Potential of different isolates of entomopathogenic fungi from Thailand as biological control agents against western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) / Möglichkeiten der Verwendung verschiedener entomopathogener Pilze aus Thailand zur biologischen Bekämpfung des Kalifornischen Blütenthrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae)

The present study aimed to investigate the potential of 41 entomopathogenic fungal isolates, belonging to 25 species from 11 genera isolated from different hosts in Thailand, as biological control agents against the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Firstly, pathogenicities of all isolates were assessed with single concentration against first instar larvae of F. occidentals. The results showed that 37 out of 41 isolates, belonging to Akan thomyces sp., Aschersonia spp., Beauveria spp., Cordyceps sp., Hirsutella spp., Metarhizium spp., Paecilomyces spp., Torrubiella petchii and Verticillium spp., were pathogenic to F. occidentalis, while Hynennostilbe sp., Torrubiella tenuis, Hypocrella dücoidea and Cordyceps pseudomilit were non-pathogenic. In general, the pathogenicities of all fungi varied significantly according to the fungal isolate, and could be classified into three pathogenicity levels. High pathogenicity level contained 14 isolates: six isolates of Beauveria, four isolates of Metarhizium, three isolates of Paecilomyces and one isolate of Cordyceps were identified as virulent isolates. Secondly, the 14 virulent isolates were screened with multiple concentrations against the first instars larvae. It was found that LC₅₀ values of the isolates varied considerably among fungal isolate, e. g. the LC₅₀ values of Beauveria spp. ranged from 2.39 × 10⁴ to 5.89 × 10⁶ conidia/ml, Metarhizium spp. from 2.00 × 10⁴ to 5.00 × 10⁵ conidia/ml, Paecilomyces spp. from 3.89 × 10⁴ to 5.49 × 10⁶ conidia/ml, and Cordyceps sp. LC50 was 4.67 × 10⁵ conidia/ml. Five isolates with LC₅₀ lower than 6.61 × 10⁴, i.e. two isolates of B. bassiana, two isolates of Metarhizium and one isolate of P. fumosoroseus displayed highest virulence isolates. Finally, the efficiency of the isolates with high virulence was investigated against various developmental stages of F. occidentalis. The virulence of these five entomopathogenic fungi differed at different developmental stages of F. occidentalis. The susceptibility of developmental stages to the entomopathogenic fungi decreased from larvae over pupae to adults. Das Ziel der vorliegenden Arbeit war, die Eignung von 41 aus unterschiedlichen Wirten in Thailand isolierten entomopathogenen Pilzen aus 25 Arten von 11 Genera zur biologischen Schädlingsbekämpfung des Kalifornischen Blütenthrips Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) zu untersuchen. Zunächst wurde die Pa