Biologische Bekämpfung von Drahtwürmern mit entomopathogenen Pilzen

We investigated the virulence of three European isolates of the entomopathogenic fungus (EPF) Metarhizium anisopliae against three wireworm species which are important pests of arable crops and vegetables in Europe: Agriotes lineatus, A. obscurus and A. sputator. In laboratory experiments, up to 90 % of the wireworms were killed by the fungus, depending on the fungal isolate and the wireworm species. Speed of kill was generally low with first wireworms showing unambiguous signs of fungal disease after two to three weeks. Maximum mortality rates were reached after six to eight weeks post inoculation. The next steps of this investigation will be to determine the most suitable fungal isolate and the validation of the laboratory results under greenhouse and field conditions. The aim of the study is to develop an easily applicable formulation with the most effective EPF isolate as the main active ingredient. In addition, applications of the EPF will be combined with entomoparasitic nematodes (EPNs) and repellent semiochemicals. Possible synergistic interactions between EPFs and EPNs or repellents may contribute significantly to improved biological control of wireworms

Entomopathogenic Fungus as a Biological Control for an Important Vector of Livestock Disease: The Culicoides Biting Midge

BACKGROUND: The recent outbreak of bluetongue virus in northern Europe has led to an urgent need to identify control measures for the Culicoides (Diptera: Ceratopogonidae) biting midges that transmit it. Following successful use of the entomopathogenic fungus Metarhizium anisopliae against larval stages of biting midge Culicoides nubeculosus Meigen, we investigated the efficacy of this strain and other fungi (Beauveria bassiana, Isaria fumosorosea and Lecanicillium longisporum) as biocontrol agents against adult C. nubeculosus in laboratory and greenhouse studies. METHODOLOGY/FINDINGS: Exposure of midges to 'dry' conidia of all fungal isolates caused significant reductions in survival compared to untreated controls. Metarhizium anisopliae strain V275 was the most virulent, causing a significantly decrease in midge survival compared to all other fungal strains tested. The LT(50) value for strain V275 was 1.42 days compared to 2.21-3.22 days for the other isolates. The virulence of this strain was then further evaluated by exposing C. nubeculosus to varying doses (10(8)-10(11) conidia m(-2)) using different substrates (horse manure, damp peat, leaf litter) as a resting site. All exposed adults were found to be infected with the strain V275 four days after exposure. A further study exposed C. nubeculosus adults to 'dry' conidia and 'wet' conidia (conidia suspended in 0.03% aq. Tween 80) of strain V275 applied to damp peat and leaf litter in cages within a greenhouse. 'Dry' conidia were more effective than 'wet' conidia, causing 100% mortality after 5 days. CONCLUSION/SIGNIFICANCE: This is the first study to demonstrate that entomopathogenic fungi are potential biocontrol agents against adult Culicoides, through the application of 'dry' conidia on surfaces (e.g., manure, leaf litter, livestock) where the midges tend to rest. Subsequent conidial transmission between males and females may cause an increased level of fungi-induced mortality in midges thus reducing the incidence of disease

Effect of fungal infection on midge survival.

<p>Mean (± SEM) cumulative proportional survival of adult <i>Culiocides nubeculosus</i> exposed for 6 days to ‘dry’ conidia of entomopathogenic fungi <i>Metarhizium anisopliae</i> V275, <i>Isaria fumosorosea</i> PFR97, <i>Isaria fumosorosea</i> CLO55, <i>Beauveria bassiana</i>, <i>Lecanicillium lecanii</i> (10¹¹ conidia m⁻² on tissue paper) and uninfected control at 20±1°C. Controls were not exposed to any fungus (‘0’ dose). Data represent survival of eight replicates of approximately 40 adult males and females/replicates.</p

Influence of substrates.

<p>Survival curves (Mean±SEM) for adult <i>Culiocides nubeculosus</i> exposed for 6 days to different doses (10⁸–10¹¹ conidia m⁻²) of ‘dry’ and ‘wet’ conidia of <i>Metarhizium anisopliae</i> V275 on separate substrates at 20±1°C. Controls were not exposed to any fungus (‘0’ dose). Data represent survival of eight replicates of approximately 40 adult males and females/replicate.</p

Mean lethal time.

<p>Adult midges were exposed to tissue paper treated with ‘dry’ conidia of entomopathogenic fungus at dose of 10¹¹ conidia m⁻² at 20±1°C. Controls were not exposed to any fungus (‘0’ doses). Dead midges were collected daily from each container for 6 days and kept at 25°C for sporulation.</p><p>* =  Mean lethal time (time taken in days to kill 50 and 90% of midges) estimated (four replicates/dose; approximately 40 adult males and females/replicate). 95% Confidence intervals in parentheses.</p><p>nc  =  not calculated (insufficient data).</p

Effects of substrate and formulation.

<p>Mean (± SEM) cumulative proportional survival of adult <i>Culiocides nubeculosus</i> exposed for 6 days to ‘dry’ and ‘wet’ conidia of <i>Metarhizium anisopliae</i> V275 in cages within a greenhouse. Treatments consisted of ‘dry’ or ‘wet’ conidia at dose of 2.5×10⁹ conidia m⁻² dusted or applied on peat and leaf litter. Corresponding control groups were exposed to the solvent only. Data represent survival of six replicates of approximately 200 adult males and females/replicate.</p