Mycoviruses are viruses that infect and replicate in fungal cells, but unlike most known viruses of plants and animals, they exceptionally produce deleterious effects on their host. Nonetheless, the last discoveries showed that some mycoviruses can decrease the virulence of their phytopathogenic fungal hosts, making them very attractive for their possible use as biological control agents. Most mycoviruses have dsRNA genomes and are widespread in all major taxa of fungi. Beauveria bassiana is one of the most studied species of entomopathogenic fungi; it has a cosmopolitan distribution and is used as biocontroller against invertebrates in agriculture. In the present work, a collection of 137 isolates of B. bassiana obtained at different locations and from different habitats in the Czech Republic was analysed. These isolates were analysed for the presence of dsRNA elements indicative of viral infections. The results revealed a high prevalence of viral infections in Czech B. bassiana isolates, with 22.6% of the isolates containing dsRNA elements with viral characteristics. Obtained dsRNA electropherotypes showed that virus diversity in infected isolates was high and that mixed virus infections occurred among them. Based on the characteristics of the electrophoretic band patterns, it could be hypothesized that B. bassiana isolates collected in the Czech Republic could harbour members of the viral families Totiviridae, Partitiviridae, Chrysoviridae and Hypoviridae.

The potential synergism between chosen species of entomopathogenic nematodes (Steinernema arenarium, Steinernema feltiae) and entomopathogenic fungi (Beauveria bassiana, Isaria fumosorosea, Lecanicillium lecanii) is investigated in this study. It is theoretically possible to expect increasing of their efficiency at the collective introduction into environment. Creating of uniform laboratory method which will be possible to use at the research of this interaction system is a part of this study.

Biological plant protection against insect pests is an important alternative to chemical protection. One of the most important group used in the biological plant protection against insect pests are the entomopathogenic fungi. Entomopathogenic fungi are microscopic fungi that are able to induce a primary disease to insect pests. It is a very heterogeneous group of species. Worldwide there were isolated and described more than 750 species of entomopathogenic fungi. Genus Beauveria is considered one of the most important genera of entomopathogenic fungi. In the Czech Republic there has been confirmed species B. bassiana, B. brongniartii and now, on the basis of this work, B. caledonica. This study is aimed to confirm the occurrence of B. caledonica in National Park Šumava. To confirm this occurrence, I used analyzes based on the methods of molecular markers. Molecular markers are an indispensable part of science in the field of mycology, for example the strain characterization, population genetics, detection and identification of fungi, phylogenetic studies and evolutionary biology. For this study there were used sequence analysis of ITS, EF1- and LSU regions. The output data of these analyzes were used to create phylogenetic trees. The result of my thesis is taxonomical classification of studied isolates on species level.

This work focuses on verifying the efficacy of the protection product Dianem (includes bioagens Heterorhabditis bacteriophora) in maize targeted against corn rootworm larvae which cause characteristic damage to stalks. The tests were initiated in April 2014 in south Moravia in three locations - Otrokovice, Čejč and Hostěradice -- in pursuance of experiments. Dianem was applied during sowing, the same way as chemical protection product Force in the chemical protection variant. The number of beetles hatched from larvae caugh in the textile cage K (untreated control), D (biologic control) and CH (chemical control) were evaluated in the tests. The evaluation took place from mid July to September in Čejč and Hostěradice where there was no statistically significant difference in the number of hatched beetles from soil in individual variants. At the end of July, goosenecks were evaluated in Otrokovice and Čejč. There was no statistically significant difference in Otrokovice between the treated and control variant. On the other hand, there was a statistically highly significant impact of Dianem in Čejč. Another part of the tests was monitoring the corn rootworm using pheromone traps Csalomon PAL.

Entomopathogenic fungus \kur{Metarhizium anisopliae} is one of the most common species used in biological control against pests. The thesis is analyzing effectiveness of original strains and continuously passaged strains of \kur{M. anisopliae} through nutrient substrates and different developmental stages mealworm \kur{(Tenebrio molitor)}. For original and continuously passaged strains were also evaluated the growth and spore production at different temperatures cultivation. In this thesis was investigated the efficacy of the original strains of \kur{M. anisopliae} on selected economically important pests. Strains were tested on populations of adults Pollen beetles \kur{(Meligethes aeneus)} and Cabbage seedpod weevil \kur{(Ceutorhynchus obstrictus)} and the eggs of Colorado potato beetle \kur{(Leptinotarsa decemlineata)} in laboratory conditions. Other entomopathogenic fungi were tested on the eggs of Colorado potato beetle eggs.

During the evolution some groups of organisms have become coevolutionary associated with other groups, as is the case of host symbiont systems. To explore coevolutionary history of hosts and their associated symbionts, phylogenetic reconstruction of symbionts and phylogenetic reconstruction of hosts are usually compared. Coevolution is described by coevolutionary events (cospeciation, host switch, duplication, failure to diverge events and linage sorting events). The aim of this work was to test the suitability of MLST method for the complex of entomopathogenic nematodes from the genus Steinernema (with detailed analysis of Steinernema feltiae) and their symbiotic bacteria Xenorhabdus bovienii and subsequently use cophylogenetic comparative analysis to determine their level of cospeciation.

This M.Sc. thesis is aimed to describe level of the compatibility between various strains of several entomopathogenic fungi with parasitoid wasp Encarsia formosa. From many species of entomopathogenic fungi Aschersonia aleyrodis, Beauveria bassiana, B, brongniartii, Lecanicillium lecanii, Metarhizium anisopliae and Paecilomyces fumosoroseus were the species which were tested in experiments. It was found, that A. aleyrodis is very selective, because it infects only unparasitized nymphs of greenhouse whitefly Trialeurodes vaporariorum. All other strains of tested fungi were much less selective, however their efficacy always increased total efficacy when compared with the efficacy of parasitoid alone. It was concluded, that fungi A. aleyrodis, L. lecanii and P. fumosoroseus posse{\crq}s big potential for construction of IPM programs.

It is known that entomopathogenic nematodes rarely live in fields where pesticides and fertilizers are used. Because they are organisms with a high potential for biological and integrated pest control the thesis tried to determine the influence of pesticides on the infectivity and mortality of selected nematodes: Steinernema feltiae, S. arenarium and S. kraussei in water solution of some pesticides. The results are that preparations Vydate (a. i. oxamyl) and Sulka (a. i. sulphur) have the highest negative influence on both characteristics. These pesticides cause a mortality of 94.3 - 99.9 % and reduce infectivity by about 50 {--} 75 % (level 3). The following preparations may be identified as having higher potential for infectivity reduction: above all, Starane 250 EC (fluroxypyr), Sumithion super (fenithrothion), and Novozir MN 80 (mancozeb); on the other hand, Treflan 48 EC (trifluralin) significantly increases mortality. Another important observation is a fact that infectivity is significantly influenced only by concentration of pesticides, not by exposure time. During an experiment with enhacement of resistance to oxamyl (Vydate) I falling mortality and increasing infectivity of entomopathogenic nematodes were observed after five rounds.

Beauveria bassiana is widely used in biological control against the economically significant pests. Detection of morphological and genetic polymorphism among single species and strains in natural environment is important to study of the distribution and the effects in the ecosystem. The aim of this study was to determine the links of "local strains" with ecological aspects of biological control in protected zone of National park and assess the polymorphism of the population monitored in NP Šumava and exotic strains using molecular markers. There were analyzed 39 strains collected in the NP Šumava and the Krkonoše National Park in the Czech Republic and 11 strains from different countries and areas. The polymorphism of these strains was evaluated by different methods based on DNA analysis. In this study, the genetic variability is evaluated by AFLP markers. The results reveal that population from NP Šumava is very closed and the "local strains" can be very well characterized thanks these methods and compared with other strains from different parts of the Czech Republic and other countries. Thanks to these screening analyses, the strain Bba I101was determined for the preparation which will be used for bark beetle (Ips typographus) control in the National Park Šumava in the Czech Republic. This study was supported by grants GACR 521/08/H042, MSM 60076658-06, MZP SP/2d1/41/08.

Bacteria of the genus Xenorhabdus live as the natural symbionts of the entomopathogenic nematodes of the family Steinernematidae. They produce a wide range of toxic secondary metabolites of different chemical structure and effect. The synthesis of particular products is specific for each strain of Xenorhabdus. The thesis is focused on evaluating the impact of bacterial metabolites on facultatively entomoparasitic nematodes Oscheius myriophila, the free-living nematode Caenorhabditis elegans and the phytophagous potato cyst nematode Globodera rostochiensis. Target species of nematodes were exposed to 37 strains of Xenorhabdus bacteria, isolated from various species of Steinernematidae. Testing the impact of bacterial metabolites on O. myriophila and C. elegans nematodes was performed both by direct cultivation of target species on solid medium with live bacterial cultures as well as in sterilized liquid bacteria cultures. The effect of toxic substances on G. rostochiensis was evaluated only in selected sterilized bacteria cultures.