Beauveria bassiana

Beauveria bassiana colonizes insect hosts initially through a yeast phase, which is common in some artificial liquid cultures, but not reported on artificial solid media. We describe a yeast-like phase for B. bassiana isolate 447 (ATCC 20872) on MacConkey agar and its virulence toward Diatraea saccharalis and Tetranychus urticae. The yeast-like cells of B. bassiana developed by budding from germinating conidia after 24-h incubation. Cells were typically and fungal colonies were initially circular and mucoid, but later were covered with mycelia and conidia. Ability to produce yeast-like cells on MacConkey medium was relatively common among different B. bassiana isolates, but growth rate and timing of yeast-like cell production also varied. Metarhizium anisopliae and Paecilomyces spp. isolates did not grow as yeast-like cells on MacConkey medium. Yeast-like cells of B. bassiana 447 were more virulent against D. saccharalis than conidia when 107 cells/ml were used. At 108 cells/ml, the estimated mean survival time was 5.4 days for the yeast suspension and 7.7 days for the conidial suspension, perhaps due to faster germination. The LC50 was also lower for yeast than conidial suspensions. Yeast-like cells and conidia had similar virulence against T. urticae; the average mortalities with yeast-like cells and conidia were, respectively, 42.8 and 45.0%, with 107 cells/ml, and 77.8 and 74.4%, with 108 cells/ml. The estimated mean survival times were 3.6 and 3.9 for yeast and conidial suspensions, respectively. The bioassay results demonstrate the yeast-like structures produced on MacConkey agar are effective as inoculum for B. bassiana applications against arthropod pests, and possibly superior to conidia against some species. Obtaining well-defined yeast phase cultures of entomopathogenic hyphomycetes may be an important step in studies of the biology and nutrition, pathogenesis, and the genetic manipulation of these fungi.

An entomopathogenic fungus, Beauveria bassiana was tested against the rice weevil Sitophilus oryzae. Bioassays were conducted by introducing 25 adult insects on 50 g of B. bassiana mixed rice in glass jars maintained at 28±2° C, and 70% RH. Mortality was ...

Beauveria bassiana (Balsamo) Vuillemin, a white muscardine fungus has drawn attention worldwide as potential biocontrol agent against insect-pests since decades. In the rice ecosystem, B. bassiana has been established as potential mycoinsecticide against major insect-pests of rice viz., Cnaphalocrocis medunalis, Nilaparvata lugens, Dicladispa armigera, Scirpophaga incertulas etc., but its efficacy against phytopathogens of rice in simultaneous application is least studied. Among major phytopathogens of rice, bacterial leaf blight incurs a yield loss of up to 12-75%, affecting crop at seedling, tillering and vegetative stages. Therefore, recent studies have inclined towards unravelling antimicrobial potential of B. bassiana as effective plant disease antagonist, thereby, opening a newer dimension in dualpurpose crop protection strategies. In the present study, antagonistic abilities of fifteen (15) native isolates of B. bassiana were evaluated against Xanthomonas oryzae pv. oryzae causing bacterial leaf blight of rice by conducting agar-plug diffusion and inverted plate assays. The results showed that, majority of B. bassiana isolates viz., Bb31, Bb45, Bb48, Bb25, Bb53 were able to inhibit bacterial growth, with maximum per cent inhibition was recorded in the range of 60-84% through development of inhibition zone. Further, antibacterial ability of B. bassiana was also attributed to release of non-volatile inhibitory metabolites responsible for the formation of inhibition zone on the bacterial lawn. These findings provide substantial evidences on antibacterial abilities of B. bassiana against X. oryzae pv. oryzae and further provides a scope to test the efficacy of B. bassiana against bacterial leaf blight of rice in the glasshouse and field condition in addition to their potential entomogenous behaviour against insect-pests of rice.

The susceptibility of the adult and larval stage of housefly, Musca domestica L. (Diptera: Muscidae), to two entomopathogenic fungi, Metarhizium anisopliae (Metsch.) Sor. and Beauveria bassiana (Bals.) Vuill., was evaluated under laboratory and simulated field bioassays. Bioassays on adult houseflies were carried out at different conidial concentrations ranging from 103 to 109 conidia/ml in petri plate and minichamber assays. Absolute mortality was observed within 4–5 days at all the concentrations tested. M. anisopliae was found to be more effective with LC50 of 6.75 × 107 conidia/ml compared with 1.21 × 108 conidia/ml of B. bassiana in petri plate bioassay. Similar trend was observed in minichamber bioassay. Larvicidal activity evaluated through petri plate bioassay also indicated that M. anisopliae was more effective larvicide with LC50 of 4.1 × 108 conidia/ml as against 3.31 × 109 conidia/ml of B. bassiana. Larvicidal activity was further evaluated in simulated field condition of decaying waste matrix using dry conidial formulations (108 conidia/g) of both the fungi. Larval mortality obtained in this assay was 43% (B. bassiana) and 63% (M. anisopliae). Remarkably better performance of M. anisopliae as an adulticidal and larvicidal agent over B. bassiana in laboratory bioassays as well as simulated field conditions suggests that it may have good potential to become part of an integrated housefly control program.

The banana weevil Cosmopolites sordidus (Germar) is the most important insect pest of bananas and plantains (Musa spp.). The larvae bore in the corm, reducing nutrient uptake and weakening the stability of the plant. Attack in newly planted banana stands can lead to crop failure. In established fields, weevil damage can result in reduced bunch weights, mat die-out and shortened stand life. Damage and yield losses tend to increase with time. This paper reviews the research on the taxonomy, distribution, biology, pest status, sampling methods, and integrated pest management (IPM) of banana weevil. Salient features of the weevil's biology include nocturnal activity, long life span, limited mobility, low fecundity, and slow population growth. The adults are free living and most often associated with banana mats and cut residues. They are attracted to their hosts by volatiles, especially following damage to the plant corm. Males produce an aggregation pheromone that is attractive to both sexes. Eggs are laid in the corm or lower pseudostem. The immature stages are all passed within the host plant, mostly in the corm. The weevil's biology creates sampling problems and makes its control difficult. Most commonly, weevils are monitored by trapping adults, mark and recapture methods and damage assessment to harvested or dead plants. Weevil pest status and control options reflect the type of banana being grown and the production system. Plantains and highland bananas are more susceptible to the weevil than dessert or brewing bananas. Banana production systems range from kitchen gardens and small, low-input stands to large-scale export plantations. IPM options for banana weevils include habitat management (cultural controls), biological control, host plant resistance, botanicals, and (in some cases) chemical control. Cultural controls have been widely recommended but data demonstrating their efficacy are limited. The most important are clean planting material in new stands, crop sanitation (especially destruction of residues), agronomic methods to improve plant vigour and tolerance to weevil attack and, possibly, trapping. Tissue culture plantlets, where available, assure the farmer with weevil-free material. Suckers may be cleaned by paring, hot water treatment and/or the applications of entomopathogens, neem, or pesticides. None of these methods assure elimination of weevils. Adult weevils may also invade from nearby plantations. As a result, the benefits of clean planting material may be limited to a few crop cycles. Field surveys suggest that reduced weevil populations may be associated with high levels of crop sanitation, yet definitive studies on residue management and weevil pest status are wanting. Trapping of adult weevils with pseudostem or corm traps can reduce weevil populations, but material and labour requirements may be beyond the resources of many farmers. The use of enhanced trapping with pheromones and kairomones is currently under study. A combination of clean planting material, sanitation, and trapping is likely to provide at least partial control of banana weevil. Classical biological control of banana weevil, using natural enemies from Asia, has so far been unsuccessful. Most known arthropod natural enemies are opportunistic, generalist predators with limited efficacy. Myrmicine ants have been reported to help control the weevil in Cuba, but their effects elsewhere are unknown. Microbial control, using entomopathogenic fungi and nematodes tend to be more promising. Effective strains of microbial agents are known but economic mass production and delivery systems need further development.

The effects of various spray-application parameters on the efficacy of Beauveria bassiana foliar treatments against Leptinotarsa decemlineata larvae were evaluated during three field seasons. Treatments were applied to small plots (6 rows × 7–12 m) using a CO2-powered backpack hydraulic sprayer with nozzles affixed to lateral drop tubes and directed upward at a 45° angle to target ventral leaf surfaces.

Dual biological control, of both insect pests and plant pathogens, has been reported for the fungal entomopathogens, Beauveria bassiana (Bals.-Criv.) Vuill. (Ascomycota: Hypocreales) and Lecanicillium spp. (Ascomycota: Hypocreales). However, the primary mechanisms of plant disease suppression are different for these fungi. Beauveria spp. produce an array of bioactive metabolites, and have been reported to limit growth of fungal plant pathogens in vitro. In plant assays, B. bassiana has been reported to reduce diseases caused by soilborne plant pathogens, such as Pythium, Rhizoctonia, and Fusarium. Evidence has accumulated that B. bassiana can endophytically colonize a wide array of plant species, both monocots and dicots. B. bassiana also induced systemic resistance when endophytically colonized cotton seedlings were challenged with a bacterial plant pathogen on foliage. Species of Lecanicillium are known to reduce disease caused by powdery mildew as well as various rust fungi. Endophytic colonization has been reported for Lecanicillium spp., and it has been suggested that induced systemic resistance may be active against powdery mildew. However, mycoparasitism is the primary mechanism employed by Lecanicillium spp. against plant pathogens. Comparisons of Beauveria and Lecanicillium are made with Trichoderma, a fungus used for biological control of plant pathogens and insects. For T. harzianum Rifai (Ascomycota: Hypocreales), it has been shown that some fungal traits that are important for insect pathogenicity are also involved in biocontrol of phytopathogens.

Three isolates of the entomopathogen Beauveria bassiana along with one strain of Metarhizium anisopliae were cultured on seven media with different carbon/nitrogen (C/N) ratios. The effect of nutrition on virulence of the isolates was evaluated via measurement of colony growth, spore yield, germination speed, conidial C/N ratio and Pr1 (a serine protease) activity. ‘Osmotic stress’ medium produced the lowest colony growth with low numbers of conidia in all isolates. However, these conidia showed a high germination rate and virulence. However, conidial Pr1 activity was low in some isolates. In most but not in all cases conidia from 1% yeast extract, 2% peptone and low (10 : 1) C/N medium had higher Pr1 activity compared with conidia from other media. However, in some instances we could not conclude that there was a relationship among germination rate, conidial Pr1 activity and virulence. C/N ratio of conidia was statistically different among various media and fungal isolates. Conidia with lower C/N ratio generally produced lower LT50 (lowest median lethal time) values (more virulent). Insect-passaged conidia from different media had lower C/N ratio compared with similar conidia from artificial cultures. Therefore, they should be more virulent than in vitro produced conidia. As germination rate, conidial Pr1 activity and C/N ratio are independent of host, it seems that host-related determinants such as insect cuticle and physiology and environmental conditions may influence host susceptibility and therefore fungal isolate virulence towards host insects.

The virulence of ten isolates of Beauvena bassiana (Balsamo) Vuillemin to the maize weevil, Sitophilus zeamais Motsch., was tested in the laboratory. All isolates tested were capable of infecting S. zeamais but their virulence, determined by adult mortalities and median lethal time, varied. A total of five (I89-481, I90-520, I89-477, I90-533, and I94-907) highly virulent, three (I92-736, I93-906 and I92-761A) intermediate and two (I93-868 and I93-870) weakly virulent isolates were identified for S. zeamais. The growth and sporulation rates and persistency of water formulated conidia of the most virulent isolates were also studied.I90-520 was selected for further work and dose-mortality relationships and the infectivity of dry conidia against Sitophilus zeamais were determined. The lowest dose (104 conidia ml−1) caused about 88% mortality within eight days. To assess the infectivity of a dry formulation of the isolate, conidial doses of 0, 0.1, 0.5 and 1 g of B. bassiana per 25 g of popping maize seeds were compared with pirimiphos-methyl at 10 ppm. This demonstrated the potential of dry conidia of the isolate to infect and cause mycosis to S. zeamais. Adult mortality of S. zeamais and damage to maize seeds treated with different levels of dry conidia were not statistically significantly different from pirimiphos-methyl-treated maize after 14 days of storage period, but the chemical pesticide killed all target insects within 24 h, whereas mortality began at day 3 for the best B. bassiana treatment.

The ectoparasitic mite Varroa destructoris Anderson and Trueman is considered a destructive pest of honey bee Apis
mellifera. Potentiality of using the entomopathogenic fungi Beauveria bassiana (Balsamo) as mycoacaricide against
V. destructor was evaluated. Considerable effect of B. bassiana on Varroa mite numbers was recorded in treated colonies
compared to the control. There were significant differences in mean numbers of mite mortality rates between treated and
untreated colonies. Results indicated that conidial concentration of 5x106 spores/g caused higher mortality rate compared
to the other tested concentrations. Results showed that B. bassiana had a good potential on V. destructor when was dusted
more than one time (0, 6 and 10day). Scanning electronic microscopy examination of infected mite showed abundant
hyphal growth and sporulation on treated mite cuticle. The results indicated that dusting of colonies with fungal
conidiospores caused a reduction in the mite population reached 47.68, 33.44, 70.00 and 46.38%, 13 days after
applications at concentrations of 1 ×106
conidia/g, 2.5×106 conidia/g, 5 ×106
conidia/g, and 7.5×106
conidia/g, respectively.
The results showed also that the impact of fungus on workers bees was very low. Obtained results can suggest using
B. bassiana as a potential effective bioacaricide against V. destructor in honey bee colonies.