Spittlebugs of Mediterranean Olive Groves: Host-Plant Exploitation throughout the Year.

Nicola Bodino,Crescenza Dongiovanni,Stefania Volani,Elisa Plazio,Domenico Bosco,Giuseppe Altamura,Anna Simonetto,Gianni Gilioli,Vincenzo Cavalieri,Daniele Tauro,Matteo Alessandro Saladini

doi:10.3390/insects11020130

Abstract

Spittlebugs are the vectors of the bacterium Xylella fastidiosa Wells in Europe, the causal agent of olive dieback epidemic in Apulia, Italy. Selection and distribution of different spittlebug species on host-plants were investigated during field surveys in 2016–2018 in four olive orchards of Apulia and Liguria Regions of Italy. The nymphal population in the herbaceous cover was estimated using quadrat samplings. Adults were collected by sweeping net on three different vegetational components: herbaceous cover, olive canopy, and wild woody plants. Three species of spittlebugs were collected: Philaenus spumarius L., Neophilaenus campestris (Fallén), and Aphrophora alni (L.) (Hemiptera: Aphrophoridae). Philaenus spumarius was the predominant species both in Apulia and Liguria olive groves. Nymphal stages are highly polyphagous, selecting preferentially Asteraceae Fabaceae plant families, in particular some genera, e.g., Picris, Crepis, Sonchus, Bellis, Cichorium, and Medicago. Host-plant preference of nymphs varies according to the Region and through time and nymphal instar. In the monitored sites, adults peak on olive trees earlier in Apulia (i.e., during inflorescence emergence) than in Liguria (i.e., during flowering and beginning of fruit development). Principal alternative woody hosts are Quercus spp. and Pistacia spp. Knowledge concerning plant selection and ecological traits of spittlebugs in different Mediterranean olive production areas is needed to design effective and precise control strategies against X. fastidiosa vectors in olive groves, such as ground cover modifications to reduce populations of spittlebug vectors.

Highlights

True spittlebugs (Hemiptera: Aphrophoridae), a family of xylem-sap feeder insects, recently gained fame as the vectors of the exotic plant pathogenic bacterium Xylella fastidiosa Wells in Europe [1,2,3].The introduction in Europe of this xylem-limited bacterium, the causal agent of the Olive QuickDecline Syndrome (OQDS), led to dramatic dieback of olives in Apulia in recent years and promptedInsects 2020, 11, 130; doi:10.3390/insects11020130 www.mdpi.com/journal/insectsInsects 2020, 11, 130 applied research on spittlebugs, previously overlooked as agricultural pests in Europe [4]
Our results provide different information on spittlebugs bionomics: (1) identification of key plant taxa that, both within and nearby olive groves, allow nymphal development and adult survival of spittlebugs and can act as reservoirs of the vectors’ populations; (2) description of exploitation of host-plants by nymphs based on their instar and plant phenology; (3) host-plant selection of P. spumarius nymphs related to the abundance of plant taxa in the sampling sites; (4) patterns of spatial distribution of nymphal stages
Three spittlebug species were collected during visual observation of herbaceous vegetation: P. spumarius, N. campestris and Aphrophora alni (Fallen), the latter sampled in Liguria olive groves only

Summary

Introduction

True spittlebugs (Hemiptera: Aphrophoridae), a family of xylem-sap feeder insects, recently gained fame as the vectors of the exotic plant pathogenic bacterium Xylella fastidiosa Wells in Europe [1,2,3].The introduction in Europe of this xylem-limited bacterium, the causal agent of the Olive QuickDecline Syndrome (OQDS), led to dramatic dieback of olives in Apulia in recent years and promptedInsects 2020, 11, 130; doi:10.3390/insects11020130 www.mdpi.com/journal/insectsInsects 2020, 11, 130 applied research on spittlebugs, previously overlooked as agricultural pests in Europe [4]. Recent field surveys in olive groves of different Mediterranean countries have shown the predominance of Aphrophoridae as xylem-sap feeder group in the Mediterranean environment, with little or no presence of sharpshooters (Hemiptera: Cicadellidae: Cicadellinae) [5,6,7,8]. These findings highlighted the profound difference between X. fastidiosa pathosystems in Europe compared to the ones occurring in the United States of America and Brazil, where sharpshooters are the predominant xylem-sap feeders and main vectors of the bacterium [9,10,11]. Spittlebug adults are characterized by extraordinary jumping ability [19] and feed on xylem vessels of both herbaceous and woody plants [2,20,21]

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