Foraging response of female bactrocera dorsalis (hendel) to a fruit fly protein food attractant

Abstract

Oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae) causes serious economic loss for papaya (Carica papaya L.) production in Hawaiʻi through direct fruit damage and restriction of export commodities. Suppression of female flies was a challenge until a protein-based bait contains reduced risk insecticide spinosad became available, GF-120 NF Fruit Fly Bait (GF-120; Dow AgroScience, Indianapolis, IN). This bait provides an environmentally sound alternative to conventional cover spraysof organophosphate insecticides. Factors that influence the attractiveness of protein bait include chemical composition, visual stimuli, and competing volatiles from host fruits. This dissertation focuses on biological factors that affect the foraging response of female B. dorsalis to volatiles emitted by protein bait. Female reproductive state and dietary experience are two biological variables that shape the manner in which a fly searches for and responds to essential resources such as food and egg-laying sites. The experiments reported in this dissertation were conducted in order to assess the influence of physiological states on the response of female B. dorsalis to protein bait in papaya orchards. In Chapter 1, baseline information on key morphological characters in B. dorsalis ovarian development and the associated morphometric parameter of each oogenesis stage is collected. Four oogenesis stages include previtellogenesis, vitellogenesis, gravid and parous. In Chapter 2, field observations were conducted to determine reproductive states of B. dorsalis females (using ovarian developmental stage as an indicator) that respond to 2 two protein bait trapping devices: visually enhanced attract-and-kill bait stations termed papaya leaf mimics (PLMs) treated with GF-120 and dome traps containing torula yeast solution. Females with ovaries at previtellogenesis stage and egg laying females are the two main classes that responded to protein bait. Visual stimuli from the bait stations enhanced the response of immature females to protein bait but this effect was not found in egg-laying females. Yellow color also increased the capture of females with greater egg loads compared to those captured by green bait stations. This is an important finding for improved fruit fly management because reducing numbers of egg-laying females within an area results in lower fruit infestation. The physiological state of foraging flies determines the level of food searching behavior. In Chapter 3, the effects of female age and dietary history on the propensity of B. dorsalis to alight on protein bait were quantified. One week old females exposed to papaya as a diet source for 4 d in the first week of adult life showed a significantly greater propensity of alighting on GF-120 protein bait than females fed on a protein or sugar diet. Delay of ovarian development from feeding on a sugar only diet resulted in significantly higher response of 4 week old females to protein bait than females fed on papaya or protein. On the contrary, ovarian development in papaya fed females was not significantly different than that of protein fed females. Feeding on papaya during weeks 2 to 4 of adult life increased the response of female flies to protein bait at a lesser level than for 1 week old females. These results are evidence of the possible physiological profile of females attracted to protein bait in the natural environments. In addition, previous exposure to papaya fruit enhanced the response of females to papaya compared to females without the experience. This is a finding that suggests sanitation practice of removing culled fruit not only removes a breeding source but may also reduce the number of females re-entering orchards. Studies conducted in this dissertation are the first documentation of the response of egg-laying female B. dorsalis to protein bait under natural and semi-natural conditions. Results suggest that protein baits such as GF-120 attract females with developing ovaries as well as egg-laying females. In addition, fruit-based diet enhances the response of female B. dorsalis to protein bait and host fruit stimuli.