Open Access

Malee Thungrabeab, Peter Blaeser, Cetin Sengonca

• The onion thrips, Thrips tabaci LINDEMAN (Thys., Thripidae) is an important pest of field and greenhouse crops around the world. It causes damage directly through feeding and indirectly through the transmission of lethal plant viruses. It is difficult to control this pest with insecticides because of its small size and cryptic habits (LEWIS 1997). Entomopathogenic fungi are currently being investigated for the control of many important insect pests on various crops around the world, and some are commercially available. There are many studies on the efficacy of several entomopathogenic fungi on thrips. CARL (1975) reported that Neozygites parvispora (MACLEOD, TYRRELL & CARL) REMAUDIERE and KELLER has been found frequently on T. tabaci but under field conditions the fungus was less successful than in the greenhouse. In addition, Entomophthora thripidum SAMSON, RAMAKERS & OSWALD was found infecting T. tabaci in Netherlands, but in field trials the fungus failed to suppress thrips populations below the economic acceptable level (SAMSON et al. 1979). In laboratory studies, T. tabaci was susceptible to Verticillium lecanii (ZIMMERMANN) VIÉGAS, Beauveria bassiana (BALSAMO) VUILLEMIN, Metarhizium anisopliae (METSCH.) SOROKIN and Paecilomyces fumosoroseus (WIZE) BROWN & SMITH (GILLESPIE 1986, FRANSEN 1990). VESTERGAARD et al. (1995) and BROWNBRIDGE (1995) showed that B. bassiana, M. anisopliae and V. lecanii were more active against the western flower thrips, Frankliniella occidentalis (PERGANDE) than P. fumosoroseus or Paecilomyces farinosus (HOLM ex S.F. GRAY) BROWN & SMITH. HALL et al. (1994) and SAITO (1991) suggested that Hirsutella sp., P. fumosoroseus and B. bassiana may be useful in the management of the melon thrips, Thrips palmi KARNY. EKESI et al. (1998) stated that B. bassiana and M. anisopliae are highly pathogenic to the legume flower thrips, Megalurothrips sjostedti (TRYBORN). In the glasshouse, V. lecanii has been used successfully to control T. tabaci on cucumber (GILLESPIE 1986).VACANTE et al. (1994) noted that N. parvispora caused up to 60 per cent mortality in motile developmental stages of F. occidentalis and reduced the insect populationdensity. Under greenhouse conditions, M. anisopliae was found to be effective in reducing the population growth of F. occidentalis on cucumber (AZAIZEH et al. 2002). Whereas, MANIANIA et al. (2001) observed that M. anisopliae had the potential to control F. occidentalis on chrysanthemum. The studies of MANIANIA et al. (2003) indicated that M. anisopliae had a potential to control T. tabaci in the field. Akanthomyces, Aschersonia, Cordyceps, Hypocrella, Hynennostilbe and Torrubiella were never observed to control thrips. Therefore, this study was conducted to investigate the pathogenicity of different entomopathogenic fungi from Thailand against T. tabaci larvae under controlled climatic conditions in the laboratory.
• Thrips tabaci LINDEMAN (Thys., Thripidae) ist ein weltweit verbreiteter Schädling mit einem breiten Wirtspflanzenspektrum an verschiedenen Freiland und Gewächshauskulturen, dessen Bekämpfung durch die geringe Größe und ihre versteckte Lebensweise erschwert wird. Entomopathogene Pilze sind wichtige Krankheitserreger zahlreicher Insektenarten und infizieren Individuen verschiedenen Alters und verschiedener Entwicklungsstufen. In der vorliegenden Studie wurden 41 Isolate von 25 entomopathogenen Pilzarten aus 11 Gattungen (Akanthomyces, Aschersonia, Beauveria, Cordyceps, Hirsutella, Hymenostilbe, Hypocrella, Metarhizium, Paecilomyces, Torrubiella und Verticillium) auf ihre Pathogenität gegenüber T. tabaci-Larven untersucht. Bis auf Hymenostilbe sp., Torrubiella spp., Hypocrella discoidea und Cordyceps pseudomilitaris stellten sich alle Pilze als Pathogen für T. tabaci heraus. Zwischen den Isolaten wurden hoch signifikante Unterschiede festgestellt. Die Mortalität variierte je nach Pilzart, Pilzgattung und Isolat. Fünfzehn Isolate, 7 von Beauveria, 4 von Metarhizium, 3 von Paecilomyces und 1 von Cordyceps, wiesen die höchste Pathogenität gegenüber T. tabaci-Larven auf.