The Influence of Physiological State on Feeding Behaviour of Bactrocera tryoni(Froggatt) (Diptera: Tephritidae)
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This thesis examined the feeding behaviour of B. tryoni relative to the physiological state (sex, maturity, mated state and nutritional condition) of the fly. I particularly focused on the attraction of B. tryoni to proteinaceous food types with the intention of explaining fly response as a function of physiological state. All B. tryoni, irrespective of age, sex or mated state, preferentially feed in the first few hours after sunrise, both in the laboratory and field cage environment. Sugar feeding was greatest by mature mated females, followed closely by immature flies (both sexes). Protein feeding was greatest in immature flies, while mature unmated females spent very little time in protein feeding. Thus, proteinaceous baits used for B. tryoni control would be least effective over mature unmated females. Fly hunger is also relevant in determining how a fly will respond to food types. Some results with A. ludens suggested that sugar hungry flies had a reduced attraction to proteinaceous odours, a relevant consequence that significantly reduces the success of proteinaceous baits. Indeed, gravid female B. tryoni had a much decreased attraction to bacteria when sugar hungry, but the effect was not significant for immature flies (both sexes). Therefore, I tested B. tryoni attraction to sugar food (open fruit) and protein food (bacteria) combined, but the combined odours did not appear to be significantly more attractive than one food source alone. Gravid females were primarily attracted to fruit odour as an oviposition resource, independent of their nutritional condition. Further, gravid females were only significantly attracted bacterial odour when protein hungry and were repelled when fed. These results then lead me to a further examination of fly attraction to bacterial odours. Common phyllosphere bacteria are a known protein source for B. tryoni. Anecdotal evidence suggests that fly attraction to bacteria increases as the bacterial culture ages. However this was only found true for immature flies. Gravid females that were protein hungry initially had a strong response to bacterial odours in the exponential growth phase, but had a much reduced response to stronger bacterial odours in the stationary / death phase. This supports the theory that bacterial odours represent an ovipositional deterrent to B. tryoni. A common volatile released by phyllosphere bacteria, 2-butanone, is also thought to be the attractive volatile in cue lure (a male B. tryoni sex attractant). However, mature males had a relatively low response to bacteria, suggesting that bacterial odours do not act as a sex attractant in the same way as cue lure. My findings help explain why protein baits may or may not be effective in controlling B. tryoni and will improve the decision making process when considering how best to control B. tryoni.
Master of Philosophy (MPhil)
Griffith School of Environment
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