DEVELOPMENT OF A MITE BIOASSAY TO EVALUATE PLANT-RESISTANCE AND ITS USE IN DETERMINING REGENERATION OF SPIDER-MITE RESISTANCE

The zonal geranium (Pelargonium xhortorum) possesses tall glandular tr ichomes that secrete anacardic acids, a viscous, sticky exudate which has been suggested as the primary mechanism in two-spotted spider mite (Tetranychus urticae Koch) resistance. A new bioassay was developed u sing small Plexiglas(R) cylinders as chambers for evaluating the resis tance of geranium leaves to the two-spotted spider mite. This bioassay was easy to prepare, required only 24 hours to conduct, exhibited no problems with desiccation, condensation, or mite accountability, and y ielded reproducible results. This bioassay was then used to study the regeneration of resistance of attached geranium leaves after they were made mite-susceptible by removing the excreted anacardic acids with w ater. Washed leaves regained full resistance after 14 days.