A Study of the Toxic Effect of Plant Extracts against Philaenus spumarius (Hemiptera: Aphrophoridae)

Abstract

The meadow spittlebug Philaenus spumarius (Hemiptera: Aphrophoridae) is distributed in several habitats worldwide and has been recently recognized as the main vector of Xylella fastidiosa subsp. pauca. This bacterium has been associated with olive quick decline syndrome (OQDS) in the Salento Peninsula (Italy) and is responsible for extensive desiccation and die-off of olive trees. Current OQDS management strategies include the control of P. spumarius populations, mainly through the removal of weed hosts and insecticide treatments. In addition to the mandatory phytosanitary measures, the demand for new strategies compatible with integrated pest management is increasing. In this study, laboratory biological assays were performed to assess the potential toxic effect of vegetal formulations against P. spumarius adults. Two formulations were tested at different concentrations: Form A, an emulsion of 10% hot pepper-infused oil (Capsicum annuum subspecies Cayenna in olive oil) and Arabic gum in an aqueous solution of extracts of Salvia guaranitica, and Form B, an aqueous solution of extracts of Taxus baccata. Both Form A and B showed to be toxic against P. spumarius compared to the water control. The mean percentage of spittlebug mortality obtained with Form A one hour after treatments was dose–dependent; the lethal dose values were 0.13% (LD25), 0.36% (LD50), and 0.85% (LD75). At the same time, no significant differences in mortality rate were observed between the 0.75% treatment and the treatments with deltamethrin (about 90%). The mean percentage of spittlebug mortality obtained with Form B ranged from 21% to 53% one hour after treatment, but these values were significantly lower than those obtained with deltamethrin. The effectiveness of Form A on the P. spumarius population was also evaluated in the field. The averages of captures in the three experimental blocks were 1.8/trap for treated and 7.7/trap for untreated plots, and the spittlebug populations significantly decreased after treatments. Based on these results and the literature data, we hypothesize that the effectiveness of Form A is the result of the synergistic effect of all its components. No symptoms of phytotoxicity were recorded on olive trees treated with Form A, and the number of P. spumarius specimens collected on these plants was much lower than on untreated plants. These results suggest the potential use of Form A in the protection of olive trees. This vegetal formulation can thus be considered as a valid alternative to chemical insecticides for the control of the main vector of X. fastidiosa and could be integrated into a sustainable management system for OQDS.