Selection of Beauveria bassiana and Metarhizium anisopliae isolates to control Triatoma infestans

Laboratory and field studies for the control of Chagas disease vectors using the fungus Metarhizium anisopliae

Chagas disease is one of the most important insect-vectored diseases in Brazil. The entomopathogenic fungus Metarhizium anisopliae was evaluated against nymphs and adults of Panstrongylus megistus, Triatoma infestans, and T. sordida. Pathogenicity tests at saturated humidity demonstrated high susceptibility to fungal infection. The shortest estimates of 50% lethal time (LT₅₀ ) for P. megistus varied from 4.6 (isolate E9) to 4.8 days (genetically modified strain 157p). For T. infestans, the shortest LT₅₀ was 6.3 (E9) and 7.3 days (157p). For T. sordida, the shortest LT₅₀ was 8.0 days (157p). The lethal concentration sufficient to kill 50% of T. infestans (LC₅₀ ) was 1.9 × 10⁷ conidia/ml for strain 157p. In three chicken coops that were sprayed with M. anisopliae, nymphs especially were well controlled, with a great population reduction of 38.5% after 17 days. Therefore M. anisopliae performed well, controlling Triatominae in both laboratory and field studies.

Isolation of Beauveria bassiana from the Chagas Disease Vector Triatoma infestans in the Gran Chaco Region of Argentina: Assessment of Gene Expression during Host-Pathogen Interaction

A native strain of the entomopathogenic fungus Beauveria bassiana (Bb-C001) was isolated from a naturally infected Triatoma infestans, Klug (Hemiptera: Reduviidae) adult cadaver in the Gran Chaco region, Salta province, Argentina. The isolate was both phenotypic and molecularly characterized in a context of fungus-insect interaction, by measuring the expression pattern of toxin genes during infection and immune response of T. infestans. The commercial strain GHA of B. bassiana, which was previously used in field interventions to control these vectors, was used as reference in this study. The phylogenetic trees based on both ribosomal internal transcribed spacer (ITS) and elongation factor 1-alpha (EF1-α) indicated that Bb-C001 fits into a B. bassiana cluster, and the sequence-characterized amplified regions (SCAR) showed that Bb-C001 is different from the GHA strain. There were no differences between both strains regarding viability, radial growth, and conidia production, either in the median survival time or insect mortality. However, Bb-C001 showed a higher expression than GHA of the bassianolide synthetase gene (BbbslS) during infection, and similar levels of the beauvericin synthetase gene (BbbeaS). Immune-related genes of T. infestans nymphs (limpet-2 and defensin-1, -2, and -6) were later expressed and thus insects failed to stop the infection process. These results showed that B. bassiana Bb-C001 is a promised fungal strain to be incorporated in the current biological control programs of T. infestans in Salta province, Argentina.

Fungal isolate and crop cultivar influence the beneficial effects of root inoculation with entomopathogenic fungi in strawberry

BACKGROUND

Root inoculations of crop plants with beneficial fungi constitute a promising strategy for growth promotion and control of above-ground pests and diseases. Here, strawberry roots (cultivar 'Albion' and 'Pircinque') were inoculated with 25 different Brazilian entomopathogenic fungal isolates of three genera and the effects on Tetranychus urticae oviposition and plant growth were evaluated in greenhouse experiments.

RESULTS

Reductions in the number of T. urticae eggs compared to control treatments were observed on both cultivars inoculated with almost all isolates. For the cultivar 'Albion', Metarhizium anisopliae (ESALQ 1604, ESALQ 1669), M. robertsii (ESALQ 1622, ESALQ 1635), Metarhizium sp. Indet. (ESALQ 1684) and Beauveria bassiana (ESALQ 3323) increased dry weight of roots and leaves, and fruit yield, while M. robertsii (ESALQ 1634), Metarhizium sp. Indet. (ESALQ 1637) and (ESALQ 1636) enhanced fruit yield and dry weight of leaves, respectively. For the cultivar 'Pircinque', M. anisopliae (ESALQ 1669) was the only isolate observed to increase dry weight of roots.

CONCLUSION

The results suggest that inoculation of strawberry roots with entomopathogenic fungi may be an innovative strategy for pest management above ground. Furthermore, these inoculations may also stimulate plant growth and strawberry production, but the effects depend on fungal strains and crop cultivar. © 2019 Society of Chemical Industry.

Current status and perspectives of fungal entomopathogens used for microbial control of arthropod pests in Brazil

Entomopathogenic fungi play a central role in Brazil's biopesticide market. Approximately 50% of registered microbial biopesticides comprise mycoinsecticides and/or mycoacaricides consisting of hypocrealean fungi, with most based on Metarhizium anisopliae sensu stricto (s. str.) and Beauveria bassiana s. str. These fungi are mainly used to control spittlebugs in sugarcane fields and whiteflies in row crops, respectively, with annual applications surpassing three million hectares. Research also emphasizes the potential of fungal entomopathogens to manage arthropod vectors of human diseases. Most registered fungal formulations comprise wettable powders or technical (non-formulated) products, with relatively few new developments in formulation technology. Despite the large area treated with mycoinsecticides (i.e., approx. 2 million ha of sugarcane treated with M. anisopliae and 1.5 million ha of soybean treated with B. bassiana), their market share remains small compared with the chemical insecticide market. Nevertheless, several major agricultural companies are investing in fungus-based products with the aim at achieving more sustainable IPM programs for major pests in both organic and conventional crops. Government and private research groups are pursuing innovative technologies for mass production, formulation, product stability and quality control, which will support cost-effective commercial mycoinsecticides. Here, we summarize the status of mycoinsecticides currently available in Brazil and discuss future prospects.

Effects on Meccus pallidipennis (Hemiptera: Reduviidae) Eggs Exposed to Entomopathogenic Fungi: Exploring Alternatives to Control Chagas Disease

Meccus pallidipennis Stål is a vector for Chagas disease. The extensive use of pyrethroid insecticides to control triatomines in Mexico has resulted in the development of resistant populations. As an alternative control approach, the effects on M. pallidipennis eggs of two entomopathogenic fungi, Isaria fumosorosea Wize (Hypocreales: Cordycipitaceae) EH-511/3 and Metarhizium anisopliae (Metschn.) Sorokin (Hypocreales: Clavicipitaceae) EH-473/4, were examined. Egg mortality was estimated 1 mo after egg infection, based on hyphal growth and unsuccessful hatching as proxies for infection and death. Sporulation and conidial production rates were also recorded. Mortality rates caused by I. fumosorosea and Me. anisopliae were 92% ± 3.1 and 88% ± 3.7, respectively. Sporulation rate and conidial production were greater in I. fumosorosea than in Me. anisopliae. Transmission electron microscopy revealed hyphal penetration by both fungal species and damage to embryonic epidermal and cuticular cells. Our results demonstrated that I. fumosorosea and Me. anisopliae are promising candidates for controlling M. pallidipennis eggs and offer alternatives to control the transmission of Chagas disease under natural conditions.

Isolation, Identification, and Virulence of a New Metarhizium anisopliae Strain on the German Cockroach

The efficacy of a new and highly virulent Metarhizium anisopliae (Hypocreales: Clavicipitaceae) strain was evaluated against Blattella germanica (L.) (Blattaria: Blattellidae) in the laboratory; this strain was obtained and purified from field-collected Eupolyphaga sinensis cadavers. The status of this fungus as a new and genetically distinct species was supported by ITS sequence comparisons. The new strain was compared with other M. anisopliae isolates and was found to be highly infectious and virulent against B. germanica. The virulence of this new strain against different instars of male and female cockroaches at five conidia concentrations (1 × 105, 1 × 106, 1 × 107, 1 × 108, and 1 × 109 conidia/ml) was evaluated in vitro, and the mortality (measured as lethal concentrations, LC50) was determined. According to the pathogenicity test, M. anisopliae isolate EB0732 produced 100% mortality of one- to three-instar nymph (LC50 = 0.37 × 105conidia/ml) and 78.33% mortality of adult female (LC50 = 1.39 × 107 conidia/ml) at 15 d post-inoculation at a concentration of 1 × 109 conidia/ml. There was an overall significant effect on mortality between the age and sex of B. germanica. A M. anisopliae susceptibility test showed that the survival rate of cockroaches after treatment with topical applications and mixed infection was lower than per os. These studies shed light on a valuable integrated pest management against the German cockroach.

Synthesis and secretion of volatile short-chain fatty acids in Triatoma infestans infected with Beauveria bassiana

Physically disturbed Triatoma infestans (Hemiptera: Reduviidae) adults, as well as adults of other Chagas' disease vectors, secrete a mix of volatile organic compounds (VOCs) with alarm and possible sexual and defence functions. The aim of the present research was to test whether infection with the entomopathogenic fungus Beauveria bassiana (Ascomycota: Hypocreales: Clavicipitaceae) has an effect on VOC secretion in disturbed T. infestans and on the expression of two genes (Ti-brnq and Ti-bckdc) potentially involved in VOC biosynthesis. The volatiles released by insects at different time periods after fungal treatment were identified and their relative amounts measured. Isobutyric acid was the most abundant volatile found in both healthy and fungus-infected insects and underwent no significant relative changes through the infection process. The secretion of propionic acid, however, was significantly higher at 1-4 days post-infection (d.p. i.) compared with that in controls. A slight induction of both Ti-brnq and Ti-bckdc genes was found by real-time polymerase chain reaction at 4 d.p. i., with expression values reaching up to three-fold those in controls. The early stages of fungal infection seem to affect the composition of the alarm pheromone by changing the expression pattern of both genes analysed. These results help to elucidate the impact of fungal infections on the chemical ecology of triatomine bugs.

Metarhizium anisopliae s.l. modulation of lipid metabolism during tick infection is independent of AMPK and ERK pathways

Despite the importance of fat body in metabolism of arthropods, studies in ticks are scarce. This study evaluated the lipid composition and activation of extracellular signal-regulated protein kinase (ERK) and AMP-activated protein kinase (AMPK) enzymes in Rhipicephalus microplus fat body after infection with different isolates of the fungus Metarhizium anisopliae sensu lato (Metschnikoff, 1879) Sorokin, 1883. The isolates CG 32, GC 112, GC 148, GC 347, and GC 629 were inoculated as viable or non-viable conidia in the ticks. The engorged females were dissected, and their fat bodies were collected 24 and 48 h after infection. The lipid composition was assessed by thin layer chromatography, and enzyme activation was detected by Western blotting with antibodies against p-AMPK and p-ERK. The study showed increased levels of triacylglycerol 24 and 48 h and fatty acid after 48 h after inoculation with different isolates of viable fungi in the tick's hemocoel. Detection of the active form of ERK was demonstrated only after inoculation with non-viable conidia of all isolates tested. The active form of AMPK, only isolate CG 112 was able to activate with viable or non-viable conidia, whereas isolates CG 32 and CG 629 were able to activate with non-viable conidia. This study provides the first report about changes in important metabolic pathways in ticks infected with entomopathogenic fungi and suggests that the lipid content is modulated by non-usual pathways. However, further studies may be necessary for a better elucidation of this interaction.

Enzymatic comparison and mortality of Beauveria bassiana against cabbage caterpillar Pieris brassicae LINN

Beauveria bassiana, an entomopathogenic fungus, is the alternative biocontrol agent exploited against major economic crop pests. Pieris brassicae L. is an emerging pest of the Brassicaceae family. Therefore, in the present study, fungal isolates of Beauveria bassiana, viz. MTCC 2028, MTCC 4495, MTCC 6291, and NBAII-11, were evaluated for their virulence against third instar larvae of P. brassicae. Among all these fungal isolates, maximum mortality (86.66%) was recorded in B. bassiana MTCC 4495 at higher concentration of spores (109conidia/ml), and the minimum mortality (30.00%) was recorded in B. bassiana MTCC 6291 at a lower concentration (107conidia/ml) after ten days of treatment. The extracellular cuticle-degrading enzyme activities of fungal isolates were measured. Variability was observed both in the pattern of enzyme secretion and the level of enzyme activities among various fungal isolates. B. bassiana MTCC 4495 recorded the maximum mean chitinase (0.51U/ml), protease (1.12U/ml), and lipase activities (1.36U/ml). The minimum mean chitinase and protease activities (0.37 and 0.91U/ml, respectively) were recorded in B. bassiana MTCC 6291. The minimum mean lipase activity (1.04U/ml) was recorded in B. bassiana NBAII-11. Our studies revealed B. bassiana MTCC 4495 as the most pathogenic isolate against P. brassicae, which also recorded maximum extracellular enzyme activities, suggesting the possible roles of extracellular enzymes in the pathogenicity of B. bassiana against P. brassicae.

Screening of Fungi for Biological Control of a Triatomine Vector of Chagas Disease: Temperature and Trypanosome Infection as Factors

Entomopathogenic fungi have been investigated as an alternative tool for controlling various insects, including triatomine vectors of the protozoan Trypanosoma cruzi, the etiological agent of Chagas disease. Here we tested the pathogenicity and virulence of ten isolates of the fungi Metarhizium spp. and Beauveria bassiana against Rhodnius prolixus and found all of the isolates to be virulent. We used two isolates (URPE-11 Metarhizium anisopliae and ENT-1 Beauveria bassiana) for further screening based on their prolific sporulation in vitro (an important property of fungal biopesticides). We characterized their virulences in a dose-response experiment and then examined virulence across a range of temperatures (21, 23, 27 and 30°C). We found isolate ENT-1 to maintain higher levels of virulence over these temperatures than URPE-11. We therefore used B. bassiana ENT-1 in the final experiment in which we examined the survival of insects parasitized with T. cruzi and then infected with this fungus (once again over a range of temperatures). Contrary to our expectations, the survival of insects challenged with the pathogenic fungus was greater when they had previously been infected with the parasite T. cruzi than when they had not (independent of temperature). We discuss these results in terms of aspects of the biologies of the three organisms. In practical terms, we concluded that, while we have fungal isolates of potential interest for development as biopesticides against R. prolixus, we have identified what could be a critical problem for this biological tool: the parasite T. cruzi appears to confer a measure of resistance to the insect against the potential biopesticide agent so use of this fungus as a biopesticide could lead to selection for vector competence.

Unveiling the oxidative metabolism of Rhipicephalus microplus (Acari: Ixodidae) experimentally exposed to entomopathogenic fungi

Rhipicephalus microplus is an important tick in tropical regions due to the high economic losses caused by its parasitism. Metarhizium anisopliae and Beauveria bassiana are well-known entomopathogenic fungi that can afflict R. microplus ticks. The development of new targets and strategies to control this parasite can be driven by studies of this tick's physiology. Recently, it was reported that when exposed to adverse physiological conditions, ticks can activate fermentative pathways, indicating transition from aerobic to anaerobic metabolism. Nevertheless, the precise mechanism by which entomopathogenic fungi influence R. microplus metabolism has not been clarified, limiting understanding of the tick-fungus association. Thus, the present study aimed to evaluate the effect of infection of ticks by M. anisopliae and B. bassiana on the amount of selected carboxylic acids present in the hemolymph, enabling increased understanding of changes previously reported. The results showed preservation in the concentrations of oxalic, lactic, and pyruvic acids in the hemolymph 24 and 48 h after dropping from cattle; while there were variations in the concentration of these carboxylic acids after infection of female ticks to M. anisopliae and B. bassiana. Significant increases were observed in the concentration of oxalic and lactic acids and significant reduction of pyruvic acid for both observation times (24 and 48 h) after infection by entomopathogenic fungi. These results indicate that B. bassiana and M. anisopliae infection alters the basal metabolism of R. microplus females, resulting in the activation of fermentative pathways.

Effect of heat stress and oil formulation on conidial germination of Metarhizium anisopliae s.s. on tick cuticle and artificial medium

The effect of heat stress (45°C) versus non-heat stress (27°C) on germination of Metarhizium anisopliae sensu stricto (s.s.) isolate IP 119 was examined with conidia formulated (suspended) in pure mineral oil or in water (Tween 80, 0.01%), and then applied onto the cuticle of Rhipicephalus sanguineus sensu lato (s.l.) engorged females or onto culture medium (PDAY). In addition, bioassays were performed to investigate the effect of conidia heated while formulated in oil, then applied to blood-engorged adult R. sanguineus females. Conidia suspended in water then exposed to 45°C, in comparison to conidia formulated in mineral oil and exposed to the same temperature, germinated less and more slowly when incubated on either PDAY medium or tick cuticle. Also, conidial germination on tick cuticle was delayed in comparison to germination on artificial culture medium; for example, germination was 13% on tick cuticle 72h after inoculation, in contrast to 61.5% on PDAY medium. Unheated (27°C) conidia suspended in either water or oil and applied to tick cuticle developed appressoria 36h after treatment; whereas only heat-stressed conidia formulated in oil developed appressoria on tick cuticle. In comparison to conidia heated in mineral oil, there was a strong negative effect of heat on germination of conidia heated in water before being applied to arthropod cuticle. Nevertheless, bioassays [based primarily on egg production (quantity) and egg hatchability] exhibited high percentages of tick control regardless of the type of conidial suspension; i.e., water- or oil-formulated conidia, and whether or not conidia were previously exposed to heat. In comparison to aqueous conidial preparations, however, conidia formulated in oil reduced egg hatchability irrespective of heat or no-heat exposure. In conclusion, mineral-oil formulation protected conidia against heat-induced delay of both germination and appressorium production when applied to the cuticle of R. sanguineus.

Assessing gene expression during pathogenesis: Use of qRT-PCR to follow toxin production in the entomopathogenic fungus Beauveria bassiana during infection and immune response of the insect host Triatoma infestans

Entomopathogenic fungi secrete toxic secondary metabolites during the invasion of the insect hemocoel as part of the infection process. Although these compounds have been frequently mentioned as virulence factors, the roles of many of them remain poorly understood, including the question of whether they are expressed during the infection process. A major hurdle to this issue remains the low sensitivity of biochemical detection techniques (e.g., HPLC) within the complex samples that may contain trace quantities of fungal molecules inside the insect. In this study, quantitative reverse transcription real-time PCR (qRT-PCR) was used to measure the transcript levels within the insect fungal pathogen Beauveria bassiana, that encode for the synthetase enzymes of the secondary metabolites tenellin (BbtenS), beauvericin (BbbeaS) and bassianolide (BbbslS) during the infection of Triatoma infestans, a Chagas disease insect vector. Absolute quantification was performed at different time periods after insect treatment with various concentrations of propagules, either by immersing the insects in conidial suspensions or by injecting them with blastospores. Both BbtenS and BbbeaS were highly expressed in conidia-treated insects at days 3 and 12 post-treatment. In blastospore-injected insects, BbtenS and BbbeaS expression peaked at 24h post-injection and were also highly expressed in insect cadavers. The levels of BbbslS transcripts were much lower in all conditions tested. The expression patterns of insect genes encoding proteins that belong to the T. infestans humoral immune system were also evaluated with the same technique. This qPCR-based methodology can contribute to decifering the dynamics of entomopathogenic fungal infection at the molecular level.

Physiological changes in Rhipicephalus microplus (Acari: Ixodidae) experimentally infected with entomopathogenic fungi

Carbohydrate metabolism plays an important role in the physiology and maintenance of energy stores within living organisms. However, when organisms are exposed to adverse physiological conditions, such as during pathogenic infection, these organisms begin to use alternative substrates (proteins and lipids) for energy production. This paper studied the carbohydrate metabolism of Rhipicephalus microplus after infection with Beauveria bassiana and Metarhizium anisopliae. The parameters evaluated were glucose concentration, enzymatic activities of lactate dehydrogenase (LDH), alanine aminostransferase (ALT) and aspartate aminostransferase (AST), amounts of uric acid and urea in the hemolymph, and amount of glycogen in the fat body. The results showed changes in nitrogenous products, including an increase in the amount of urea detected 48 h after infection with both fungi. The enzymatic activities of LDH, ALT, and AST were increased after infection. The amount of glucose was increased 24 h after infection with B. bassiana and was reduced 48 h after infection with both fungi. The amount of glycogen in the fat body was reduced at different times of infection with both fungi. These results demonstrate, for the first time, the changes in carbohydrate metabolism of R. microplus after infection with M. anisopliae and B. bassiana and contribute to a better understanding of this host-parasite relationship. Together with knowledge of diseases that affect these ticks and their susceptibility to entomopathogens, an understanding of tick physiology will be necessary for the effective implementation of current biological control methods and will assist in the discovery of new methods to control this ectoparasite.

Lethal effects of a Mexican Beauveria bassiana (Balsamo) strain against Meccus pallidipennis (Stal)

The entomopathogenic fungus Beauveria bassiana (Balsamo 1835) Vuillemin is an effective alternative control agent against some agricultural pests and biological vectors of important diseases such as Chagas disease. In this work we studied an isolate of Beauveria bassiana from of the town of San Antonio Rayón, Puebla, Mexico and its entomopathogenic effects on Meccus pallidipennis (Stal 1872). Phylogenetic analysis using molecular comparison of the ITS and EF1α genes, showed that the resulting cladogram places the BUAP 04 strain with a relationship closer to the AFAO 9-6 strain, within the diversity of the B. bassiana sensu lato group. Although there was the possibility that BUAP 04 strain was a direct descendant of strains used in campaigns of biologic control, molecular study allowed us to recognize that it was a different fungus due to numerous inserts. A strain isolated from a T. dimiata was evaluated for pathogenicity against another triatoma (Meccus pallidipennis) species obtaining an LC₅₀ of 4.16 × 10⁶ spores/mL, confirming that the BUAP 04 strain is virulent for M. pallidipennis and could be a good prospect for formulations to control M. pallidipennis.

Diatomaceous earth and oil enhance effectiveness of Metarhizium anisopliae against Triatoma infestans

Entomopathogenic fungi, especially Metarhizium anisopliae, have potential for integrated control of peridomestic triatomine bugs. However, the high susceptibility of these vectors to fungal infection at elevated ambient humidities decreases in the comparatively dry conditions that often prevail in their microhabitats. A formulation adapted to this target pest that induces high and quick mortality can help to overcome these drawbacks. In the present study diatomaceous earth, which is used against pests of stored grains or as an additive to mycoinsecticides, delayed but did not reduce in vitro germination of M. anisopliae s.l. IP 46 conidia after >24h agitation without affecting viability, and did not hamper the survival of Triatoma infestans nymphs exposed to treated surfaces. The settling behavior of nymphs on a treated surface in choice tests depended on the concentration of diatomaceous earth and ambient light level. Conidia formulated with diatomaceous earth and a vegetable oil synergized the insecticidal effect of the fungus in nymphs, and quickly killed all treated insects, even at 75% relative humidity (LT(90) 8.3 days) where unformulated conidia caused only 25% mortality after a 25 days exposure. The improved performance of a combined oil and desiccant dust formulation of this Metarhizium isolate raises the likelihood for its successful mycoinsecticidal use for triatomine control and, apparently, against other domestic insect pests.

Susceptibility of different populations of ticks to entomopathogenic fungi

This study aimed to evaluate the in vitro effect of the entomopathogenic fungi Metarhizium anisopliae sensu lato (s.l.) and Beauveria bassiana sensu lato (s.l.) on two distinct populations of Rhipicephalus microplus, from two different experimental farms. Bioassays were performed with engorged females, eggs and larvae. Fungal infection was evaluated based on biological parameters of treated engorged females, percentage of hatch from treated eggs, and percentage of mortality and mean lethal time (LT90) of treated larvae. When the treatments were compared between the two populations, there were significant differences in the following parameters: pre-oviposition period, hatching period and egg production index. Moreover, the results showed that B. bassiana s.l., isolate Bb 986, was more virulent than M. anisopliae s.l., isolate 959, for engorged females, showing a control percentage of 49%. In the bioassay with eggs, the hatching percentage ranged from 3.1% to 49.5% in one population and from 3.4% to 42.7% in the other, with no significant difference between the two populations. In the bioassay with unfed larvae, the mortality percentage ranged from 91.8% to 98.7% in one population and from 71.0% to 94.0% in the other. The LT(90) varied from 19.52 to 27.51 days in one of the populations and 22.89 to 37.31 days in the other. These results suggest that populations of R. microplus show distinct variation in their susceptibility to B. bassiana s.l. and M. anisopliae s.l.

Metagenomic analysis of taxa associated with Lutzomyia longipalpis, vector of visceral leishmaniasis, using an unbiased high-throughput approach

Background

Leishmaniasis is one of the most diverse and complex of all vector-borne diseases worldwide. It is caused by parasites of the genus Leishmania, obligate intramacrophage protists characterised by diversity and complexity. Its most severe form is visceral leishmaniasis (VL), a systemic disease that is fatal if left untreated. In Latin America VL is caused by Leishmania infantum chagasi and transmitted by Lutzomyia longipalpis. This phlebotomine sandfly is only found in the New World, from Mexico to Argentina. In South America, migration and urbanisation have largely contributed to the increase of VL as a public health problem. Moreover, the first VL outbreak was recently reported in Argentina, which has already caused 7 deaths and 83 reported cases.

Methodology/Principal Findings

An inventory of the microbiota associated with insect vectors, especially of wild specimens, would aid in the development of novel strategies for controlling insect vectors. Given the recent VL outbreak in Argentina and the compelling need to develop appropriate control strategies, this study focused on wild male and female Lu. longipalpis from an Argentine endemic (Posadas, Misiones) and a Brazilian non-endemic (Lapinha Cave, Minas Gerais) VL location. Previous studies on wild and laboratory reared female Lu. longipalpis have described gut bacteria using standard bacteriological methods. In this study, total RNA was extracted from the insects and submitted to high-throughput pyrosequencing. The analysis revealed the presence of sequences from bacteria, fungi, protist parasites, plants and metazoans.

Conclusions/Significance

This is the first time an unbiased and comprehensive metagenomic approach has been used to survey taxa associated with an infectious disease vector. The identification of gregarines suggested they are a possible efficient control method under natural conditions. Ongoing studies are determining the significance of the associated taxa found in this study in a greater number of adult male and female Lu. longipalpis samples from endemic and non-endemic locations. A particular emphasis is being given to those species involved in the biological control of this vector and to the etiologic agents of animal and plant diseases.

Leishmaniasis is a vector-borne disease with a complex ecology and epidemiology. It has three main clinical forms of which visceral leishmaniasis (VL) is the most severe, as it is fatal if untreated. It is caused by a protist parasite, Leishmania spp., and is transmitted to humans by phlebotomine sandflies. The best method to interrupt any vector-borne disease is to reduce man-vector contact. Vector-targeted strategies are particularly attractive because the vectorial capacity to transmit infectious diseases to humans is proportional to vector density and, in an exponential way, to vector survival. Biological control is an effective means of reducing or mitigating pests through the use of natural enemies and is more environmentally friendly than traditional insecticide treatments. Nevertheless, there is very scanty information on the biological control of sandflies and their potential control agents. In this context, a detailed knowledge of the microorganisms that are associated with these vectors would aid in the development of novel strategies for controlling them. This is the first study to survey the taxa associated with leishmaniasis vectors and, more importantly, with any infectious disease vector, using an unbiased and high-throughput approach.

An intensive search for promising fungal biological control agents of ticks, particularly Rhipicephalus microplus

Entomopathogenic fungi have been investigated worldwide as promising biological control agents of the cattle tick Rhipicephalus microplus. The current study evaluates the virulence of several fungal isolates to R. microplus larva in the laboratory as part of an effort to identify isolates with promise for effective biocontrol of R. microplus in the field. Sixty fungal isolates, encompassing 5 Beauveria spp. and 1 Engyodontium albus (=Beauveria alba), were included in this study. In addition to bioassays, the isolates were characterized morphologically and investigated as to their potential for conidial mass production. These findings were correlated with previous reports on the same fungal isolates of their natural UV-B tolerance (Fernandes et al., 2007), thermotolerance and cold activity (Fernandes et al., 2008), and genotypes (Fernandes et al., 2009). R. microplus larvae obtained from artificially infested calves were less susceptible to Beauveria bassiana infection than ticks acquired from naturally infested cattle from a different location. Isolates CG 464, CG 500 and CG 206 were among the most virulent Beauveria isolates tested in this study. All fungal isolates presented morphological features consistent with their species descriptions. Of the 53 B. bassiana isolates, five (CG 481, CG 484, CG 206, CG 235 and CG 487) had characteristics that qualified them as promising candidates for biological control agents of R. microplus, viz., mean LC(50) between 10(7) and 10(8)conidiaml(-1); produced 5000 conidia or more on 60mm(2) surface area of PDAY medium; and, in comparison to untreated (control) conidia, had the best conidial tolerances to UV-B (7.04 kJ m(-2)) and heat (45°C, 2h) of 50% or higher, and conidial cold (5°C, 15d) activity (mycelial growth) higher than 60%. The current study of 60 Beauveria spp. isolates, therefore, singles out a few (five) with high potential for controlling ticks under field conditions.

Activity of Metarhizium spp. and Isaria spp. from the Central Brazilian Cerrado against Triatoma infestans nymphs

Entomopathogenic fungi attack Chagas disease vectors, and there is a need of effective isolates for development of biological control. Ten isolates of Metarhizium spp., four of Isaria cateniannulata and two of an Isaria sp., all isolated with Triatoma infestans as a bait insect from soils collected in Central Brazil, and tested under laboratory conditions were effective against third instar nymphs of T. infestans. This is the first report of pathogenicity of M. flavoviride var. pemphigi, M. robertsii and I. cateniannulata against T. infestans. M. robertsii IP 34 and I. cateniannulata IP 141 are among the most virulent fungi reported, and both have potential for integrated control of triatomine vectors.

Visible light during mycelial growth and conidiation of Metarhizium robertsii produces conidia with increased stress tolerance

Light conditions during mycelial growth are known to influence fungi in many ways. The effect of visible-light exposure during mycelial growth was investigated on conidial tolerance to UVB irradiation and wet heat of Metarhizium robertsii, an insect-pathogenic fungus. Two nutrient media and two light regimens were compared. Conidia were produced on (A) potato dextrose agar plus yeast extract medium (PDAY) (A1) under dark conditions or (A2) under continuous visible light (provided by two fluorescent lamps with intensity 5.4 W m(-2)). For comparison, the fungus was also produced on (B) minimal medium (MM) under continuous-dark incubation, which is known to produce conidia with increased tolerance to heat and UVB radiation. The UVB tolerances of conidia produced on PDAY under continuous visible light were twofold higher than conidia produced on PDAY medium under dark conditions, and this elevated UVB tolerance was similar to that of conidia produced on MM in the dark. The heat tolerance of conidia produced under continuous light was, however, similar to that of conidia produced on MM or PDAY in the dark. Conidial yield on PDAY medium was equivalent when the fungus was grown either under continuous-dark or under continuous-light conditions.

Biocontrol of almond bark beetle (Scolytus amygdali Geurin-Meneville, Coleoptera: Scolytidae) using Beauveria bassiana (Bals.) Vuill. (Deuteromycotina: Hyphomycetes)

AIMS

To formulate the entomopathogenic fungus Beauveria bassiana in invert emulsion, then apply it against adults of almond bark beetle (Scolytus amygdali) under laboratory and field conditions.

METHODS AND RESULTS

The effect of formulated B. bassiana in invert emulsion against S. amygdali adults was shown by comparing the mortality percentage of adults exposed to the formulated fungus using a Petri dish treatment method and by field applications to infested peach trees with mortality of adults exposed to the unformulated fungus or the untreated control. Results obtained from both exposure methods have indicated that treatment of S. amygdali adults with the formulated fungus resulted in a significantly higher mean mortality percentage (P < 0.05) when compared with the treatment with the unformulated fungus or the untreated control. This mortality ranged from 81.2 to 100%, 10 days after treatment with the formulated fungus when compared with 6.7 to 49.6% mortality, 10 days after treatment with the control or the unformulated fungus, respectively. Viability of the fungus conidia in invert emulsion was assessed by calculating the germination percentage of the conidia over time. Results indicated a high storage stability shown by a small loss of germination percentage for the formulated conidia of both strains (5.8 to 8.4% over a 12-week period) vs a low storage stability shown by a high loss of germination percentage for the unformulated conidia of the same strains (58.9 to 61.0% over the same period). The presence of B. bassiana in the galleries of beetles following the treatment of infested trees was shown in the present research.

CONCLUSIONS

The results obtained have demonstrated a significantly higher level of efficacy of formulated B. bassiana in invert emulsion against S. amygdali adults under laboratory and field conditions. The ingredients of invert emulsion used in the formulation of the fungus had a negligible effect on the viability of formulated conidia when compared with the unformulated.

SIGNIFICANCE AND IMPACT OF THE STUDY

Results obtained in the present research are promising and may be exploited commercially to control S. amygdali adults on various species of stone fruit trees, especially peach trees. This type of biocontrol of this insect may be used as an alternative means to chemical control for management of the insect. No adverse environmental impacts of the fungus or its formulation have been observed during application.

COMPORTAMENTO E ASPECTOS CITOLÓGICOS DE BEAUVERIA BASSSIANA APÓS PASSAGEM EM OVO, LARVA E ADULTO DE CHRYSOMYA ALBICEPS

RESUMO O objetivo desta pesquisa foi avaliar o comportamento do fungo Beauveria bassiana Balsamo Vuillemin reisolado de diferentes fases de desenvolvimento de Chrysomya albiceps. O fungo B. bassiana foi originalmente isolado de Castnia licus Drury (Lepidoptera: Castniidae), e está depositado na Coleção de Cultura (Micoteca-URM) do Departamento de Micologia da Universidade Federal de Pernambuco, sob o número de acesso 3.447. O experimento foi realizado em condições artificiais sob umidade e temperatura 60 ± 10% e 27 ± 1o C, respectivamente. O percentual de germinação foi elevado, com o maior índice observado no reisolado de larva; o crescimento radial no intervalo de tempo estipulado foi satisfatório, o número de conídios no 12o dia do reisolado de adulto foi maior do que o reisolado de ovo. O número de colônias de todos os reisolados foi superior ao controle. Não foram observadas diferenças nos aspectos citológicos do ciclo de vida de B. bassiana pós-passagem em ovos, larvas e adultos.

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.

Allee effect in the infection dynamics of the entomopathogenic Fungus Beauveria bassiana (Bals) Vuill. on the beetle, Mylabris pustulata

Successful infection by Beauveria bassiana as with all other entomopathogenic fungi, is accomplished only at a high conidial dose while, theoretically, a single conidium should be sufficient. Indeed, this is a major deterrent in its use as a biocontrol agent. High pathogen load for infection is required by organisms which display 'Allee' effect. In such organisms, a threshold exists for pathogen dose, below which no infection can be caused. B. bassiana has a semelparous life cycle and, therefore, its infection dynamics are expected to conform to the mass action principle with a linear relationship between dose and successful infection observable as mortality of the insect. Whether the need for a high conidial dose to induce insect mortality by B. bassiana is due to the operation of Allee effect was examined. A sample of 34 isolates was bioassayed on Mylabris pustulata (Coleoptera: Meloidae) at four conidial concentrations. With more than half of the isolates in the sample, the lowest dose tested (10(4) conidia/insect) did not cause insect mortality. Thus, a threshold pathogen load is required to cause successful infection. In these isolates, the dose-mortality relationship was sigmoid. Allee effect is thus identified in the infection dynamics of B. bassiana-M. pustulata system. The isolates that induced mortality at the lowest dose tested are concluded to be highly virulent with a lower threshold dose required for successful infection. With some isolates, at high conidial dose, the infection rate decreased either due to a decrease in the proportion of insects showing mycosis, to the speed of death, or both. Such a response could result from intra scramble competition arising from overload of pathogen at very high dose.

Impact of moisture on in vitro germination of Metarhizium anisopliae and Beauveria bassiana and their activity on Triatoma infestans

The in vitro germination of 11 Metarhizium anisopliae and 11 Beauveria bassiana isolates originating from substrates collected in rural peridomestic areas in Central Brazil where triatomines are common was tested. Conidia completed germination up to 24 h after exposure to water activity of > 0.99 aw in all isolates tested. At lower 0.93 aw germination was delayed but conidia of most isolates germinated at high rates (> 98%) within 216 h of incubation. Activities of 2 M. anisopliae and 2 B. bassiana isolates with different patterns of germination at 0.93 aw were tested in Triatoma infestans third instar nymphs. There was no relationship between germination kinetics in vitro at 0.93 aw and their activity in vivo at 98, 75 and 43% relative humidity (rh). Isolates with accelerated germination at 0.93 aw were not more virulent at 75 and 43% rh compared with isolates with retarded or no germination. Highest mortalities were observed at 98% rh, and they did not exceed 25% after 25 d incubation at lower 75 and 43% rh. Isolates that originated from a region with an extensive annual arid period showed no adaptation to lower humidity in their activity against T. infestans.

Study on morphology, pathogenicity, and genetic variability of Beauveria bassiana isolates obtained from Boophilus microplus tick

Fifty isolates of Beauveria bassiana (Balsamo) Vuillemin, 1912 (Ascomycota: Clavicipitaceae) were analyzed by morphology, for their pathogenic potential to Boophilus microplus (Canestrini, 1887) (Acari: Ixodidae) larvae, and by Random Amplified Polymorphic DNA-Polymerase Chain Reaction technique. Morphological analysis demonstrated that isolates present characteristics compatible to those described for B. bassiana in the literature. Virulence test demonstrated that all isolates present lethal effect on larvae and that the lethal concentration varies among isolates. The most virulent isolate was the only one obtained from human infection, which was also the only isolate presenting synnemata. The study on genetic variability among the isolates allowed the identification of 23 electrophoretic profiles. The established groupings suggest that most of the isolates obtained from B. microplus of the same locality present low genetic variation. In this way, the data in the present study will contribute to a meticulous characterization of these B. bassiana isolates.

Potential of oil-based formulations of Beauveria bassiana to control Triatoma infestans

The in vitro development of Beauveria bassiana conidia was monitored when immersed in six concentrations of seven non-ionic (MP 6400, MP 600, Renex 60, Renex 95, Span 80, Tween 20 and Tween 80) and three anionic (DOS 75, Hostapaval BVQ 9 and Surfax 220) surfactants and 11 vegetable oils (linseed, soybean, groundnut, rapeseed, thistle, sunflower, olive, sesame, corn, castor, and babassu). The influence of the oils on the settling behavior of Triatoma infestans nymphs and the activity of an oil-water formulation of the fungus against this vector under laboratory and simulated field conditions were also determined. With exception of DOS 75 and Surfax 220 germination of conidia on complete medium was >98% at 24 h after exposure to surfactants up to 10%. Elevated rates of germination (>25%) were observed in 10% corn, thistle and linseed oil 8 days after incubation. Pure oils had a significant repellent effect to T. infestans. Repellency decreased generally at 10% of the oil and some oils showed some attractiveness for nymphs when tested at 1%. Nymphs were highly susceptible to oil-water formulated conidia, even at unfavorable moisture for extra-tegumental development of the fungus on the insect cuticle.

Morphological alterations of Metarhizium anisopliae during penetration of Boophilus microplus ticks

Chronological histological alterations of Metarhizium anisopliae during interaction with the cattle tick Boophilus microplus were investigated by light and scanning electron microscopy. M. anisopliae invades B. microplus by a process which involves adhesion of conidia to the cuticle, conidia germination, formation of appressoria and penetration through the cuticle. Twenty-four hours post-infection conidia are adhered and germination starts on the surface of the tick. At this time, the conidia differentiate to form appressoria exerting mechanical pressure and trigger hydrolytic enzyme secretion leading to penetration. Massive penetration is observed 72 h post-inoculation, and after 96 h, the hyphae start to emerge from the cuticle surface to form conidia. The intense invasion of adjacent tissues by hyphae was observed by light microscopy, confirming the ability of M. anisopliae to produce significant morphological alterations in the cuticle, and its infective effectiveness in B. microplus.

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

This research tested the suppressive ability of Beauveria bassiana (Balsamo) Vuillemin alone and in combination with diatomaceous earth against the red flour beetle, Tribolium castaneum (Herbst). Adults did not show a dose response to B. bassiana, and the addition of diatomaceous earth (DE) did not result in a significant increase in mortality. Against larvae, however, DE at 190 mg/kg grain enhanced the efficacy of B. bassiana at all concentrations ranging from 33 to 2,700 mg of conidia per kilogram of grain. The presence of DE resulted in 17- and 16-fold decreases in the median lethal concentration of B. bassiana at 56 and 75% RH, respectively. No significant differences in larval mortality in response to B. bassiana and diatomaceous earth alone or in combination were found between 56 and 75% RH. Conidial attachment to larvae was significantly greater with 190 mg/kg DE than without it. The partial analysis of lipids taken up by DE from the larvae revealed the removal of phospholipids and long-chain fatty acids. These results support the hypothesis that diatomaceous earth enhances the efficacy of B. bassiana against larval T. castaneum, at least in part by damaging the insect cuticle, thus increasing conidial attachment and making nutrients more available to conidia for their germination.

Activity of oil-formulated Beauveria bassiana against Triatoma sordida in peridomestic areas in central Brazil

Field tests were carried out during the rainy season of 2001/2002 in São Luís de Montes Belos, Goiás, Brazil, to evaluate the potential of the entomopathogenic fungus, Beauveria bassiana, against peridomestic Triatoma sordida. An oil-water formulation of the isolate CG 14 (Embrapa) was applied in triatomine infested hen houses of four farms at a final concentration of 10(6) conidia/cm2. Numbers of T. sordida decreased over the next 25 days, after application of the fungus, and B. bassiana developed on dead insects in one hen house. A high number of B. bassiana colonies was detected in substrates collected in treated hen houses 24 h after application of CG 14. In the following three months the presence of B. bassiana declined to values found before treatment.

Pathogenicity of Evlachovaea sp (Hyphomycetes), a new species isolated from Triatoma sordida, in Chagas' disease vectors

Evlachovaea sp was tested on nymphs of 5 Triatoma spp 5 Rhodnius spp, Panstrongylus herreri and Dipetalogaster maximus at 25°C, 75% humidity and humidity >98%. Most species showed susceptibility to fungal infection at high humidity. Mortality was reduced at 75% humidity. Fungal development was observed on 69.5% of cadavers.

Record of Evlachovaea sp. (Hyphomycetes) on Triatoma sordida in the state of Goiás, Brazil, and its activity against Triatoma infestans (Reduviidae, Triatominae)

A fungal isolate was detected on a dead Triatoma sordida (Stål) collected in a peridomestic area in central Brazil. The fungus belongs to Evlachovaea Borisov and Tarasov, a new genus that was recently described in Russia. The isolate seems to be a third species and the second new and undescribed species from Brazil. The fungus was shown to be active against Triatoma infestans (Klug) third-instar nymphs at a humidity close to saturation. However, activity was reduced at a lower humidity (75%). Values of LC50 varied between 1.1 x 10(5) and 1.5 x 10(4) conidia/cm2 treated surface, 15 and 20 d after fungal application and incubation at humidity close to saturation. This new fungus may have a potential for biological control of peridomestic Chagas' disease vectors during the rainy season.

Control of Triatoma infestans (Klug) (Reduviidae: Triatominae) with Beauveria bassiana (Bals.) Vuill.: preliminary assays on formulation and application in the field

Beauveria bassiana (Bals.) Vuill., isolate CG 306, was assayed against Triatoma infestans (Klug) using indirect application by contact with a treated filter paper. The fungus was deposited on filter paper by vacuum-filtration of a conidial suspension. Estimates of 50% survival time of insects were between 15 and 21 days at 3x10(6) and 10(7) conidia/cm² of treated support, respectively, without significant difference between concentrations. A concentration of 2.4x10(6) conidia/cm² of CG 306 was necessary to kill 50% of T. infestans third instar nymphs 25 days after inoculation at 25°C and 50% relative humidity, when insects were continuously exposed to conidia. The LC50 was significantly higher (2.0x10(7) conidia/cm²) when insects were exposed for 1 h to the treated filter paper, than with continuous exposure. A mineral oil based emulsifier (2%) had no effect on germination of conidia in vitro. Fewer formulated conidia were necessary to kill 50% of insects after constant exposure to the treated surface, compared with unformulated conidia. After a 1 h exposure, unformulated conidia were more effective than formulated. After spraying B. bassiana (10(7) conidia/cm²) and releasing third instar nymphs of T. infestans in small wooden test houses, the rate of insect recovery after 25 days was significantly lower in the fungus treated houses compared to the control house. Mortality due to fungal infection of recovered insects transferred to the laboratory was between 38.1 and 93.8%, compared with no mortality in the control group. The rate of mortality of insects exposed to treated filter paper in gauze covered cups in the houses was between 35 and 78.8% after 25 days. Persistence of conidia on filter paper exposed inside the houses was > 98% during the field tests. There was no development of CG 306 on cadavers originating from laboratory infection and exposed to field conditions in the houses.