A modification of the droplet feeding method is described which reduces the time and cost of conducting bioassays of pathogens in suitable lepidopterous larvae. The procedure uses a single, large surface for treatment of the insects, and the inoculum for a given dose is administered in a single step by means of a simple applicator. A Petri dish with diet is inverted over the larvae and surrounding droplets of each dose group, permitting the larvae to move directly onto the diet after ingesting the inoculum. This method eliminates the need to transfer individual larvae, and the moist diet prevents evaporation from the droplets during the period of acquisition. After administration of the inoculum, the dishes are removed from the treatment surface, larvae that have not ingested are discarded, and the dishes are covered and placed in an incubator. The mean volume of inoculum ingested per larva was the same for both the applicator and the individual droplet procedures. Results with the applicator technique compare well with other methods, but considerably less time and materials are required to conduct an assay.
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Hughes et al. (1986) studied this question.
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