Xylella Fastidiosa Wells Research Articles

Population Dynamics of Potential Insect Vectors of Xylella fastidiosa (Xanthomanadales: Xanthomonadaceae) and Other Auchenorrhyncha in Olive and Citrus Groves of Crete, Greece

This study investigated the phenology and population dynamics of potential insect vectors of Xylella fastidiosa Wells et al. and other Auchenorrhyncha species in olive and citrus groves of Chania province, Crete, Greece. Although X. fastidiosa has not been reported in Greece, its introduction could cause serious diseases in many crops, including olives and citrus. Olive groves of Olea europaea L. ‘Koroneiki’ were sampled systematically using sweep net and Malaise traps over 24 months. One citrus grove was sampled for one year using a Malaise trap. Sweep net samples were taken from the herbaceous cover, tree canopy, and field borders of olive groves. Auchenorrhyncha were more abundant on the herbaceous cover compared to the canopy and field margins. Aphrophoridae species were mostly found on the herbaceous cover and in low numbers during fall (October–December) and spring (April–May). Cicadellidae species, such as Euscelis spp., were frequently found on the herbaceous cover of both olive and citrus groves. One Aphrophoridae and several Cicadellidae species were recorded in the citrus grove. Altitude was found to influence the population abundance of some Auchenorrhyncha species in olive groves. These results provide information for effective integrated management of insect vectors and their vector-borne pathogens.

Brindley’s Glands Volatilome of the Predator Zelus renardii Interacting with Xylella Vectors

Alien species must adapt to new biogeographical regions to acclimatise and survive. We consider a species to have become invasive if it establishes negative interactions after acclimatisation. Xylella fastidiosa Wells, Raju et al., 1986 (XF) represents Italy’s and Europe’s most recent biological invasion. In Apulia (southern Italy), the XF-encountered Philaenus spumarius L. 1758 (Spittlebugs, Hemiptera: Auchenorrhyncha) can acquire and transmit the bacterium to Olea europaea L., 1753. The management of XF invasion involves various transmission control means, including inundative biological control using Zelus renardii (ZR) Kolenati, 1856 (Hemiptera: Reduviidae). ZR is an alien stenophagous predator of Xylella vectors, recently entered from the Nearctic and acclimated in Europe. Zelus spp. can secrete semiochemicals during interactions with conspecifics and prey, including volatile organic compounds (VOCs) that elicit conspecific defence behavioural responses. Our study describes ZR Brindley’s glands, present in males and females of ZR, which can produce semiochemicals, eliciting conspecific behavioural responses. We scrutinised ZR secretion alone or interacting with P. spumarius. The ZR volatilome includes 2-methyl-propanoic acid, 2-methyl-butanoic acid, and 3-methyl-1-butanol, which are consistent for Z. renardii alone. Olfactometric tests show that these three VOCs, individually tested, generate an avoidance (alarm) response in Z. renardii. 3-Methyl-1-butanol elicited the highest significant repellence, followed by 2-methyl-butanoic and 2-methyl-propanoic acids. The concentrations of the VOCs of ZR decrease during the interaction with P. spumarius. We discuss the potential effects of VOC secretions on the interaction of Z. renardii with P. spumarius.

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As a part of the research, the species composition of almond diseases, as well as the susceptibility of different almond varieties, was studied. The following diseases and pests were detected at Armavir Marz: shot hole disease, almond leaf scorch, foamy canker, chlorosis, gummosis, peach twig borer, and green peach aphid. Trees of the Guara variety were infected with shot hole and gummosis, Penta - with gummosis, leaf scorch, and chlorosis. Diseases were not detected in trees of the Lauranne variety. Almond leaf scorch (Xylella fastidiosa Wells et al.) and foamy canker (Zymomonas Kluyver and van Niel) diseases were recorded in Armenia for the first time. Plant pathogenic fungi Arthrinium sp./Apiospora sp., Fusarium acuminatum, F. Incarnatum-equiseti, F. oxysporum, Valsa sordida (Cytospora chrysosperma), as well as non-pathogenic fungi Clonostachys rosea, Lachancea quebecensis, Mucor circinelloides, Pichia kudriavzevii and Torulaspora sp. have been isolated and identified from almond branches and trunks infected with gummosis.

Monitoring of disease and pests in vineyards and their levels of harmfulness

This article monitors the spread and damage of oidium (Uncinula necator Burrill), anthracnose (Gloeosporium ampelophagum Sacc) and mildew (Plasmopara viticola Berl & De Toni) diseases in the vineyards of Tashkent, Samarkand and Fergana regions of Uzbekistan. In addition, additional monitoring work was carried out on the spread of the external quarantine vine bacteriosis Pierce's disease (Xylella fastidiosa Wells et al) in the vineyards of Uzbekistan. According to the results of research and observation in 2022, vine oidium disease is relatively low in the vineyards of Samarkand and Fergana regions (from 5.0% to 30.0% in leaves, branches and grape bunches), and strongly in the vineyards of Tashkent region (12% in leaves, branches and grape bunches). .0% to 100.0%) have been found to be harmful. Anthracnose disease is widespread in the vineyards of Tashkent and Samarkand regions (from 10.0% to 75.0% on leaves, branches and bunches of grapes), causing severe damage to vineyards, and it is relatively rare in Fergana region (from 5.0% to 20.0% on leaves, branches and bunches of grapes) was found to be spread.

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.

Contributions to the knowledge of the Cicadellini sharpshooters (Hemiptera: Cicadellidae) associated with citrus orchards in Argentina

Xylella fastidiosa Wells et al. is a xylem-borne bacterium that causes some of the most important plant diseases to woody plants such as citrus, olives, almonds and other cultures. This pathogen is mainly transmitted by sharpshooters, among which the tribe Cicadellini (Cicadellinae) includes the largest number of proven vectors. The correct identification of the vectors, along with biological and phenological information, are necessary to identify the key vectors involved in the spread of the bacterium and, consequently, establish control strategies and evaluate risks at a local or regional scale. However, lack of information on the Cicadellini from Argentina has delayed the implementation of control measures. Based on surveys conducted in the main citrus producing areas along with bibliographic data, this contribution provides the first list of Cicadellini species from Argentina that are potential vectors of X. fastidiosa; an identification key to these sharpshooters is provided. Twelve species were recorded from northeastern citrus groves, while from northwestern orchards, with previous information totally absent, 10 species were recorded. Eight species are shared by all producing regions, and five of them are proven vectors of X. fastidiosa (Bucephalogonia xanthophis (Berg), Dilobopterus costalimai Young, Macugonalia cavifrons (Stål), M. leucomelas (Walker), Sonesimia grossa (Signoret)). This contribution provides 22 new insect-plant relationships, information on their natural enemies, the geographic distribution of all species is broadened and the female genitalia of three proven vectors are described for the first time.

Nutritional and Physiological Regulation of Glassy-Winged Sharpshooter Oogenesis.

The glassy-winged sharpshooter (Homalodisca vitripennis (Germar); Hemiptera: Cicadellidae: Cicadellinae) is an invasive insect that transmits the plant pathogenic bacterium Xylella fastidiosa Wells et al. (Xanthomonadales: Xanthomonadacae). While adult glassy-winged sharpshooter must feed to produce eggs, the role of nutritional status on initiating oogenesis is poorly understood. To determine the effects of glassy-winged sharpshooter nutrition on nymphal development, oogenesis, and fecundity, glassy-winged sharpshooter were reared on cowpea, sunflower, sorghum, and a mixture of the three plant species. Adults emerging from cowpea, sunflower, or plant mixture treatments had shorter development times, attained larger size, and had greater estimated lipid reserves than females reared on sorghum. In choice tests, nymphs avoided sorghum and preferentially fed on cowpea and sunflower. Adult females provisioned with a single plant species during the nymphal stage were provided with either the same host plant species or a mixture of host plant species (cowpea, sunflower, sorghum) for a 9-wk oviposition period, with 37% of females initiating oogenesis. Ovipositing females had greater juvenile hormone and octopamine levels than reproductively inactive females, although topical application of the juvenile hormone analog Methoprene did not promote oogenesis. Across nymphal diets, reproductively active females produced more eggs when held on plant mixtures than on single plant species. In choice tests, adult females were observed most frequently on cowpea, although most eggs were deposited on sorghum, the host least preferred by nymphs. Results suggest that fecundity is largely determined by the quality of the adult diet, although the stimulus that initiates oogenesis does not appear to be related to nutrition.

A new spittlebug of the genus Aphrophora Germar, 1821 (Hemiptera: Cercopoidea: Aphrophoridae) abundant on invasive iceplant, Carpobrotus edulis (L.) N. E. Brown (Aizoaceae), in coastal California

A spittlebug of the genus Aphrophora Germar, 1821 (Hemiptera: Cercopoidea: Aphrophoridae) occurs in profusion on many coastal California populations of invasive exotic iceplant, Carpobrotus edulis (L.) N. E. Brown (Aizoaceae), a spreading, mat-forming, perennial succulent. Described here as Aphrophora moscoviciae sp. nov., it occurs along the Pacific Coast and San Francisco Bay, from Marin County south to at least Ventura County, and achieves remarkably high population levels in some localities, with a maximum density of 2700 nymphs/m2, an apparent world record for spittlebugs. While it appears to be endemic to California, native hosts are unknown. It shares habitats with three demonstrated spittlebug vectors of the plant pathogen Xylella fastidiosa Wells et al. (Xanthomonadaceae), including one, Philaenus spumarius (Linnaeus, 1758), that is common on iceplant. This suggests that it could play a role in broader transmission networks among cultivated and wild plants.

Probing behavior of Neophilaenus campestris on various plant species

AbstractThe recent history of Xylella fastidiosa Wells et al. introduction in Europe illustrates how the lack of knowledge about the bacterium‐vector‐host interactions hinders the application of effective containment strategies, with the bacterial spread that currently appears relentless. Vector behavior is a key component in plant pathogen transmission; therefore, detailed knowledge of vector probing behavior on various host plants would furnish useful data for containing the bacterium. Aiming at this goal, we carried out electrical penetration graph (EPG)‐assisted probing behavior observations of the spittlebug, Neophilaenus campestris (Fallen) (Hemiptera: Aphrophoridae), a candidate vector widespread in all the areas where X. fastidiosa is currently established. Spittlebug probing was first characterized on one of its preferred host plants, Bromus madritensis L. (Poaceae), over short (6 h) and long (16 h) time spans. Thereafter, we performed comparative observations of the spittlebug probing on B. madritensis, olive, and grapevine. Overall, the probing behavior of N. campestris, that is, the main characteristic waveforms, did not differ substantially from that of Philaenus spumarius (L.) (Hemiptera: Aphrophoridae); however, here we report and describe a new kind of xylem activity interruption, provisionally termed N2, not previously observed in P. spumarius. Considering the time spent in xylem ingestion as a percentage of the total probing time (host‐suitability indicator used for spittlebugs), grapevine and B. madritensis are the preferred hosts for N. campestris, with olive as the least suitable among the plants tested. Successful probes, that is, probes during which xylem ingestion occurred, on grapevine were 2.5× greater than olive. Therefore, our data on N. campestris probing behavior suggest that the spittlebug role in X. fastidiosa epidemiology in European vineyards should be given more attention. In the present manuscript, we also discuss the current difficulties in interpreting and analyzing the outcomes of EPG studies on spittlebugs.

Field-Collected Glassy-Winged Sharpshooters (Hemiptera: Cicadellidae) Perform More Xylella fastidiosa-Inoculating Behaviors on Susceptible Vitis vinifera cv. 'Chardonnay' Than on Resistant Vitis champinii Grapevines.

The glassy-winged sharpshooter, Homalodisca vitripennis (Germar) (Hemiptera: Cicadellidae: Cicadellinae), is an introduced vector of the xylem-dwelling bacterium Xylella fastidiosa Wells et al. (Xanthomonadales: Xanthomonadaceae) in California. Once acquired, X. fastidiosa colonizes the functional foregut of the vector. Bacteria can be inoculated directly into grapevine xylem during the xylem cell acceptance process in sharpshooter stylet probing, represented by the X wave using electropenetrography (EPG). Since 2001, an effort has been underway to develop PD-resistant grapevines, Vitis vinifera L., through classical breeding of various species of resistant wild grapevines with more susceptible V. vinifera. The present study used EPG to compare H. vitripennis stylet probing behaviors in a factorial experiment between V. champinii (a V. candicans/V. rupestris natural hybrid with moderate trichomes) and V. vinifera cv. 'Chardonnay' (which lacks trichomes) that had been gently scraped to remove trichomes or was not scraped. Results showed that sharpshooters performed significantly more X waves/X. fastidiosa inoculation behaviors of overall longer duration on Chardonnay than on V. champinii, regardless of shaving or not-shaving to remove trichomes. In addition, trichomes caused more frequent standing/walking/test-probing behaviors on V. champinii, whose xylem was rapidly accepted for sharpshooter ingestion once probing began. Thus, EPG can detect a novel type of grapevine resistance to X. fastidiosa-to the vector's probing process and inoculation of bacteria-in addition to the bacterial infection and symptom development processes that are the basis for most resistance breeding today. Future research could use EPG to screen grapevines for this novel type of resistance.

Xylella fastidiosa in Olive: A Review of Control Attempts and Current Management.

Since 2013, Xylella fastidiosa Wells et al. has been reported to infect several hosts and to be present in different areas of Europe. The main damage has been inflicted on the olive orchards of southern Apulia (Italy), where a severe disease associated with X. fastidiosa subspecies pauca strain De Donno has led to the death of millions of trees. This dramatic and continuously evolving situation has led to European and national (Italian and Spanish) measures being implemented to reduce the spread of the pathogen and the associated olive quick decline syndrome (OQDS). Research has been also carried out to find solutions to better and directly fight the bacterium and its main insect vector, Philaenus spumarius L. In the course of this frantic effort, several treatments based on chemical or biological substances have been tested, in addition to plant breeding techniques and integrated pest management approaches. This review aims to summarize the attempts made so far and describe the prospects for better management of this serious threat, which poses alarming questions for the future of olive cultivation in the Mediterranean basin and beyond.

A new species of Erythrogonia Melichar, 1926 (Insecta: Hemiptera: Cicadellidae: Cicadellini) from the Mantiqueira mountain range, southeastern Brazil, associated with olive orchards.

A new species of the diverse Neotropical sharpshooter genus Erythrogonia Melichar, 1926 is described and illustrated from the Mantiqueira mountain range, municipality of Maria da F, state of Minas Gerais, southeastern Brazil. The new taxon is associated with olive orchards and has been implicated as a vector of the bacterium Xylella fastidiosa Wells et al., 1987, which causes a disease known in Brazil as olive leaf scorch syndrome. Erythrogonia sinvali sp. nov. can be distinguished from the other 90 known species of the genus by the following combination of features: (1) crown black without conspicuous contrasting spots; (2) frons with large yellow median spot; (3) pronotum black with large yellow area covering most of disk; (4) forewing dark red, without contrasting spots or stripes, costal margin narrowly black, apical portion dark brown; (5) aedeagus elongate, curved dorsally, with pair of spiniform apical processes; (6) paraphyses greatly reduced; (7) basal portion of male anal tube with pair of spiniform curved processes; (8) posterior margin of female abdominal sternite VII broadly emarginate and with broad central lobe; (9) female sternite VIII with sclerotized areas, including a transverse bar located at bases of ovipositor valvulae I, followed by a pair of elongate sclerites and a posterior bilobed sclerite. Both males and females of the new species are described in detail. A putative group of five species within Erythrogonia is preliminarily proposed, including the new taxon, E. separata Melichar, 1926, E. dorsalis (Signoret, 1853), E. calva (Taschenberg, 1884), and E. melichari Schmidt, 1928. Among these species, the male terminalia of E. sinvali sp. nov. are more similar to those of E. separata.

Population structure, adaptation and divergence of the meadow spittlebug, Philaenus spumarius (Hemiptera, Aphrophoridae), revealed by genomic and morphological data.

Understanding patterns of population differentiation and gene flow in insect vectors of plant diseases is crucial for the implementation of management programs of disease. We investigated morphological and genome-wide variation across the distribution range of the spittlebug Philaenus spumarius (Linnaeus, 1758) (Hemiptera, Auchenorrhyncha, Aphrophoridae), presently the most important vector of the plant pathogenic bacterium Xylella fastidiosa Wells et al., 1987 in Europe. We found genome-wide divergence between P. spumarius and a very closely related species, P. tesselatus Melichar, 1899, at RAD sequencing markers. The two species may be identified by the morphology of male genitalia but are not differentiated at mitochondrial COI, making DNA barcoding with this gene ineffective. This highlights the importance of using integrative approaches in taxonomy. We detected admixture between P. tesselatus from Morocco and P. spumarius from the Iberian Peninsula, suggesting gene-flow between them. Within P. spumarius, we found a pattern of isolation-by-distance in European populations, likely acting alongside other factors restricting gene flow. Varying levels of co-occurrence of different lineages, showing heterogeneous levels of admixture, suggest other isolation mechanisms. The transatlantic populations of North America and Azores were genetically closer to the British population analyzed here, suggesting an origin from North-Western Europe, as already detected with mitochondrial DNA. Nevertheless, these may have been produced through different colonization events. We detected SNPs with signatures of positive selection associated with environmental variables, especially related to extremes and range variation in temperature and precipitation. The population genomics approach provided new insights into the patterns of divergence, gene flow and adaptation in these spittlebugs and led to several hypotheses that require further local investigation.

Isolation protocol trials for grapevine bacteriosis (Pierce's disease) agent <i>Xylella fastidiosa</i> Wells et al. during research monitoring of the Republic of Crimea

Xylella fastidiosa Wells et al. causes grapevine bacteriosis and is among most hazardous malicious bacterial phytopathogens affecting a wide variety of important crops and ornamental plants. The agent colonises plant xylem and transmits with insects feeding on xylem sap. The insect vectors of X. fastidiosa belong to the order Hemiptera, suborder Auchenorrhyncha, families Cicadellidae, Cercopidae, Aphrophoridae and Cicadidae. A phytosanitary control survey conducted by the All-Russian Research Institute for Plant Quarantine in 2014 identified a high risk of X. fastidiosa introduction and adaptation in the Russian Federation. The Crimean Peninsula is a potential introduction area of the Pierce’s disease agent due to suitable climatic conditions, the ample availability of major host plants, as well as insect vectors. During a research monitoring in 2018-2020, the Institute assessed the phytosanitary status of the Crimean territory. The survey sampled vegetative parts of grapevines, stone fruits (peach, cherry, plum, merry, almond), selected essential-oil and ornamental shrubs and trees. Diagnostic procedures were performed in accordance with the international standards. A three-year phytosanitary survey of the Crimean plantations revealed no presence of X. fastidiosa. Two protocols of sample preparation and DNA extraction from various substrates have been tested. A real-time PCR-based protocol was proved highly specific for zero false positive and nonspecific rates.

Functional foregut anatomy of the blue\u2013green sharpshooter illustrated using a 3D model

Sharpshooter leafhoppers (Hemiptera: Cicadellidae: Cicadellinae) are important vectors of the plant pathogenic bacterium Xylella fastidiosa Wells et al. (Xanthomonadales: Xanthomonadaceae). This pathogen causes economically significant diseases in olive, citrus, and grapes on multiple continents. Bacterial acquisition and inoculation mechanisms are linked to X. fastidiosa biofilm formation and fluid dynamics in the functional foregut of sharpshooters, which together result in egestion (expulsion) of fluids likely carrying bacteria. One key X. fastidiosa vector is the blue–green sharpshooter, Graphocephala atropunctata (Signoret, 1854). Herein, a 3D model of the blue–green sharpshooter functional foregut is derived from a meta-analysis of published microscopy images. The model is used to illustrate preexisting and newly defined anatomical terminology that is relevant for investigating fluid dynamics in the functional foregut of sharpshooters. The vivid 3D illustrations herein and supplementary interactive 3D figures are suitable resources for multidisciplinary researchers who may be unfamiliar with insect anatomy. The 3D model can also be used in future fluid dynamic simulations to better understand acquisition, retention, and inoculation of X. fastidiosa. Improved understanding of these processes could lead to new targets for preventing diseases caused by X. fastidiosa.

Ecology of the meadow spittlebug Philaenus spumarius in the Ajaccio region (Corsica) - I: spring.

The meadow spittlebug, Philaenus spumarius (L.) (Hemiptera: Aphrophoridae), is the main vector in Europe of the recently detected plant pathogen bacterium Xylella fastidiosa Wells et al. (Xanthomonadales: Xanthomonadaceae). While the ecology of continental populations is well documented, nothing is known about the insular populations of P. spumarius, such as in Corsica, where the bacterium was detected in 2015. Hence, in an epidemiological context, the ecology of P. spumarius has been studied in a maquis landscape in the Ajaccio region between 2017 and 2019. Adults and nymphs were almost exclusively collected on Cistus monspeliensis L. (Cistaceae). However, very few specimens were collected in summer, suggesting a movement of the adults to sheltered habitats. Unfortunately, despite several trapping methods used, the location of adult summer habitat remains unknown for the studied population. It might be tempting to destroy the central plant host of P. spumarius populations. However, as spittlebug nymphs are highly polyphagous on low-growing plant species and as the females can lay eggs in any dead plant tissues, such practice could have limited the impact. Instead, the strong relationship between P. spumarius and C. monspeliensis could be used to monitor spittlebug populations, to limit/concentrate the means of insect control, or in an agronomic context to lure insects away from crops. Maintaining natural arboreal vegetation around agronomic systems could help decrease insect abundance - and potentially, pathogen load - on cultivated species. Such hypotheses need to be further studied by landscape experiments.

Dispersal of Philaenus spumarius (Hemiptera: Aphrophoridae), a Vector of Xylella fastidiosa, in Olive Grove and Meadow Agroecosystems.

The introduction of the Xylella fastidiosa Wells bacterium into Apulia (South Italy) has caused the massive dieback of olive trees, and is threatening olive production throughout the Mediterranean Region. The key vector of X. fastidiosa in Europe is the spittlebug Philaenus spumarius L. The dispersal capabilities of P. spumarius are poorly known, despite being a key parameter for the prediction of the spread of the bacterium. In this study, we have examined the dispersal of P. spumarius adults in two different agroecosystems in Italy: an olive grove in Apulia (Southern Italy) and a meadow in Piedmont (Northern Italy). Insects were marked with albumin and released during seven independent trials over 2 yr. The recapture data were pooled separately for each agroecosystem and used to estimate the dispersal kernels of P. spumarius in the olive grove and in the meadow. The diffusion coefficient estimate for P. spumarius was higher in the meadow than in the olive grove. The median distance from the release point for 1 d of dispersal was 26 m in the olive grove and 35 m in the meadow. On the basis of our model, we estimated that 50% of the spittlebug population remained within 200 m (98% within 400 m) during the 2 mo period of high abundance of the vector on olives in Apulia. The dispersal of P. spumarius is thus limited to some hundreds of meters throughout the whole year, although it can be influenced to a great extent by the structure of the agroecosystem.

The relationship among host plant species, egg clutch size, and level of parasitism for the sharpshooter Tapajosa rubromarginata

AbstractThe sharpshooter Tapajosa rubromarginata (Signoret) (Hemiptera: Cicadellidae, Proconiini), a vector of the bacterium Xylella fastidiosa Wells et al. (Xanthomonadaceae) that causes citrus variegated chlorosis, has more than 30 reported host plant species. The fitness of a phytophagous insect is determined by the host plant suitability, plant resistance, and the natural enemies. The aim of this study was to: (1) identify plant species utilized as oviposition substrate by T. rubromarginata in the field; (2) establish the relationship between plants and clutch size; (3) establish the relationship among host plants, clutch size, and level of parasitism; and (4) establish variations in parasitoid composition and abundance in the various host plants. Egg masses of the sharpshooter were surveyed on plants reported as hosts, or those that were abundant in the study site. The number of eggs of the sharpshooter and emerged parasitoids were recorded for all the collected masses. We found egg masses of T. rubromarginata on 12 out of 21 plant species sampled. The size of the egg masses was greatly influenced by the type of leaf venation and to a lesser extent by the plant species. Parasitism rates were influenced by both leaf venation and host plant. Trichogrammatidae species were mostly associated with egg masses in plants with parallel‐veined leaves, whereas Mymaridae attacked masses laid in reticular‐veined leaves. The choice between a good host plant, but heavily attacked by parasitoids, and the host plants that are less suitable for nymphs but less frequently attacked by natural enemies, was a trade‐off for T. rubromarginata females to increase their fitness. We conclude that the host plant utilization by T. rubromarginata females in the field could be influenced by leaf structure and the strategy to avoid parasitism by selecting plants that were less attractive for parasitoids.

Biology and Prevalence in Northern Italy of Verrallia aucta (Diptera, Pipunculidae), a Parasitoid of Philaenus spumarius (Hemiptera, Aphrophoridae), the Main Vector of Xylella fastidiosa in Europe.

Simple SummaryThe meadow spittlebug, Philaenus spumarius is the major vector of Xylella fastidiosa in Europe. The spread of X. fastidiosa depends almost exclusively on insect transmission, and therefore, it is vital to keep vector populations low. To achieve this goal, natural enemies should be identified and their efficacy evaluated. The aim of this work was to assess the presence and abundance of a parasitoid fly, Verrallia aucta, in field-collected spittlebugs. At first, we developed a new species-specific molecular tool (PCR) to identify the parasitoid, then we estimated the parasitization rate in different sites of northern Italy using both PCR and the dissection of insect bodies. Finally, we established a small-scale rearing to describe the life cycle of the fly on its spittlebug host. Verrallia aucta is quite common in northern Italy but displayed low prevalence, reaching a maximum parasitization rate of 17.5% in vineyards of the Piemonte region. The fly has one generation per year, lays eggs in newly emerged adults of spittlebugs, and develops inside the host throughout the summer. The mature larva abandons the dead victim at the beginning of autumn and pupates in the soil where it overwinters.The meadow spittlebug, Philaenus spumarius (L.) (Hemiptera Aphrophoridae), the main vector of Xylella fastidiosa Wells et al. in Europe, has few known natural enemies. The endoparasitoid Verrallia aucta (Fallén) (Diptera, Pipunculidae) was first noticed a long time ago but very little is known about its biology and prevalence. In this study, the presence and prevalence of V. aucta were investigated in different regions of northern Italy, both in plain–foothill and montane zones. Parasitic larvae were identified by the dissection of spittlebug adults, P. spumarius and Neophilaenus campestris (Fallén), and by a new species-specific molecular tool targeting the ITS2 and COI genomic regions, developed in this work. A small-scale rearing was set up to gain information on the life cycle of V. aucta on its main host P. spumarius. During the four-year investigation (2016–2019) the pipunculid parasitoid displayed low prevalence, reaching a maximum parasitization rate of 17.5% (calculated over the adult spittlebug season) in vineyards of the Piemonte region. Over the whole period, no significant difference in the prevalence was found between male and female spittlebugs. Collected data and rearing observations suggest that V. aucta is monovoltine and synchronous with P. spumarius, laying eggs in newly emerged adults, developing as an endoparasitoid through two larval stages during the whole summer, and overwintering as a pupa in the soil.

Do Sharpshooters From Around the World Produce the Same EPG Waveforms? Comparison of Waveform Libraries From Xylella fastidiosa (Xanthomonadales: Xanthomonadaceae) Vectors Kolla paulula (Hemiptera: Cicadellidae) From Taiwan and Graphocephala atropunctata From California.

When an exotic invasive species is a vector-borne plant pathogen, vector feeding behavior must be studied to identify potential host plant range and performance of specialized pathogen transmission behaviors. The most rigorous tool for assessing vector feeding behavior is electropenetrography (EPG). Xylella fastidiosa Wells et al. is a gram-negative bacterium native to the Americas, where it is the causal agent of lethal scorch-type diseases such as Pierce's disease (PD) of grapevines. In 2002, a PD strain of X. fastidiosa invaded Asia for the first time, as confirmed from grape vineyards in Taiwan. Kolla paulula (Wallker), a native Asian species of sharpshooter leafhopper, was found to be the primary vector in Taiwanese vineyards. This study used an AC-DC electropenetrograph to record stylet probing behaviors of K. paulula on healthy grapevines. The main objective was to create an EPG waveform library for K. paulula. Waveform description, characterization of R versus emf components (electrical origins), and proposed biological meanings of K. paulula waveforms are reported. In addition, comparison of K. paulula waveforms with those from the most efficient, native vector of X. fastidiosa in California vineyards, Graphocephala atropunctata, is also reported. Overall, both species of sharpshooters had similar-appearing waveforms. Five new findings were identified, especially that the previously described but rare waveform subtype, B1p, was extensively produced in K. paulula recordings. Sharpshooter waveforms from species worldwide share a high degree of similarity. Thus, EPG methods can be rapidly applied to potential vectors where X. fastidiosa is newly introduced.