## 2 Semiochemicals and Reproductive Behaviour--An Overview
In _Bactrocera musae_ (Tryon), a polyphagous pest distributed in Australia and Papua New Guinea mainland [75], both sexes produce volatile pheromones, but its complexity is higher in females than males [76]. In the olive fruit fly, _Bactrocera oleae_ (Rossi), females release the pheromone that plays a central role in the mating system of this species [77; 78; 79; 80]. However, earlier and most recent studies suggested that male-emitted chemicals elicit female attraction [81; 82; 83]. The finding that both sexes emit and perceive chemicals during courtship [84; 50], together with the identification of male wing vibration in this species [50], encourage further research to better understand the role of chemical communication in the mating behaviour of _B. oleae_. So far, males have been regarded to swarm before settling on olive canopy [42]. The modality of male aggregation to form leks in this species needs to be further clarified too, in order to understand the relevance of chemical communication in a species where female-borne pheromones have been well documented both as a short- and long-distance cue [42]. Recently it was proven that ethyl decanoate emitted by olive fruit fly females attracts other females, and hence may be involved in female-female aggressive interactions on oviposition sites [85]. Courtship implies a series of ritualized actions, and it is much more complex in the genus _Ceratitis_, particularly in _C. capitata_[86], than in other tephritids, such as many species of _Anastrepha_[87; 88] and _Bactrocera_[89]. However, recent studies are revealing that, even in species where it was believed to be simplified, such as in _Bactrocera tryoni_ (Froggatt), courtship is more complex than previously thought [49]. During courtship, volatile chemicals are perceived by either one of both sexes using the antennae, while less volatile compounds, such as CHs, have been suggested to be important in later stages, when male and female touch each other during mating attempts and mating _per se_[35; 42; 90]. Indeed, in several tephritids, fore- and hind-leg interactions, as well as male foreleg interaction with the female abdomen, 'kissing' (i.e., touching of the labella), and male tapping with the labellum on female thorax have been reported [49; 91; 42]. For example, in _Ceratitis rosa_ Karsch and _A. fraterculus_, sex-specific differences in the quantitative composition of CH profile, together with reported mating incompatibilities, further suggest the role of CHs as short-range semiochemicals [92; 93; 90]. Trophallaxis (i.e., female provision with gifts -oral, genital or transdermal- by males [94; 95; 91]), a common behaviour in tephritids, is considered as a courtship signal as well (see [96] for a review). While in _Anastrepha_ species a pre-mating transfer of male oral products to females by labrum-to-labrum contact is well known [97; 98; 91], this phenomenon has been described in medfly only recently [96]. In this species, the consumption of male-produced oral droplets by the female appeared to increase her receptivity to mating, suggesting that the chemical composition of these droplets may be a tool to assess male quality [35; 96]. Further research in the medfly and in other major tephritid fruit fly species is thus essential to unravel how these substances are perceived and how this behaviour fits in the complex semiochemical-based communication frame. Interestingly, a recent work demonstrates that _A. ludens_ males regurgitate more than females, and propose that regurgitation and deposition of series of droplets organized in lines or spirals by some fruit fly species may play multiple functions (e.g., collecting bacteria from the environ ment, or eliminating ingested toxicants), including the production of oral pheromones [99]. Moreover, signalling males in some _Anustrepha_ spp. deposit pheromone on the leaf surface by abdominal tip dipping [100]. Some of these deposited components persist on leaves up to one hour after removal of signalling males and are able to attract females [100].