## 2 Semiochemicals and Reproductive Behaviour--An Overview
Abdominal dipping with deposition of a viscous substance from the male cercus (i.e., the external appendage close to the digestive tract) has also been observed in _Rhugoletis boyci_ Cresson [101]. After mating, tephritid females undergo an almost immediate switch from response to male pheromone to host plant-oriented olfactory behaviour to seek for appropriate oviposition background. This phenomenon has been well documented for the medfly at the behavioural level [102] and molecular data suggest that genes related to olfaction and/or foraging are also changing in their transcriptional profiles [103]. Mating-related differential expression in genes involved in chemosensory perception has also been detected in _Bactrocera_[104; 105], and _Anustrepha_ spp. [106], with females of _B. tryoni_ showing mating-induced switches in olfactory preference [107]. The oviposition behaviour of tephritids is highly heterogeneous and display species-specific differences, such as daily patterns of oviposition, clutch size, patterns of positioning the ovipositor, duration of the oviposition bout, and preferred plant site for the oviposition [108]. In the medfly, oviposition behaviour has been widely studied and described as being structured in four steps: arrival to the fruit, exploring (i.e., survey of fruit surface with head, labellum and ovipositor), ovipositor puncturing and drawing following oviposition conclusion [109; 110]). In the last phase, the fruit surface is again explored by the females, with the aculeus of the ovipositor protracted, and a HMP is deposited [111]. The presence of conspecific eggs and developing larvae in breeding substrates may dramatically alter the oviposition behaviour in phytophagos insects. In tephritids, females often mark already used hosts with a pheromone to avoid overexploitation of the specific resource and hence reduce/eliminate competition [112; 113]. To maximise the chances of survival and success of their progeny, phytophagous insects tend to avoid egg laying in already explored host resources [29; 108]. Host marking is particularly important in endophytic species, such as tephritids, in which females oviposit inside fruits or other plant tissues, with no visible damage and no emission of specific plant volatiles in response to infestation and presence of fruit fly eggs [114]. HMPs are generally applied by female drawing the ovipositor following an egg-laying event [112]. Mechano-, hygro- and gustatory receptors are located on female ovipositor in tephritids [115]. Gustatory sensilla present on the tarsi of _R. pomonella_ exhibit sensitivity to HMP [116]. Sensilla types on female ovipositor have been described in several _Bactrocera_ and _Zeugodacus_ species (i.e., _Z. cucurbiae, Zeugodacus diaphragm_ (Hendel), _B. dorsalis, Bacteria minax_ (Enderlein), _Zeugodacus scutellatus_ (Hendel) and _Zeugodacus tau_ (Walker) [117]; _B. tryoni_[118]), as well as in _R. pomonella_[119; 120; 121], but their characterisation is still patchy in species of the _Ceratitis_ and _Anustrepha_ genera [122]. Interestingly, HMPs have been shown to either deter or enhance oviposition, depending on concentration and other factors [123]. Deterent effects induce different behaviours in responding females including suppression/disruption of oviposition, reduction of the number of egg clutches per fruit and egg number per clutch, and dispersion to less infested (occupied) areas [124; 125; 126; 127; 128]. Although HMPs are predominantly recognised by individuals of the same species [29; 129], interspecific perception of HMPs has also been described in tephritids. Cross-recognition has been demonstrated among species of the _Rhugoletis_[130; 131], _Anustrepha_[132] and _Ceratitis_ genera [33; 34]. The host-marking behaviour may display different features even among species of the same genus. For example, small-sized fruit specialists (e.g., _Rhugoletis alternata_ (Fallen), _Rhugoletis indiffrens_ Curran, _R. pomonella_ and _R. cerasi_) often deposit HMPs [133].