Inundative mass application of Metarhizium brunneum BIPESCO 5 (Hypocreales, Clavicipitaceae) is used for the biological control of Diabrotica v. virgifera (Coleoptera, Chrysomelidae). Long-term field trials were performed in three Austrian maize fields—with different cultivation techniques and infestation rates—in order to evaluate the efficacy of the treatment to control the pest larvae. In addition, the indigenous Metarhizium spp. population structure was assessed to compare the different field sites with BIPESCO 5 mass application. Annual application of the product Granmet-PTM (Metarhizium colonized barley kernels) significantly increased the density of Metarhizium spp. in the treated soil above the upper natural background level of 1000 colony forming units per gram dry weight soil. Although a decrease in the pest population over time was not achieved in heavily infested areas, less damage occurred in treated field sites in comparison to control sites. The Metarhizium population structure was significantly different between the treated field sites. Results showed that inundative mass application should be repeated regularly to achieve good persistence of the biological control agent, and indicated that despite intensive applications, indigenous populations of Metarhizium spp. can coexist in these habitats. To date, crop rotation remains the method of choice for pest reduction in Europe, however continuous and preventive application of M. brunneum may also present an alternative for the successful biological control of Diabrotica.
Due to their versatile way of life as saprophytes, endophytes, and entomopathogens, fungi of the genera Metarhizium and Beauveria are exposed to varying illumination conditions in their natural habitats, which makes a thorough adaptation to light very likely. While the few available studies for these genera support this assumption, research in this field is still in its infancy and the data material restricted to only a few fungal species. Thus, the aim of this work was to explore how light influences growth, conidial production and secondary metabolite formation of two industrial relevant strains of M. brunneum (MA 43, formerly M. anisopliae var. anisopliae BIPESCO 5/F52) and B. brongniartii (BIPESCO 2). To achieve this, we constructed an easily adjustable illumination device for highly standardized photophysiological studies of fungi on Petri dishes, the so-called LIGHT BOX. With the aid of this device, M. brunneum and B. brongniartii were grown on S4G or S2G agar at 25 °C for 14 days either in complete darkness or under constant illumination with red light (λpeak = 635 nm), green light (λpeak = 519 nm) or blue light (λpeak = 452 nm). In addition, for each wavelength the effect of different illumination intensities was tested, i.e., intensities of red light ranging from 22.1 ± 0.1 to 136.5 ± 0.3 µW cm-2, green light from 16.5 ± 0.1 to 96.2 ± 0.1 µW cm-2, and blue light from 56.1 ± 0.2 to 188.9 ± 0.6 µW cm-2. Both fungi strongly responded in terms of growth, conidial production, pigmentation and morphology to changes in the wavelength and irradiation intensity. The wavelength-dependent production of the well-known secondary metabolite oosporein which is secreted by the genus Beauveria in particular, was also increased under green and blue light exposure. The established LIGHT BOX system allows not only to optimize conidial production yields with these biotechnologically relevant fungi, but also allows the photobiological exploration of other fungi.
The volatile organic compounds (VOCs) 1-octen-3-ol and 3-octanone produced by the entomopathogenic fungus Metarhizium brunneum are known to have pesticidal properties at high doses against a range of invertebrate pests. Very little is known about their behavior-modifying (semiochemical) properties. This study focused on investigating the behavioral responses of three subterranean crop pests, wireworm (Agriotes lineatus), western corn rootworm (Diabrotica virgifera virgifera), and garden chafer (Phyllopertha horticola), to relatively low doses of 1-octen-3-ol and 3-octanone. The behavior of wireworms and corn rootworms were slightly influenced by the VOCs, yet not significantly. Western corn rootworms appeared to be slightly attracted by 100 µl and 200 µl 1-octen-3-ol and 100 µl dose of 3-octanone, respectively but slightly repelled by the higher dose of 3-octanone. Wireworms appeared to be slightly repelled by 1-octen-3-ol and high dose 3-octanone, but slightly attracted by the 100 µl dose of 3-octanone. The VOCs had no significant impact on garden chafer. In silico studies showed that corn rootworm odorant binding proteins (OBPs) had a strong binding affinity of 1-octen-3-ol and high dose 3-octanone, indicating that these VOCs can be detected and recognized by corn rootworm. OBPs are well conserved between species; thus, wireworm and garden chafer OBPs should also be able to bind with the VOCs. Further trials will be done to confirm that VOCs could be used as semiochemicals. Appropriate formulation of the VOCs should increase their efficacy and prevent rapid dissipation of the VOCs.
Due to their versatile lifestyle as saprophytes, endophytes and entomopathogens, fungi of the genera Metarhizium and Beauveria are exposed to varying illumination conditions in their natural habitats, which makes a thorough adaptation to light very likely. While the few available studies for these genera support this assumption, research in this field is still in its infancy and the data material restricted to only a few fungal species. Thus, the aim of this work was to explore how light influences growth, conidial production and secondary metabolite formation of two industrial relevant strains of M. brunneum (MA 43, formerly M. anisopliae var. anisopliae BIPESCO 5/F52) and B. brogniartii (BIPESCO 2). To achieve this, we constructed an easily adjustable illumination device for highly standardized photophysiological studies of fungi on Petri dishes, the so-called LIGHT BOX. With the aid of this device, M. brunneum and B. brongniartii were grown on S4G or S2G agar at 25°C for 14 days either in complete darkness or under constant illumination with red light (λpeak = 635 nm), green light (λpeak = 519 nm) or blue light (λpeak = 452 nm). In addition, for each wavelength the effect of different illumination intensities was tested, i.e., intensities of red light ranging from 22.1 ± 0.1 to 136.5 ± 0.3 µW cm-², green light from 16.5 ± 0.1 to 96.2 ± 0.1 µW cm-², and blue light from 56.1 ± 0.2 to 188.9 ± 0.6 µW cm-². Both fungi strongly responded in terms of growth, conidial production, pigmentation and morphology to changes in the wavelength and irradiation intensity. The wavelength-dependent production of the well-known secondary metabolite oosporein which is secreted by the genus Beauveria in particular, was also increased under green and blue light exposure. The established LIGHT BOX system allows not only to optimize spore production yields with these biotechnologically relevant fungi, but also allows the photobiological exploration of other fungi.
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