Abstract
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.
Highlights
The western corn root worm Diabrotica virgifera virgifera LeConte (Coleoptera, Chrysomelidae), an accidentally introduced, but firmly established maize pest, causes major damage in maize growing areas in Austria, in regions of Southeast Styria with continuous maize cultivation
The application of the biocontrol agent Metarhizium brunneum (Petch) against D. v. virgifera larvae has been investigated in a few studies [1,2,3], but very limited data is available on long-term field trials using only the entomopathogenic fungus (EPF) as insecticide against the maize pest Diabrotica
We investigated whether long-term inundative mass application of the biocontrol agent M. brunneum BIPESCO 5 improves the efficacy of this EPF to control D. v. virgifera
Summary
The western corn root worm Diabrotica virgifera virgifera LeConte (Coleoptera, Chrysomelidae), an accidentally introduced, but firmly established maize pest, causes major damage in maize growing areas in Austria, in regions of Southeast Styria with continuous maize cultivation. The inundative use of Metarhizium aims at controlling the pest within a short period of time and the application has to be repeated if the pest population increases again, because reproduction and/or a permanent establishment of the fungus is not expected This strategy is mostly used for short-term crops where high population densities of the pest need to be controlled to prevent damage [4]. Annual field processing such as mechanical cultivating or ploughing bears the risk of substantially diminishing the applied microbial agent [5,6] It was suggested by Rauch et al [1], that the fungus should be applied preventively, before the pest has established a large population, and pest pressure is still low (i.e., number of beetles should not exceed the economic threshold value of approximately one beetle per ten plants for continuous maize cultivation). The necessary information was gained by isolation and cultivation of Metarhizium species from the soil, by molecular genetic analyses of isolates, by evaluation of fungal and pest densities, as well as by evaluation of effects on plant damage caused by larval feeding
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