Phenology, Seasonal Abundance, and Host-Plant Association of Spittlebugs (Hemiptera: Aphrophoridae) in Vineyards of Northwestern Italy

Prosapia bicincta (Hemiptera: Cercopidae) abundance, plant associations, and impacts on groundcover in Hawai'i Island rangelands

The twolined spittlebug, Prosapia bicincta (Say), is a major economic pest of forage grass and turfgrass. Prosapia bicincta was first detected in rangelands on Hawai'i Island in 2016 and has since spread to an estimated 72,000 ha in the North and South Kona districts. This study aimed to quantify P. bicincta abundance, plant associations, and impacts on groundcover over time. Monthly surveys of P. bicincta nymphs and adults were conducted from February 2018 to September 2022 along 17 established 100-m transects at 4 ranches located in Kona, Hawai'i Island, spanning an elevation gradient from 519 to 1,874 m above sea level (a.s.l.). Monitoring revealed P. bicincta occurs from 519 to 1,679 m a.s.l., primarily in Kikuyu grass (Cenchrus clandestinus (Hochst. ex Chiov.)) Morrone (Poales: Poaceae) pastures. Peaks in P. bicincta abundance coincided with the wet season, with most activity occurring from April to October and little to no activity between November and March. Mid elevation (1,000-1,300 m) transects had significantly higher mean P. bicincta abundance (126 nymphs/m2) relative to low (500-999 m) (64 nymphs/m2) and high elevations (>1,300 m) (20 nymphs/m2). Sites with the highest abundance of P. bicincta were also associated with the greatest decrease in mean grass cover (30%) and were replaced by forbs, bare ground, and shrubs. Grasses accounted for 72% of the total P. bicincta detections, with the remaining plants comprised of legumes (16%), sedges (6%), and forbs (6%). Twenty new P. bicincta plant associations were found. This information will help improve the effectiveness of management to suppress populations below economic thresholds.

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

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.

The most polyphagous insect herbivore? Host plant associations of the Meadow spittlebug, Philaenus spumarius (L.)

A comprehensive list of all known host plant species utilised by the Meadow Spittlebug (Philaenus spumarius (L.)) is presented, compiled from published and unpublished sources. P. spumarius feeds on 1311 host plants in 631 genera and 117 families. This appears, by a large margin, to be the greatest number of host species exploited by any herbivorous insect. The Asteraceae (222 species) and Rosaceae (110) together account for 25% of all host species. The Fabaceae (76) and Poaceae (73), are nearly tied for third and fourth place and these four families, combined with the Lamiaceae (62), Apiaceae (50), Brassicaceae (43) and Caprifoliaceae (34), comprise about half of all host species. Hosts are concentrated among herbaceous dicots but range from ferns and grasses to shrubs and trees. Philaenus spumarius is an "extreme polyphage", which appears to have evolved from a monophage ancestor in the past 3.7 to 7.9 million years. It is also the primary European vector of the emerging plant pathogen Xylella fastidiosa. Its vast host range suggests that it has the potential to spread X. fastidiosa among multiple hosts in any environment in which both the spittlebug and bacterium are present. Fully 47.9% of all known hosts were recorded in the Xylella-inspired BRIGIT citizen science P. spumarius host survey, including 358 hosts new to the documentary record, 27.3% of the 1311 total. This is a strong demonstration of the power of organized amateur observers to contribute to scientific knowledge.

Bioecological Traits of Spittlebugs and Their Implications for the Epidemiology and Control of the Xylella fastidiosa Epidemic in Apulia (Southern Italy)

Spatial-temporal dynamics of spittlebug populations, together with transmission biology, are of major importance to outline the disease epidemiology of Xylella fastidiosa subsp. pauca in Apulian olive groves. The spread rate of X. fastidiosa is mainly influenced by (i) the pathogen colonization of the host plant; (ii) the acquisition of the pathogen by the vector from an infected plant, and its inoculation to healthy plants; (iii) the vector population dynamics and abundance at different spatial scales; and (iv) the dispersal of the vector. In this contribution we summarize the recent advances in research on insect vectors' traits-points ii, iii, and iv-focusing on those most relevant to X. fastidiosa epidemic in Apulia. Among the vectors' bioecological traits influencing the X. fastidiosa epidemic in olive trees, we emphasize the following: natural infectivity and transmission efficiency, phenological timing of both nymphal and adult stage, the role of seminatural vegetation as a vector reservoir in the agroecosystem and landscape, and preferential and directional dispersal capabilities. Despite the research on X. fastidiosa vectors carried out in Europe in the last decade, key uncertainties on insect vectors remain, hampering a thorough understanding of pathogen epidemiology and the development of effective and targeted management strategies. Our goal is to provide a structured and contextualized review of knowledge on X. fastidiosa vectors' key traits in the Apulian epidemic, highlighting information gaps and stimulating novel research pathways on X. fastidiosa pathosystems in Europe. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Cicadomorpha Community (Hemiptera: Auchenorrhyncha) in Portuguese Vineyards with Notes of Potential Vectors of Xylella fastidiosa

Cicadomorpha (Hemiptera) insects are currently responsible for a growing negative impact on the agricultural economy due to their ability to directly damage crops or through the capacity to act as vectors for plant pathogens. The phytopathogenic bacterium Xylella fastidiosa, the causal agent of Pierce's disease in vineyards, is exclusively transmitted by insects of this infraorder. Therefore, knowledge of the Cicadomorpha species and understanding their biology and ecology is crucial. In this work, in 2018 and 2019, the canopy and inter-row vegetation of 35 vineyards distributed in mainland Portugal were sampled to investigate species composition, richness, and diversity of the Cicadomorpha community, with a special focus given to vectors and potential vectors of X. fastidiosa. A total of 11,834 individuals were collected, 3003 in 2018 and 8831 in 2019. Of the 81 species/morphospecies identified, only five are considered vectors or potential vectors of this pathogen, namely, Cicadella viridis (Linnaeus, 1758), Philaenus spumarius (Linnaeus, 1758), Neophilaenus campestris (Fallén, 1805), Lepyronia coleoptrata (Linnaeus, 1758), and N. lineatus (Linnaeus, 1758). Cicadella viridis was the most abundant xylem sap feeder, followed by P. spumarius. In addition, Cicadomorpha that cause direct damage to vines and vectors of grapevine yellows' phytoplasmas were also collected and identified in the sampled vineyards. The results suggested that vectors and potential vectors of X. fastidiosa and a large proportion of the population of Cicadomorpha have a positive correction with inter-row vegetation.

Environmental factors driving the abundance of Philaenus spumarius in mesomediterranean habitats of Corsica (France)

Philaenus spumarius (Ps) is considered the main insect vector of the bacterium Xylella fastidiosa (Xf) in Europe. As such, it is a key actor of the Xf pathosystem on which surveillance and management strategies could be implemented. Although research effort has increased in the past years, the ecological factors shaping Ps abundance and distribution across landscapes are still poorly known in most regions of Europe. We selected 64 plots of 500m² in Corsican semi-natural habitats in which we sampled nymphs and adults of Ps during three years. While local or surrounding vegetation structure (low or high scrubland) had little effect on Ps abundance, we highlighted a positive relationship between Ps abundance and the density of Cistus monspeliensis in the plots. We also found larger populations of Ps in cooler and moister plots. The pattern of host association highlighted here is unique, which calls for more studies on the ecology of Ps in Europe, to help designing surveillance and management strategy for Xf.

Transmission of Xylella fastidiosa subsp. pauca ST53 by the Sharpshooter Cicadella viridis From Different Source Plants and Artificial Diets

The sharpshooter Cicadella viridis L. (Hemiptera: Cicadellidae) is the most common sharpshooter in Europe and, given its xylem feeding behavior, is considered a potential vector of the plant pathogenic bacterium Xylella fastidiosa Wells et al. (Xanthomonadales: Xanthomonadaceae). We tested X. fastidiosa subsp. pauca ST53 (Xfp) transmission capabilities of C. viridis adults, namely 1) acquisition efficiency from four host plant species-periwinkle, milkwort, lavender, alfalfa-and from two artificial diets (PD3 and Xfm), 2) inoculation efficiency to periwinkle at different times post acquisition from different plant and artificial diet sources. The main European vector species-Philaenus spumarius L. (Hemiptera: Aphrophoridae)-was used as a control. C. viridis was able to acquire Xfp from periwinkle, milkwort, and lavender, although with low efficiency (3-16%) and from artificial diets (23-25%). Successful inoculation on periwinkle was extremely rare, being observed only three times, following feeding on milkwort plant and PD3 artificial diet sources. Our study shows that C. viridis is not a relevant vector of Xfp, given the very low transmission rate in controlled conditions, and the inability to feed on olive. The low efficiency reported here correlates with ecological constraints of the vector (mainly monocots host plants, humid environments) that make it difficult to forecast a relevant role in dispersing X. fastidiosa, at least within the present distribution of the exotic bacterium in Europe. However, a possible role of this species in spreading Xf in other agroecosystems, e.g., vineyard and stone fruits grown in humid areas, cannot be excluded.

Landscape and Vegetation Patterns Zoning Is a Methodological Tool for Management Costs Implications Due to Xylella fastidiosa Invasion

Philaenus spumarius (Linnaeus 1758, hereafter Ps) is considered one of the main insect vectors responsible for the spread of an alien biota, Xylella fastidiosa (Wells 1987, hereafter Xf), in the Salento area, Apulia region (Southern Italy). Effective management of this biological invader depends on the continuous surveillance and monitoring of its insect vector. As such, this research elicits the invasion drivers (i.e., landscape and vegetation indicators) that influence the abundance and the dynamics of this vector and, consequently, the spatial spread of this bacterium in this Italian region. For this purpose, a spatial pattern clustering methodological approach is considered. The results reveal that spatial variation and territorial differentiation may differ from zone to zone in the same invaded area, for which effective management and monitoring planning should be addressed. Further, six agro-ecosystems zones have been identified with respect to five indicators: (i) vegetation index, (ii) intensity of cultivation, (iii) cultural diversity, (iv) density of agricultural landscape elements, and (v) altitude. This paper has public implications and contributes to an understanding of how zoning of an infected area, by an alien biota, into homogenous zones may impact its effective management costs. This approach could also be applied in other countries affected or potentially affected by the phenomenon of Xf invasion.