DEVELOPMENT OF A BIOASSAY METHOD FOR THE SELECTION OF ENTOMOPATHOGENIC FUNGI VIRULENT TO THE DESERT LOCUST, SCHISTOCERCA-GREGARIA (FORSKAL)

An inoculation technique was developed to assay isolates of entomopath ogenic fungi, mainly Metarhizium spp., against the desert locust Schis tocerca gregaria. Both sexes can be used and neither feeding nor maint enance of a high humidity is necessary. Assays were routinely conducte d at 35% relative humidity and 30 degrees C. The technique uses a dose of 2-5 mu l conidial suspension formulated in vegetable oil, which is applied with a micropipette or an automatic applicator beneath the do rsal pronotal shield of an adult locust 7-10 days post-fledging. The s peed of kill is dose dependent; at a dose of 3.75 x 10(5) conidia/g bo dy weight (7.5 x 10(5) conidia/insect) chosen as a standard, locusts b egan dying 4 days post application. Several vegetable oils were suitab le as diluents for the conidial suspensions, but neem was toxic to the insects. After inoculation, locusts had to be maintained in individua l boxes. If inoculated and uninoculated insects were placed in close p roximity immediately after inoculation with an oil suspension of conid ia, the uninoculated insects succumbed to infection 2-3 days later tha n the inoculated ones, indicating transfer of inoculum.