Tracking Short-Range Attraction and Oviposition of European Grapevine Moths Affected by Volatile Organic Compounds in a Four-Chamber Olfactometer

The identification of volatile organic compounds (VOCs) leading to short-range attraction and oviposition of the European grapevine moth Lobesia botrana and European grape berry moth Eupoecilia ambiguella (Lepidoptera: Tortricidae) is crucial in order to establish bait-based decision support systems for control of these pests. Therefore, we developed a method to measure the real-time behavioral response of female moths to VOCs using a four-chamber olfactometer coupled with a video tracking system. Ten synthetic VOCs were selected for this study: (S)-(−)-perillaldehyde, (E)/(Z)-linalool oxide, (±)-limonene, linalool, (E)-β-caryophyllene, α/β-farnesene, (−)-α-cedrene, methyl salicylate and cumene. The effect of VOCs on egg deposition was determined using a dual-choice oviposition test, whereas perception by female antennae was verified using electroantennography (EAG). During video tracking, females responded to volatile compounds emitted by grapevine with higher antennae and ovipositor activity than to air control. (E)/(Z)-linalool oxide, cumene and (S)-(−)-perillaldehyde released ovipositor activity of L. botrana, while the latter provoked oviposition. (R)/(S)-limonene affected ovipositor activity of E. ambiguella, whereas none of the VOCs tested attracted for oviposition. The results suggest that females have the ability to perceive specific VOCs by the antennae but also by the ovipositor, which could attract or repel for egg deposition

Plant-specific factors affecting short-range attraction and oviposition of European grapevine moths

The spread of pests and pathogens is increasingly intensified by climate change and globalization. Two of the most serious insect pests threating European viticulture are the European grape berry moth, Eupoecilia ambiguella (Hübner) and the European grapevine moth Lobesia botrana (Denis & Schiffermüller). Larvae feed on fructiferous organs of grapevine Vitis vinifera, resulting in high yield and quality losses. Under the aspects of integrated pest management, insecticide measures are only reasonable when other control strategies become ineffective. In order to support the development of novel decision support system for the application of insecticides, the aim of this thesis was to decipher plant-specific factors, which affect the short-range attraction and oviposition of L. botrana and E. ambiguella. The focus was set on the visual, volatile, tactile and gustatory stimuli provided by their host plant after settlement. The use of artificial surfaces as model plant showed that oviposition of both species is affected by the color, the shape and the texture of the oviposition site. To explain a susceptibility of certain grapevine cultivars and phenological stages of the berries to egg infestations, we analysed and compared the chemical composition of the epicuticular waxes of the berry surface as well as the volatile organic compounds emitted by the berries. Thereby it turned out that the attractiveness to wax extracts decreased during ripening of the berries, highlighting a preference of earlier phenological stages of the berries for oviposition. In addition, grapevine cultivars exhibited variations in their volatile composition. The principle components perceived by female’s antennae could not explain the differentiation between cultivars, suggesting volatiles do not trigger orientation to certain cultivars. Furthermore, a method was developed to measure real-time behavioural response of female moths to volatiles. The setup allowed to quantify the orientation to a volatile source as well as movements of the antennae and ovipositor. They could be linked to the olfactory and gustatory perception of volatiles during the evaluation of suitable host plants for oviposition. In addition, the risk of potential alternative host plants in the vicinity of the vineyard was investigated. This confirmed that L. botrana in particular prefers the stimuli provided by some plants to those of grapevine. Overall, the results suggest that during oviposition, volatiles emitted by the plants and the composition of the plant surface are the most important factors for host plant differentiation

Analysis of vector behavior as a tool to predict xylella fastidiosa patterns of spread

The most likely scenarios for Xylella fastidiosa introduction in Central Europe is through infected ornamental plants, with a successive spillover from gardens and parks to cultivated orchards. Given its polyphagy and wide distribu-tion, the meadow spittlebug Philaenus spumarius, the only ascertained vector of X. fastidiosa in Europe so far, might play an important role in such a scenario. Here, we combined and analyzed spittlebug’s behavioral data obtained through Electrical Penetration Graph (EPG), preference and survival tests as well as field surveys, in order to infer possible bacterium patterns of spread. For our case study, we selected oleander and rosemary as potential introductory hosts and grapevine and cherry as economically important threatened plants. Philaenus spumarius was collected in field near all the four plant species, although choice and no-choice tests indicated that the spittlebug rather prefers to settle on cherry and grapevine than on rosemary and oleander. Considering the results of the EPG, the duration of xylem sap ingestion was longer in cherry, grapevine and rosemary than in oleander. However, P. spumarius spent on rosemary most of the time in resting activities, this implying a lower duration of xylem sap ingestion compared to grapevine and cherry. Overall, our data suggest that cultivated plants as grapevine and cherry could be more relevant than oleander and rosemary as X. fastidiosa source plants; therefore, P. spumarius might acquire the bacterium from cultivated plants, then first spread it within cultivated orchards, and successively to ornamental plants during its dispersal

Tracking Short-Range Attraction and Oviposition of European Grapevine Moths Affected by Volatile Organic Compounds in a Four-Chamber Olfactometer

The identification of volatile organic compounds (VOCs) leading to short-range attraction and oviposition of the European grapevine moth Lobesia botrana and European grape berry moth Eupoecilia ambiguella (Lepidoptera: Tortricidae) is crucial in order to establish bait-based decision support systems for control of these pests. Therefore, we developed a method to measure the real-time behavioral response of female moths to VOCs using a four-chamber olfactometer coupled with a video tracking system. Ten synthetic VOCs were selected for this study: (S)-(−)-perillaldehyde, (E)/(Z)-linalool oxide, (±)-limonene, linalool, (E)-β-caryophyllene, α/β-farnesene, (−)-α-cedrene, methyl salicylate and cumene. The effect of VOCs on egg deposition was determined using a dual-choice oviposition test, whereas perception by female antennae was verified using electroantennography (EAG). During video tracking, females responded to volatile compounds emitted by grapevine with higher antennae and ovipositor activity than to air control. (E)/(Z)-linalool oxide, cumene and (S)-(−)-perillaldehyde released ovipositor activity of L. botrana, while the latter provoked oviposition. (R)/(S)-limonene affected ovipositor activity of E. ambiguella, whereas none of the VOCs tested attracted for oviposition. The results suggest that females have the ability to perceive specific VOCs by the antennae but also by the ovipositor, which could attract or repel for egg deposition

DC-EPG assisted comparison of European spittlebugs and sharpshooters feeding behaviour on grapevine

Xylem-feeding is apparently the only requirement making an insect a competent vector of the bacterium Xylella fastidiosa, an organism responsible for the devastation of the Southern Italian olive forest and nowadays considered one of the most feared threats to agriculture and landscape in Europe, including vineyards. Here, we used the direct current-electrical penetration graph (DC-EPG) technique to compare and describe the feeding behaviour on grapevine of four xylem-feeding species considered candidate vectors of X. fastidiosa widespread in Europe, namely two spittlebugs (the meadow spittlebug Philaenus spumarius and the spittlebug Neophilaenus campestris) and two sharpshooter leafhoppers (the rhododendron leafhopper Graphocephala fennahi and the green leafhopper Cicadella viridis). We created a standard for the analysis of EPG waveforms recorded with a DC-EPG device, describing feeding activities performed by these insects from stylet insertion into the plant to withdrawal. This standard, along with freely available software, has been developed to harmonize the calculation of feeding behavioural parameters in xylem-feeders. The most relevant differences between the two vector taxa were the probing frequency and the dynamics of xylem ingestion. Sharpshooters tended to perform significantly more probes than spittlebugs. In contrast, the latter spent longer times in low-frequency xylem ingestion, characterized by scattered contractions of the cibarial dilator muscle interspersed with periods of pump inactivity. Cicadella viridis was the species displaying the highest frequency of the electrical pattern found to be associated with X. fastidiosa inoculation in spittlebugs (Xe). Feeding behavioural data presented here represent an important step forward for deepening our knowledge of xylem-sap feeding insects' interaction with both the host plants and the bacterium they transmit

DC-EPG raw data on European spittlebugs and sharpshooters feeding behaviour on grapevine

The Direct Current-Electrical Penetration Graph (DC-EPG) technique was used to compare and describe the feeding behaviour on grapevine of four xylem sap-feeding species considered candidate vectors of X. fastidiosa and widespread in Europe: the meadow spittlebug Philaenus spumarius, the spittlebug Neophilaenus campestris, the rhododendron leafhopper Graphocephala fennahi and the green leafhopper Cicadella viridis. The four species were settled on potted grapevine plants for a period of 6 hours and the feeding activities performed by these insects, from stylet insertion into the plant to withdrawal were recorded by DC-EPG coupled with Stylet+d software. Characteristic waveforms were marked with Stylet+a software and analysed by the macro XylFeed. The raw data of the sequential and non-sequential EPG parameters generated by the XylFeed are reported in this database as part of the connected publication.Peer reviewe

Risk Assessment for the Spread of Flavescence Dorée-Related Phytoplasmas from Alder to Grapevine by Alternative Insect Vectors in Germany

“Flavescence dorée” (FD)-related phytoplasmas are widespread in alder in Germany and their transmission to grapevine represents a high risk for FD outbreaks when the primary vector, Scaphoideus titanus, becomes present in the future. Therefore, the potential role of the Deltocephalinae leafhopper species in transmitting FD-related phytoplasmas from alder to grapevine was studied in extensive transmission trials conducted between 2017 and 2020. The transmission capacity of autochthonous Allygus spp. and the invasive Orientus ishidae captured on infected alder trees was tested under controlled conditions using various test designs, including grouped insects and single-insect studies. The latter experiments were analyzed in terms of survival probability, transmission success and phytoplasma load in the insects, measured by quantitative PCR. A minimum inoculation titer (MIT) required for successful transmission to alder was defined for both Allygus spp. and O. ishidae. While Allygus spp. exhibited slightly better survival on Vitis vinifera compared to O. ishidae, the latter displayed higher phytoplasma loads and greater transmission success. Although all species were capable of infecting alder seedlings, O. ishidae was able to transmit 16SrV-phytoplasmas directly to single grapevines. Infective adults of O. ishidae were captured from the beginning of July until the end of August, while Allygus spp. were only considered infective towards the end of the season. Thus, O. ishidae likely poses a higher risk for FD transmission from alder to grapevine, albeit at a very low level, as only five out of 90 transmission trials to V. vinifera were successful

Vectors of Xylella fastidiosa around the world: an overview

Peer reviewe

An overview on the worldwide vectors of xylella fastidiosa

The Gram-negative bacterium Xylella fastidiosa causes disease in a number of important crops and plants within natural ecosystems. Most notable among these diseases are Pierce’s disease of grapevine, Citrus Variegated Chlorosis, Almond Leaf Scorch, Oleander Leaf Scorch and Olive Quick Decline Syndrome. In response to substantial economic losses, extensive research efforts have been underway over the past several decades in North and South America. Recently, X. fastidiosa has been detected in several countries of Europe and Asia, likely appearing as a result of global trading of plant material. Once established in a new region, X. fastidiosa spread is dependent on the obligate transmission by xylem-sap feeding insects. Sharpshooter leafhoppers (Hemiptera: Cicadellidae: Cicadellinae) are the best-studied group of vectors of this bacterium; however the list of known vector species is expanding. As X. fastidiosa moves into new regions, the combination of an introduced pathogen with existing or introduced vectors carries the potential of increasing economically important disease problems in the local context. By reviewing ecological and biological information of known X. fastidiosa vectors and the epidemiology of local X. fastidiosa outbreaks, this paper aims at increasing our understanding of vector– X. fastidiosa interactions