Significant mortality of eggs and young larvae of two pine processionary moth species due to the entomopathogenic fungus Metarhizium brunneum

Bioassays were conducted to determine the susceptibility of egg masses and young larvae of two pine processionary moth species, Thaumetopoea pityocampa and Thaumetopoea wilkinsoni, to two strains (ARSEF4556, V275) of the entomopathogenic fungus Metarhizium brunneum. Mortality of treated eggs by both strains ranged from 96% to 99% but not all of this was caused by M. brunneum since control groups also experienced egg mortality due to saprophytic fungi. Still, larvae hatched in the laboratory from eggs treated with M. brunneum were all killed by this fungus, acquiring M. brunneum conidia, whereas larval mortality was 0% in the control groups. Young larvae of both pine processionary moth species were also highly susceptible to ARSEF4556 and V275 with larval mortality ranging between 94% and 100%, 8 days post-inoculation, with the vast majority of larvae being killed within the first 2–4 days. Larval mortality was dose dependent. Results were consistent across the two pine processionary moth species, showing that the pathogenicity of M. brunneum to both eggs and young larvae might be promising for biological control of these insect pests. The study also showed that non-target parasitoids of pine processionary moth eggs were also susceptible to M. brunneum. Further work is required to understand and reduce the M. brunneum effect on non-target insects.     

Improving biocontrol of black vine weevil (<Emphasis Type="Italic">Otiorhynchus sulcatus</Emphasis>) with entomopathogenic fungi in growing media by incorporating spent mushroom compost

Amending a peat-based growing medium with 10% v/v spent mushroom compost, a source of fungal chitin and other nutrients, prolonged the persistence of entomopathogenic fungi (Metarhizium brunneum Petsch and Beauveria bassiana (Balsamo) Vuillemin; Hypocreales: Clavicipitaceae). This resulted in improved efficacy of M. brunneum against black vine weevil, Otiorhynchus sulcatus F. (Coleoptera: Curculionidae) larvae compared with using inoculum without spent mushroom compost. B. bassiana only controlled larvae when used in combination with spent mushroom compost (75?±?7% reduction in live larvae). Mixing entomopathogenic fungal inoculum with spent mushroom compost and growing medium was as effective in controlling black vine weevil larvae as using spent mushroom compost colonised with M. brunneum or B. bassiana in the growing medium (80?±?12% reduction in live larvae). The former method is preferable since it does not require production and storage of colonised spent mushroom compost, or registration of new substrate formulations of M. brunneum or B. bassiana.     

Comparison of the relative efficacy of an insect baiting method and selective media for diversity studies of Metarhizium species in the soil

Metarhizium are a commonly occurring group of entomopathogenic fungi normally found in soil. The most common methods to assess the diversity of Metarhizium species in soil are (i) the use of selective media and (ii) insect baiting using Galleria mellonella larvae. We compared the recovery efficiency from soil of four common species of Metarhizium (Metarhizium anisopliae, Metarhizium pingshaense, Metarhizium brunneum and Metarhizium robertsii) using these two methods. Firstly, we compared the number of colony forming units (CFU) produced in vitro when grown on two selective media, one containing chloramphenicol, thiabendazole and cycloheximidethe (CTC) and one based on the fungicide dodine (n-dodecylguanidine acetate) (DOD). Secondly, we artificially inoculated natural/non-sterile soil with the four fungal species at a rate of 2×10² and 2×10³ conidia g^?1of soil, baited with G. mellonella, and processed for evaluation using the selective media. The in vitro results showed that the greatest number of CFUs were recorded for M. brunneum. In contrast, when inoculated into soil, more G. mellonella larvae became infected by M. anisopliae. Finally, when using selective media, most CFUs recovered were for M. robertsii. The importance of our results in selecting a method to study the natural occurrence of Metarhizium in soil are discussed.     

Establishment and persistence of the entomopathogenic fungus Metarhizium anisopliae in maize fields

The entomopathogenic fungus Metarhizium anisopliae (Metsch.) Sorokin (Hypocreales: Clavicipitaceae) was applied in maize fields to control the Western Corn Rootworm Diabrotica virgifera virgifera Le Conte (Coleoptera: Chrysomelidae). Establishment and persistence of two strains of M. anisopliae were investigated after application as ‘fungal colonized barley kernels’ (FCBK) into the soil and as a spore suspension on maize leaves and on the soil surface in 2006 and 2007 at two locations in Hungary. The applied fungal strains were able to establish at both locations and a long‐term persistence of at least 15 months could be recorded in the soil. A positive correlation between density of colony forming units (CFU) in the soil and the soil inhabiting stages of the host insect D. v. virgifera could be found. M. anisopliae spores applied on maize leaves were able to survive for no longer than 3 days after application, whereas on the soil surface a noticeably increase of fungus densities were found after treatments. Molecular markers were used to identify the applied M. anisopliae strains before and after application of FCBK into the soil of the maize field.     

The symbiotic bacteria Alcaligenes faecalis of the entomopathogenic nematodes Oscheius spp. exhibit potential biocontrol of plant- and entomopathogenic fungi

Soil-dwelling entomopathogenic nematodes (EPNs) kill arthropod hosts by injecting their symbiotic bacteria into the host hemolymph and feed on the bacteria and the tissue of the dying host for several generations cycles until the arthropod cadaver is completely depleted. The EPN–bacteria–arthropod cadaver complex represents a rich energy source for the surrounding opportunistic soil fungal biota and other competitors. We hypothesized that EPNs need to protect their food source until depletion and that the EPN symbiotic bacteria produce volatile and non-volatile exudations that deter different soil fungal groups in the soil. We isolated the symbiotic bacteria species (Alcaligenes faecalis) from the EPN Oscheius spp. and ran infectivity bioassays against entomopathogenic fungi (EPF) as well as against plant pathogenic fungi (PPF). We found that both volatile and non-volatile symbiotic bacterial exudations had negative effects on both EPF and PPF. Such deterrent function on functionally different fungal strains suggests a common mode of action of A. faecalis bacterial exudates, which has the potential to influence the structure of soil microbial communities, and could be integrated into pest management programs for increasing crop protection against fungal pathogens.     

Responses of entomopathogenic fungi to the mutagen 4-nitroquinoline 1-oxide

Survival of entomopathogenic fungi under solar ultraviolet (UV) radiation is paramount to the success of biological control of insect pests and disease vectors. The mutagenic compound 4-nitroquinoline 1-oxide (4-NQO) is often used to mimic the biological effects of UV radiation on organisms. Therefore, we asked whether tolerance to 4-NQO could predict tolerance to UV radiation in thirty isolates of entomopathogenic fungi and one isolate of a xerophilic fungus. A dendrogram obtained from cluster analyses based on the 50 and 90 % inhibitory concentrations (IC₅₀ and IC₉₀, respectively) divided the fungal isolates into six clusters numbered consecutively based on their tolerance to 4-NQO. Cluster 6 contained species with highest tolerance to 4-NQO (IC₅₀ > 4.7 μM), including Mariannaea pruinosa, Lecanicillium aphanocladii, and Torrubiella homopterorum. Cluster 1 contained species least tolerant to 4-NQO (IC₅₀ < 0.2 μM), such as Metarhizium acridum (ARSEF 324), Tolypocladium geodes, and Metarhizium brunneum (ARSEF 7711). With few exceptions, the majority of Metarhizium species showed moderate to low tolerances (IC₅₀ between 0.4 and 0.9 μM) and were placed in cluster 2. Cluster 3 included species with moderate tolerance (IC₅₀ between 1.0 and 1.2 μM). In cluster 4 were species with moderate to high tolerance (IC₅₀ between 1.3 and 1.6 μM). Cluster 5 contained the species with high tolerance (IC₅₀ between 1.9 and 4.0 μM). The most UV tolerant isolate of M. acridum, ARSEF 324, was the least tolerant to 4-NQO. Also, L. aphanocladii, which is very susceptible to UV radiation, showed high tolerance to 4-NQO. Our results indicate that tolerance to 4-NQO does not correlate with tolerance to UV radiation. Therefore this chemical compound is not a predictor of UV tolerance in entomopathogenic fungi.     

Susceptibility of apple clearwing moth larvae,Synanthedon myopaeformis (Lepidoptera: Sesiidae) to Beauveria bassiana and Metarhizium brunneum

Apple clearwing moth larvae, Synanthedon myopaeformis (Lepidoptera: Sesiidae) were found to be susceptible to infection by two entomopathogenic fungi: an indigenous fungus isolated from S. myopaeformis cadavers and identified as Metarhizium brunneum (Petch); and Beauveria bassiana isolate GHA. In laboratory bioassays, larvae exhibited dose related mortality after exposure to both the M. brunneum and Beauveria bassiana with 7 day LC₅₀'s of 2.9×10⁵ and 3.4×10⁵ spores/mL, respectively. Larval mortalities caused by the two isolates at 1×10⁶ spores/mL were not significantly different and 73% of the M. brunneum-treated, and 76% of the B. bassiana-treated larvae were dead 7 days post treatment, with LT₅₀'s of 5.5 and 5.1 days, respectively.     

Cellulase enhances endophytism of encapsulated Metarhizium brunneum in potato plants

The recent discovery that entomopathogenic fungi can grow endophytically in plant tissues has spurred research into novel plant protection measures. However, current applications of fungi aiming at endophytism mostly lack targeted formulation strategies resulting in low efficacy. Here, we aimed at enhancing Metarhizium brunneum CB15 endophytism in potato plants by (i) improvement of fungal growth from beads and (ii) cellulase formation or addition to encapsulated mycelium. We found that beads supplemented with cellulose alone or in addition with inactivated baker's yeast exhibited cellulase activity and increased mycelial growth by 12.6 % and 13.6 %, respectively. Higher enzymatic activity achieved by cellulase co-encapsulation promoted a shift from mycelial growth to spore formation with maximum numbers of 2.5 × 10⁸ ± 6.1 × 10⁷ per bead. This correlated with improved endophytism in potato plants by 61.2 % compared to non-supplemented beads. Our study provides first evidence that customized formulations of fungal entomopathogens with enzymes can improve endophytism and this may increase efficacy in plant protection strategies against herbivorous pests.     

Distribution and characterisation of entomopathogenic fungi from Korean soils

We investigated the occurrence of entomopathogenic fungi in 1080 soil samples representing multiple locations and conditions in Korea. Entomopathogenic fungi were isolated from soils using a selective medium containing dodine and antibiotics. Following an initial identification based on morphology, the fungal isolates were more precisely identified by the sequence of their nuclear ribosomal RNA (rRNA) internal transcribed spacer (ITS) regions. As a result, entomopathogenic fungi were found to occur in 32% (342 isolates) of the soil samples studied. The most abundant species were Beauveria spp. (125 isolates) and Metarhizium spp. (82 isolates). Entomopathogenic fungi were more often recovered from natural mountain and riparian soils than from agricultural habitats. The pathogenicity of isolated fungi was evaluated by using wax moth Galleria mellonella L. (Lepidoptera: Pyralidae) larvae. It was determined that 60% (207 isolates) of the isolates were pathogenic using this model. These entomopathogenic fungi may, therefore, have potential use against a variety of agricultural pests. This is the first study of the isolation and distribution of entomopathogenic fungi in representative sampling locations throughout Korea.     

Effects on Diversity of Soil Fungal Community and Fate of an Artificially Applied Beauveria bassiana Strain Assessed Through 454 Pyrosequencing

The entomopathogenic fungus Beauveria bassiana is widely used as a biological control agent (BCA) for insect pest control, with fungal propagules being either incorporated into the potting media or soil or sprayed directly onto the foliage or soil. To gain a better understanding of entomopathogenic fungal ecology when applied as a BCA to the soil environment, a case study using tag-encoded 454 pyrosequencing of fungal ITS sequences was performed to assess the fate and potential effect of an artificially applied B. bassiana strain on the diversity of soil fungal communities in an agricultural field in India. Results show that the overall fungal diversity was not influenced by application of B. bassiana during the 7 weeks of investigation. Strain-specific microsatellite markers indicated both an establishment of the applied B. bassiana strain in the treated plot and its spread to the neighboring nontreated control plot. These results might be important for proper risk assessment of entomopathogenic fungi-based BCAs.     

The effect of simulated seasonal temperatures on Metarhizium brunneum-associated mortality in Agriotes spp. click beetles,and a degree-day infection model

Entomopathogens tend to have a slow speed of kill when used for targeting agricultural insect pests. Relating temperature as a driver of this speed is important to predict pest mortality, and extending this to a degree-day infection model has rarely been studied. Many species of wireworms (Coleoptera: Elateridae), the larvae of click beetles, are subterranean and generalist agricultural pests that can be difficult to control with pesticides. Targeting adult beetles, however, may be an effective method to reduce larval recruitment. Metarhizium brunneum Petch (Hypocreales), an entomopathogenic fungus, kills click beetles but the mortality rate and speed of kill are expected to vary according to temperature. Using a thermal gradient plate to simulate daily oscillating temperatures in Agassiz, British Columbia, Canada, for April, May, and June, the effectiveness of M. brunneum strains LRC112 and F52 in causing mortality to Agriotes obscurus (L.) and Agriotes lineatus (L.) click beetles was studied in the laboratory. Mortality was fastest in beetles exposed to June temperatures and slowest in those exposed to April temperatures, with differences among beetle species × M. brunneum strain combinations. Higher temperatures resulted in more rapid mycelial outgrowth and conidiation in beetle cadavers, with only A. obscurus infected with M. brunneum LRC112 attaining near 100% conidiation. The number of degree days required to kill 50% of the beetles (LDD₅₀) was least for A. obscurus infected with M. brunneum LRC112 (176) followed by A. obscurus × M. brunneum F52 (212), A. lineatus × M. brunneum LRC112 (215), and A. lineatus × M. brunneum F52 (292). Hypothetical calculations showed that M. brunneum exposure earlier in the season resulted in a longer time to kill 50% of the beetles (LT₅₀) but the earliest LT₅₀ calendar date. Later M. brunneum exposure dates resulted in lower LT₅₀'s, but later LT₅₀ dates. This conceptual work demonstrates that daily temperature oscillations, seasonality, and degree days must be considered to predict the efficacy and speed of kill of different fungal entomopathogen strains when targeting different click beetle species.     

Occurrence and diversity of entomopathogenic fungi in cultivated and uncultivated soils in Pakistan

The distribution of entomopathogenic fungi in various geographical areas of Punjab, Pakistan, is poorly understood. The present study was planned to explore the occurrence and diversity of entomopathogenic fungi from soils collected from cultivated and non‐cultivated habitats. The detailed survey of different habitats (crop fields, fruits, vegetables, forests) was conducted to collect soil samples and the associated fungi were isolated using Galleria bait method. Among 210 soil samples, 168 fungal isolates were recovered and identified, with 98 from forests, 32 from vegetables, 30 from field crops and 8 from fruits. The major entomopathogenic fungi recovered from these samples were Beauveria bassiana, Metarhizium anisopliae, Paecilomyces lilacinus, B. brongniartii, P. chlamydosporia and Lecanicillium attenuatum. The diversity of entomopathogenic fungi was greater in soil samples from forests compared to crop fields, vegetables and fruits, respectively. The geographical attributes (altitude, longitude, latitude) greatly influenced the occurrence of entomopathogenic fungi with the highest number of isolates found from >600 m altitude, 33°–34′N latitude, and 73°74′E longitude from soil samples. The results of the surveys clearly indicated that the entomopathogenic fungi are distributed in the soils which may be used in successful IPM programs in future.     

Growth response of crops to soil microbial communities from conventional monocropping and tree-based intercropping systems

Background and aims

Recent studies have shown that tree-based intercropping (TBI) systems support a more diverse soil microbial community compared to conventional agricultural systems. However, it is unclear whether differences in soil microbial diversity between these two agricultural systems have a functional effect on crop growth.

Methods

In this study, we used a series of greenhouse experiments to test whether crops respond differently to the total soil microbial community (Experiment 1) and to arbuscular mycorrhizal (AM) fungal communities alone (Experiment 2) from conventionally monocropped (CM) and TBI systems.

Results

The crops had a similar growth response to the total soil microbial communities from both cropping systems. However, when compared to sterilized controls, barley (Hordeum vulgare) and canola (Brassica napus) exhibited a negative growth response to the total soil microbial communities, while soybean (Glycine max) was unaffected. During the AM fungal establishment phase of the second experiment, ‘nurse’ plants had a strong positive growth response to AM fungal inoculation, and significantly higher biomass when inoculated with AM fungi from the CM system compared to the TBI system. Soybean was the only crop species to exhibit a significant positive growth response to AM fungal inoculation. Similar to the total soil microbial communities, AM fungi from the two cropping systems did not differ in their effect on crop growth.

Conclusion

Overall, AM fungi from both cropping systems had a positive effect on the growth of plants that formed a functional symbiosis. However, the results from these experiments suggest that negative effects of non-AM fungal microbes are stronger than the beneficial effects of AM fungi from these cropping systems.     

Technical scale production of encapsulated Saccharomyces cerevisiae and Metarhizium brunneum attractive to wireworms

Wireworms (Coleoptera: Elateridae) have recently become an increasing problem as agricultural insect pests due to the phasing out of effective control options. Entomopathogenic fungi such as Metarhizium brunneum have proven to be a promising microbial antagonist for wireworm control. Here, we tested whether the efficacy of M. brunneum can be increased through a combination with CO₂, emitted by Saccharomyces cerevisiae, as an attractant (=attract-and-kill). We aimed at a technical scale production of a formulated biological control agent offering a practical and economically feasible application for wireworm control. Therefore, a novel technical formulation process for encapsulated S. cerevisiae (Attract beads) and M. brunneum (Kill beads) was investigated. For the bead production by jet cutting, the parameters nozzle diameter, pump speed, cutting device speed and collecting distance were evaluated. In order to dry the beads in a short time while maintaining a high cell viability, different drying temperatures during fluidised-bed drying were tested and the best results were obtained with an inlet air temperature profile between 50°C and 40°C. CO₂ production of the beads in the soil was highest for co-applied Attract and Kill beads. The potential of beads to modify wireworm behaviour (Agriotes sputator) was tested in a rhizotron experiment. The Attract-and-Kill treatment (co-applied beads) significantly attracted wireworms, whereas Attract beads and Kill beads alone showed a weak, but non-significant attraction. Wireworm mortality could not be enhanced due to a low rate of mycosis from M. brunneum infection.     

Effect of Norwegian entomopathogenic fungal isolates against Otiorhynchus sulcatus larvae at low temperatures and persistence in strawberry rhizospheres

Biological control of belowground stages of the black vine weevil Otiorhynchus sulcatus F. (Coleoptera: Curculionidae) in strawberries in cool temperate regions using entomopathogens is challenged by low temperatures during the periods when larvae are vulnerable to infections. In a laboratory study we tested six indigenous Norwegian isolates of entomopathogenic fungi (one Beauveria bassiana, three Beauveria pseudobassiana, and two Metarhizium brunneum; Ascomycota: Hypocreales) for their efficacy against O. sulcatus larvae at 6, 12, and 18 °C. At the lowest temperature only Beauveria spp. affected survival of O. sulcatus while all three fungal species reduced larval survival compared to the control treatment at 12 and 18 °C. Two of the Norwegian isolates, one B. pseudobassiana and one M. brunneum, were then evaluated for long-term persistence (>1 year) in the bulk soil and the rhizosphere soil of strawberries in a semi-field experiment. An exotic isolate of M. brunneum sharing origin with a widespread commercial biocontrol agent (F52/Met52 (Novozymes)) was included for comparison. All three isolates showed significantly higher abundances in the rhizosphere soil compared to bulk soil at 153, 366, and 471 days after inoculation, thus indicating rhizosphere competence for B. pseudobassiana. Notably, CFU levels for both Norwegian isolates were much higher than for the exotic M. brunneum isolate. Selection of locally adapted isolates may therefore be of importance when considering biocontrol strategies of belowground pests in strawberry production.     

Moderate Warming in Microcosm Experiment Does Not Affect Microbial Communities in Temperate Vineyard Soils

Changes in the soil microbial community structure can lead to dramatic changes in the soil ecosystem. Temperature, which is projected to increase with climate change, is commonly assumed to affect microbial communities, but its effects on agricultural soils are not fully understood. We collected soil samples from six vineyards characterised by a difference of about 2 °C in daily soil temperature over the year and simulated in a microcosm experiment different temperature regimes over a period of 1 year: seasonal fluctuations in soil temperature based on the average daily soil temperature measured in the field; soil temperature warming (2 °C above the normal seasonal temperatures); and constant temperatures normally registered in these temperate soils in winter (3 °C) and in summer (20 °C). Changes in the soil bacterial and fungal community structures were analysed by automated ribosomal intergenic spacer analysis (ARISA). We did not find any effect of warming on soil bacterial and fungal communities, while stable temperatures affected the fungal more than the bacterial communities, although this effect was soil dependent. The soil bacterial community exhibited soil-dependent seasonal fluctuations, while the fungal community was mainly stable. Each soil harbours different microbial communities that respond differently to seasonal temperature fluctuations; therefore, any generalization regarding the effect of climate change on soil communities should be made carefully.     

庞泉沟自然保护区常见禾本科植物内生真菌分布及其影响因素

以庞泉沟自然保护区4种不同群落类型林地和灌丛下的优势禾草为研究对象,调查不同禾草内生真菌感染率,研究内生真菌感染的禾草种群与原生生境的土壤理化性质、土壤酶活性及土壤微生物群落结构的相互关系。结果发现,影响紫羊茅、中亚薹草和野燕麦染菌率的主要因子是土壤水分含量和碳氮比,且土壤C、N、S以及土壤水分含量与紫羊茅的内生真菌染菌率成正相关,土壤蔗糖酶、脲酶和酸性磷酸酶与紫羊茅的感染率显著正相关,但中亚薹草与紫羊茅的结果相反。丝盖伞科是华北落叶松林和油松林土壤微生物群落的优势真菌,但不同染菌植被群落类型下的优势细菌微生物群落组成不同。总体看来,4种森林群落类型下禾草内生真菌染菌率与土壤理化性质相关性不同,且受到的生态因子影响大小也有差异,内生真菌感染导致各植被群落类型的土壤微生物群落结构具有差异,其优势土壤真菌和土壤细菌组成不同,这有助于进一步认识原生生境下不同感染率的禾草种群对土壤微生物群落结构的影响及其在生态系统中的各异生态学功能。     

Habitat matters: The role of spore bank fungi in early seedling establishment of Florida slash pines

This study investigated broad patterns in communities of ectomycorrhizal fungi from three Florida habitats (sandhills, scrub, and pine rocklands) and the ability of spore bank fungi to associate with Pinus elliottii (slash pine) and Pinus densa (south Florida slash pine). Efforts to replant pines in the endangered pine rocklands are vital to the persistence of this habitat, yet little is known about the ectomycorrhizal fungi communities or how they may differ from those in other pine-dominated habitats in Florida. We used high-throughput amplicon sequencing (HTS) to assess baseline fungal communities and greenhouse bioassays to bait ectomycorrhizal fungi using seedlings. HTS soil data recovered 188 ectomycorrhizal species but only a few subsequently colonized the bioassay seedlings. We recovered 21 ectomycorrhizal species on pine seedlings including common spore bank fungi such as Cenococcum, Suillus, and Tuber, but Rhizopogon species were dominant across all sites and habitats. Habitat type and site were significant variables influencing the community composition of the total soil fungal community, soil ectomycorrhizal community, and the fungi found on seedling root tips. However, we found no significant differences between the ectomycorrhizal communities on seedling roots from the two Pinus species.     

CTC medium: A novel dodine-free selective medium for isolating entomopathogenic fungi,especially Metarhizium acridum,from soil

The selective media most commonly used for isolating hyphomycetous species of entomopathogenic fungi from non-sterile substrates rely on N-dodecylguanidine monoacetate (dodine) as the selective fungicide. Although these media are effective for isolating many species of Metarhizium and Beauveria from soil, they are inefficient media for isolation of an important Metarhizium species, Metarhizium acridum, from non-sterile soil. Our current study was directed to formulating a dodine-free selective medium that is efficient for isolating naturally occurring Beauveria spp. and Metarhizium spp., especially M. acridum, from soil. The selective medium (designated CTC medium) consists of potato dextrose agar plus yeast extract (PDAY) supplemented with chloramphenicol, thiabendazole and cycloheximide. In comparisons with selective media previously reported in the literature, the CTC medium afforded colonies that were larger and had both earlier and more abundant conidiation of entomopathogenic fungi, features which greatly facilitated identification of the emerging entomopathogenic fungi. In addition to efficient re-isolation of M. acridum, this medium also is an effective tool for selective isolation of Metarhizium brunneum, Metarhizium robertsii, Beauveria bassiana and Beauveria brongniartii from non-sterile field-collected soil samples inoculated (spiked) with fresh conidia in the laboratory.     

The Xenon Test Chamber Q-SUN® for testing realistic tolerances of fungi exposed to simulated full spectrum solar radiation

The low survival of insect-pathogenic fungi when used for insect control in agriculture is mainly due to the deleterious effects of ultraviolet radiation and heat from solar irradiation. In this study, conidia of 15 species of entomopathogenic fungi were exposed to simulated full-spectrum solar radiation emitted by a Xenon Test Chamber Q-SUN XE-3-HC 340S (Q-LAB^® Corporation, Westlake, OH, USA), which very closely simulates full-spectrum solar radiation. A dendrogram obtained from cluster analyses, based on lethal time 50 % and 90 % calculated by Probit analyses, separated the fungi into three clusters: cluster 3 contains species with highest tolerance to simulated full-spectrum solar radiation, included Metarhizium acridum, Cladosporium herbarum, and Trichothecium roseum with LT₅₀ > 200 min irradiation. Cluster 2 contains eight species with moderate UV tolerance: Aschersonia aleyrodis, Isaria fumosorosea, Mariannaea pruinosa, Metarhizium anisopliae, Metarhizium brunneum, Metarhizium robertsii, Simplicillium lanosoniveum, and Torrubiella homopterorum with LT₅₀ between 120 and 150 min irradiation. The four species in cluster 1 had the lowest UV tolerance: Lecanicillium aphanocladii, Beauveria bassiana, Tolypocladium cylindrosporum, and Tolypocladium inflatum with LT₅₀ < 120 min irradiation. The QSUN Xenon Test Chamber XE3 is often used by the pharmaceutical and automotive industry to test light stability and weathering, respectively, but it was never used to evaluate fungal tolerance to full-spectrum solar radiation before. We conclude that the equipment provided an excellent tool for testing realistic tolerances of fungi to full-spectrum solar radiation of microbial agents for insect biological control in agriculture.