The Effect of Leaf Wax Extracts from the Leaves of Eight Azalea Genotypes (Rhododendron spp.) on Feeding and Oviposition by Azalea Lace Bug [Stephanitis pyrioides (Scott)]

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  • 1 Univ. of Georgia, Dept. of Horticulture, Griffin, GA 30223
  • 2 Univ. of Georgia, Dept. of Horticulture, Griffin, GA 30223
  • 3 Univ. of Georgia, Dept. of Horticulture, Griffin, GA 30223
  • 4 Univ. of Georgia, Dept. of Horticulture, Griffin, GA 30223

Azalea Lace Bug (ALB) is a significant pest on azalea species. ALB feeding injury causes a stippled appearance on the leaves of susceptible genotypes from late spring until leaf drop. To determine whether leaf surface lipids are a factor in determining resistance or susceptibility to ALB, epicuticular leaf wax was extracted from the leaves of eight azalea genotypes, half with resistance and half susceptible to ALB. Leaf wax from each genotype was extracted and re-suspended in an 2 ethanol: 1 water solution for application to all entries in a full diallel manner, including a control of solution only. Each treatment included three replications. The leaf wax solution was applied to each replication (single leaf) by painting the solution on one side of the midrib, on both abaxial and adaxial surfaces. By applying solution to one side of the leaf, the untreated leaf surface served as a control. Each leaf and two female ALB were placed in separate 50-mL sealed tubes at 24 °C and 12-hour daylength for 48 hours, at which time the number of live adults, frass spots, and eggs were counted. Frass and egg data were recorded separately for treated and untreated sides of each leaf. The application of leaf wax solution had an impact on the level of frass and egg deposition by ALB in all genotypes. The effect was most pronounced when solution of resistant genotypes was placed on susceptible genotypes, resulting in lower numbers of frass spots and eggs. The solution alone had little effect on frass or egg numbers. This research acknowledges that a major constituent of an azalea's resistance or susceptibility to ALB is via epicuticular wax components.

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