# Brandley's Glands Volatilome of the Predator _Zelus renardii_ Interacting with _Xylella_ Vectors
## 1 Introduction  
Current global trade and the movement of plant material increase the introduction of alien species [1]. These species must overcome biotic and abiotic stresses to survive, colonise, and reproduce [2]. In this scenario, native species meet allochthonous ones, generating new interactions. These interactions can lead to mutualistic interplays (positive interactions) or biological invasions (negative interactions) [3]. Negative interactions can turn alien species into invasives, leading to infestations of plant pests or pathogen epidemics. The quarantine bacterium _Xytella fastidiosa_ [PERSON] et al., 1987 (XF) subsp. _Pauca_ ST53 [4; 5] entered from Costa Rica to Italy (Apulia), developing the consequent epidemic on olive trees, showing how an alien species can invade new hitherto-unexplored territories. Indeed, XF-infected plants ultimately cease production and die within a few years [6]. In Apulia, XF encountered Aphrophoridae xylem-feeders (Spittlebugs, Hemiptera: Auchenorrhyncha), which acquire, transmit, and spread the bacterium in _Olea europaea_ L, 1753 populations, a new host. Several Aphrophoridae can acquire and transmit XF. However, _Phileanus spumaritus_ L., 1758 (PS) is the main vector for population size and infective abilities [7]. The ability to transmit XF has changed PS's status from a marginal insect to a key pest for olive trees in the Mediterranean Basin, leading to increased attention in managing PS infections [8]. The currently recommended strategy first suggests minimising PS populations during juvenile stages. Management then focuses on surviving adults, to prevent acquisition and transmission, or limiting infection events to one per plant adult to slow or to stop XF invasion. The aim is to kill vectors during their first feeding on olive trees, particularly in areas still free from the bacterium [7]. The basis of the infection management strategy is the integration of several control actions. This strategy involves resistant olive tree cultivars, mechanical and chemical control of PS juvenile instars, and chemical and biological control of PS adults [9; 10; 11; 7; 12; 13; 14]. The biological control of PS can involve the predator _Zelus rerandii_ [PERSON], 1856 (ZR, Hemiptera: Reduviidae) [12; 14], recently acclimated in the Mediterranean Basin [14; 15]. The reduviid will attack adult PS and other olive pests such as _Bactrocera oleae_ ([PERSON], 1790) (Diptera: Tephritidae) [14]. Furthermore, ZR could be a potential biological control agent for other invasive alien pests recently entering Europe, such as _Macrolomotoma gladita_ [PERSON], 1908 (Hemiptera: Psyllidae) and _Drosophila suzukii_ [PERSON], 1931 (Diptera: Drosophilidae) [16; 17]. As a biocontrol agent, ZR provides new interactions among alien and native species. These novel interactions offer the opportunity to unveil the mechanisms of integrating alien species into pre-existing trophic networks in the biogeographical area of entrance. Therefore, analysing how they interact with their biotic environment is relevant. Olfaction is the primary sense by which insects perceive single or semiochemical blends [18; 19], which are carbon-based volatile organic compounds (VOCs) vaporising at 20 \({}^{\circ}\)C and 0.01 kPa [20]. VOCs can play the role of interspecific (pheromones) and intraspecific (allelochemicals) communication [19; 21; 22; 23]. Semicochemicals serve as olfactory cues [18; 24; 25], eliciting behavioural or physiological replies. Cimicomorpha and Pentatomomorpha (Hemiptera: Heteroptera) possess peculiar metathoracic glands [26], whose secretions dictate several adult insect behaviours [27]. Many Reduviidae species have [PERSON]'s and metathoracic exocrine glands in pairs [27; 28; 29; 30; 31]. Secreted VOCs are involved in defence, alarm, and mating [29; 31; 32; 33]. [PERSON]'s glands have orifices located dorsally in the metathorax [34; 35] and secrete alarm pheromones in the event of disturbance of the reduviids [29].