| Abstract: | The pathogenicity of several isolates of the hyphomycete fungi Verticillium lecanii and Metarhizium anisopliae to Frankliniella occidentalis was investigated. Treatment of adult thrips with M. anisopliae resulted in at least 94% mortality at 7 days post-inoculation. In contrast, V. lecanii isolates only gave mortalities of between 20 and 70%. Detailed studies were made on the most virulent isolate of M. anisopliae (275) to determine its efficacy at different doses and temperatures. At 23 C the LC was ca. 3 105 conidia ml-1 after 5 days and the LTs were 50 50 3 and 4.5 days at 10 7 and 106 conidia ml-1 respectively. Temperature influenced fungal virulence to adult thrips; the LT at 18 and 20 C was ca. 4 days and at 23 or 26 C it was ca. 3 days. 50 Larvae were less susceptible to infection than adult thrips (27% versus 100% mortality), presumably due to the inoculum being shed with the exuvium during ecdysis. Conidia of M. anisopliae isolate 275 germinated rapidly on the surfaces of larvae, pupae and adults, with most germlings producing appressoria within 24 h post-inoculation. Fungal elements were present in significant amounts in the body 3 days after treatment. |
