Susceptibility of the legume flower thrips to Metarhizium anisopliae on different varieties of cowpea

The susceptibility of Megalurothrips sjostedti to Metarhizium anisopliae wh en reared on susceptible, tolerant, and moderately resistant varieties of c owpea at different constant temperatures was evaluated in the laboratory. I nsects were exposed either to direct spray of the conidia or to fungus-trea ted floral tissues. Mortality was significantly higher on the moderately re sistant variety at all temperatures compared to the susceptible and toleran t varieties. Correspondingly, lethal time and lethal concentration values w ere significantly shorter and lower, respectively, on the moderately resist ant variety compared to the other varieties, thus indicating that the two c ontrol methods are compatible as part of an integrated pest management stra tegy. Thrips raised on the tolerant variety incurred an exceptionally low l evel of mortality when the inoculum was sprayed directly on the insects or when the insects were exposed to fungus-treated floral tissues. Observation s on the effects of airborne volatiles and crude extracts of this variety r evealed an inhibitory effect on fungal germination, colony forming units an d growth. This suggests the existence of anti-fungal substances in the tole rant variety.