Ambrosia fungi in the insect-fungi symbiosis in relation to cork oak decline

Ambrosia fungi live associated with beetles (Scolytidae and Platypodidae) in host trees and act as a food source for the insects. The symbiotic relation is important to the colonizing strategies of host trees by beetles. Ambrosia fungi are dimorphic: they grow as ambrosial form and as mycelium. The fungi are highly specialized, adapted to a specific beetle and to the biotope where they both live. In addition other fungi have been found such as tree pathogenic fungi that may play a role in insects host colonization success. Saprophytic fungi are also present in insects galleries. These may decompose cellulose and/or be antagonistic to other less beneficial fungi. This paper summarizes the importance of ambrosia fungi and the interaction with insects and hosts. The possibility of the transport of pathogenic fungi by Platypus cylindrus to cork oak thus contributing for its decline is discussed.

Development of a population-based threshold model of conidial germination for analysing the effects of physiological manipulation on the stress tolerance and infectivity of insect pathogenic fungi

Entomopathogenic fungi are being used as biocontrol agents of insect pests, but their efficacy can be poor in environments where water availability is reduced. In this study, the potential to improve biocontrol by physiologically manipulating fungal inoculum was investigated. Cultures of Beauveria bassiana, Lecanicillium muscarium, Lecanicillium longisporum, Metarhizium anisopliae and Paecilomyces fumosoroseus were manipulated by growing them under conditions of water stress, which produced conidia with increased concentrations of erythritol. The time-course of germination of conidia at different water activities (water activity, aw) was described using a generalized linear model, and in most cases reducing the water activity of the germination medium delayed the onset of germination without affecting the distribution of germination times. The germination of M. anisopliae, L. muscarium, L. longisporum and P. fumosoroseus was accelerated over a range of aw levels as a result of physiological manipulation. However, the relationship between the effect of physiological manipulation on germination and the osmolyte content of conidia varied according to fungal species. There was a linear relationship between germination rate, expressed as the reciprocal of germination time, and aw of the germination medium, but there was no significant effect of fungal species or physiological manipulation on the aw threshold for germination. In bioassays with M. anisopliae, physiologically manipulated conidia germinated more rapidly on the surface of an insect host, the melon cotton aphid Aphis gossypii, and fungal virulence was increased even when relative humidity was reduced after an initial high period. It is concluded that physiological manipulation may lead to improvements in biocontrol in the field, but choice of fungal species/isolate will be critical. In addition, the population-based threshold model used in this study, which considered germination in terms of physiological time, also called hydrotime, could have general application in mycology and environmental microbiology.

Control of gastrointestinal nematodes in goats on pastures in South Africa using nematophagous fungi Duddingtonia flagrans and selective anthelmintic treatments

The effectiveness of selective anthelmintic treatments and use of nematophagous fungi Duddingtonia flagrans in reducing levels of gastrointestinal nematodes in goats was investigated at Onderstepoort, South Africa. Nineteen (19) naturally infected indigenous male goats, aged 10 months, were separated into four groups and grazed in separate previously ungrazed paddocks for two worm seasons (February 2002-March 2003). Two groups of goats were fed D. flagrans chlamydospores daily and two groups did not receive fungi. The FAMACHA system was used to determine which goats required anthelmintic treatments. Twice as many goats in the no-fungi fed group required treatments as compared with the fungi fed group. Mean FAMACHA scores in the no-fungi fed group were higher during most of the sampling occasions compared to the group fed fungi, but the difference was not significant. The group-mean faecal egg counts and PCV% were comparable between the two treatment groups throughout the study. Haemonchus was the predominant parasite genus in composite group faecal cultures. Group-mean body weights and body condition scores were higher for the no-fungi fed group from May 2002 up to the end of the study, though statistical differences were not significant. Mean worm burdens indicated that the most abundant species infecting animals were Haemonchus contortus and Trichostrongylus spp. and were higher in the fungi fed group. More animals required individual anthelmintic treatments in the no-fungi fed group. The requirement for extra treatments in the no-fungi fed group must, however, be considered against the financial cost of the fungi, the requirement of daily feeding of the fungi, the lower performance and higher worm burdens in the fungi fed group.

A fungal endophyte of black spruce (Picea mariana) needles is also an aquatic hyphomycete

An aquatic hyphomycete, Dwayaangam sp., was isolated from superficially sterilized black spruce (Picea mariana) needles submerged in aerated water in a small glass chamber (microcosm). The internal transcribed spacer (ITS) sequence of this fungus and of a commonly encountered foliar endophyte isolated from P. mariana showed a high degree of similarity. When sporulation was induced in the microcosm, both the aquatic hyphomycete and the endophyte isolate produced similar aquatic conidia after 30 days, which is longer than previously documented in similar studies. Without the use of molecular tools, the link between the aquatic and endophytic phases of the fungus would have gone unnoticed. This is the first time that a fungal endophyte of conifer needles has been shown to have an aquatic phase. Its presence both as a foliar endophyte and a sporulating aquatic fungus suggests an alternating life cycle between the two environments.

In vitro entomopathogenic activity of Beauveria bassiana against Psoroptes spp. (Acari: Psoroptidae)

An indigenous strain (IHEM 18747) of Beauveria bassiana (Balsamo) Vuillemin (Deuteromycetes) was evaluated for its in vitro entomopathogenic activity against the parasitic mite Psoroptes ovis Hering (Acari: Psoroptidae) from rabbits. The following aspects were evaluated: (1) effects of conidial concentration on the viability of adult females; (2) influence of the infection on the fertility, and on the hatchability of eggs; (3) and transmission of infection between mites, and from contaminated surface. Adult females immersed into increasing concentrations of conidia (10(4)-10(9)conidia ml(-1)) showed a dose-related susceptibility. At the highest concentration of conidia, LT50 was 1.6 days while LT50 of the controls reached 5.8 days. The fungus was able to sporulate on the body surface and 100% of the mites were covered with mycelium after immersion in solutions containing 10(7)-10(9)conidia ml(-1). One hundred percent of healthy mites exposed to infected cadavers or surfaces acquired the infection (LT50 reached 1.9 and 1.73 days, respectively, versus 6.1 and 5.1 days in controls, respectively). Egg laying was not reduced by the fungal infection but both the hatchability of the eggs and the life span of the emerging larvae were significantly reduced. Eggs directly infected with the fungus did not show reduced hatchability but the life span of the larvae was shortened. It is concluded that B. bassiana has a high entomopathogenic activity against Psoroptes spp. The in vivo use of this biocontrol agent against Psoroptes spp. in rabbit, sheep and cattle deserves further attention.

Immune responses of locusts to challenge with the pathogenic fungus Metarhizium or high doses of laminarin

Two isolates of Metarhizium anisopliae var acridum were tested for their effects on the locust immune system and for comparison with the effects of challenge by injection with laminarin. Isolate IMI 330189 (referred to hereafter as Met 189) is highly pathogenic whether applied topically as conidia or injected as blastospores. However, isolate ARSEF 728 (referred to hereafter as Met 728) is pathogenic only when injected as blastospores, suggesting that the lack of pathogenicity of topically applied conidia from this isolate is due to a failure to penetrate the insect cuticle and gain access to the haemocoel. After topical application of conidia from Met 189, no activation of prophenoloxidase is detected, but injection of blastospores from Met 189 brings about a transient increase in phenoloxidase activity in the haemolymph in both adult locusts and 5th instar nymphs, although this does not prevent fungal-induced mortality. Co-injection of adipokinetic hormone-I (AKH-I) with blastospores prolongs the activation of prophenoloxidase in the haemolymph of adult locusts, and enhances it in nymphs. It is argued that the lack of activation of prophenoloxidase in nymphs shown previously (Mullen, L., Goldsworthy, G., 2003. Changes in lipophorins are related to the activation of phenoloxidase in the haemolymph of Locusta migratoria in response to injection of immunogens. Insect Biochemistry and Molecular Biology 33, 661-670), reflects differences in the sensitivity of the immune system between adults and nymphs rather than distinct qualitative differences, and this is confirmed in this study by the demonstration that doses of laminarin higher than those used previously (>or=100 microg) do activate the prophenoloxidase cascade in 5th instar nymphs. Nodules are formed in locusts of all ages in response to fungal infection or injection of laminarin, although there is wide variation in the number, size and distribution of nodules formed. During the examination of 5th instar nymphs for nodule formation, a previously unknown phenomenon was observed in which the salivary glands melanise in response to injections of blastospores or high doses of laminarin. In c. 85% of such nymphs, this reaction is so strong that the whole salivary gland is intensely black. Such a response is not observed in the salivary glands of mature adult locusts.

[In vitro predatory activity of fungi Arthrobotrys robusta, Duddingtonia flagrans and Monacrosporium thaumasium on infective larvae of Ancylostoma spp. of dogs]

The predatory capacity of isolates of nematode-trapping fungus Arthrobotrys robust (I31), Duddingtonia flagrans (CG768) and Monacrosporium thaumasium (NF34A) on infective larvae of Ancylostoma spp. was evaluated in laboratorial conditions in experimental assay in medium water-agar 2% (WA 2%). There was significant reduction (p <0.05) of 89.89%, 97.75% and 88.76% in the average of infective larvae of Ancylostoma spp. recovered of medium WA 2% from the treatments with isolated CG768, I31 and NF34A, respectively. The isolated I31 was the most effective in the capture of the infective larvae. The results show that these fungi can be used in the environmental control of the free-living stages of Ancylostoma spp. of dogs.

[Evaluation of nematode predacious fungus Duddingtonia flagrans on infective Haemonchus contortus and Strongyloides papillosus larvae of goats]

One brazilian isolate of nematode-trapping fungus Duddingtonia flagrans AC 001 was evaluated regarding the capacity of supporting passage through the gastrointestinal tract of goats without losing the ability to entrap infective Haemonchus contortus and Strongyloides papillosus larvae (L3). Ten saneen goats of eight months old, males and infected naturally were divided in two groups of five animals. In the group 1, the animals received orally 20 g of pellets of the D. flagrans. In the group 2 (control), the animals received orally 20 g of pellets without fungi. Fecal Samples were collected at 14, 20, 24, 36 and 46 hours after the treatments and were allocated in fecal cultures at 25 degrees C during fifteen days. There was significant reduction (p<0.05) of the average number of S. papillosus larvae recovered of the fecal cultures in the animals treated with fungus when compared with the control animals at 14 and 46 hours, in the end of the experiment, this difference was 82.3%. There was significant reduction (p<0.05) of the average number of H. contortus larvae recovered of the fecal cultures in the animals treated with fungus when compared with the control animals at 14, 20 and 46 hours, in the end of the experiment, this difference was 59.3%. Such evidences confirm the transit of these fungi pellets by the digestive tract of the goats without loss of the predatory viability on L3 of H. contortus and S. papillosus.

Aquatic hyphomycete diversity and identity affect leaf litter decomposition in microcosms

We conducted a microcosm experiment with monocultures and all possible combinations of four aquatic hyphomycete species, Articulospora tetracladia, Flagellospora curta, Geniculospora grandis and Heliscus submersus, to examine the potential effects of species richness on three functional aspects: leaf litter decomposition (leaf mass loss), fungal production (ergosterol buildup) and reproductive effort (released spores). Both species richness and identity significantly affected fungal biomass and conidial production (number and biomass of released spores), whereas only species identity had a significant effect on leaf mass loss. In mixed cultures, all measures of fungal functions were greater than expected from the weighted performances of participating species in monoculture. Mixed cultures outperformed the most active monoculture for biomass accumulation but not for leaf mass loss and conidial production. The three examined aspects of aquatic hyphomycete activity tended to increase with species richness, and a complementary effect was unequivocally demonstrated for fungal biomass. Our results also suggest that specific traits of certain species may have a greater influence on ecosystem functioning than species number.

Two-component signal transduction in human fungal pathogens

Signal transduction pathways provide mechanisms for adaptation to stress conditions. One of the most studied of these pathways is the HOG1 MAP kinase pathway that in Saccharomyces cerevisiae is used to adapt cells to osmostress. The HOG1 MAPK has also been studied in Candida albicans, and more recently observations on the Hog1p functions have been described in two other human pathogens, Aspergillus fumigatus and Cryptococcus neoformans. The important, but not surprising, concept is that this pathway is used for different yet similar functions in each of these fungi, given their need to adapt to different environmental signals. Current studies of C. albicans focus upon the identification of two-component signal proteins that, in both C. albicans and S. cerevisiae, regulate the HOG1 MAPK. In C. albicans, these proteins regulate cell wall biosynthesis (and, therefore, adherence to host cells), osmotic and oxidant adaptation, white-opaque switching, morphogenesis, and virulence of the organism.

Susceptibility of biological stages of the horn fly, Haematobia irritans, to entomopathogenic fungi (Hyphomycetes)

The susceptibility of the egg, pupa, and adult of Haematobia irritans (L.) (Diptera: Muscidae) to isolates of the fungi Metarhizium anisopliae (Metsch.) Sor., Beauveria bassiana (Bals.) Vuill., and Paecilomyces fumosoroseus (Wize) Brown and Smith, was evaluated under laboratory conditions. Groups of 20 eggs than 4 h old, pupae less than 48h old and adults were sprayed with a conidial suspension of each isolate. Eggs, pupae and adults of horn fly were susceptible to these entomopathogenic fungi. For treated eggs, the isolates Ma3, Ma 15, Ma25, Pfr1, and Pfr8 reduced adult emergence to 3.8% to 6.3% in comparison with the control (72%). The mortality of pupae infected by the isolates Ma2, Ma25, and Pfr10 ranged between 50% and 71.3%. Mortality of adults after treatment with the isolates Ma6, Ma 10, Ma 14, Ma 15, Pfr 1, Pfr 9, Pfr 10, Pfr 11, and Pfr12 were higher than 90%. The isolate Ma6 produced the lowest LC(50) against adult horn flies (8.08 × 10(2)conidia/ml). These findings supported the hypotheses that isolates of M. anisopliae, and P. fumosoroseus are pathogenic against the different biological stages of horn flies by reducing adult emergence when applied on groups of eggs and pupae, and producing mortality when applied to adults.

The development and endophytic nature of the fungus Heteroconium chaetospira

The root endophytic fungus Heteroconium chaetospira was isolated from roots of Chinese cabbage grown in field soil in Japan. This fungus penetrates through the outer epidermal cells of its host, passes into the inner cortex, and grows throughout the cortical cells, including those of the root tip region, without causing apparent pathogenic symptoms. There are no ultrastructural signs of host resistance responses. H. chaetospira has been recovered from 19 plant species in which there was no disruption of host growth. H. chaetospira has a symbiotic association with Chinese cabbage. The fungus provides nitrogen in exchange for carbon. These associations are beneficial for the inoculated plants, as demonstrated by increased growth rate. When used as a preinoculum, H. chaetospira suppresses the incidence of clubroot and Verticillium yellows when the test plant is post-inoculated with the causal agents of these diseases. H. chaetospira is an effective biocontrol agent against clubroot in Chinese cabbage at a low to moderate soil moisture range and a pathogen resting spore density of 10(5) resting spores per gram of soil in situ. Disease caused by Pseudomonas syringae pv. macricola and Alternaria brassicae on leaves can be suppressed by treatment with H. chaetospira. The fungus persists in the roots and induces systemic resistance to the foliar disease.

Assessment of Fungal Isolates for Development of a Myco-Acaricide for Cattle Tick Control

Entomopathogenic fungal isolates of Arachnid origin were assessed for their ability to produce mortality and inhibit egg hatching in Boophilus microplus with the aim of selecting an isolate for development into a myco-acaricide for control of cattle ticks. The ability of the most promising isolate to target developmental stages of more than one tick species and the optimum concentration of fungal inoculum to be used for future studies were determined. Metarhizium anisopliae was the most pathogenic of the three fungal species tested on B. microplus, producing shorter average survival times (ASTs) for engorged adults (AST = 5.2 +/- 0.1 days) and larvae (AST = 9.3 +/- 0.4 days), and a longer average hatching times (AHT; AHT = 19.8 +/- 0.5 days) in comparison to Simplicillium lamellicola and Paecilomyces farinosus. In comparative studies on two tick species with similar life cycles, M. anisopliae produced a shorter AST in engorged adult B. microplus (AST = 8.8 +/- 0.3 days) than Rhipicephalus sanguineus (AST = 10.3 +/- 0.3 days). M. anisopliae was pathogenic to larvae of B. microplus (AST = 7.7 +/- 0.4 days), however, had no effect on larvae of R. sanguineus (AST = 14.6 +/- 0.3 days) as the AST of this treatment was similar to its untreated control (AST = 14.1 +/- 0.4 days). M. anisopliae lengthened the AHTs in both B. microplus (AHT = 16.4 +/- 0.3 days) and R. sanguineus (AHT = 16.7 +/- 0.3 days) in comparison to the controls. The ASTs of engorged adult B. microplus treated with M. anisopliae shortened as the concentration was increased from 1 x 10(7) to 5 x 10(8) conidia/ mL. A further increase in concentration, 1 x 10(9) conidia/mL (AST = 10.2 +/- 0.4 days) did not shorten or lengthen the AST in comparison to 5 x 10(8) conidia/mL (AST = 9.4 +/- 0.3 days).

Influence of Autoclaved Fungal Materials on Spearmint (Mentha spicata L.) Growth, Morphogenesis, and Secondary Metabolism

The influence of autoclaved fungal materials such as culture filtrate, freeze-dried mycelium (FDM), mycelium suspension, and spore suspension (SS) on the growth, morphogenesis, and carvone production of spearmint (Mentha spicata L.) plants was studied. Fungal materials were either applied as a drench or spray on the plants. Spearmint plants (cv. "294099") drenched with SS (1 x 10(8) spores/ml) of Trichoderma reesei showed no significant differences in leaf numbers, root numbers, or shoot numbers compared with nontreated controls. However, significantly higher fresh weights and carvone levels were observed in plants drenched with T. reesei SS compared with the untreated controls. Fungal materials derived from Aspergillus sp., Fusarium graminearum, F. sporotrichoides, Penicillium sp., P. acculeatum, Rhizopus oryzae, and T. reesei were sprayed on spearmint foliage. F. graminearum, F. sporotrichoides, or R. oryzae elicited no enhanced growth, morphogenesis, or secondary metabolism responses. The best growth and morphogenesis responses were obtained employing Aspergillus sp., Penicillium sp., or T. reesei foliar sprays. For example, spearmint cv. "557807" plants sprayed with 100 mg/l FDM T. reesei isolate NRRL 11460 C30 stimulated higher fresh weights (75%), shoot numbers (39%), leaf numbers (57%), and root numbers (108%) compared with untreated plants. This effect was not dose-dependent because similar growth and morphogenesis responses were obtained by testing 10, 100, or 1000 mg/l FDM concentrations. Carvone levels in fungal-treated foliar-sprayed plants were comparable to nontreated controls. However, total carvone levels per plant were higher in fungal-treated plants because of their increased fresh weight.

An entomopathogenic fungus for control of adult African malaria mosquitoes

Biological control of malaria mosquitoes in Africa has rarely been used in vector control programs. Recent developments in this field show that certain fungi are virulent to adult Anopheles mosquitoes. Practical delivery of an entomopathogenic fungus that infected and killed adult Anopheles gambiae, Africa's main malaria vector, was achieved in rural African village houses. An entomological inoculation rate model suggests that implementation of this vector control method, even at the observed moderate coverage during a field study in Tanzania, would significantly reduce malaria transmission intensity.

Fungal Pathogen Reduces Potential for Malaria Transmission

Using a rodent malaria model, we found that exposure to surfaces treated with fungal entomopathogens following an infectious blood meal reduced the number of mosquitoes able to transmit malaria by a factor of about 80. Fungal infection, achieved through contact with both solid surfaces and netting for durations well within the typical post-feed resting periods, was sufficient to cause >90% mortality. Daily mortality rates escalated dramatically around the time of sporozoite maturation, and infected mosquitoes showed reduced propensity to blood feed. Residual sprays of fungal biopesticides might replace or supplement chemical insecticides for malaria control, particularly in areas of high insecticide resistance.

[Prevention efficiency of Exserohilum monoceras with chemical herbicides against Echinochloa crus-galli in paddy field]

This paper studied the impact of several herbicides on the conidium germination of Exserohilum monoceras strain X27 in petri dish, and the synergistic effects of the pathogen and chemical herbicide quinclorac or propanil against Echinochloa crus-galli in greenhouse. The prevention efficiency of the tank-mixture of pathogen and quinclorac was also evaluated in paddy field. The results showed that test herbicides except quinclorac and bensulfulfuronmethyl could inhibit conidium germination and hypha growth to different degree. A significant synergism was observed between the pathogen and quinclorac. Adding quinclorac could obviously increase the prevention efficiency against Echinochloa crus-galli. Under field condition, the single use of pathogen could only control about 60% of the weed, while the efficiency of pathogen-quinclorac mixture could reach 90%.

Quantification of the effects of Septoria tritici blotch on wheat leaf gas exchange with respect to lesion age, leaf number, and leaf nitrogen status

Quantification of the damaging effects of pathogens on diseased plants and inclusion of these damaging functions in crop simulation models is of great importance for a more complete understanding of yield response to diseases. In this study, the effect of Septoria tritici blotch (STB) on net photosynthetic and dark respiration rates of wheat flag leaves was quantified. Bastiaans' model: Y=(1-x)beta was used to characterize the relationship between relative leaf photosynthesis (Y, considering Ynet and Ygross) and STB severity (with x the proportion of the diseased area). The value of beta indicates whether the effect of disease on photosynthesis is larger (beta >1), lower (beta <1), or equal (beta =1) to the proportion of visible diseased area. In the experimental conditions used here, leaf nitrogen content (in a range from 0.18 to 0.24 mg cm(-2)), and leaf number (flag and second leaves) did not significantly influence the effect of STB on leaf gas exchange. By contrast, damage depended strongly on the developmental stages of the STB lesions. STB lesions had no effect on inoculated leaves before visible symptoms appeared. Chlorotic symptoms had less effect on leaf net photosynthetic rate than could be accounted for by the visible diseased area (betanet=0.81). The effect of necrotic lesions on the leaf net photosynthetic capacity was slightly greater than that accounted for by visible symptoms (betanet=1.35). Our results suggest that the effect of the necrotic symptoms on the net photosynthesis expressed by betanet >1 is due to a combination of a decrease in the gross photosynthesis (betagross still >1) and to an increase in the dark respiration rate (betagross<betanet). Finally, it is discussed how the results could improve the prediction of crop loss caused by an STB epidemic in wheat fields.

Diffusible and volatile compounds produced by an antagonistic Bacillus subtilis strain cause structural deformations in pathogenic fungi in vitro

An efficient antagonistic strain of Bacillus subtilis, originally isolated from the rhizosphere of established tea bushes, was found to cause structural deformities in six pathogenic fungi under in vitro culture conditions. This effect was attributed to the production of diffusible and volatile antifungal compounds. Out of the selected test fungi four were phytopathogenic, while the remaining two were of clinical importance. The bacterial strain successfully restricted the growth of all test fungi in dual cultures, and induced morphological abnormalities such as mycelial and conidial deviations. The inhibitory effect caused by volatiles was greater than that by diffusible compounds.

Longitudinal melanonychia of the toenails with presence of Medlar bodies on biopsy

A 9-year-old girl presented with a 2-year history of pigmented streaks on her second right toenail as well as on her fourth and fifth left toenails. The patient was otherwise asymptomatic with no other physical findings. Owing to parental concern, a biopsy was performed, which revealed numerous bacteria as well as Medlar bodies overlying the nail bed with no evidence of a nevomelanocytic lesion. To our knowledge, this is the first report of Medlar bodies causing pigmented streaks in the toenails.

[The structure of micromycete communities and their synecologic interactions with basidiomycetes during decomposition of plant debris]

We investigated the interactions between micromycetes and basidiomycete mycelium on plant substrates in the course of their 3-year incubation in the litter of ecologically intact spruce forests of the Central State Biosphere Forest Sanctuary (Nelidovo District, Tver oblast). Only 40-60% of the micromycetes were involved in direct antagonistic interactions with basidiomycetous fungi. In terms of the ratio between physiologically active strains and those which did not interact with basidiomycete mycelium, we revealed differences in the structure of micromycete communities developing on various types of substrates (xylem, bark, sphagnum, leaves, needles, litter, and cotton grass). The micromycetes tested belonged to 49 species. At the end of the observation period, the fraction of microscopic fungi that actively influenced basidiomycete mycelium was four times lower in the inactive litter fraction (lignin-containing xylem debris) than in the active fraction (grass substrates). The mechanisms of indirect regulation of the structure and functions of micromycete communities are discussed, which may be based on the accumulation of phenolic compounds in the medium and changes in the enzyme activities of basidiomycete mycelium.

Pathogenicity of Metarhizium anisopliae (Deuteromycetes) and permethrin to Ixodes scapularis (Acari: Ixodidae) nymphs

Effectiveness of the entomopathogenic fungus Metarhizium anisopliae, for controlling nymphal Ixodes scapularis, was tested in laboratory and field trials. In the laboratory, M. anisopliae (Metschnikoff) Sorokin strain ESC1 was moderately pathogenic, with an LC50 of 10(7) spores/ml and induced 70% mortality at 10(9) spores/ml. In a field study, however, 10(9) spores/ml M. anisopliae did not effectively control questing I. scapularis nymphs, and significant differences were not detected in pre- and post-treatment densities. For nymphs collected and returned to the laboratory for observation, mortality was low in treatment groups, ranging from 20 to 36%. To assess whether a chemical acaricide would synergistically enhance pathogenicity of the fungus, we challenged unfed nymphal I. scapularis with combinations of M. anisopliae and permethrin, a relatively safe pyrethroid acaricide, in two separate bioassays. Significant interactions between M. anisopliae and permethrin were not observed, supporting neither synergism nor antagonism.

Competitive interaction between two aquatic hyphomycete species and increase in leaf litter breakdown

Aquatic hyphomycete species produce large numbers of conidia which rapidly colonize the leaf litter that falls into rivers during autumn. Our objective was to understand how a species which produces many fewer conidia than another in laboratory conditions can nevertheless be codominant in a natural setting. In microcosm studies with two pioneer dominant species, Flagellospora curvula and Tetrachaetum elegans, inoculated on alder leaves, we first verified that the ratio of the conidium production of both species (6 to 7:1) was inverse to that of individual conidial masses (1:7) as previously described. Calculating the percentage of leaf mass loss that corresponds to 1A mg of conidial mass produced, the combination of the two species produced 2.9-fold more loss than the mean of each species. By contrast, the reproductive biomasses of F. curvula and T. elegans were 5.2- and 2.6-fold lower, respectively. As a result, the conidium production of F. curvula in the combination was only 3.2-fold that of T. elegans instead of 6- to 7-fold in pure culture. In a mixed culture of the two species, T. elegans conidia had a high germination potential (>90%) whereas the proportion of germinated F. curvula conidia was only 50%. Moreover, T. elegans reduced the area on which F. curvula could grow on poor and rich solid media. These results indicate that the dominance of F. curvula conidia in the river may be partly controlled by T. elegans and suggest that a negative interaction between microfungi may have a positive effect on the ecosystem functioning.

Sublethal effects of Metarhizium anisopliae (Deuteromycetes) on engorged larval, nymphal, and adult Ixodes scapularis (Acari: Ixodidae)

Ixodes scapularis Say adults, nymphs, and larvae were treated with the entomopathogenic fungus Metarhizium anisopliae in a combination of field and laboratory experiments to assess sublethal effects of the fungus on I. scapularis fecundity and body mass. Postengorgement and egg mass weights were 33 and 50% lower, respectively, in adult females treated with M. ansiopliae in the field before engorging on laboratory rabbits. M. anisopliae did not significantly reduce egg mass weight, conversion efficiency, or oviposition period in I. scapularis females treated with the fungus after engorging on white-tailed deer, although only 33% of treated females oviposited. Engorged nymphs and larvae treated with M. anisopliae converted significantly lower percentages of their engorged weight to their molted adult and nymphal weights. This study indicates that M. anisopliae reduces fitness (fecundity and body mass) in all active I. scapularis stages and indicates that its impact as a biocontrol agent might be higher than that suggested by direct mortality alone.

[Biological properties of the phosphate-mobilizing Bacillus subtilis strain IMV V-7023]

Biological characteristics of a new phosphate-mobilizing bacillus strain are reported. Species-level identification of the strain was performed according to morphological, cultural, and biochemical characteristics and the sequence of the 16S rRNA gene. The strain was identified as Bacillus subtilis IMV V-7023 and displayed a very high ability to mobilize phosphorus from its sparingly soluble inorganic and organic compounds and the capability of synthesizing biologically active substances; in addition, the strain essentially suppressed the growth of phytopathogenic bacteria, micromycetes, and agents causing various diseases of vegetable, cereal, leguminous, and other plants. The strain Bacillus subtilis IMV V-7023 is promising for developing bacterial preparations for crop production.