Development of a bioassay method for the selection of entomopathogenic fungi virulent to the desert locust, <i>Schistocerca gregaria</i> (Forskål)

Abstract

Abstract An inoculation technique was developed to assay isolates of entomopathogenic fungi, mainly Metarhizium spp., against the desert locust Schistocerca gregaria. Both sexes can be used and neither feeding nor maintenance of a high humidity is necessary. Assays were routinely conducted at 35% relative humidity and 30°C. The technique uses a dose of 2–5 μl conidial suspension formulated in vegetable oil, which is applied with a micropipette or an automatic applicator beneath the dorsal pronotal shield of an adult locust 7–10 days post‐fledging. The speed of kill is dose dependent; at a dose of 3.75 × 10 5 conidia/g body weight (7.5 × 10 5 conidia/insect) chosen as a standard, locusts began dying 4 days post application. Several vegetable oils were suitable as diluents for the conidial suspensions, but neem was toxic to the insects. After inoculation, locusts had to be maintained in individual boxes. If inoculated and uninoculated insects were placed in close proximity immediately after inoculation with an oil suspension of conidia, the uninoculated insects succumbed to infection 2–3 days later than the inoculated ones, indicating transfer of inoculum.