The role of phenolics and other mechanisms of resistance of poinsettia to the silverleaf whitefly

The silverleaf whitefly (SLWF), Bemisia tabaci biotype B, is one of the most prevalent insect pests found attacking poinsettias (Euphorbia pulcherrima, Euphorbiaceae), USA’s top selling potted ornamental. This project is the first one to evaluate the impact of physical and chemical resistance traits in economically relevant poinsettia cultivars on SLWF. Preliminary data showed that dark green leaf cultivars appeared to be more resistant and less preferred by the SLWF than light green leaf cultivars. Based on this evidence, physical mechanisms of resistance were investigated. Visual cues were observed to be strongly associated with preferential adult SLWF settling and oviposition, significantly contributing to the higher susceptibility of light green leaf cultivars. Chlorophyll content and leaf thickness were physical traits found associated with this visual preference. Susceptible cultivars have significantly less chlorophyll content and thinner leaves compared to the resistant cultivars. Trichome density was also evaluated but no significant differences were observed. To elucidate the role of phenolic compounds, as a possible chemical trait associated with resistance, one resistant and one susceptible cultivar were chosen and to evaluate effects on SLWF survivorship and fecundity of F1 will be assessed. Research in a similar system with cassava (Euphorbiaceae) and mealybugs has shown a correlation between phenolics present in the phloem sap and antibiotic resistance. Phenolic compounds have been detected in phloem sap of poinsettias, but characterization and concentration of such compounds has not been reported. The applications for integrated pest management arising from this study will be discussed.