## 2 Semiochemicals and Reproductive Behaviour--An Overview  
Semiochemicals are involved in the different phases of the reproductive behaviour of many tephritids, which include male lek formation and sexual signalling (sexual calling), courtship, acceptance of a mating partner and successful population (Figure 2). The release and perception of semiochemicals are often accompanied by a range of intense behavioural interactions, including wing vibration and buzzing and head rocking [48; 49; 50; 51]. There is a variety of mating systems in tephritid fruit flies, with leak-based ones being common in many species of economic importance [52]. Leks are mating arenas where males aggregate and perform sexual signalling without controlling the access to resources that may be critical for females or offering parental care, and provide only the sperm to females that freely choose their mates [53]. Males perform sexual signalling mainly on the under surface of leaves of preferred host trees that either bear fruits as in _Anastrepha fraterculus_ (Wiedemann) and _B. dorsalis_, or do not bear fruits as in certain populations of the Mediterranean fruit fly (medfly) _Cenatitis capitata_ (Wiedemann) (see [54] for a review). Instead, in _Zeugodacus cucurbitae_ (Coquillett), lekking takes place more frequently on non-host plants [55; 56]. Likewise, in _Bactrocera acuminata_ (Hering), the wild tobacco fruit fly, non-host plants containing the male attractant methyl eugenol (ME) serve as the main mating sites [57]. Lekking males, in groups of 2-10 individuals [54], perform sexual signalling that includes a set of visual, acoustic and olfactory signals, with volatile pheromone acting as the longer-distance cue. On the other hand, at variance with many tephriids, most _Rhagoeletis_ spp. do not exhibit male lekking [52]. For example, males of _Rhagoeletis pomonella_ (Walsh), _Rhagoeletis_ (L.), _Rhagoeletis ribicola_ Doane and _Rhagoeletis mendax_ Curran individually search for potential males mainly on host fruits and the top surface of leaves [58], mostly during the late afternoon and at dusk [52; 59; 60]. However, in _Rhagoeletis batava_ Hering individuals have been reported to form small groups in response to male-released pheromone that might be considered leks [61]. While olfactory cues seem not to play a role in lek location for _Anastrepha obliqua_ (Macquart) and _Anastrepha ludens_ (Loew), data are rather controversial for _C. capitata_, _B. dorsalis_, and _Z. cucurbitae_[54]. Whether the cues exploited by males to aggregate in leks derives from their own pheromone emissions, or from the plants where leks occurs is still under debate. Indeed, in _C. capitata_ it has been proposed that  
Figure 2: Diagram showing the main steps of mating behaviour in tephritids and the signals transmitted and perceived. Lekking behaviour is common in Tephritidae, but notably absent in _Rhagoeletis_ species. Similarly, pre-mating trophallaxis is common, but this phenomenon is known to occur also during and post mating [47]. HMP, host-marking pheromone. plant volatiles, rather than male-emitted pheromones, contribute to male aggregation in leks [62; 63], with \(\alpha\)-copaene, a natural sesquiterpene widely present in plants, being regarded as the primary male cue for lek formation [64; 65; 66; 67]. Male pheromone has been shown to attract conspecific males thus acting as aggregation pheromone in some _Bactrocera_ species [68; 69; 70; 71; 72; 73]. Nonetheless, Kobayashi and colleagues reported no male-male attraction in _B. dorsalis_[74]. Interestingly, sex pheromones are not uniquely produced by males in all tephritid species. In the _Ceratitis_, _Anastrepha_ and _Rlagoletis_ genera, the volatile chemicals identified in the adult headspace are of male origin. Instead, the role of females in emitting volatiles is evident in the genus _Bactrocera_. In all _Bactrocera_ species studied so far, both sexes produce and release pheromone chemicals, albeit interspecific differences exist.