Effects of Pseudomonas chlororaphis on Pythium aphanidermatum and Root Rot in Peppers Grown in Small-scale Hydroponic Troughs

The ability of Pseudomonas (Ps.) chlororaphis isolate Tx-1 to suppress Pythium aphanidermatum and control root rot was investigated in sweet peppers grown in small-scale hydroponic trough units with recirculating nutrient solution. The agent was introduced to the nutrient solution 3 days after the peppers were inoculated with P. aphanidermatum, or 4 days before and 3 days after inoculation, or 4 days before and 3 and 10 days after. Controls either received no agent or pathogen, or the agent only (applied once, 4 days before the time of pathogen inoculations), or the pathogen only. The experiment was conducted in a greenhouse with repetitions beginning in January, March, and May. Severity of root browning associated with P. aphanidermatum, in the absence of Ps. chlororaphis, increased in the first, second and third repetitions, respectively, to 74% at 21 days, 28% at 21 days, and 68% at 11 days. In treatments with one, two, or three applications of Ps. chlororaphis, respectively, areas under root browning progress curves were reduced by 18-48%, 50-73%, and 62-79% compared to the pathogen controls, and recovery incidence of the pathogen from roots at 21 days after inoculation was reduced by 14-47%, 62-82%, and 60-89%. Roots not inoculated with P. aphanidermatum were whitish and not colonized by the pathogen. Density of Ps. chlororaphis in treated plants was usually 2×10³-1.2×10⁵ cfu g^-1 fresh roots. The Ps. chlororaphis treatments almost invariably prevented reductions in plant height, leaf area, fresh mass and dry mass of the shoots and of the roots, and root volume associated with P. aphanidermatum and root browning. It is concluded that Ps. chlororaphis Tx-1 strongly antagonized P. aphanidermatum in the pepper roots and that the agent has considerable potential for controlling root rot and maintaining productivity in commercial hydroponic peppers.     

Media and Fermentation Processes for the Rapid Production of High Concentrations of Stable Blastospores of the Bioinsecticidal Fungus Paecilomyces fumosoroseus

In shake flask and fermentor studies, various media components and culture inocula were tested to improve P. fumosoroseus spore production rates, yield and stability. To evaluate inoculum potential and inoculum scale-up for fermentor studies, conidia and liquid culture-produced spores of various strains of P. fumosoroseus were compared as inoculum. Inoculation of liquid cultures with blastospores at concentrations of at least 1×10⁶ spores mL^-1 resulted in the rapid production of high concentrations of blastospores (∼1×10⁹ spores mL^-1, 48 h fermentation time) for all strains tested. The rapid germination rate of blastospores (90% after 6 h incubation) compared to conidia (>90% after 16 h incubation) and the use of higher inoculum rates reduced the fermentation time from 96 to 48 h for maximal spore yields. A comparison of various complex nitrogen sources showed that liquid media supplemented with acid hydrolyzed casein or yeast extract supported the production of high concentrations of blastospores that were significantly more desiccation-tolerant (79-82% survival after drying) when compared to blastospores produced in media supplemented with other nitrogen sources (12-50% survival after drying). For rapid spore production, requirements for trace metals and vitamin supplementation were dependent on the type of hydrolyzed casein used in the medium. Fermentor studies with two strains of P. fumosoroseus showed that high concentrations (1.3-1.8×10⁹ spores mL^-1) of desiccation-tolerant blastospores could be produced in 48-h fermentations. These studies have demonstrated that the infective spores of various strains of the fungal bioinsecticide Paecilomyces fumosoroseus can be rapidly produced using deep-tank, liquid culture fermentation techniques.     

Laboratory investigations on the potential of entomopathogenic fungi for biocontrol of Helicoverpa armigera (Lepidoptera: Noctuidae) larvae and pupae

The susceptibility of third instar Helicoverpa armigera to seven strains of three entomopathogenic fungal species, i.e. Metarhizium anisopliae, Beauveria bassiana and Paecilomyces fumosoroseus, was tested under laboratory conditions using the larval immersion method. High efficacies ranging from 68 to 100% corrected mortality were recorded with more profound effects in treatments with B. bassiana and P. fumosoroseus strains. The median lethal concentration (LC₅₀) for L3 was 6.0×10⁵ in M. anisopliae 79, 1.5×10⁵ in B. bassiana 124 and 4.2×10⁴ in P. fumosoroseus 14. These three strains were further used to characterize the age-dependent mortality of different larval stages (L2-L5) and the effect against pupae of H. armigera. Larval stages did not differ in their mortality but differed i in median lethal time, with shorter values recorded in the second instar. Tested fungi also caused a high reduction between 74.4 and 100% in the emergence of pupae using the soil inoculation method and the pupal immersion technique. All three fungal species, especially P. fumosoroseus, have a high potential for biocontrol of H. armigera larvae and also as a soil treatment targeting the pupae.     

Screening the physical properties of novel Pseudomonas exopolysaccharides by HPSEC with multi-angle light scattering and viscosity detection

The physical properties of three novel acidic exopolysaccharides obtained from P. marginalis types A, B and C, one from P. ‘gingen’, one from P. andropogenis and one from P. fluorescens have been partially characterized. These EPSs were chromatographed on three serially placed SE Shodex OH pak columns covering a molar mass range for pullulans from about 4 × 10⁷ to 1 × 10³. The mobile phase was 0.05 M NaNO₃. Physical measurements were performed on about 30 mg of sample for each EPS. The weight average molar mass of these EPSs ranged from about 0.71 to 2.85 × 10⁶, the weight average intrinsic viscosity from 7.15 to 35.3 dl/ g and the radius of gyration from 62 to 123nm. The polydispersities of these EPSs ranged from 1.01 to 1.37. The large molar mass, size and viscosities of these EPSs may indicate that they have potential for use as thickeners, stabilizers, emulsifiers, and gelling agents in the food and non-food industries.     

Effect of Plant Type on the Persistence of Beauveria bassiana

Field evaluation of isolate MK 2001 of the entomopathogenic fungus Beauveria bassiana (Balsamo) Vuillemin, revealed conidia persistence and infectivity up to 26 days on foliage of lettuce and celery, two crops with substantial plant differences. Plants were treated at a rate of 100 ml/cage at a concentration of 1×10⁸ conidia/ml. The number of colony-forming units (CFU) recovered immediately after treatments from discs sampled on lettuce and celery leaves were not significantly different, due to similar foliar coverage of conidia by application. Significant differences were observed between both host plants during the 26 days of the field trial. The number of CFUs recovered on lettuce was significantly higher than that on celery leaves. However, for each host plant, there were no significant differences either between lettuce external leaves and internal leaves or between celery canopy and bottom leaves. An in vitro pathogenicity test carried out on Lygus lineolaris adults fed with leaf discs harvested from treated cages resulted in a high pathogenicity of B. bassiana isolate MK 2001. The mortality immediately after treatment did not differ from the death counts taken every other day for 26 days. However, efficacy was significantly different between both plants. Mortality was 91% on lettuce and 78% on celery, 7 days post-treatment. This study highlighted that plant type must be taken into account in foliar application of B. bassiana.     

Biological Control and Use of Adjuvants against Multiple Seeded Cocklebur (Xanthium strumarium) in Comparison with Several Other Cocklebur Types

Common cocklebur has several biotypes including multiple seeded cocklebur (MSC), NCC-TX, and NCC-MS. Alternaria helianthi applied at 2.5×10⁴ conidia mL^-1 in a 50% micro-emulsion of unrefined corn oil (MESUCO) or 0.2% Silwet L 77 caused 60-75% mortality on NCC-TX and MSC. Increasing the conidial concentration to 5×10⁴ mL^-1 increased mortality to 100% on MSC and NCC-TX, and 75% on NCC-MS. At 10×10⁴ conidia mL^-1, A. helianthi caused 100% mortality in all three biotypes. No mortality occurred in any biotype at inoculation rates of 2.5 and 5×10⁴ conidia mL^-1 when applied in water. Increasing the dew period from 0 to 12 h increased mortality from 0 to 100% on all three biotypes at a rate of 2.5×10⁴ conidia mL^-1 in Silwet and MESUCO. MSC appears to be the most sensitive biotype.     

Effects of nutrients on germination of Verticillium lecanii (=Lecanicillium sp.) conidia and infection of greenhouse whitefly, (Trialeurodes vaporariorum)

Laboratory experiments were conducted to assess effects of nutrients on germination of Verticillium lecanii (=Lecanicillium sp.) conidia and infection of the greenhouse whitefly, Trialeurodes vaporariorum. Suspensions of V. lecanii conidia were prepared in four nutrient solutions: 2% glucose, 2% sucrose, 2% maltose, and 2% peptone. Suspensions in de-mineralized water served as the control. At 23°C the germination rate was highest in the 2% glucose solution, followed by sucrose, maltose, demineralized water, and peptone, respectively. Germ tube growth was greatest at 23°C in the 2% glucose solution after 10 h incubation. Results of the bioassays indicated that the nutrients influenced whitefly infection. Infection levels were highest for conidial suspensions (1×10⁶ conidia/mL) prepared in 2% glucose, and were significantly greater than for peptone, demineralized water and maltose. Infection levels at 1×10⁸ conidia/mL were not significantly different from each other for all materials tested. The potential use of nutrients in a spray formulation as a means of enhancing field efficacy are discussed.     

Evaluation of the Entomopathogenic Fungi Metarhizium anisopliae and Paecilomyces fumosoroseus (Deuteromycotina: Hyphomycetes) for Control of the Green Leafhopper Empoasca decipiens (Homoptera: Cicadellidae) and Potential Side Effects on the Egg Parasitoid Anagrus atomus (Hymenoptera: Mymaridae)

The efficacy of Metarhizium anisopliae strain Ma43 and Paecilomyces fumosoroseus strain Pfr12 (both Deuteromycotina: Hyphomycetes) against adults of Empoasca decipiens (Homoptera: Cicadellidae) and potential side effects on the egg parasitoid Anagrus atomus (Hymenoptera: Mymaridae), were investigated in greenhouse cage and laboratory experiments. Treating leafhopper-infested faba bean plants at a dose rate of 1×10⁷ conidia mL^-1 resulted in up to 97% mortality 7 days after application and a 100% infection rate. Experiments on the residual effects revealed a significant decrease in adult E. decipiens mortality with increasing time from application to insect release. The decrease in mortality over time corresponded well with data from conidia germination tests. The germination of conidia on agar medium after washing them from the surafce of sprayed plants declined significantly from 95 and 96% immediately after application for M. anisopliae Ma43 and P. fumosoroseus Pfr12, respectively, to 29 and 27% 5 days later. Experiments on potential side effects of the entomopathogenic fungi on A. atomus showed that the tested isolates had no influence on adult emergence and longevity; however, the rates of parasitism were significantly reduced by the fungal treatments. The latter might be due to either density effects and/or could indicate that A. atomus avoids fungal-treated plants. However, the parasitoid is substantially less susceptible to the fungal strains tested than the host itself.     

Augmentation of Soil with Sporangia of Actinoplanes spp. for Biological Control of Pythium Damping-off

A method was developed for applying strains of Actinoplanes spp. that are hyper-parasites of oospores of Pythium ultimum to soil for reducing Pythium damping-off of plants. The method is based on the augmentation of soil with sporangia of a strain of Actinoplanes spp. borne on clay granules. In vitro sporulation of strains K30, W57, W257 and 25844 was: (1) greater for most strains on dilute Czapek-Dox agar than on four other agar media; (2) inhibited by continuous exposure to fluorescent light of intensity 4-150 μEm^-2s^-1, but not by exposure to 1 μEm^-2s^-1 or darkness; (3) greater at 20-307deg;C than at 10°C;and (4) greater at pH 6-7 than at pH 5 or 8. On solid carriers treated with dilute Czapek-Dox broth (pH 7) and incubated in the dark at 30°C for 3 weeks, strains sporulated poorly or not at all on vermiculite, perlite and rice hulls, but sporulated abundantly (10⁷-10⁹ colony-forming units (CFU) g^-1 of granules) on montmorillonite clay granules. When strains 25844, W57 and W257 were applied as granules (4 10⁷ - 4 × 10⁸ CFU g^-1) at 5% (w/w) to field plots infested with 750-1000 oospores of P. ultimum g^-1 of soil, only strain 25844 consistently increased emergence and reduced root rot of table beets 8- 1 at 24-28 days after planting compared with controls. Strain 25844 (10⁸ CFU g^-1 of granules) at 1% (w/w) also increased the emergence of bush beans at 28 days after planting in P. ultimum-infested plots, but lower rates were ineffective. The inoculum viability of strain 25844 on clay granules declined 100-fold during 2 months of storage at 5-35°C, but thereafter remained stable for another 4 months. Strain 25844 on 6-month-old granules retained a high degree of hyper-parasitic activity toward oospores of P. ultimum. Augmentation of field soil with sporangia of Actinoplanes spp. is a valid approach to the biological control of pythium damping-off.     

Biological control of Strophosoma spp. (Coleoptera: Curculionidae) in greenery (Abies procera) plantations using Hyphomycetes

In Abies procera plantations Strophosoma melanogrammum and S. capitatum cause economic damage due to the adult stage feeding on the needles. No chemical treatments of these weevils are allowed in Denmark, so the potential of biological control was evaluated. We studied pathogenicity of thirteen isolates of entomopathogenic fungi and the field effect of soil application of Metarhizium anisopliae against Strophosoma spp. All of the tested isolates were capable of causing infections under laboratory conditions and average survival time at 20°C ranged between 13 and 23 days for S. melanogrammum and between 23 and 28 days for S. capitatum when dipped in a fungal suspension adjusted to 1×10⁷ conidia mL^-1. Under field conditions up to 90% of the living collected individuals died due to M. anisopliae infection in the treated plots, whereas less than 1% died of M. anisopliae infection in control plots. In accordance, the population of Strophosoma spp. was reduced in plots where the fungus was applied compared to control plots.     

Microbial characterization during composting of municipal solid waste

This study investigates the prevailing physico-chemical conditions and microbial community; mesophilic bacteria, yeasts and filamentous fungi, bacterial spores, Salmonella and Shigella as well as faecal indicator bacteria: total coliforms, faecal coliforms and faecal Streptococci, present in a compost of municipal solid waste. Investigations were conducted in a semi-industrial pilot plant using a moderate aeration during the composting process. Our results showed that: (i) auto-sterilization induced by relatively high temperatures (60–55°C) caused a significant change in bacterial communities. For instance, Escherichia coli and faecal Streptococci populations decreased, respectively, from 2×10⁷ to 3.1×10³ and 10⁷ to 1.5×10³ cells/g waste dry weight (WDW); yeasts and filamentous fungi decreased from 4.5×10⁶ to 2.6×10³ cells/g WDW and mesophilic bacteria were reduced from 5.8×10⁹ to 1.8×10⁷ bacteria/g WDW. On the other hand, the number of bacterial spores increased at the beginning of the composting process, but after the third week their number decreased notably; (ii) Salmonella disappeared completely from compost by the 25th day as soon as the temperature reached 60°C; and (iii) the bacterial population increased gradually during the cooling phase. While Staphylococci seemed to be the dominant bacteria during the mesophilic phase and at the beginning of the thermophilic phase, bacilli predominated during the remainder of the composting cycle. The appearance of gram-negative rods (opportunistic pathogens) during the cooling phase may represent a serious risk for the sanitary quality of the finished product intended for agronomic reuse. Compost sonication for about 3 min induced the inactivation of delicate bacteria, in particular gram-negatives. By contrast, gram-positive bacteria, especially micrococcus, spores of bacilli, and fungal propagules survived, and reached high concentrations in the compost.     

Pectinase and cellulase enhance the control of Abutilon theophrasti by Colletotrichum coccodes

Inundative mycoherbicidal biocontrol agents are typically insufficiently virulent to be commercially competitive with herbicides in row crop agriculture, and require enhancement. Pectinase and cellulase are typically used by pathogens during infection. Thus, it was hypothesized that adding exogenous cell wall degrading enzymes might enhance fungal infection. Pectinase or cellulase was added to inocula of aqueous chopped mycelial suspensions of a strain of Colletotrichum coccodes for control of Abutilon theophrasti. Plants treated with 5.3×10⁶ C. coccodes propagules mL^-1 and 1.65 U mL^-1 pectinase had more rapid and complete disease development. Similar trend was achieved when 10 U mL^-1 of cellulase were added to 2.2×10⁶ C. coccodes propagules mL^-1. Adding pectinase or cellulase did not increase the host range of the wild-type fungus. The results suggest that there might be value to transforming biocontrol agents to overproduce these enzymes.     

Non-Susceptibility of Earthworm Eisenia fetida to the Rhabditid Nematode Phasmarhabditis hermaphrodita, a Biocontrol Agent of Slugs

The rhabditid nematode Phasmarhabditis hermaphrodita is a lethal parasite for slugs that is sold commercially in Europe under the trade name Nemaslug™. We evaluated the effects of P. hermaphrodita on the earthworm Eisenia fetida (Savigny). Adults of E. fetida were exposed in one-liter glass beakers to P. hermaphrodita at three concentrations (1×, 10× and 50× of the field recommended rate of 3×10⁹ billion nematodes/ha) during a 14-day period in an artificial soil substrate. The average body weight, burrowing behavior, mortality and other clinical signals of the earthworms were recorded at 0, 7, and 14 days after exposure to the treatments. In addition, injured earthworms (posterior ends removed) were exposed to the 10× field recommended rate of the commercial formulation. Neither intact nor injured E. fetida showed susceptibility to the slug-parasitic nematode P. hermaphrodita during the 14 days of exposure even at concentrations 10 and 50 times higher than the label dose. However, the worms in the attenuated control (autoclaved formulation) had higher mortality and lost less weight compared to the other treatments. Under the conditions of the test, we conclude that the use of the commercially available strain of P. hermaphrodita is safe to E. fetida.     

Biocontrol of Pythium tracheiphilum in Chinese Cabbage by Clonostachys rosea under Field Conditions

Control of leaf and head rot of Chinese cabbage (Brassica campestris L. ssp. pekinensis), caused by Pythium tracheiphilum, was obtained by Clonostachys rosea (isolate IK726) in field trials conducted in 1995 and 1999 on naturally infested land in a commercial crop in Denmark. A significant 2-3-fold disease reduction was obtained at an application rate of 10⁸-10⁹ conidia m^-2 (high application rate) in both years, but not at a 10-fold reduced rate in 1999. Disease reduction by Trichoderma harzianum (Supresivit) was almost significant at the high application rate (1 g product m^-2 corresponding to 7×10⁹ colony forming units (CFUs) m^-2) in both years, but not at a 10-fold reduced rate applied in 1999. In both 1995 and 1999 trials, the percentage of marketable heads increased significantly by 10% following a full application rate of C. rosea. Supresivit applied at the full application rate gave a significant 13% yield improvement in 1995 but not in 1999. No yield improvement was found when the two agents were applied at 10-fold reduced rates. A Danish T. harzianum isolate significantly increased yield by 13% in 1995, but gave no disease control. Plant growth promotion may have been responsible for yield improvements obtained by Supresivit and the Danish isolate of T. harzianum. The 1995 trial also evaluated the products Binab T (T. harzianum+T. polysporum), Mycostop (Streptomyces griseoviridis), Polyversum (P. oligandrum) and Aliette (fosetyl-Al) and Danish isolates of P. oligandrum (2) and T. virens (1), none of which gave disease control or yield effects.     

A Multiple-Pathogen System for Bioherbicidal Control of Several Weeds

A novel system using four host-specific fungal plant pathogens applied in a single, postemergent spray to control pigweed, sicklepod, and showy crotalaria was tested under greenhouse conditions. The four pathogens were Phomopsis amaranthicola (a pathogen of pigweed species), Alternaria cassiae (a pathogen of sicklepod and showy crotalaria), Colletotrichum dematium f. sp. crotalariae and Fusarium udum f. sp. crotalariae (pathogens of showy crotalaria). Spore suspensions of each pathogen alone (10⁶ spores mL^-1) or a mixture of the four pathogens (1:1:1:1, v/v, 2.5×10⁵ spores mL^-1 of each pathogen, total 10⁶ spores mL^-1) were tested on four- to six-leaf stage seedlings of the three weed species grown together in pots. One week after inoculation (WAI), all sicklepod and showy crotalaria seedlings were killed, and all pigweed seedlings were killed by 6 WAI when inoculated with their respective pathogen(s) alone or a mixture of the pathogens. None of the weeds inoculated with the root-infecting pathogen F. udum developed wilt disease by the time the experiment was completed (6WAI). The results demonstrate the feasibility to control three weeds simultaneously with different fungi without loss of efficacy or alterations in host-specificity of each fungus in the given mixture. Scanning electron microscopy showed visual differences in the appearance or germination and further development of conidia of each pathogen on its respective host leaf surface compared to nonhost leaf surfaces, whether the pathogen was applied alone or in a mixture with the other pathogens studied. Application of several host-specific fungal pathogens in a bioherbicide mixture as a multi-component bioherbicide system may be advantageous for further development of simultaneous, broad-spectrum weed control.     

Factors Affecting Disease Development by Rhynchosporium alismatis in Starfruit (Damasonium minus), a Weed of Rice

The fungal pathogen Rhynchosporium alismatis is being developed for biological control of starfruit (Damasonium minus), an important aquatic weed in Australian rice fields. The development of R. alismatis in starfruit differs between juvenile and adult plants. Juvenile starfruit plants are stunted as a result of fungal infection, while in adult plants, the main effect is necrosis and chlorosis of floating leaves. A conidial concentration of 1×10⁴ conidia mL^-1 was adequate to cause disease symptoms on floating leaves, but the stunting effect on juveniles was caused by concentrations of at least 1×10⁵ conidia mL^-1. To successfully inoculate juvenile plants, the water must be drained before inoculation to expose plants to the inoculum. The artificial addition of dew periods did not enhance disease development in plants. The stunting of juvenile starfruit plants caused by the infection of R. alismatis may give rice plants a competitive advantage over the weed at the seedling stage     

Lack of effect of the nematophagous fungus Duddingtonia flagrans on the development of the dung beetle, Aphodius constans

The nematode-trapping fungus Duddingtonia flagrans may be used as a biological control agent of gastro-intestinal nematode larvae of ruminants by feeding the hosts with fungal spores. This trial was intended to search an eventual detrimental impact of the presence of spores of D. flagrans in high numbers in goat feces on the common dung beetle, Aphodius constans (Coleoptera: Aphodiidae). A. constans eggs were settled in feces derived from grazing goats fed spores at daily dose rates of 0, 0.25 × 10⁶, 0.5 × 10⁶ or 10⁶ spores/kg BW. At the end of the incubation period, the number of adults that have emerged from eggs were counted and compared between dose rates. No difference in emergence rate between treatments can be seen. The presence of D. flagrans spores in goat feces, even in large numbers, did not alter the development of A. constans.     

农杆菌介导海洋草酸青霉转化体系及聚酮合酶Pks生物学功能*

为研究南海柳珊瑚共附生草酸青霉SCSGAF0023的聚酮合酶(PKS)生物学功能,采用农杆菌介导法构建草酸青霉SCSGAF0023的Pks敲除株ΔPks,比较野生菌株及ΔPks的生长发育及环境适应性差异。以草酸青霉SCSGAF0023分生孢子为受体,p0380-hygB为双元载体,成功实现草酸青霉SCSGAF0023的遗传转化。结果表明:农杆菌浓度为OD₆₀₀=0.5,在200μmol/L 乙酰丁香酮(AS)诱导下与10⁷个/ml草酸青霉SCSGAF0023孢子于25℃共孵育时转化效率最高。基于上述转化体系,成功获得Pks敲除株ΔPks,并首次证实Pks正向调控草酸青霉SCSGAF0023产孢,但不影响其对环境的适应性。这为进一步系统研究真菌PKSs及聚酮化合物对真菌生长发育与环境适应性的影响提供素材。     

Alternative methods for genetic transformation of Pseudozyma antarctica, a basidiomycetous yeast-like fungus

Electroporation and Agrobacterium tumefaciens-mediated transformation (ATMT) were adapted and optimized for genetic transformation of the basidiomycetous yeast-like fungus Pseudozyma antarctica as alternatives to the cumbersome PEG/CaCl₂-mediated transformation of protoplasts. Electroporation yielded 100–200 transformants per μg of DNA per 10⁸ cells after 3 days on selective medium. For its part, ATMT yielded 60–160 transformants per 10⁶ input cfu after 5–10 days on a selective medium. Transformants obtained from both methods showed stable hygromycin resistance and strong expression of green fluorescent protein. Analysis of integration events revealed a limited number of predominantly tandem insertions in the genome of transformants, an improvement over PEG/CaCl₂-mediated transformation. Both protocols relied on intact conidia of P. antarctica as starting material and thus eliminated the need for cell wall-degrading or weakening agents such as lytic enzymes or chemicals. Other advantages over protoplast transformation included higher yield of transformants and shorter recovery time of transformed colonies on selective medium.     

Horizontal Transmission of the Entomopathogenic Fungus Beauveria bassiana among the Spruce Bark Beetle, Ips typographus (Col., Scolytidae) in the Laboratory and under Field Conditions

In laboratory and field cage experiments, the horizontal transmission of the entomopathogenic fungus Beauveria bassiana (Boverol®) between adults of the spruce bark beetle Ips typographus was examined. In a laboratory experiment, conidia transfer between treated and untreated beetles at different ratios resulted in 96% mortality (MST 4.3 days) at a ratio of 1:1 and 90% mortality (MST 4.5 days) at a ratio of 1:2. At ratios of 1:5, 1:10 and 1:20, the mortalities at 7 days were 83, 77 and 75%, respectively. In a second laboratory experiment, the efficacy of B. bassiana was investigated after transmission from contaminated to healthy beetles over a period of 5 days. Two weeks later, the mortality of treated and untreated beetles was 99% (control mortality was 44%), while the rate of mycosis was 79% in the treatment compared to 10% in the control beetles. A single contact between one treated male (2.0×10⁵ conidia/beetle) and an untreated female was found to be sufficient to transmit a lethal dose of B. bassiana of about 1.2×10⁴ conidia. Two experiments in field cages in a spruce stand demonstrated horizontal transmission of B. bassiana (Boverol®) between beetles. In the first experiment the transmission was investigated following the introduction of B. bassiana-inoculated beetles into a population of untreated beetles. Significant reductions were observed in the length of maternal galleries, and the number of larvae and pupae. In the second field cage experiment, natural populations of beetles were lured into a flight cage using a pheromone trap, and treated with B. bassiana or left untreated on alternate days. In this experiment, significant reductions were observed in the number of bore holes and the length of maternal galleries, while no larvae, pupae or juveniles were found under the bark of spruce trunks in the Boverol® transmission treatment. It is concluded that B. bassiana has potential for control of I. typographus, and further field experiments are warranted to investigate its efficacy under more practical conditions.