# Detection of Volatile Constituents from Food Lures by Tephritid Fruit Flies
## 1 Introduction  
Fruit flies in the family Tephritidae are among the most economically important pests worldwide, and are a major threat to fruit production in Africa. Some of these fruit flies have been introduced outside their region of origin and become invasive pests [1]. _Bactrocera dorsalis_, _Bactrocera zomata_ ([PERSON]), and _Zeugodacus cucurbitate_ ([PERSON]) have been introduced to Africa [2; 3; 4]. Following introduction, _B. dorsalis_ has quickly dispersed throughout the region, causing unprecedented direct and indirect damages, including crop losses, quarantine restrictions and competitive displacement of native fruit flies such as _Ceratitis cosyra_ ([PERSON]) [5]. The host range of tephritid flies varies with species, some being polyphagous, such as _B. dorsalis_, _B. zomata_ and _Ceratitis capitata_ ([PERSON]), whereas others are oligophagous (_Z. cucurbite_) or even monophagous (_Bactrocera oleae_, [PERSON]) [6]. In spite of their diverse oviposition substrates, however, all adult tephritid species need proteinaceous substrates for sexual maturation and development of ovaries [7; 8]. Adult flies, particularly females, extensively forage for proteinaceous food sources [9]. Various food-baits have been developed and are being used as a main component of female-biased attractants [10]. Food-baits offer substantial advantages, as they attract both males and femalesof multiple species [11]. An important alternative to a food-bait for monitoring or control is male annihilation. This uses male lures, often called parapheromones [12], which, although highly attractive to males and species specific, seems inadequate for African smallholder settings as the small farm size causes a steady influx of dispersing flies from surrounding plots [13]. In addition, the relatively high specificity seems a disadvantage when a diverse guild of fruit flies co-occurs on a crop. Suppression of a single species may result in a competitive increase and replacement of the main pest species by another [5]. In contrast, synthetic lures derived from food volatiles that are universally detected across sexes and species, may be used in simultaneously suppressing multiple species and target population control more directly by removing females. Volatiles from food sources that attract tephritid fruit flies are largely byproducts of microbial metabolic pathways, lysis and protein breakdown, and serve as important indicators of resources critically needed for tephritid reproductive success [14; 15]. Accordingly, the life history of tephritids is closely associated with microorganisms. Microbes are a source of protein, minerals and vitamins, and contribute to fitness and reproductive success [16; 17]. In addition, microbes take part in the host interaction of larval and adult fruit flies by either detoxifying toxic substances during feeding or by degrading or modifying oviposition substrates [18]. Fruit flies inoculate microorganisms from one fruit to another in order to facilitate oviposition and larval development [19]. Many bacteria associated with fruit flies are also capable of fixing atmospheric nitrogen into usable forms such as ammonia [17], which may be important as fruits are generally low in protein content. Identification of volatile constituents of food lures include protein-signifying compounds such as nitrogen-containing compounds, some of which are important fruit fly attractants [20; 21]. Nitrogen-free volatiles are also produced and important for the attraction of fruit flies to protein sources [11]. A three-component synthetic lure containing putrescine, trimethylamine and ammonium acetate, Biolure(r), is a good example of how such research can lead to new odor-based tools for fruit fly monitoring and control [22; 23; 24; 25; 26; 27]. However, none of the efforts have used the fly's sensory organs to identify which compounds in the fermentation and protein hydrolysate baits are actually detected by the antennae.