Diatomaceous earth increases the efficacy of Beauveria bassiana against Tribolium castaneum larvae and increases conidia attachment

A life-and-death struggle: interaction of insects with entomopathogenic fungi across various infection stages

Insects constitute approximately 75% of the world's recognized fauna, with the majority of species considered as pests. Entomopathogenic fungi (EPF) are parasitic microorganisms capable of efficiently infecting insects, rendering them potent biopesticides. In response to infections, insects have evolved diverse defense mechanisms, prompting EPF to develop a variety of strategies to overcome or circumvent host defenses. While the interaction mechanisms between EPF and insects is well established, recent findings underscore that their interplay is more intricate than previously thought, especially evident across different stages of EPF infection. This review primarily focuses on the interplay between EPF and the insect defense strategies, centered around three infection stages: (1) Early infection stage: involving the pre-contact detection and avoidance behavior of EPF in insects, along with the induction of behavioral responses upon contact with the host cuticle; (2) Penetration and intra-hemolymph growth stage: involving the initiation of intricate cellular and humoral immune functions in insects, while symbiotic microbes can further contribute to host resistance; (3) Host insect's death stage: involving the ultimate confrontation between pathogens and insects. Infected insects strive to separate themselves from the healthy population, while pathogens rely on the infected insects to spread to new hosts. Also, we discuss a novel pest management strategy underlying the cooperation between EPF infection and disturbing the insect immune system. By enhancing our understanding of the intricate interplay between EPF and the insect, this review provides novel perspectives for EPF-mediated pest management and developing effective fungal insecticides.

Transcriptomic landscape of the interaction between the entomopathogenic fungus Beauveria bassiana and its tolerant host Tribolium castaneum revealed by dual RNA-seq

Entomopathogenic fungi such as Beauveria bassiana are the only insect pathogens able to start the infection process by penetrating through the host cuticle. However, some insects try to avoid fungal infection by embedding their cuticle with antifungal compounds. This is the case of the red flour beetle Tribolium castaneum, which generates economical loss of great significance in stored product environments worldwide. In this study, T. castaneum adults were fed during different time periods (from 3 to 72 h) on B. bassiana conidia-covered corn kernels. The progression of fungal infection was monitored using the dual RNA-seq technique to reconstruct the temporal transcriptomic profile and to perform gene enrichment analyses in both interacting organisms. After mapping the total reads with the B. bassiana genome, 904 genes were identified during this process. The more expressed fungal genes were related to carbon catabolite repression, cation binding, peptidase inhibition, redox processes, and stress response. Several immune-related genes from Toll, IMD, and JNK pathways, as well as genes related to chitin modification, were found to be differentially expressed in fungus-exposed T. castaneum. This study represents the first dual transcriptomic approach to help understand the interaction between the entomopathogenic fungus B. bassiana and its tolerant host T. castaneum.

The Registration Situation and Use of Mycopesticides in the World

Mycopesticides are living preparations that use fungal cells, such as spores and hyphae, as active ingredients. They mainly include mycoinsecticides, mycofungicides, mycoherbicides and nematophagous fungi. The utilization of fungi for controlling agricultural pests can be traced back to approximately 1880, when entomopathogenic fungi were initially employed for this purpose. However, it was not until 1965 that the world's first mycopesticide, Beauveria bassiana, was registered as Boverin® in the former Soviet Union. In past decades, numerous novel mycopesticides have been developed for their lower R&D costs, as well as the environmentally friendly and safe nature. In this review, we investigated the mycopesticides situation of registration in USA, EU, China, Canada and Australia. Superisingly, it was found that the registered mycopesticides are extremely raised in recent years. Currently, the insecticides, fungicides (nematocides) and herbicides were respectively registered 27, 53 and 8 fungal strains. This paper also analyzes the main problems currently faced by mycopesticides and offers suggestions for their future development.

The Potential of Two Entomopathogenic Fungi and Enhanced Diatomaceous Earth Mixed with Abamectin: A Comprehensive Study on Mortality, Progeny Production, Application Method, and Surface Application against Tribolium castaneum

This study determined the efficacy of Beauveria bassiana (Bals. -Criv.) Vuill., Metarhizium anisopliae (Metchnikoff) Sorokin, and diatomaceous earth mixed with abamectin (DEA) alone and in their combinations for the integrated management of larvae and adults of Tribolium castaneum (Herbst) from three field populations of Pakistan (Multan, Rawalpindi, and Rahim Yar Khan) and one laboratory population (Faisalabad). Treatments were applied on three surfaces, namely, viz. steel, concrete, and jute bags, implementing two application methods, dusting and spraying. The combined treatments were more effective in comparison with single treatments for both larvae and adults. Overall, the highest mortality rates were recorded in the Faisalabad population, followed by the Rehaim Yar Khan, Rawalpindi, and Multan populations. Progeny production was suspended 21 days after exposure to the combined treatment of DEA and both fungi in all populations except Rawalpindi. Larvae were found to be more susceptible than adults in all treatments and intervals. Dusting was more efficient than spraying for both larvae and adults and for all the populations studied. The present study provides a wholistic understanding of the impact of different factors on the success of the combined treatments using DEA and entomopathogenic fungi, supporting their use as surface treatments.

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.

Two are better than one: the combinations of Beauveria bassiana, diatomaceous earth, and indoxacarb as effective wheat protectants

The current study evaluates the efficacy of the entomopathogenic fungus Beauveria bassiana (Balsamo-Crivelli) Vuillemin (Hypocreales: Cordycipitaceae), diatomaceous earth (DE) (Protect-It), and the oxadiazine indoxacarb, at single or combined applications on wheat kernels, for the management of the rusty grain beetle, Cryptolestes ferrugineus (Stephens) (Coleoptera: Laemophloeidae), the red flour beetle, Tribolium castaneum (Herbst) (Coleoptera: Tenebrionidae), the khapra beetle, Trogoderma granarium Everts (Coleoptera: Dermestidae), and the lesser grain borer, Rhyzopertha dominica (F.) (Coleoptera: Bostrychidae). The study was conducted between November 2020 and August 2021 in Faisalabad under a complete randomized block design. The combination of DE + indoxacarb was the most efficient as it caused higher overall mortalities ranging between 59.34 and 100%, and lower overall progeny production ranging between 8.35 and 33.70 individuals per vial, than all other treatments. Beauveria bassiana alone exhibited the lowest mortality rates ranging between 22.33 and 47.76%, and the highest offspring emergence, ranging between 51.33 and 78.55 individuals per vial. Similar pattern was observed when persistence bioassays were conducted. For a period of 120 days, the DE + indoxacarb was the most powerful combination against all tested species, providing overall mortality rates between 17.06 and 63.80%. The overall progeny production was lower for the insect individuals exposed on wheat treated with the DE + indoxacarb combination, ranging between 13.66 and 52.23 individuals per vial, and higher for those exposed to B. bassiana alone, ranging between 44.03 and 107.67 individuals per vial, for the entire duration of storage. However, the efficacy of all treatments decreased gradually during the course of storage. The findings of the current study indicate that the combinations of entomopathogenic fungi, DE, and indoxacarb can be used for the prolonged protection of stored wheat from the tested noxious insect species of stored products. Further research, which will include other inert dusts in combination with entomopathogenic fungi and indoxacarb, may provide additional knowledge towards an effective management of noxious species occurring in storages.

Optimization of Submerged Culture Parameters of the Aphid Pathogenic Fungus Fusarium equiseti Based on Sporulation and Mycelial Biomass

Fusarium equiseti (JMF-01), as an entomopathogenic fungus, can effectively control agricultural pests and has the potential to be a biocontrol agent. To promote mycelial growth and sporulation, we investigated the optimal submerged culture conditions for F. equiseti. In this study, we used the single-factor method and Box-Behnken design and determined the virulence of the submerged culture against Myzus persicae after optimization. As a result, the highly significant factors affecting the spore concentration of strain JMF-01 were the primary inoculum density and the initial pH, and the highly significant factor affecting the mycelial biomass was the medium-to-flask ratio. The highest mycelial biomass value was 0.35 g when the incubation time was 5.68 days, the initial pH was 5.11, the medium-to-flask ratio was 0.43, and 1 mL of the primary inoculum with spore density of 0.97 × 10⁷ conidia/mL was added. When the incubation time was 6.32 days, the initial pH was 4.46, the medium-to-flask ratio was 0.35, the primary inoculum density was 1.32 × 10⁷ conidia/mL of 1 mL, and the highest spore concentration of 6.49 × 10⁸ blastospores/mL was obtained. Compared with the unoptimized medium conditions, the optimized submerged culture had the highest mycelial biomass and spore concentration, which were 3.46 and 2.06 times higher, respectively. The optimized submerged culture was highly pathogenic toward M. persicae, reaching a 95% mortality rate. Our results provide optimal submerged culture conditions for F. equiseti and lay the basis for later research to expand production for pest control.

Laboratory and field studies on the combined application of Beauveria bassiana and fipronil against four major stored-product coleopteran insect pests

In the current study we have tested the application of Beauveria bassiana (Hypocreales: Cordycipitaceae) alone and in combination with fipronil at two doses against Tribolium castaneum (Coleoptera: Tenebrionidae), Rhyzopertha dominica (Coleoptera: Bostrychidae), Sitophilus granarius (Coleoptera: Curculionidae), and Trogoderma granarium (Coleoptera: Dermestidae) under laboratory and field conditions. At laboratory conditions, the combination of B. bassiana with the highest dose of fipronil produced the highest mortality. At different temperatures, mortality was increased with the increase in temperature. Maximum mortality was observed at 30 °C, followed by 25 °C and 20 °C for all tested species. Different treatments significantly reduced the progeny number in comparison to control groups for all tested species at all temperatures. In the persistence trial, all treatments that included the combinations of B. bassiana with fipronil produced significantly higher mortalities than the single treatments for all tested species over a period of 6 months. Furthermore, all treatments significantly reduced the number of progenies of all insect species in comparison with the control groups over the same storage period. In field trials, mortalities of all tested insect species were significantly higher on wheat treated with B. bassiana, fipronil, or their combinations than on controls for an entire storage period of 180 days. Overall, R. dominica was found the most susceptible species followed by S. granarius, T. castaneum, and T. granarium. The findings of the current study suggest that the use of B. bassiana and fipronil as grain protectants may provide elevated control against major stored-grain insect species during a prolonged period of storage.

Secretion and Detection of Defensive Compounds by the Red Flour Beetle Tribolium castaneum Interacting with the Insect Pathogenic Fungus Beauveria bassiana

Entomopathogenic fungi such as Beauveria bassiana are extensively used for the control of insect pests worldwide. They infect mostly by adhesion to the insect surface and penetration through the cuticle. However, some insects, such as the red flour beetle Tribolium castaneum (Herbst), have evolved resistance by embedding their cuticle with antifungal compounds. Thus, they avoid fungal germination on the cuticle, which result in low susceptibility to entomopathogenic fungi. In adult T. castaneum, these antifungals are the well-known defensive compounds methyl-1,4- and ethyl-1,4-benzoquinone. In this study, we added B. bassiana conidia on the diet of adult beetles to study the effect of the entomopathogen on the secretion and detection of the beetle volatile blend containing both benzoquinones. The compounds were analyzed by solid phase microextraction coupled to gas chromatography–flame ionization detection, and were detected by electroantennography. In addition, we measured the expression level of four genes encoding for two odorant-binding proteins (OBP), one chemosensory protein (CSP), and one odorant receptor (OR) in both healthy and fungus-treated insects. Significant alterations in the secretion of both benzoquinones, as well as in the perception of methyl-1,4-benzoquinone, were found in fungus-treated insects. TcOBP7D, TcOBP0A and TcCSP3A genes were down-regulated in insects fed conidia for 12 and 48 h, and the latter gene was up-regulated in 72 h samples. TcOR1 expression was not altered at the feeding times studied. We conclude that fungus-treated insects alter both secretion and perception of benzoquinones, but additional functional and genetic studies are needed to fully understand the effects of fungal infection on the insect chemical ecology.

Diatomaceous Earth for Arthropod Pest Control: Back to the Future

Nowadays, we are tackling various issues related to the overuse of synthetic insecticides. Growing concerns about biodiversity, animal and human welfare, and food security are pushing agriculture toward a more sustainable approach, and research is moving in this direction, looking for environmentally friendly alternatives to be adopted in Integrated Pest Management (IPM) protocols. In this regard, inert dusts, especially diatomaceous earths (DEs), hold a significant promise to prevent and control a wide range of arthropod pests. DEs are a type of naturally occurring soft siliceous sedimentary rock, consisting of the fossilized exoskeleton of unicellular algae, which are called diatoms. Mainly adopted for the control of stored product pests, DEs have found also their use against some household insects living in a dry environment, such as bed bugs, or insects of agricultural interest. In this article, we reported a comprehensive review of the use of DEs against different arthropod pest taxa, such as Acarina, Blattodea, Coleoptera, Diptera, Hemiptera, Hymenoptera, Ixodida, Lepidoptera, when applied either alone or in combination with other techniques. The mechanisms of action of DEs, their real-world applications, and challenges related to their adoption in IPM programs are critically reported.

Isolation, fermentation, and formulation of entomopathogenic fungi virulent against adults of Diaphorina citri

BACKGROUND

Mycopesticides are important for integrated management of the Asian citrus psyllid, Diaphorina citri. However, there are few reports on the fermentation and formulation for mycopesticides with high virulence against D. citri.

RESULTS

From four different locations in South China, 12 fungal strains were isolated and classified into Beauveria bassiana (two isolates), Fusarium fujikuroi (five isolates), and Cordyceps javanica (five isolates) based on the phylogenetic analysis of ITS1-5.8S rDNA-ITS4 and morphology of colonies and conidia. Based on the highest initial virulence (86.52 ± 2.35%) and best growth characteristics, F-HY002-ACPHali was further optimized for biphasic fermentation (7.85 ± 2.62 × 10⁹  g^-1  dry substrate) with soybean meal + cottonseed flour (1:1) as the solid substrate and full light as the light/dark cycle. Furthermore, the oil-based conidial formulation was optimized with sesame oil as an effective carrier, which significantly enhanced conidial shelf life up to 16 weeks at 26 °C and 4 °C, thermo-stress (50 °C) and UV-B stress resistance, and virulence against adults of D. citri with increased mortalities and decreased LT₅₀ in comparison to that of unformulated conidia.

CONCLUSION

Our results not only provide a valuable native strain with high virulence against adults of D. citri, but also imply the soybean meal + cottonseed flour as valuable solid substrate, full-light exposure as environmental stimuli for solid-state fermentation, and the sesame oil as an effective carrier for the formulation of the C. javanica. These findings will facilitate the development of a potential mycopesticide for the biological control of Asian citrus psyllid.

The Interaction between Tribolium castaneum and Mycotoxigenic Aspergillus flavus in Maize Flour

Simple Summary

It is important to hold cereals in storage conditions that exclude insect pests such as the red flour beetle and fungi, especially mycotoxin-producing ones (as a few strains of Aspergillus flavus). This work aims to investigate the interaction between these two organisms when thriving in maize flour. It was observed that when both organisms were together, the mycotoxins detected in maize flour were far higher than when the fungi were on their own, suggesting that the presence of insects may contribute positively to fungi development and mycotoxin production. The insects in contact with the fungi were almost all dead at the end of the trials, suggesting a negative effect of the fungi growth on the insects. Both organisms interacted when in contact. This is the first study on this issue, although further investigation would benefit from clarification on the mechanisms leading to the nature of the detected interactions.

Abstract

Tribolium castaneum is one of the most common insect pests of stored products. Its presence makes cereals more susceptible to the spread of the fungi Aspergillus flavus, which may produce mycotoxins. The aim of this work was to evaluate the influence of T. castaneum adults on the development of a mycotoxigenic A. flavus strain in maize flour as well as the influence of this fungus on the insects. Maize flour was exposed to T. castaneum, spores of A. flavus or to both. The results revealed an interaction between T. castaneum and A. flavus as the flour exposed to both organisms was totally colonized by the fungus whereas almost all the insects were killed. Aflatoxin B1 (AFB1) revealed a significantly higher concentration in the flour inoculated with both organisms (18.8 µg/kg), being lower when exposed only to A. flavus, suggesting that the presence of insects may trigger fungal development and enhance mycotoxin production. The ability of these organisms to thrive under the same conditions and the chemical compounds they release makes the interaction between them a subject of great importance to maintain the safety of stored maize. This is the first work evaluating the interaction between T. castaneum and A. flavus mycotoxin production.

Not Only a Formulation: The Effects of Pickering Emulsion on the Entomopathogenic Action of Metarhizium brunneum

Growing global population and environmental concerns necessitate the transition from chemical to eco-friendly pest management. Entomopathogenic fungi (EPF) are rising candidates for this task due to their ease of growing, broad host range and unique disease process, allowing EPF to infect hosts directly through its cuticle. However, EPF’s requirement for high humidity negates their integration into conventional agriculture. To mitigate this problem, we formulated Metarhizium brunneum conidia in an oil-in-water Pickering emulsion. Conidia in aqueous and emulsion formulations were sprayed on Ricinus communis leaves, and Spodoptera littoralis larvae were introduced under low or high humidity. The following were examined: conidial dispersion on leaf, larval mortality, conidial acquisition by larvae, effects on larval growth and feeding, and dynamic of disease progression. Emulsion was found to disperse conidia more efficiently and caused two-fold more adhesion of conidia to host cuticle. Mortality from conidia in emulsion was significantly higher than other treatments reaching 86.5% under high humidity. Emulsion was also found to significantly reduce larval growth and feeding, while conferring faster fungal growth in-host. Results suggest that a Pickering emulsion is able to improve physical interactions between the conidia and their surroundings, while weakening the host through a plethora of mechanisms, increasing the chance of an acute infection.

Persistence and efficacy of enhanced diatomaceous earth, imidacloprid, and Beauveria bassiana against three coleopteran and one psocid stored-grain insects

The residual efficacy of the enhanced diatomaceous earth (DE) formulation DEBBM alone and in combination with Beauveria bassiana (Hypocreales: Cordycipitaceae) or with the neonicotinoid insecticide imidacloprid against Tribolium castaneum (Coleoptera: Tenebrionidae), Rhyzopertha dominica (Coleoptera: Bostrychidae), Cryptolestes ferrugineus (Coleoptera: Laemophloeidae), and Liposcelis paeta (Psocoptera: Liposcelididae) was investigated in the laboratory. The combination treatments were more effective compared to the single treatments against all examined species. The combinations of DEBBM and imidacloprid and imidacloprid with the highest dose rate of B. bassiana provided the highest mortality values against all tested species for 90 days of storage period. The combination of DEBBM plus B. bassiana resulted to the highest mortalities and to the lowest offspring production of all combinations tested after 180 days of storage. Mortality of adults for each test insect species was decreased over the storage period of 6 months, and the progeny production was increased with the extended storage period. Among the tested insect species, L. paeta was the most susceptible to all three grain protectants followed by C. ferrugineus, R. domina, and T. castaneum. The findings of the current study suggest that the use of DEBBM, imidacloprid, and B. bassiana as grain protectants may provide elevated control of major stored-grain insect species during a prolonged period of storage.

The Effect of Grain Type on Virulence of Entomopathogenic Fungi Against Stored Product Pests

Fungal virulence is multifaceted and dependent on multiple abiotic factors. The present study represents an investigation of the effect of one such abiotic factor, that of the grain type, on the insecticidal action of three entomopathogenic fungal species, Beauveria bassiana (Balsamo) Vuillemin (Hypocreales: Cordycipitaceae), Metarhizium anisopliae (Metschinkoff) Sorokin (Hypocreales: Clavicipitaceae) and Isaria fumosorosea Wize (Hypocreales: Clavicipitaceae) on larvae of the three very common and destructive stored product pests: the khapra beetle (Trogoderma granarium Everts) (Coleoptera: Dermestidae), the confused flour beetle (Tribolium confusum Jacquelin du Val) (Coleoptera: Tenebrionidae) and the Mediterranean flour moth (Ephestia kuehniella Zeller) (Lepidoptera: Pyralidae). To this end, we selected four different grains, i.e., Triticum aestivum L. (Poales: Poaceae), Oryza sativa L. (Poales: Poaceae), Arachis hypogaea L. (Fabales: Fabaceae) and Vicia faba L. (Fabales: Fabaceae). Bioassays were carried out in the lab, where experimental grains were sprayed with 1 mL of conidial suspension (108 conidia/mL) from each isolate. Mean mortality, median survival time and weight loss of seeds were estimated for each species. Our results suggest that the differences in the efficacy of entomopathogenic fungi were dependent both on the isolates and the grain. The grain type as a factor is equally important to other abiotic factors.

The Time-Concentration-Mortality Responses of Western Flower Thrips, Frankliniella occidentalis, to the Synergistic Interaction of Entomopathogenic Fungus Metarhizium flavoviride, Insecticides, and Diatomaceous Earth

Western flower thrips (WFT), Frankliniella occidentalis (Pergande), is a highly invasive pest which is harmful to many cash crops globally and resistant to various insecticides. Entomopathogenic fungi (EPF), as biological control agents, have demonstrated a good control effect on WFT. The aim of this study was to evaluate the synergistic and pathogenicity efficacy of the fungal strain Metarhizium flavoviride WSWL51721 when distributed with diatomaceous earth (DE) and the active ingredient imidacloprid using four bioassay methods against adult and second instar larvae of WFT. The data of the four bioassays have been fitted to the time–concentration–mortality (TCM) model. The corrected mortality ranges of WFT adults were 75–100%, 82.69–100%, 78.85–100%, and 92.31–100%, and the corrected mortality ranges of WFT second instar larvae were 72.22–100%, 85.19–100%, 77.77–100%, and 100% in the four bioassays at concentrations of 1.2 × 10⁶ to 1.2 × 10⁸ conidia/mL, respectively. At 1.2 × 10⁸ conidia/mL, assays 2 (M. flavoviride with DE), 3 (M. flavoviride with imidacloprid), and 4 (M. flavoviride with DE and imidacloprid) had the shortest median lethal time (LT₅₀), compared with that of assay 1 (M. flavoviride alone) for adults at 2.26 d, 2.06 d, and 1.53 d, and second instar larvae at 2.45 d, 1.70 d, and 1.41 d, respectively. The median lethal concentration (LC₅₀) in the four bioassays decreased within 3–10 days of inoculation. On the third day, it was found that the lowest median lethal concentrations in assays 2, 3, and 4 were 1.58 × 10⁷, 1.13 × 10⁷, and 3.39 × 10⁶ conidia/mL, respectively, which were significantly different from that in assay 1 for the adults. For the second instar larvae, assays 2, 3, and 4 also had the lowest lethal concentrations and were significantly different from those of assay 1. There were significant differences in sporulation between adults and second instar larvae under the four bioassays. Our results indicate that assays 2 (M. flavoviride with DE), 3 (M. flavoviride with imidacloprid), and 4 (M. flavoviride with DE and imidacloprid) demonstrate synergistic effects on the control of both adult and second instar larvae of WFT under laboratory conditions.

Activity of additives and their effect in formulations of Metarhizium anisopliae s.l. IP 46 against Aedes aegypti adults and on post mortem conidiogenesis

BACKGROUND

Oil formulations of entomopathogenic fungi have interest for biological mosquito control.

OBJECTIVES

The activities of M. anisopliae s.l. IP 46 conidia were tested in Aedes aegypti adults either without any formulation or formulated with vegetable or mineral oil and in combination with diatomaceous earth.

FINDINGS

IP 46 was highly active against adults, the vector of important arboviruses in the tropics and subtropics. At an exposure of adults to 3.3 × 10⁷ conidia/cm², values of lethal times TL₅₀ and TL₉₀ reached minimal 3.8 and 4.6 days, respectively, and lethal concentrations LC₅₀ and LC₉₀ were 2.7 × 10⁵ and 2.4 × 10⁶ conidia/cm², respectively, after 10 days of exposure. Activity against adults was improved by diatomaceous earth (KeepDry^® KD) combined with mineral oil (Naturol^® N) or vegetable oil (Graxol^® G). Additives KD or N separately (and G to a lesser extent) or in combination, KD + N and KD + G without conidia had also a clear adulticidal effect. Efficacy of conidia formulated or not with KD + N decreased somewhat at shorter exposure periods. Time of exposure (0.017, 12, 48, 72 or 120 h) of adults to KD and N or IP 46 or conidia and KD and N had no significant effect on mortality. M. anisopliae s.l. recycled on fungus-killed mosquitoes producing high quantities of new conidia regardless of the conidial concentrations or formulations tested. Additives tested had no clear effect on quantitative conidiogenesis on cadavers.

MAIN CONCLUSIONS

Formulations of IP 46 conidia with mineral oil and diatomaceous earth represent a promising tool for the development of potent strategies of focal control of this important vector with entomopathogenic fungi.

Combining electrostatic powder with an insecticide: effect on stored-product beetles and on the commodity

BACKROUND

The opportunity to reduce the amount of pirimiphos-methyl applied to grain by formulating it in an electrostatic powder was investigated. The insecticidal efficacy of pirimiphos-methyl in EC formulation or formulated using electrostatic powder (EP) as an inert carrier was investigated against Sitophilus oryzae (L.), Oryzaephilus surinamensis (L.), Rhyzopertha dominica (F.) and Tribolium confusum Jacquelin du Val. Furthermore, the adhesive properties of EP to rice, corn and wheat, together with the effect on bulk density and bread- and pasta-making properties, were investigated.

RESULTS

The results showed that pirimiphos-methyl formulated with EP provided better efficacy against adults when compared with EC formulation for O. surinamensis and T. confusum, but there was no difference for R. dominica. Progeny production was consistently lower in grain treated with the EP formulation than in grain treated with the EC. Tests showed that EP adhered to the kernels for longer on hard wheat than on maize or rice. In most commodities, EP did not alter the bulk density. Finally, the addition of EP did not affect flour- and bread-making properties, nor the pasta-making properties.

CONCLUSIONS

The results of the present study suggest that an EP could be used to reduce the amount of pirimiphos-methyl applied to grain for effective pest control, with no detrimental effects on grain quality. © 2016 Society of Chemical Industry.

Improving Efficacy of Beauveria bassiana against Stored Grain Beetles with a Synergistic Co-Formulant

The potential of a dry powder co-formulant, kaolin, to improve the control of storage beetles by the entomopathogenic fungus Beauveria bassiana, isolate IMI389521, was investigated. The response of Oryzaephilus surinamensis adults to the fungus when applied to wheat at 1 × 10¹⁰ conidia per kg with and without kaolin at 1.74 g per kg wheat was assessed. Addition of kaolin increased control from 46% to 88% at day 7 and from 81% to 99% at day 14 post-treatment. Following this the dose response of O. surinamensis and Tribolium confusum to both kaolin and the fungus was investigated. Synergistic effects were evident against O. surinamensis at ≥0.96 g of kaolin per kg of wheat when combined with the fungus at all concentrations tested. For T. confusum, adult mortality did not exceed 55%, however, the larvae were extremely susceptible with almost complete suppression of adult emergence at the lowest fungal rate tested even without the addition of kaolin. Finally, the dose response of Sitophilus granarius to the fungus at 15 and 25 °C, with and without kaolin at 1 g per kg of wheat, was examined. Improvements in efficacy were achieved by including kaolin at every fungal rate tested and by increasing the temperature. Kaolin by itself was not effective, only when combined with the fungus was an effect observed, indicating that kaolin was having a synergistic effect on the fungus.

Tenebrionid secretions and a fungal benzoquinone oxidoreductase form competing components of an arms race between a host and pathogen

Entomopathogenic fungi and their insect hosts represent a model system for examining invertebrate-pathogen coevolutionary selection processes. Here we report the characterization of competing components of an arms race consisting of insect protective antimicrobial compounds and evolving fungal mechanisms of detoxification. The insect pathogenic fungus Beauveria bassiana has a remarkably wide host range; however, some insects are resistant to fungal infection. Among resistant insects is the tenebrionid beetle Tribolium castaneum that produces benzoquinone-containing defensive secretions. Reduced fungal germination and growth was seen in media containing T. castaneum dichloromethane extracts or synthetic benzoquinone. In response to benzoquinone exposure, the fungus expresses a 1,4-benzoquinone oxidoreductase, BbbqrA, induced >40-fold. Gene knockout mutants (ΔBbbqrA) showed increased growth inhibition, whereas B. bassiana overexpressing BbbqrA (Bb::BbbqrA(O)) displayed increased resistance to benzoquinone compared with wild type. Increased benzoquinone reductase activity was detected in wild-type cells exposed to benzoquinone and in the overexpression strain. Heterologous expression and purification of BbBqrA in Escherichia coli confirmed NAD(P)H-dependent benzoquinone reductase activity. The ΔBbbqrA strain showed decreased virulence toward T. castaneum, whereas overexpression of BbbqrA increased mortality versus T. castaneum. No change in virulence was seen for the ΔBbbqrA or Bb::BbbqrA(O) strains when tested against the greater wax moth Galleria mellonella or the beetle Sitophilus oryzae, neither of which produce significant amounts of cuticular quinones. The observation that artificial overexpression of BbbqrA results in increased virulence only toward quinone-secreting insects implies the lack of strong selection or current failure of B. bassiana to counteradapt to this particular host defense throughout evolution.

Characterization, mode of action, and efficacy of twelve silica-based acaricides against poultry red mite (Dermanyssus gallinae) in vitro

Poultry red mite infestation still is an unsolved problem in poultry farms. Legal regulations, residue risks, and resistances limit chemical control of mites. Alternatives to chemical acaricides for control of poultry red mite are silica-based products, which have as a main constituent silicon dioxide. The acaricidal effect is attributed to sorptive properties of the particles, which result in the mite's death by desiccation. In the present study, the acaricidal efficacy of 12 products containing natural or synthetic silica, 9 in powder form, and 3 for liquid application was tested under laboratory conditions. Mite mortality was measured at several intervals and the mean lethal time (LT₅₀) determined by Probit analysis after Abbott's correction. The LT₅₀ values of the products significantly differed (Tukey's HSD p < 0.05). LT₅₀ values of powdery formulations ranged from 5.1 to 18.7 h and overlapped with those of the fluid ones which ranged from 5.5 to 12.7 h. In order to explain the differences in efficacy of the tested silica products, further characterizations were carried out. X-ray fluorescence, specific surface, cation exchange capacity (CEC), and water absorption capacity (WAC) were measured. Furthermore, electron microscopy was conducted and different products compared. Silicon dioxide content (ranging from 65 to 89% for powders and 57 to 80% for fluids) had no significant impact on efficacy, while specific surface and CEC (2.4-23.2 mEq 100(-1) g(-1) for powders and 18-30.8 mEq 100(-1) g(-1)) were positively and WAC (1.3-4.4 wt% for powders and 3.3-4.8 wt% for fluids) negatively related to the acaricidal efficacy. Influence of these parameters on acaricidal efficacy was significant according to the results of a stepwise regression analysis (p < 0.01).

Synergistic interaction between the fungus Beauveria bassiana and desiccant dusts applied against poultry red mites (Dermanyssus gallinae)

The poultry red mite, Dermanyssus gallinae, is a major pest in egg production, feeding on laying hens. Widely used non-chemical control methods include desiccant dusts, although their persistence under field conditions is often short. Entomopathogenic fungi may also hold potential for mite control, but these fungi often take several days to kill mites. Laboratory experiments were carried out to study the efficacy of 3 types of desiccant dusts, the fungus Beauveria bassiana and combinations of the two control agents against D. gallinae. There was significant synergistic interaction between each of the desiccant dusts and the fungus, with observed levels of mite mortality significantly higher than those expected for an additive effect (up to 38 % higher). Synergistic interaction between desiccant dust and fungus was found also when different application methods were used for the fungus and at different levels of relative humidity. Although increased levels of mortality were reached due to the synergistic interaction, the speed of lethal action was not influenced by combining the two components. The persistence of the control agents applied separately or in combination did not change over a period of 4 weeks. Overall, combinations of desiccant dusts and fungus conidia seem to hold considerable promise for future non-chemical control of poultry red mites.

Naturally occurring entomopathogenic fungi infecting stored grain insect species in Punjab, Pakistan

The occurrence of entomopathogenic fungi isolated from stored grain insect pests sampled from various geographical regions of Punjab, Pakistan, was investigated. In total, 25,720 insects from six different species were evaluated, and 195 isolates from 24 different fungal species were recovered. These included the Ascomycetes Beauveria bassiana sensu lato (Balsamo) Vuillemin (Hypocreales: Clavicipitaceae), Metarhizium anisopliae sensu lato (Metschnikoff) Sorokin (Hypocreales: Clavicipitaceae), Purpureocillium lilacinum (Thorn) Samson (Hypocreales: Ophiocordycipitaceae), and Lecanicillium attenuatum (Zare and W. Gams) (Hypocreales: Clavicipitaceae). The cadavers of red flour beetle Tribolium castaneum (Herbst.) (Coleoptera: Tenebrionidae) were significantly infected with the fungi followed by rice weevil Sitophilus oryzae (L.) (Coleoptera: Curculionidae), lesser grain borer Rhyzopertha dominica (F.) (Coleoptera: Bostrichidae), rusty grain beetle Cryptolestes ferrugineus (Stephens) (Coleoptera: Cucujidae), and cowpea weevil Callosobruchus maculatus (F.) (Coleoptera: Bruchidae); however, the least were recovered from khapra beetle Trogoderma granarium (Everts) (Coleoptera: Dermestidae). The geographical attributes (altitude, longitude, and latitude) greatly influenced the occurrence of entomopathogenic fungi with highest number of isolates found from >400 (m) altitude, 33°-34' N latitude, and 73°-74' E longitude. The findings of the current surveys clearly indicated that the entomopathogenic fungi are widely distributed in the insect cadavers, which may later be used in successful Integrated Pest Management programs.

Action on the Surface: Entomopathogenic Fungi versus the Insect Cuticle

Infections mediated by broad host range entomopathogenic fungi represent seminal observations that led to one of the first germ theories of disease and are a classic example of a co-evolutionary arms race between a pathogen and target hosts. These fungi are able to parasitize susceptible hosts via direct penetration of the cuticle with the initial and potentially determining interaction occurring between the fungal spore and the insect epicuticle. Entomogenous fungi have evolved mechanisms for adhesion and recognition of host surface cues that help direct an adaptive response that includes the production of: (a) hydrolytic, assimilatory, and/or detoxifying enzymes including lipase/esterases, catalases, cytochrome P450s, proteases, and chitinases; (b) specialized infectious structures, e.g., appressoria or penetrant tubes; and (c) secondary and other metabolites that facilitate infection. Aside from immune responses, insects have evolved a number of mechanisms to keep pathogens at bay that include: (a) the production of (epi) cuticular antimicrobial lipids, proteins, and metabolites; (b) shedding of the cuticle during development; and (c) behavioral-environmental adaptations such as induced fever, burrowing, and grooming, as well as potentially enlisting the help of other microbes, all intended to stop the pathogen before it can breach the cuticle. Virulence and host-defense can be considered to be under constant reciprocal selective pressure, and the action on the surface likely contributes to phenomena such as strain variation, host range, and the increased virulence often noted once a (low) virulent strain is "passaged" through an insect host. Since the cuticle represents the first point of contact and barrier between the fungus and the insect, the "action on the surface" may represent the defining interactions that ultimately can lead either to successful mycosis by the pathogen or successful defense by the host. Knowledge concerning the molecular mechanisms underlying this interaction can shed light on the ecology and evolution of virulence and can be used for rational design strategies at increasing the effectiveness of entomopathogenic fungi for pest control in field applications.

Dietary stress increases the susceptibility of Tribolium castaneum to Beauveria bassiana

Sanitation being an important component of chemical-free management of stored-products pests, the nutritional stress on insects that results from a clean environment may prove advantageous to the use of microbial controls. Dietary stress by food deprivation or suboptimal diet increased susceptibility of the red flour beetle, Tribolium castaneum (Herbst), larvae to Beauveria bassiana (Balsamo) Vuillemin. Fungus-related mortality increased linearly with the number of days of food deprivation. Rearing of larvae on a rice meal diet resulted in slower development and greater susceptibility to B. bassiana than rearing on whole wheat flour with brewer's yeast. Larvae that were fed for 24 h on flour with B. bassiana conidia consumed significantly less and weighed significantly less than those that were fed fungus-free flour. Thus, the presence of B. bassiana conidia is itself a cause of dietary stress.

Beauveria bassiana infection alters colony development and defensive secretions of the beetles Tribolium castaneum and Ulomoides dermestoides (Coleoptera: Tenebrionidae)

We studied the effect of the entomopathogenic fungus Beauveria bassiana strain GHA on a) colony development of the beetles Tribolium castaneum (Herbst) and Ulomoides dermestoides (Fairmaire) (Coleoptera: Tenebrionidae) under laboratory conditions; and 2) the volatile blend released by both beetles, containing defensive pheromones, by using the solid phase microextraction technique. Colony development of both species was strongly altered 3 mo after treatment with B. bassiana, showing a significant reduction in progeny of 37.5% for T. castaneum and 50.0% for U. dermestoides. We also showed that the volatiles released by T. castaneum diminished close to 20% compared with those of healthy beetles, whereas in U. dermestoides secretions dramatically dropped to 5%, 7 d after immersion in 1 x 10(9) conidia per ml. These results suggest that after infection events take place, fungus-induced diminished secretion of the defensive pheromones may be a physiologic clue for behavioral changes in infected beetles.

FATORES A SEREM CONSIDERADOS NA UTILIZAÇÃO DE BEAUVERIA BASSIANA VISANDO O MANEJO DE POPULAÇÕES DE ALPHITOBIUS DIAPERINUS EM AVIÁRIOS COMERCIAIS

RESUMO O trabalho foi desenvolvido com o objetivo de comparar a eficiência de preparações líquida e em pó do fungo Beauveria bassiana e também verificar quais efeitos que o tipo de solo e cama de aviário podem causar sobre o fungo, em condições de laboratório. A formulação em pó mostrouse mais eficiente que a líquida, causando mortalidade confirmada de larvas de 83,3 e de 33,4% de adultos, contra 18,7 e 12%, respectivamente para larvas e adultos. A CL50 da preparação em pó foi de 2,41 x 107 e 5,33 x 107 conídios/g e TL50 de 4,7 e 5,3 dias para larvas e adultos, respectivamente. O fungo em contato com o solo de aviário teve sua eficiência reduzida em cerca de 40% em relação ao tratamento com solo de barranco, e a mortalidade de larvas não diferiu quando se utilizou cama nova ou usada. A mortalidade de adultos foi baixa tanto para solo combinado à cama nova (11,5%) quanto usada (25%), bem como a mortalidade de larvas na aplicação do fungo sobre (58,7%) e abaixo (38,7%) da cama nova. Constatou-se que o aumento do tempo de contato dos insetos com os substratos tende a diminuir a mortalidade em cerca de 12 vezes, independente do substrato.

Biochemistry of insect epicuticle degradation by entomopathogenic fungi

The biochemical interaction between fungal pathogens and their insect host epicuticle was studied by examining fungal hydrocarbon degrading ability. As a contact insecticide, entomopathogenic fungi invade their host through the cuticle, covered by an outermost lipid layer mainly composed of highly stable, very long chain structures. Strains of Beauveria bassiana and Metarhizium anisopliae (Deuteromycotina: Hyphomycetes), pathogenic both to the blood-sucking bug Triatoma infestans (Hemiptera: Reduviidae) and the bean-weevil Acanthoscelides obtectus (Coleoptera, Bruchidae), were grown on different carbon sources. Alkane-grown cells showed a lipid pattern different from that of glucose-grown cells, evidenced by a major switch in the triacylglycerol and sterol components. Radiolabelled hydrocarbons were used to investigate the catabolic pathway and the by-product incorporation into fungal cellular components. The first oxidation round is presumably carried out by a cytochrome P450 enzyme system, the metabolites will traverse the peroxisomal membrane, and after successive transformations will eventually provide the appropriate fatty acyl CoA for complete degradation in the peroxisomes, the site of beta-oxidation in fungi. In this review, we will show the relationship between fungal ability to catabolize very long chain hydrocarbons and virulence parameters.