Cultivation of Entomopathogenic Fungi for the Search of Antibacterial Compounds

Entomopathogenic fungi are a rich source of natural bioactive compounds. To establish cultivation conditions which facilitate the production of bioactive compounds and to select good genera among entomopathogenic fungi as the producer, 47 typical entomopathogenic fungi were tested for their ability to produce antibiotic activity. Thirty-eight strains (81%) and 30 strains (64%) of these fungi produced either anti-Bacillus compounds or anti-Staphylococcus compounds, respectively, indicating that the majority of the entomopathogenic fungi tested possessed the ability to produce antibacterial compounds. Using 9 representative strains (Aschersonia sp. HF724, Beauveria bassiana HF338, Cordyceps ramosopulvinata HF746, Metarhizium anisopliae HF293, Metarhizium flavoviride HF698, Nomuraea rileyi HF588, Paecilomyces fumosoroseus HF254, Paecilomyces tenuipes HF419, and Verticillium lecanii HF238), the cultivation conditions in liquid medium were surveyed with respect to the cultivation procedure and medium composition, particularly in terms of the presence or absence of insect-derived materials. At 26 °C, M. anisopliae HF293, N. rileyi HF588, and V. lecanii HF238 strains produced clear antibiotic activity against Bacillus and Saccharomyces, but only in the presence of insect-derived materials, suggesting that the production of antibacterial/antifungal compounds by entomopathogenic fungi is triggered by the presence of insect-derived materials.     

Effect of Soil Texture and Moisture on the Activity of Entomopathogenic Nematodes Against Female Boophilus annulatus Ticks

Soil texture, chemistry and moisture have a profound effect upon the activity and persistence of entomopathogenic nematodes (EPNs). Whereas nematodes’ natural habitat is within the soil, ticks and other arthropod pests prefer to stay on the soil surface and under stones or leaf litter; they spend much of their life cycle in the humid environment of the soil upper layer, therefore consideration of the effect of the soil environment on nematode activity is a pre-requisite for the sucessful use of EPNs against arthropod pests. In the present study we investigated the effects of soil type, and humidity on various nematode strains and on their effectiveness against ticks. Many infective juveniles (IJs) of Steinernema carpocapsae and S. riobrave were found in the uppermost soil layer whereas the heterorhabditid strains were almost absent from the upper 6 cm of the soil profile. The IJs of S. feltiae, and the S. carpocapsae strain S-20, exhibited an intermediate behavior. It was found that the activity of IJs of S. carpocapsae in the soil upper layer (1 cm depth) was strongly affected by soil type: the greatest number of IJs were recorded from sandy loam soil; less were found in the lighter soils – ‘Marine sand’ and ‘Calcareous sandstone’ – and only very few were recovered from heavy soils. Strikingly, even when the soil moisture was low and the number of nematodes found in the upper layer correspondingly low, tick mortality remained high. The results demonstrate: (a) the possible use of the nematodes as an anti-tick agent; (b) the importance of knowing the exact interaction of nematodes with the immediate environment of the pest, in order to optimize the pest-control activity of the nematode.     

Susceptibility of Ceratitis capitata Wiedemann (Diptera: Tephritidae) to Entomopathogenic Fungi and Their Extracts

The effectiveness of seven strains of entomopathogenic fungi against Ceratitis capitata adults was evaluated in the laboratory. Adults were susceptible to five of seven aqueous suspensions of conidia. Metarhizium anisopliae and strain CG-260 of Paecilomyces fumosoroseus were the most pathogenic fungi, with 10-day LD₅₀ values of 5.1 and 6.1 × 10³ conidia/fly, respectively, when applied topically. Sublethal effects on fecundity and fertility of the fungal-exposed females were also studied. The most effective fungus in reducing fecundity was P. fumosoroseus CECT 2705, with reductions on the order of 65% at 1 × 10⁶ conidia/fly. M. anisopliae and Aspergillus ochraceus also showed significant reductions of fecundity (40–50% for most of the assayed concentrations). Fertility was moderately affected by the fungi. M. anisopliae at 1 × 10⁶ conidia/fly was the most effective fungus, showing egg eclosion reduction of over 50% compared with the control. In addition, culture broth dichloromethane extracts from the entomopathogenic fungi were tested for insecticide activity against C. capitata, including effects on fecundity and fertility. The extract from M. anisopliae was the most toxic, resulting in about 90% mortality at a concentration of 25 mg/g of diet; under these conditions, fecundity and fertility of treated females were reduced by 94 and 53%, respectively, compared with untreated controls.     

Effect of fungicides on growth,germination and cuticle-degrading enzyme production by Lecanicillium muscarium

Lecanicillium muscarium Zare and Gams (previously known as Verticillium lecanii) is a well-known pathogen of arthropods. The influence of six fungicides on growth, sporulation, conidial germination and cuticle-degrading enzyme production by L. muscarium was investigated under laboratory conditions. The maximum reduction in vegetative growth, sporulation and conidial germination in relation to the control treatment was observed for propiconazole, whereas mancozeb and chlorothalonil caused the lowest reduction in these parameters. Propiconazole and pyraclostrobin caused higher reduction in enzyme activities (chitinase, Pr1, Pr2 and lipase) at all three concentrations (10, 100 and 1000 µg/ml), whereas low reduction in enzyme activities was caused by chlorothalonil and mancozeb when used at 10 µg/ml. The data presented can be used for future recommendations of these fungicides in Integrated Pest Management (IPM) programmes where L. muscarium is an important control agent.     

Influence of commercial fungicides on the germination,growth and virulence of four species of entomopathogenic fungi

The influence of 15 commercially available fungicides on the germination, growth and virulence of Metarhizium anisopliae, Beauveria bassiana, Isaria fumosorosea, and Lecanillium longisporum was evaluated. The influence of the fungicides on conidial germination was dependant on the fungicide type and dose. Most fungicides retarded conidial germination of all the fungi tested at 10× and at the recommended rate of application, however, their toxicity declined at lower concentrations. Most of the fungicides inhibited mycelial growth of B. bassiana, whereas L. longisporum growth was unaffected. Only two and eight fungicides influenced mycelial growth of I. fumosorosea and M. anisopliae, respectively. None of the fungicides influenced the virulence of B. bassiana and L. longisporum, however, tolylfluanid and azoxystrobin reduced the virulence of M. anisopliae and I. fumosorosea, respectively. These studies clearly show that certain fungicides have the potential to inhibit germination of entomopathogenic fungi in vitro but appear to have little or no effect on their virulence against target insects.     

Effect of Fusarium,Paecilomyces and Trichoderma formulations against aphid Schizaphis graminum

Fungal strains belonging to the genera Fusarium Paecilomyces and Trichoderma were tested in vitro in order to study their effects against Schizaphis graminum one of the major pests of cereal crops around the world. Biological assays were performed using a solid formulation that was obtained from fungal cultures grown on rice and then finely ground (0.2 mm). The occurrence of toxic secondary metabolites (fumonisin B₁ and beauvericin) produced by these fungi was also investigated. In each experiment, three groups of aphids: 15-hour old larvae, 5-day old nymphs with wing buds and wingless morphs were treated with a suspension of a fungal formulation. Some strains belonging to the genera Fusarium and Trichoderma significantly controlled the specimens of the three groups of S. graminum. The F. proliferatum strain ITEM 1407, producing a high level of fumonisin B₁ in the culture (1250 g/g), and F. larvarum strain ITEM 2139 had high insecticidal activity (>60%) within 10 minutes after application. As F. larvarum ITEM 2139 did not produce metabolites toxic to mammals, it might be a good candidate as a biocontrol agent of S. graminum in the field.This revised version was published online in October 2005 with corrections to the Cover Date.     

Susceptibility of the cactus weevil Metamasius spinolae to Beauveria bassiana and Metarhizium anisopliae under laboratory and field conditions

Aims: To evaluate different entomopathogenic fungal isolates against the cactus weevil Metamasius spinolae under laboratory and field conditions, and select an isolate to be used as a tool in the management of this insect pest. Methods and Results: Four experiments were carried out. The effect of temperature on the in vitro growth of eight isolates of entomopathogenic fungi (two Metarhizium anisopliae and six Beauveria bassiana) was assessed. The susceptibility of adult M. spinolae to the same isolates was evaluated. Using three selected isolates, the interaction between susceptibility and sex of the insect was studied. Finally, a field experiment was carried out to evaluate infection of adult M. spinolae by the same three isolates under natural abiotic conditions. Overall, growth rate was greatest at 25°C for all the isolates. In vitro growth of M. anisopliae was greater than B. bassiana. Mortality of adult M. spinolae was greater when inoculated with B. bassiana compared with isolates of M. anisopliae. Susceptibility had no interaction with the sex of the insect. The proportion of insects succumbing to infection was smaller when incubated under field conditions than when incubated under laboratory conditions. Conclusions: The experiments described here showed a complex interaction between entomopathogenic fungi and M. spinolae, and these data allows us to select isolate Bb107 as a first step towards its use in the management of this pest insect. Significance and Impact of the Study: Our results showed that entomopathogenic fungi can be used for the control of M. spinolae, which may help reduce the use of chemical insecticides and, therefore, the exposure of Opuntia ficus‐indica producers to pesticides.     

Quality of the Entomopathogenic NematodeSteinernema carpocapsaeProduced on Different Media

The characteristics of morphometric (body length and width), biochemical (fatty acid content), motility, and penetration rate of infective juveniles ofSteinernema carpocapsaeBeijing strain reared on four different culture media [e.g., plant protein medium (I), animal protein medium (II), plant and animal protein medium (III), andin vivoculture (IV) were systematically compared in this research. The results showed that the average lengths of infective juveniles were 497.4 ± 0.09, 514.3 ± 0.08, 525.7 ± 0.09, and 556.6 ± 0.09 μm, the average widths were 24.9 ± 0.006, 25.6 ± 0.005, 26.1 ± 0.006, and 27.9 ± 0.004 μm, and the average dry weights per million infective juveniles were 49.2 ± 2.2, 58.6 ± 2.4, 59.6 ± 1.8, and 80.7 ± 1.7 mg cultured by media I, II, III, and IV, respectively. The highest relative content of fatty acid of infective juveniles was obtained from medium IV at 15.4 ± 1.2 × 10⁵μV/s, and the lowest one was 6.76 ± 0.3 × 10⁵μV/s from medium I and 11.8 ± 0.2 × 10⁵and 13.7 ± 0.3 × 10⁵μV/s from media II and III, respectively. The numbers of nematodes that moved a vertical distance of 5 cm in sand column within 48 h were 24 ± 3.6, 75 ± 11.6, 69 ± 9.7, and 92 ± 13.2 and the penetration rates into theGallerialarva within 24 h were 2.8 ± 0.45, 6.0 ± 1.14, 6.4 ± 0.74, and 6.0 ± 0.7% from media I to IV, respectively. The results indicated that the quality of entomopathogenic nematode was influenced by the cultural medium component. The animal protein, especially from insects which were presented in media II, III, and IV, has a strong positive effect on nematode quality.     

Toxicity of Xanthene Dyes to Entomopathogenic Fungi

Effects of xanthene dyes on mycelial growth and conidial germination in three species of entomopathogenic fungi, Beauveria bassiana, Metarhizium anispoliae and Paecilomyces fumosoroseus, were evaluated in a variety of assay systems. In a disk-diffusion assay, erythrosin B and phloxine B (but not eosin B) produced zones of inhibition in colonies of all three species under continuous exposure to light at disk-loadings of 100mug. None of the dyes produced zones of inhibition in the absence of light at disk loadings of 100mug. Both erythrosin B and phloxine B inhibited mycelial growth of all three species in the light in a dose-dependent manner. Weaker dose-responses for inhibition of growth in the dark were observed for some fungus/dye combinations. Erythrosin B, tested singly, completely inhibited conidial germination in the light in all eight fungal strains tested at 100mug ml-1 medium, but failed to inhibit conidial germination in any of these strains in the dark at the same concentration of dye. For single strains of each of the three fungi, erythrosin B and phloxine B inhibited conidial germination in a dose-dependent manner in the light with IC50s < 6.2mug dye ml-1 medium for all fungus/dye combinations. Phloxine B was a more potent inhibitor of germination than erythrosin B for all three fungal species. At fixed dosages of erythrosin B and phloxine B, inhibition of conidial germination in all three species increased with time of exposure to light. These results constitute the first quantitative demonstration of photodynamic inhibition of conidial germination in fungi by xanthene dyes.     

Food Web Responses to Augmenting the Entomopathogenic Nematodes in Bare and Animal Manure-Mulched Soil

Factorial treatments of entomopathogenic nematodes (EPN) and composted, manure mulches were evaluated for two years in a central Florida citrus orchard to study the post-application biology of EPN used to manage the root weevil, Diaprepes abbreviatus. Mulch treatments were applied once each year to study the effects of altering the community of EPN competitors (free-living bactivorous nematodes) and antagonists (nematophagous fungi (NF), predaceous nematodes and some microarthro-pods). EPN were augmented once with Steinernema riobrave in 2004 and twice in 2005. Adding EPN to soil affected the prevalence of organisms at several trophic levels, but the effects were often ephemeral and sometimes inconsistent. EPN augmentation always increased the mortality of sentinel weevil larvae, the prevalence of free-living nematodes in sentinel cadavers and the prevalence of trapping NF. Subsequent to the insecticidal effects of EPN augmentation in 2004, but not 2005, EPN became temporarily less prevalent, and fewer sentinel weevil larvae died in EPN-augmented compared to non-augmented plots. Manure mulch had variable effects on endoparasitic NF, but consistently decreased the prevalence of trapping NF and increased the prevalence of EPN and the sentinel mortality. Both temporal and spatial abundance of NF were inversely related to the prevalence of Steinernema diaprepesi, whereas Heterorhabditis zealandica prevalence was positively correlated with NF over time. The number of weevil larvae killed by EPN was likely greatest in 2005, due in part to non-target effects of augmentation on the endemic EPN community in 2004 that occurred during a period of peak weevil recruitment into the soil.     

Susceptibility of the tobacco whitefly,Bemisia tabaci (Hemiptera: Aleyrodidae) biotype Q to entomopathogenic fungi

Recently, the Q biotype of tobacco whitefly has been recognized as the most hazardous strain of Bemisia tabaci worldwide because of increased resistance to some insecticide groups requiring alternative strategies for its control. We studied the susceptibility of this biotype of B. tabaci to 21 isolates of Beauveria bassiana, three isolates of Isaria fumosorosea, one isolate of I. cateni, three isolates of Lecanicillium lecanii, one isolate of L. attenuatum, and one isolate of Aschersonia aleyrodis. These isolates were evaluated on pruned eggplant seedlings, at a concentration of 10⁸ conidia/mL (deposited at 6000±586 conidia mm^?2). The mortality based on mycosis varied from 18 to 97% after 6 days. Isaria fumosorosea isolate Pf04, B. bassiana isolates Bb06, Bb12, and L. lecanii L14 were found the most effective. Furthermore, five isolates were chosen for concentration–mortality response assays and compared to B. bassiana GHA as a standard. The numbers of nymphs infected by fungi were correlated with the spore concentration. L. lecanii L14 and I. fumosorosea Pf04 had the shortest LT₅₀ at 3.5 and 3.3 days at 6000±586 conidia mm^?2. Mortality declined and LT₅₀ values were longer as the concentration of conidia was reduced. The LD₅₀ values were calculated as 87, 147, 191, 263, and 269 conidia mm^?2 for isolates L14, GHA, AS1260, Bb13, and Pf04, respectively. These results indicated that the Q biotype of sweetpotato whitefly was susceptible to the five isolates of entomopathogenic fungi and these isolates have potential to be developed as microbial pesticides for whitefly control.     

Combinations of Biocontrol Agents for Management of Plant-Parasitic Nematodes and Soilborne Plant-Pathogenic Fungi

Numerous microbes are antagonistic to plant-parasitic nematodes and soilborne plant-pathogenic fungi, but few of these organisms are commercially available for management of these pathogens. Inconsistent performance of applied biocontrol agents has proven to be a primary obstacle to the development of successful commercial products. One of the strategies for overcoming inconsistent performance is to combine the disease-suppressive activity of two (or more) beneficial microbes in a biocontrol preparation. Such combinations have potential for more extensive colonization of the rhizosphere, more consistent expression of beneficial traits under a broad range of soil conditions, and antagonism to a larger number of plant pests or pathogens than strains applied individually. Conversely, microbes applied in combination also may have antagonistic interactions with each other. Increased, decreased, and unaltered suppression of the target pathogen or pest has been observed when biocontrol microbes have been applied in combination. Unfortunately, the ecological basis for increased or decreased suppression has not been determined in many cases and needs further consideration. The complexity of interactions involved in the application of multiple organisms for biological control has slowed progress toward development of successful formulations. However, this approach has potential for overcoming some of the efficacy problems that occur with application of individual biocontrol agents.     

中国革菌一新记录种

柔丝纹枯状革菌（Hypochnicium bombycinum）采于中国青海省,为中国革菌一新记录种。文中根据所采集的材料对其进行了详细的描述和显微结构绘图。     

Variability of the Mitochondrial SSU rDNA of <Emphasis Type="Italic">Nomuraea</Emphasis> Species and Other Entomopathogenic Fungi from Hypocreales

Hypocrealean arthropod pathogenic fungi have profound impact on the regulation of agricultural and medical pests. However, until now the genetic and phylogenetic relationships among species have not been clarified, such studies could clarify host specificity relationships and define species boundaries. Our purpose was to compare the sequences of the mitochondrial SSU rDNA fragments from several mitosporic entomopathogenic Hypocreales to infer relationships among them and to evaluate the possibility to use these sequences as species diagnostic tool in addition to the more commonly studied sequences of nuclear SSU rDNA. The SSU mt-rDNA proved to be useful to help in differentiation of species inside several genera. Clusters obtained with Parsimony, Bayesian, and Maximum Likelihood analyses were congruent with a new classification of the Clavicipitaceae (Sung et al. Stud Mycol. 2007;57:5-59) in which the anamorphic genera Nomuraea and Metarhizium species remain in the Clavicipitaceae and Isaria species sequenced here are assigned to the family Cordycipitaceae. Mitochondrial genomic information indicates the same general pattern of relationships demonstrated by nuclear gene sequences.     

Zinc Phosphate and Pyromorphite Solubilization by Soil Plant-Symbiotic Fungi

Acidolysis, complexolysis and metal accumulation were involved in solubilization of zinc phosphate and pyromorphite by a selection of soil fungi representing ericoid and ectomycorrhizal plant symbionts and an endophytic/entomopathogenic fungus, Beauveria caledonica. Zinc phosphate was much more readily solubilized than pyromorphite. According to the relationship between metal mobilization and pH, acidolysis (protonation) was found to be the major mechanism of both zinc phosphate and pyromorphite dissolution for most of the fungi examined. In general, the more metal tolerant fungal strains yielded more biomass, acidified the medium more and dissolved more of the metal mineral than less tolerant strains. However, B. caledonica 4 excreted a substantial amount of oxalic acid (～ 0.8 mM) in the presence of pyromorphite that coincided with a dramatic increase in lead mobilization providing a clear example of complexolysis. Organic acid excretion by fungi was inter- and intraspecific and was strongly influenced by the presence of the toxic metal minerals. When grown on zinc phosphate or pyromorphite, Hymenoscyphus ericae DGC3(UZ) accumulated the lowest metal concentration, but Thelephora terrestris accumulated the highest metal concentration in the biomass. The ability to accumulate water-soluble lead species, representing mainly cytosolic and vacuolar pools, seemed to be connected with pyromorphite-solubilizing ability. B. caledonica 4, which demonstrated the highest ability to dissolve pyromorphite, accumulated the highest water-soluble fraction and total lead concentration in the mycelium. Generally, isolates with a higher zinc-tolerance accumulated significantly less total zinc from zinc phosphate (including the sum of water-soluble and NaCl-extractable zinc) than non-tolerant strains.     

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.     

Freezing and Desiccation Tolerance in Entomopathogenic Nematodes: Diversity and Correlation of Traits

The ability of entomopathogenic nematodes to tolerate environmental stress such as desiccating or freezing conditions, can contribute significantly to biocontrol efficacy. Thus, in selecting which nematode to use in a particular biocontrol program, it is important to be able to predict which strain or species to use in target areas where environmental stress is expected. Our objectives were to (i) compare inter- and intraspecific variation in freeze and desiccation tolerance among a broad array of entomopathogenic nematodes, and (ii) determine if freeze and desiccation tolerance are correlated. In laboratory studies we compared nematodes at two levels of relative humidity (RH) (97% and 85%) and exposure periods (24 and 48 h), and nematodes were exposed to freezing temperatures (-2°C) for 6 or 24 h. To assess interspecific variation, we compared ten species including seven that are of current or recent commercial interest: Heterorhabditis bacteriophora (VS), H. floridensis, H. georgiana, (Kesha), H. indica (HOM1), H. megidis (UK211), Steinernema carpocapsae (All), S. feltiae (SN), S. glaseri (VS), S. rarum (17C&E), and S. riobrave (355). To assess intraspecific variation we compared five strains of H. bacteriophora (Baine, Fl1-1, Hb, Oswego, and VS) and four strains of S. carpocapsae (All, Cxrd, DD136, and Sal), and S. riobrave (355, 38b, 7-12, and TP). S. carpocapsae exhibited the highest level of desiccation tolerance among species followed by S. feltiae and S. rarum; the heterorhabditid species exhibited the least desiccation tolerance and S. riobrave and S. glaseri were intermediate. No intraspecific variation was observed in desiccation tolerance; S. carpocapsae strains showed higher tolerance than all H. bacteriophora or S. riobrave strains yet there was no difference detected within species. In interspecies comparisons, poor freeze tolerance was observed in H. indica, and S. glaseri, S. rarum, and S. riobrave whereas H. georgiana and S. feltiae exhibited the highest freeze tolerance, particularly in the 24-h exposure period. Unlike desiccation tolerance, substantial intraspecies variation in freeze tolerance was observed among H. bacteriophora and S. riobrave strains, yet within species variation was not detected among S. carpocapsae strains. Correlation analysis did not detect a relationship between freezing and desiccation tolerance.     

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.     

Pathogenicity of individual isolates of entomopathogenic fungi affects feeding preference of red imported fire ants Solenopsis invicta

Seven isolates of entomopathogenic fungi, Isaria fumosorosea (IFCF-H and IFCF-L), Beauveria bassiana s.l. (Bb02 and Bb04) and Metarhizium anisopliae s.l. (Ma01, SM076 and M09), were selected for their pathogenicity against Solenopsis invicta as well as feeding preference of S. invicta. When ants were treated with a conidial suspension at a concentration of 1 × 10⁸ conidia/ml, the median lethal times (LT₅₀) of IFCF-H, IFCF-L, Bb02, Bb04, Ma01, SM076 and M09 were 3.4, 162.6, 7.3, 2.8, 3.8, 7.3 and 2.7 days, respectively, after 10 days. The median lethal concentrations (LC₅₀) on the 10th day after inoculation were 1.20 × 10⁷, 1.56 × 10¹⁰, 4.23 × 10⁷, 3.04 × 10⁶, 6.13 × 10⁶, 2.90 × 10⁷ and 9.90 × 10⁵ conidia/ml, respectively. Furthermore, S. invicta consumed significantly less solution flavoured with Bb04 conidia than the control, which was demonstrated by the lowest preference index (PREF = 0.09). S. invicta did not have a significant feeding preference for other fungal isolates. The pathogenicity (LC₅₀) of fungal isolates was not significantly correlated (R² = 0.013) with the PREF of S. invicta. However, in the paired-choice experiments between different virulent isolates belonging to the same genera, S. invicta tended to select the solution flavoured with conidia of relatively lower pathogenic isolates such as IFCF-L, Bb02 and SM076. We conclude that the pathogenicity of congeneric fungi may affect the feeding preference of S. invicta. Red imported fire ants might adjust their feeding response to entomopathogenic fungi based on the profile of microbial volatile organic compounds.