## 3 Volatile Pheromones  
### Tissues Involved in Volatile Pheromone Production  
Male pheromones seem to be released primarily from glands positioned in the rectum in _Ceratitis_[144; 145], _Bactrocera_[74; 79; 146; 147; 148], and _Anastrepha_ spp. [149; 150; 151]. However, interesting variations have been reported. This is the case of the goldenrod gall tephritid fly _Eurosta solidaginis_ (Fitch), which possess no anal glands but enlarged rectum and pleural epidermis that have been suggested to be involved in pheromone production and/or storage [152].  
In general, the rectal valve of _A. fraterulus_ and _C. capitata_ is located at the distal portion of the colon, while the intestinal canal enlarges in a chamber comprising four rectal papillae projecting in the lumen of the rectal ampulla (i.e., the anterior rectum) [153]. In its proximal region, the ampulla is lined with epithelial cells that increase in number and are organized in folds in the distal portion. In several _Anastrepha_ species, the structure of the female rectum is similar, with differences in the features of the epithelium [154]. In _Bactrocera_ spp. (e.g., _B. oleae_, _B. dorsalis_ and _B. tryoni_), the rectal glands of males and females display a remarkable sexual dimorphism [155; 156; 157]: muscles surrounding male glands are more abundant, suggesting a more complex contraction capacity to support the pheromone-storage and -release functions. The rectal sac (i.e., an evagination in the rectal gland) is present only in males. Because they are not surrounded by muscles and directly exposed to the haemolymph, the rectal pads, which extend into the gland as rectal papillae, have been suggested to be involved in transporting chemicals into the rectal gland [157].  
During sexual calling, the anal tube is protruded to allow the epithelium of the distal rectum to be extruded. In medfly, when exerted, the folded rectal epithelium is expanded in a balloon-like structure [144]. This evagination of the anal membranes at the abdominal tip, which appears as a droplet, has been described in _Anastrepha_ and _Ceratitis_ species, and it has been explained as a mean of expanding the evaporative surface, thus increasing pheromone emission and, consequently, attractiveness [158; 100; 150]. In addition, this behaviour is accompanied by protrusion of male expansion of the pleural abdominal region generating two lateral blisters [149; 159].  
Males of _C. capitata_ and _C. rosa_ display three types of sex-specific glands, _(i)_ the anal glands, _(ii)_ the pleural glands and _(iii)_ the dimorphic salivary glands [160]. The pair of anal glands open onto the external cuticle close to the anal opening [161; 160]. Males of _Anastrepha_ species display only the pleural glands and dimorphic salivary glands [151; 160]. In _Bactrocera_ species (e.g., _B. oleae_, _B. tryoni_ and _B. dorsalis_), both the anal glands and the dimorphic salivary glands are absent [160; 162; 146]. Currently, detailed information on _Rhagoletis_ species are lacking, although the early work of Nation [160] found neither dimorphic salivary glands nor pleural glands in both _R. pomonella_ and _R. juglandis_ (Cresson).  
In addition to the key function played by rectal tissues, pheromones have been later found to be also released orally. Salivary glands release pheromone components in _Anastrepha_ spp. [149; 150; 151; 163; 164]. These glands are sexually dimorphic, with male salivary glands being ball-like structures associated with the crop [99; 160; 165]. Salivary glands have been suggested to be involved in the storage and, potentially, synthesis of pheromone components in medfly males [166]. This is supported by the fact that some chemicals of the pheromone blend identified in medfly male headspace were also detected in the extracts of salivary glands. Figure 3 summarizes the tissues involved in pheromone production in rebritidis.