Feeding on Papaya Flowers Enhances Mating Competitiveness of Male Oriental Fruit Flies, Bactrocera dorsalis (Diptera: Tephritidae)

Males of the oriental fruit fly, Bactrocera dorsalis (Hendel), are attracted to and feed on methyl eugenol. The goal of the present study was to determine whether feeding on a methyl eugenol-bearing plant, papaya (Carica papaya L.) would result in a mating advantage for B. dorsalis males. Mating frequencies of males given access to flowers (treated) and flower-deprived males (control) were compared in trials conducted 2 and 7 d after treated males were exposed to the flowers. For both intervals, treated males accounted for a significantly larger number of matings than control males. A second experiment compared female attraction to control and treated males. When at a lek, males display vigorous wing-fanning behavior, presumably to increase dispersal of the sex pheromone. Floral feeding resulted in a significant increase in wingfanning activity but did not appear to affect the attractiveness of the pheromonal signal per se. A field experiment revealed that male captures in methyl eugenol-baited traps were not reduced by prior feeding on papaya flowers. Males of the oriental fruit fly, Bactrocera dorsalis (Hendel), are strongly attracted to methyl eugenol (ME hereafter), a compound found in the leaves, flowers, or fruits of plants in over 10 families (Fletcher 1987, Metcalf 1990). Male attraction is so powerful that ME, when mixed with an insecticide, constitutes an effective suppression tool via ‘male annihilation’(Cunningham 1989). This method was, in fact, used successfully to eradicate B. dorsalis from entire islands in the western Pacific (Steiner et al. 1965, 1970). Despite the frequent use of ME in control programs, little attention has been given to the biological function underlying male attraction to this chemical. However, there is increasing evidence that ME has an important role in sexual communication and mating competition. Nishida et al. (1988) demonstrated that B. dorsalis males fed pure ME concentrated metabolites of this compound in their rectal glands (the presumed site of sex pheromone production), whereas ME-deprived males did not. Tan and Nishida (1996) confirmed this result and also noted (as had Shelly and Dewire 1994) that ME-fed males had a mating advantage over control (unfed) males (see Hee and Tan 1998 for similar results with B. papayae Drew and Hancock). Importantly, enhanced mating success was also noted when B. dorsalis males were provided with flowers of Fagraea berteriana A. Gray (Loganiaceae; Nishida et al. 1997) and Cassia fistula L. (Fabaceae; Shelly 2000a) both natural sources of