Identification of fungal pathogens of the spider mites, Tetranychus neocaledonicus André and Tetranychus urticae Koch from natural associations and through artificial inoculations.

Abstract

In an effort to identify fungal pathogens of two economically important phytophagous mites, viz. the vegetable spider mite, TetranychuS neocaledonicus Andre and the two-spotted spider mite, T. urticae Koch, the species naturally associated were studied before experimentally testing other known acaro- and entomofungal species for pathogenicity towards the two. A comprehensive search in and around Bangalore during 2001-2005 indicated the recurrent association of many fungal genera, which were classified as acaropathogens, non-specific entomopathogens and opportunistic or minor pathogens. The entomophthoralean fungus, Neozygites floridana (Weiser&Muma) Remaudire&Keller and several species of the hyphomycetous genera, Acremonium, Aspergillus, Fusarium, Lecanicillium, Paecilomyces and Penicillium were found on field-collected as well as greenhouse- and laboratory-reared tetranychids. Koch's postulates were proved wherever required to confirm pathogenicity. When artificially inoculated with nine pathogens from other mite and insect hosts, only Hirsutella thompsonii Fisher, H. thompsonii var. synnematosa Samson, McCoy&O'Donnell. L. lecanii (Zimm.) Zare&W. Gams and L. psalliotae (Treschew) Zare&W. Gams caused death by way of pathogenicity. Acremonium sp., Beauveria bassiana (Bals.) Vuill., Metarhizium anisopliae (Metschn.) Sorokin and Sporothrix fungorum de Hoog&de Vries, despite causing mortality, could not be recovered from dead mites, thus suggesting that mortality alone did not guarantee pathogenic host-fungus interaction. Nomuraea (Farlow) Samson was unable to cause mortality in either of the test mites.