PATHOGENICITY OF THE HYPHOMYCETE FUNGI VERTICILLIUM-LECANII AND METARHIZIUM-ANISOPLIAE TO THE WESTERN FLOWER THRIPS, FRANKLINIELLA-OCCIDENTALIS

The pathogenicity of several isolates of the hyphomycete fungi Vertici llium lecanii and Metarhizium anisopliae to Frankliniella occidentalis was investigated. Treatment of adult thrips with M. anisopliae result ed in at least 94% mortality at 7 days post-inoculation. In contrast, V. lecanii isolates only gave mortalities of between 20 and 70%. Detai led studies were made on the most virulent isolate of M. anisopliae (2 75) to determine its efficacy at different doses and temperatures. At 23 degrees C the LC(50) was Ca. 3 X 10(5) conidia ml(-1) after 5 days and the LT(50)S were 3 and 4.5 days at 10(7) and 10(6) conidia ml(-1) respectively. Temperature influenced fungal virulence to adult thrips; the LT(50) at 18 and 20 degrees C was ca. 4 days and at 23 or 26 degr ees C it was ca. 3 days. Larvae were less susceptible to infection tha n adult thrips (27% versus 100% mortality), presumably due to the inoc ulum being shed with the exuvium during ecdysis. Conidia of M. anisopl iae isolate 275 germinated rapidly on the surfaces of larvae, pupae an d adults, with most germlings producing appressoria within 24 h post-i noculation. Fungal elements were present in significant amounts in the body 3 days after treatment.