalooliferum; moreover synergism may have occurred between the substances. The EOs from C. cassia and C. camphora var. linalooliferum were also toxic to B. bassiana (Unioeste 88). Thus, EOs from C. cassia and C. camphora var. linalooliferum are promising candidates for use in D. gallinae control, but cannot be used in conjunction with the fungus B. bassiana.

Possibilities for IPM Strategies in European Laying Hen Farms for Improved Control of the Poultry Red Mite (Dermanyssus gallinae): Details and State of Affairs

The Poultry Red Mite (PRM), Dermanyssus gallinae, is a major threat to the poultry industry worldwide, causing serious problems to animal health and welfare, and huge economic losses. Controlling PRM infestations is very challenging. Conventionally, D. gallinae is treated with synthetic acaricides, but the particular lifestyle of the mite (most of the time spent off the host) makes the efficacy of acaracide sprays often unsatisfactory, as sprays reach only a small part of the population. Moreover, many acaricides have been unlicensed due to human consumer and safety regulations and mites have become resistant to them. A promising course of action is Integrated Pest Management (IPM), which is sustainable for animals, humans and the environment. It combines eight different steps, in which prevention of introduction and monitoring of the pest are key. Further, it focusses on non-chemical treatments, with chemicals only being used as a last resort. Whereas IPM is already widely applied in horticulture, its application is still in its infancy to control D. gallinae in layer houses. This review presents the currently-available possibilities for control of D. gallinae in layer houses for each of the eight IPM steps, including monitoring techniques, established and emerging non-chemical treatments, and the strategic use of chemicals. As such, it provides a needed baseline for future development of specific IPM strategies, which will allow efficient and sustainable control of D. gallinae in poultry farms.

Beauveria bassiana Culturing and Harvesting for Bioassays With House Flies

The entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae) has been widely studied against a wide range of arthropod pests, including many of medical and veterinary importance. New investigators must sort through a wide array of published methods for the production, harvest, storage, and bioassay methods for this pathogen. Simplified methods for production of conidia using Sabouraud dextrose agar with yeast (SDYA) plates and two conidial harvesting methods are described. Dry harvesting yields conidia that are ready to incorporate into dusts and food baits, but the fungal product includes mycelial debris that can hamper quantification and introduces variable amounts of unwanted bulk. Wet harvesting with filtration produces a cleaner product that is immediately ready for testing in liquid formulations. Examples of bioassays with house flies are presented that include conidia applied topically to the dorsal thorax for dose-mortality assays and conidial suspensions applied to filter paper disks for concentration mortality assays.

Laboratory and field evaluation of an autoinoculation device as a tool to manage poultry red mite, Dermanyssus gallinae, infestations with Beauveria bassiana

The poultry red mite, Dermanyssus gallinae, is a cosmopolitan ectoparasite in hens and has been considered an important threat to the egg production industry. This study evaluated an alternative to manage poultry red mite populations as a complement to conventional chemical treatments and other control strategies in poultry houses. A simple autoinoculation device prepared with corrugated cardboard (CB) or loofah sponge (LS) as inert supports to anchor Beauveria bassiana conidia was used to aggregate and infect mites from infested poultry houses. In the laboratory, mites gathered inside the traps and the average mortalities by the fungus were higher than 70% in CB and LS traps after 5 and 4 days of exposure, respectively. Conidial viability was around 80% in CB and LS traps after 14 and 60 days under unrefrigerated conditions (26 °C), respectively. Both trap types tied to hen cages efficiently captured fed mites after blood meal, and fungal infection was observed in 65-90% of the mites in field tests. Between 5 and 25% of the mites recaptured in monitoring cardboard traps installed immediately after CB and LS removal were infected by B. bassiana. According to our results, the use of B. bassiana in an autoinoculation strategy is a potential alternative method for D. gallinae control.

First record of Aspergillus oryzae as an entomopathogenic fungus against the poultry red mite Dermanyssus gallinae

The poultry red mite, Dermanyssus gallinae, is a blood-feeding ectoparasite that affects egg-laying hens worldwide. Strategies to control this parasite have focused in the use of entomopathogenic fungi, such as Metarhizium anisopliae. However, only a few studies have evaluated the use of Aspergillus oryzae to control D. gallinae and none of them have employed native strains. In the work presented here, a novel entomopathogenic fungus was isolated from a dead D. gallinae. The results of phylogenetic analysis showed 100% similarity between the isolated strain and those of two species, A. oryzae and Aspergillus flavus, and 99.82% similarity with A. parvisclerotigenus, which were in the same branch of the Flavi section of the genus Aspergillus. This entomopathogenic fungus was a non-aflatoxin B1 producer, as shown by the presence of aflatoxin B1 in the conidial infection suspension. Morphological features of fungus in comparison with A. oryzae and A. flavus indicated that the isolated strain belonged to A. oryzae, and was named Aspergillus sp. Dg-1. The pathogenicity of Aspergillus sp. Dg-1 on D. gallinae at different life stages was then assessed under laboratory conditions. The experiments showed that the isolated strain significantly increased the mortality rate in adult mites, up to 24.83 ± 2.25, compared to the mortality rates in the control group, which were 15.17 ± 2.75 (P ＜ 0.05). However, Aspergillus sp. Dg-1 did not have pathogenic effects on the second nymph stage of D. gallinae. Our findings demonstrate that Aspergillus sp. Dg-1 has pathogenic effects on D. gallinae in their adult stage, presenting biocontrol potential against D. gallinae.

Mortality Effects of Three Bacterial Pathogens and Beauveria bassiana When Topically Applied or Injected Into House Flies (Diptera: Muscidae)

The house fly, Musca domestica L., is a global pest of public health and agricultural importance. The efficacy of conventional management has been waning due to increasing insecticide resistance. A potential management tool is the entomopathogenic fungus, Beauveria bassiana Vuillemin (Hypocreales: Cordycipitaceae) (strain L90), although time-to-death is slower than desired by potential users. This research investigated the effectiveness of three gram-negative bacteria (Pseudomonas protegens Ramette (Psuedomonadales: Pseudomonadaceae) pf-5, Photorhabdus temperata Fischer-Le Saux (Enterobacteriales: Enterobacteriaceae) NC19, and Serratia marcescens Bizio (Enterobacteriales: Enterobacteriaceae) DB11) on house fly mortality when topically applied, compared to B. bassiana. Each pathogen's virulence was measured by injection into adult female house flies or by topical applications to their thorax. All bacterial strains were highly virulent after injection with 1 × 104 colony forming units (cfu), causing fly mortality within 24 h. Beauveria bassiana resulted in high mortality, 3 d postinjection at the high dose of 1 × 104 conidia/µl. Mortality due to topical treatments of P. temperata and S. marcescens was low even at the highest dose of 1 × 106 cfu/µl. Mortality after topical treatments with P. protegens was evident 4 d after application of 1 × 106 cfu/µl. Mortality from B. bassiana was low at 4 d but increased at 5 d. These results imply that P. protegens holds great potential as a biological control agent for incorporation into an integrated pest management program against adult house flies.

Chemical characterization and acaricidal activity of Drimia maritima (L) bulbs and Dittrichia viscosa leaves against Dermanyssus gallinae

The emergence of resistance to chemical acaricides in Dermanyssus gallinae, together with their toxicity and high costs, has prompted investigations into the use of plant extracts as alternatives to chemical acaricidal treatments. Drimia maritima bulbs and Dittrichia viscosa (D. viscosa) leaf extracts were here characterized by HPLC-PDA-ESI-MS/MS, and their toxicity against D. gallinae was evaluated using contact methods. Twenty-nine compounds were identified in D. maritima extracts, with glucoscilliphaeoside derivatives (i.e., quercetin, kaempferol and bufadienolides) as the major components. Twenty-four phenolic compounds, mainly caffeic acid derivatives, were detected in D. viscosa extracts. D. maritima extracts displayed a significantly higher (p < 0.05) acaricidal activity than D. viscosa extracts, with 100% of D. gallinae mortality at a concentration of 100 mg/mL following 24 h exposure. The mortality rate of D. gallinae induced by D. viscosa extracts ranged from 25 to 45% following 48 h exposure at a concentration of 200 mg/mL. The acetonic extract of D. viscosa and D. maritima displayed the highest efficacy against D. gallinae. This study provides evidence of the diversity of bioactive compounds present in D. maritima bulbs and D. viscosa leaf extracts, which are both efficacious against D. gallinae. The higher efficacy of D. maritima bulb extracts might be linked to the presence of bufadienolides in its extracts.

Activity of native and commercial strains of Metarhizium spp. against the poultry red mite Dermanyssus gallinae under different environmental conditions

The poultry red mite (PRM), Dermanyssus gallinae, is a major pest of laying hens with extremely limited control means. To evaluate the potential of natural and commercial entomopathogenic fungi (EPF) for use against D. gallinae, we tested four wild populations of D. gallinae from Israeli farms. The genus Aspergillus was identified as the most abundant isolates from the mites. Additionally, eight new isolates of Metarhizium belonging to the specie M. brunneum were identified. At all sites from which mites were collected in both seasons, the abundance of fungi on D. gallinae was greater during the winter season than during the summer season. Through indirect inoculations of adult D. gallinae, we examined the virulence of the native Metarhizium species, the commercial strain Ma-43 and a previously described acaropathogenic strain (Ma-7). All of the Metarhizium strains caused 56-95% mortality of adult mites by seven days after inoculation at a concentration of 5 × 10⁵ conidia per cm². The efficacies of Ma-43, Ma-7 and the most promising native strain were tested under optimal abiotic conditions (28°C; 85-100% RH) and abiotic conditions similar to those typically found in a poultry house (30 °C; 60% RH). Under optimal conditions, the efficacy of all three stains ranged between 85 and 92%. In contrast, under poultry-house conditions, the efficacy of control ranged between 30 and 40%. The incidence of mycoses on mite cadavers was significantly decreased under poultry-house conditions. These results demonstrate the potential of native and commercial Metarhizium strains for use as biopesticides. Future research should address suitable delivery methods and formulations for the effective control of D. gallinae under poultry-house conditions.

Essential oils and Beauveria bassiana against Dermanyssus gallinae (Acari: Dermanyssidae): Towards new natural acaricides

Essential oils (EOs) and entomopathogenic fungi such as Beauveria bassiana (Bb) strains have the potential to be used as alternative insecticides and acaricides for controlling ectoparasites as Dermanyssus gallinae. These compounds have some limitations in their use: the acaricidal effect of EOs is rapid, but short-lived, whilst that of Bb is delayed, but long-lived. To evaluate the effect of both compounds combined against D. gallinae, the non-toxic dose of Eucalyptus globulus, Eucalyptus citriodora, Thymus vulgaris and Eugenia caryophyllata essential oils were firstly calculated for "native" strains of Bb. Subsequently, the effects of the combination of selected EOs with Bb against nymph and adult poultry red mites (PRMs) was assessed. EO concentrations ranging from 0.0015 to 8% v/v (i.e., nine double dilutions) were used to evaluate their effect on germination, sporulation and vegetative growth rates of native strains of Bb. A total of 1440 mites (720 nymphs and 720 adults) were divided into three-treated group (TGs) and one control group (CG). In TGs, mites were exposed to Bb in combination with the selected EO (TG1), EO alone (TG2) or Bb (TG3) alone. In the CG, mites were exposed to 0.1% tween 80 plus EO solvent (CG). E. globulus and E. citriodora were toxic for Bb in concentrations higher than 0.2% and 0.003% respectively, whilst E. caryophyllata and T. vulgaris were toxic at all concentrations tested against Bb. Based on the results of the toxicity assays against Bb, E. globulus was chosen to be tested as acaricide resulting non-toxic for Bb at concentration lower than 0.4%. Increased mortality of D. gallinae adults was recorded in TG1 than those in other TGs from 4days post-infection (T+4DPI). A 100% mortality of D. gallinae was recorded in adults at T+9DPI and at T+10DPI in nymphs in TG1 and later than T+11DPI in the other TGs. Used in combination with E. globulus, Bb displayed an earlier acaricidal effect towards both haematophagous D. gallinae stages. The combination of B. bassiana and E. globulus at 0.2% might be used for controlling arthropods of medical and veterinary importance as D. gallinae.