Leaf wax extracts of four deciduous azalea genotypes affect azalea lace bug (Stephanitis pyrioides Scott) survival rates and behavior

Abstract

Azaleas (Ericales: Ericaceae: Rhododendron L.) are a staple plant in many landscapes of the United States and are largely resistant to predation by insects, with the exception of azalea lace bug [ALB (Heteroptera: Tingidae: Stephanitis pyrioides)]. Within deciduous azalea (Rhododendron: section Pentanthera G. Don) varying levels of resistance to ALB are observed with a continuous distribution from susceptible to highly resistant. In this study, epicuticular leaf wax from two ALB-resistant [R. canescens Michaux and R. periclymenoides (Michaux) Shinners] and two ALB-susceptible ('Buttercup' and 'My Mary') deciduous azalea genotypes was extracted and re-applied to fresh azalea foliage. Leaf wax extracted from ALB-resistant genotypes and applied to ALB-susceptible genotypes conferred a high level of resistance to both ALB feeding and oviposition in the treated ALB-susceptible genotypes. Conversely, leaf wax extracted from ALB-susceptible genotypes and applied to ALB-resistant genotypes conferred susceptibility to the treated ALB-resistant genotypes. However, the effect was much less substantial than the effect of resistant wax extracts on susceptible genotypes and confined to ALB oviposition. When applied to the same genotype from which the extract was collected, leaf wax extract from ALB-susceptible genotypes had no effect on susceptibility, whereas resistant wax extract had a moderate effect on ALB oviposition rate. The results indicate that leaf wax serves as a primary mechanism of resistance of deciduous azalea to ALB.