On-farm evaluation of Beauveria bassiana for control of Ostrinia nubilalis in Iowa, USA

Ostrinia nubilalis is (Lepidoptera: Crambidae) a severe pest ofcorn in the major corn growing areas of theUnited States. The efficacy of a Beauveria bassiana application, for season-long suppression of O. nubilalis was evaluated in 1996 and 1997 at locationsacross Iowa. Beauveria bassiana,Mycotech 726 (Mycotech Corporation, Butte, MT)formulated on corn grit granules (14–20 mesh)at 2.2 × 10⁹ conidia/g and applied with ahand-held applicator at the rate of 0.4 g/plant(8.8 × 10⁸ conidia/plant). Applicationswere made when plants were in the V7 or R1growth stage. The length of larval tunneling,percentage of plants not infested with O.nubilalis, percentage of plants with anendophyte, and yield from treated and controlplots were determined. Whorl-stage applicationof B. bassiana in 1996 resulted in asignificant reduction in centimeters oftunneling (46–55%) and the percentageplants not infested by O. nubilalis. In1997, B. bassiana caused significantreductions in larval tunneling at all locations(20–53%); however, a significant increase inthe percentage of plants not infested with O. nubilalis occurred at only one location. Treatment of plants with B. bassiana in1997 did not significantly increase thepercentage of plants with an endophyte;however, the trend, with the exception of onesite, was for a greater percentage ofendophytic plants in treated versus untreatedplots. A whorl-stage application of a granularformulation of B. bassiana was mostefficacious in reducing O. nubilalis larval damage.     

Evaluation of Beauveria bassiana (Hyphomycetes) isolates as potential agents for control of Dendroctonus valens

Abstract The red turpentine beetle (RTB), Dendroctonus valens LeConte, as a destructive invasive pest, has become one of the most economically important forest pest in China. Effective control measures are desperately needed. Entomopathogenic fungi, such as Beauveria bassiana, have shown great potential for the management of some bark beetle species. In this study, 12 isolates of B. bassiana from bark beetle were examined for biological characteristics and virulence, to assess their potential as biocontrol agents for RTB. There were significant differences (at P= 0.05) in colony growth rate, conidial yield, conidial germination, tolerance to UV light and extracellular proteases activity among the tested B. bassiana isolates. Isolates, including Bb1801, Bb1906, Bb789 and Bb773, exhibited the best characteristics, because they have faster hyphal growth rate, higher spore production and faster spore germination, higher UV tolerance and protease (Pr1) production. The results of a pathogenicity test of B. bassiana on RTB larvae showed that most isolates of B. bassiana have demonstrated high efficacy and the highest virulent isolate was Bb1801, which killed 100% of the treated insects and had a median lethal time (LT₅₀) of 4.60 days at a concentration of 1×10⁷ conidia/mL. Therefore, isolate Bb1801 has a great potential for sustainable control of RTB in the forest. The correlation between biological characteristics and virulence of the fungal isolates is discussed and the possibility of combination of entomopathogenic fungi with semiochemicals, as one of the promising strategy for RTB control, is considered.     

Field evaluation of Beauveria bassiana efficacy for the control of Tetranychus urticae Koch (Acari: Tetranychidae)

Trials with eggplants were conducted to evaluate field efficacy of Beauveria bassiana (Bb) applications against Tetranychus urticae, during spring of 2006 and 2007. In the 2006‐Trial, a rate of ca. 0.7 × 10¹² conidia/ha was sprayed onto plants at intervals. In the 2007‐Trial, the rates of ca. 0.8 × 10¹² and 1.6 × 10¹² conidia/ha were sprayed at 1‐ or 2‐week intervals. Based on population densities of mites and leaf damage assessed throughout the trial, the Bb sprays with 1‐ or 2‐week interval showed better control than those of 3 or 4 weeks. In both trials there was no statistical difference between 1‐week and 2‐week spray interval for all parameters measured. Furthermore, the higher rate performed significantly better than the lower rate, regardless of the intervals. No interaction was found between the spraying interval and the applied rate. Ultimately, to suppress the population density of T. urticae and prevent the eggplant damage in spring, the higher rate applied at 2‐week interval was effective.     

Selection of Beauveria bassiana isolates to control Alphitobius diaperinus

This paper presents results on isolates of the entomopathogenic fungus Beauveria bassiana for Alphitobius diaperinus (Coleoptera: Tenebrionidae) control. Of the 30 isolates tested, four (CG 71, CG 152, UNIOESTE 4, and UNIOESTE 40) resulted in mortality rates >or= 40% within 10 days. These mortality rates could be considered high because of the resistance of these species to B. bassiana. Tests were conducted using these isolates to estimate LC(50), mortality rate over time, vegetative growth, and conidial production on artificial medium and on insects. Isolates CG 71, CG 152, and UNIOESTE 4 showed the best performance and great potential to be used in an integrated management program in poultry farms to control A. diaperinus. Also, the molecular profiles of 12 isolates were analyzed using the RAPD technique. The high-virulence isolates presented a more homogeneous RAPD pattern than the others. Genetic sequencing of the ITS region was performed for one of the virulent isolates (UNIOESTE 4) and compared with sequences deposited at the NCBI database, confirming its taxonomical position as belonging to B. bassiana Clade A.     

美国白蛾高毒力球孢白僵菌菌株筛选

【目的】美国白蛾Hyphantria cunea(Drury)是世界性检疫害虫,目前已经入侵到我国长江下游地区(从辽宁丹东至安徽芜湖)。作者在前期研究中,在芜湖地区成功获得了被球孢白僵菌Beauveria bassiana侵染的美国白蛾僵虫。本研究拟在前期已获取菌株的基础上,筛选生物学性状良好且对美国白蛾幼虫具有高致病力的球孢白僵菌菌株,以期为我国长江下游地区利用昆虫病原真菌防治美国白蛾奠定基础。【方法】对采集自美国白蛾僵虫的7株球孢白僵菌菌株(Bb01-1,Bb08-5,Bb08-6,Bb08-11,Bb22-2,Bb22-3和Bb22-5)进行生物学特性研究,以候选菌株菌落形态、生长速率、产孢量、萌发率和抗紫外能力等参数确定优良菌株;并将生物学性状良好的球孢白僵菌菌株配制成5个浓度(5×10~6,1×10~7,5×10~7,1×10~8和5×10~8孢子/m L)的孢悬液,采用浸渍法处理美国白蛾4龄幼虫,以幼虫死亡率、侵染率等指标评价菌株的致病力。【结果】供试菌株Bb22-2,Bb22-3和Bb22-5为粉状菌落,其菌落直径大,产孢早且孢子层厚;同时,这3个菌株在菌落生长速率和产孢量以及孢子萌发率、紫外照射处理后的萌发率也均显著优于其他4个菌株。毒力测定结果表明,这3个菌株对美国白蛾4龄幼虫表现出很强的致病力,各菌株处理11 d后美国白蛾幼虫校正死亡率为80%~90%。这3个菌株对美国白蛾幼虫的侵染率均高(侵染率53%~87%),并且呈现随浓度升高侵染率上升的趋势。其中,菌株Bb22-2侵染率均要高于其他2个菌株。【结论】本研究成功筛选获得了生物学性状良好且对美国白蛾高毒力的球孢白僵菌菌株。鉴于中国长江下游地区气候特点与美国白蛾生物学习性,可以预期采用昆虫病原真菌防治美国白蛾在该地区将具有很好的应用前景,但其实际应用价值尚需进一步的田间试验进行确认。     

白僵菌防治菜青虫的研究

通过应用6株白僵菌不同菌株对菜青虫幼虫进行室内和田间防治试验比较,结果表明,不同菌株间的毒力存在显著差异,以筛选自菜青虫僵虫尸上的Bpr3菌株毒力最强,用浓度为1×108 mL-1的孢子液对菜青虫幼虫进行室内和田间感染,室内幼虫校正死亡率达100%,LT50为2.9806 d,田间防治效果达96.6%,经大面积示范应用,取得了显著的防治效果.     

Beauveria bassiana: endophytic colonization and plant disease control

Seed application of Beauveria bassiana 11-98 resulted in endophytic colonization of tomato and cotton seedlings and protection against plant pathogenic Rhizoctonia solani and Pythium myriotylum. Both pathogens cause damping off of seedlings and root rot of older plants. The degree of disease control achieved depended upon the population density of B. bassiana conidia on seed. Using standard plating techniques onto selective medium, endophytic 11-98 was recovered from surface-sterilized roots, stems, and leaves of tomato, cotton, and snap bean seedlings grown from seed treated with B. bassiana 11-98. As the rate of conidia applied to seed increased, the proportion of plant tissues from which B. bassiana 11-98 was recovered increased. For rapid detection of B. bassiana 11-98 in cotton tissues, we developed new ITS primers that produce a PCR product for B. bassiana 11-98, but not for cotton. In cotton samples containing DNA from B. bassiana11-98, the fungus was detected at DNA ratios of 1:1000; B. bassiana 11-98 was detected also in seedlings grown from seed treated with B. bassiana 11-98. Using SEM, hyphae of B. bassiana11-98 were observed penetrating epithelial cells of cotton and ramifying through palisade parenchyma and mesophyll leaf tissues. B. bassiana11-98 induced systemic resistance in cotton against Xanthomonas axonopodis pv. malvacearum (bacterial blight). In parasitism assays, hyphae of B. bassiana 11-98 were observed coiling around hyphae of Pythium myriotylum.     

Laboratory and greenhouse evaluation of a new entomopathogenic strain of Beauveria bassiana for control of the onion thrips Thrips tabaci

Abstract

The onion thrips Thrips tabaci is one of the most important pests of greenhouse and open-field broccoli, onion and other crops. However, the current strategy of using synthetic pesticides for its control is inadequate and unsustainable, leading to a growing interest in novel and effective biological control alternatives such as entomopathogenic fungi. Among 20 isolates of Beauveria bassiana tested for virulence against T. tabaci in laboratory bioassays, we found strain SZ-26 as the most potent, causing 83–100% mortality in adults at 1×10⁷ mL^?1conidia after 4–7 days. Further experiments in greenhouses showed the strain SZ-26 significantly lowered the numbers of adult and larval stages.     

The potential of Beauveria bassiana inoculum formulated into a polymeric matrix for a microbial control of spruce bark beetle

Two local strains of Beauveria bassiana originally isolated from naturally infected spruce bark beetles in Slovakia were tested for their virulence to Ips typographus (IT) and for their compatibility with a polymeric matrix composed of low-molecular polyethylene. Conidia could be homogenously immobilized in the low-molecular polyethylene matrix with no adverse effect on their viability and infectivity. At constant temperature (25°C), viability of immobilized conidial decreased only by 1–2% after 7 or 14 days when compared with non-formulated conidia. In field conditions, viability of conidia formulated in the matrix was even significantly higher than non-formulated conidia 35 days after their application in traps. Conidia incorporated into the polymeric matrix were infective to IT adults in laboratory bioassays. Mean values of LC₅₀ for native conidia (0.72–2.05?×?10⁶ conidia?ml^?1) and conidia immobilized in the polymeric matrix (0.64–1.03?×?10⁵ conidia?mm^?2) demonstrated high virulence. The efficacy of the local strains was significantly higher than that of B. bassiana strains from mycoinsecticides (Boverol^®, Botanigard^® ES and Naturalis-L^®). Results showed potential of this polymeric material for its use in microbial control of IT when mixed with conidia of B. bassiana.     

The potential of Metarhizium anisopliae and Beauveria bassiana isolates for the control of Aedes aegypti (Diptera: Culicidae) larvae

Fungal isolates were screened against Aedes aegypti larvae. Exposure of larvae to conidial suspensions resulted in 6–90% mortality. An inoculum persistence assay using one of the most virulent isolates showed an approximate half-life of 10 days in water containers. Not all larvae surviving to form pupae resulted in adult emergence.     

The influence of relative humidity on Beauveria bassiana infectivity and replication in the chinch bug,Blissus leucopterus

Beauveria bassiana conidia were bioassayed for pathogenicity against adult chinch bugs, Blissus leucopterus leucopterus, at varying percent relative humidities (RH). The conidia were found to be invasive and pathogenic at all humidities tested. Normal fungal replication and conidiogenesis, however, occurred only on the hosts incubated at the 75% or higher RH levels.     

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

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

Bioassay method for assessing the virulence of Beauveria bassiana against tarnished plant bug, Lygus lineolaris (Hem., Miridae)

A standard bioassay method for assessing the pathogenicity of Beauveria bassiana (Balsamo) Vuillemin (GHA strain) against second instar tarnished plant bug, Lygus lineolaris (Palisot de Beauvois) (Hem., Miridae) was developed. Several types of inoculation methods, assay containers and incubation times were tested. Our goal was to minimize control mortality and maximize treatment mortality. Five inoculation methods (immersing broccoli florets or bean pods, spraying broccoli florets or bean pods, and immersing insects) and four types of plastic containers (114‐, 171‐, 228‐ and 455‐ml) were tested. Immersing insects directly in a fungal suspension was the most effective inoculation method, which resulted in a treatment mortality of 70–81.3% at a concentration of 1 × 10⁷ conidia/ml. The 114‐ml plastic container was the most suitable assay container when 10 tarnished plant bug nymphs were treated together, resulting in a control mortality of only 6% 12 days after treatment. Within the first 6 days after treatment, 71.1% of the insects were killed, compared with a total mortality of 81.3% after 12 days. Nymphs infected with the test fungus changed colour from green to black. Mycelial outgrowth and sporulation on the cadavers demonstrated that most nymphs died of fungal infection. A total of 61.1 and 80.5% of the cadavers showed signs of mycelial outgrowth 9 days after death among those that were surface sterilized and those that were not, respectively.     

Plant oils for improving thermotolerance of Beauveria bassiana

Conidia of Beauveria bassiana ARSEF-7060 produced in millet amended with plant oils such as sunflower, corn, or cotton seed oil, were exposed to 45 degrees C of wet heat for 90 min. Conidia from millet+corn oil medium had the highest thermotolerance (LT50 (median survival time): 45.7 min). The mycotized millet grains were coated with each of the same plant oils as a granular formulation and subjected to 50 degrees C of dry heat for 8 h. Corn oil coating (LT50: 8.68 h) was superior to sunflower- and cotton seed oil coatings, suggesting the feasibility of using corn oil to increase conidial thermotolerance.     

Transformations of steroids by Beauveria bassiana

The course of transformations of testosterone and its derivatives, including compounds with an additional C1,C2 double bond and/or a 17alpha-methyl group, a 17beta-acetyl group or without a 19-methyl group, by a Beauveria bassiana culture was investigated. The fungi promoted hydroxylation of these compounds at position 11alpha, oxidation of the 17beta-hydroxyl group, reduction of the C1,C2 or C4,C5 double bonds and degradation of the progesterone side-chain, leading to testosterone. The structure of 4-ene-3-oxo-steroids had no influence on regio- and stereochemistry of hydroxylation. In a similar manner, dehydroepiandrosterone was hydroxylated by Beauveria bassiana at position 11alpha, however, a small amount of 7alpha-hydroxylation product was also formed.     

Effects of fluctuating moisture and temperature regimes on the infection potential of Beauveria bassiana for Rhodnius prolixus

The effect of both moisture and temperature on the infective potential of Beauveria bassiana to the Chagas' disease vector, Rhodnius prolixus, was studied under fluctuating regimes. At constant 25 degrees C, contaminated first-instar nymphs exposed to increasing daily periods of initial exposure to 97% RH, followed by transfer to reduced humidity (43, 53, 75, and 86% RH), showed a significant reduction in mortality when the 97% RH exposure time declined from 12 to 8 h per day. The duration of disease incubation depended on the daily 97% RH exposure time. Under fluctuating regimes of both humidity (97% RH versus 75% RH) and temperature (15/28, 20/25, 25/28, and 25/35 degrees C), first-instar mortality was affected by weather conditions, daily 97% RH exposure time (8, 12, and 16 h per day), and number of temperature and humidity fluctuations before transferring tested insects to constant unfavorable conditions. In most cases, at 12/12 h alternating cycles, high and rapid mortality required five cycles. Under these fluctuating regimes, fungus-induced mortality and mortality time were similarly affected in third- and fifth-instar nymphs by the daily 97% RH exposure time. Despite a lower susceptibility of older larval stages, mortality rates in insects exposed for at least 12 h per day at 97% RH remained very high except at 15 degrees C. Moisture and temperature regimes at 12/12 h cycling significantly affected the dose-mortality response in first-instar nymphs. The most favorable conditions consisted of 97%-20 degrees C combined with either 75%-25 degrees C or 43%-25 degrees C. Under less favorable alternating conditions (lower and higher temperatures) the amounts of inoculum required for killing 50% of first-instar nymphs were 10 or 20 times higher. From a vector control standpoint, daily high humidity appears to be the most crucial climatic constraint. B. bassiana has the potential to control R. prolixus populations with applications made during the rainy seasons when humidity is high.     

Transformation of cinoxacin by Beauveria bassiana

The ability of the fungus Beauveria bassiana ATCC 7159 to transform the antibacterial agent cinoxacin was investigated. Cultures in sucrose-peptone broth were dosed with cinoxacin, grown for 20 days, and then extracted with ethyl acetate. Two metabolites were detected and purified by high-performance liquid chromatography. The major metabolite was identified by mass and proton nuclear magnetic resonance spectra as 1-ethyl-1,4-dihydro-3-(hydroxymethyl)[1,3]dioxolo[4,5-g]cinnolin-4-one and the minor metabolite was identified as 1-ethyl-1,4-dihydro-6,7-dihydroxy-3-(hydroxymethyl)cinnolin-4-one. B. bassiana also reduced quinoline-3-carboxylic acid to 3-(hydroxymethyl)quinoline.     

应用白僵菌与溴氰菊酯混合防治马尾松毛虫研究

通过应用白僵菌粉与4种浓度溴氰菊酯粉混合后不同时间孢子萌发情况测定,以及用纯菌粉、药粉和菌药不同比例混合粉,对马尾松毛虫室内毒力测定和林间防治试验比较,筛选出菌粉与0．05％溴氰菊酯粉按4：1比例混合,防治效果最好,并经大面积推广防治示范,平均防治效果达95％以上,分别较纯菌粉和药粉效果提高14．9％和29．5％,具有明显的增效作用,马尾松毛虫死亡高峰期提前5－7天,减少松针损失量,能及时控制住高虫口林分害虫的严重危害、经济、社会和生态效益显著。