SummaryCaloric restriction (CR) has been widely accepted as a mechanism explaining increased lifespan (LS) in organisms subjected to dietary restriction (DR), but recent studies investigating the role of nutrients have challenged the role of CR in extending longevity. Fuelling this debate is the difficulty in experimentally disentangling CR and nutrient effects due to compensatory feeding (CF) behaviour. We quantified CF by measuring the volume of solution imbibed and determined how calories and nutrients influenced LS and fecundity in unmated females of the Queensland fruit fly, Bactocera tryoni (Diptera: Tephritidae). We restricted flies to one of 28 diets varying in carbohydrate:protein (C:P) ratios and concentrations. On imbalanced diets, flies overcame dietary dilutions, consuming similar caloric intakes for most dilutions. The response surface for LS revealed that increasing C:P ratio while keeping calories constant extended LS, with the maximum LS along C:P ratio of 21:1. In general, LS was reduced as caloric intake decreased. Lifetime egg production was maximized at a C:P ratio of 3:1. When given a choice of separate sucrose and yeast solutions, each at one of five concentrations (yielding 25 choice treatments), flies regulated their nutrient intake to match C:P ratio of 3:1. Our results (i) demonstrate that CF can overcome dietary dilutions; (ii) reveal difficulties with methods presenting fixed amounts of liquid diet; (iii) illustrate the need to measure intake to account for CF in DR studies and (iv) highlight nutrients rather than CR as a dominant influence on LS.

. Adult diet is an important determinant of sexual activity in many tephritid fruit flies. Whether availability of protein (hydrolysed yeast) in addition to sucrose influences sexual activity or longevity of male and female Queensland fruit flies ( Bactrocera tryoni Froggatt, 'Q-flies'), and whether irradiation of flies as pupae modifies their dietary needs, is investigated. Previous studies on groups of flies suggest that protein is required for sexual maturation of females but not males. By contrast, this study of individual flies demonstrates that protein in the adult diet provides a massive boost to sexual activity of both males and females. Mating probability increases with age from 4-14 days as the flies began to mature. However, mating probability reaches much higher levels when the flies are provided with protein. Although males and females mate at similar rates when provided with protein, females suffer a greater reduction in mating probability than males when deprived of protein.In addition to increased mating probability, access to dietary protein is also associated with reduced latency from onset of dusk until copulation. Furthermore, young male flies with access to dietary protein have longer copula duration than males fed only sucrose. Irradiation of flies as pupae has no apparent effect on mating probability, the latency to copulate or copula duration. However, when deprived of protein, sterile flies (especially males) suffer a greater reduction in longevity compared with fertile flies. Overall, access to dietary protein increases longevity for both males and females, although females live longer than males on both diets. These findings suggest that prerelease provision of dietary protein has the potential to greatly enhance the efficacy of Q-flies used in the sterile insect technique. & Lloyd, 1987;Vijaysegaran et al. , 1997 ). Under laboratory conditions, and in mass-reared cultures, protein is usually provided in the form of hydrolysed yeast ( Monro & Osborn, 1967;. found that although mixed sex groups of Q-flies fed just sucrose and water have very low fecundity, low fertility, and short lifespan, improvements in each of these measures can be achieved through protein-rich supplements of hydrolysed yeast or bacteria cultures. Drew (1987) later reported that, although groups of flies produce fertile offspring regardless of whether the males had received protein, they fail to produce eggs if females are denied protein. KeyThese studies indicate that protein is important for Q-fly populations and that there are sex differences in dependence on protein for production of fertile offspring. However, despite the clear trends in these studies of group fecundity and fertility, the effects of protein on individual mating performance remain to be investigated. Furthermore, there has not been any investigation of whether sterilization of flies for use in SIT has any influence on their protein requirements for mating. The present study builds upon the earlier work of Drew and colleagues by invest...

1 Recent studies have shown that continuous access to a protein source (yeast hydrolysate) can greatly enhance the sexual performance of male Queensland fruit flies ( Bactrocera tryoni ; 'Q-flies'). However, in Sterile Insect Technique programmes used to eradicate or suppress wild populations, mass-reared Q-flies are typically fed only sucrose and water for up to 2 days before release. 2 We investigated whether adding a protein source to the diet of male Q-flies for a 24-or 48-h window after emergence and then removing it is sufficient to enhance mating probability, latency to mate, copula duration, probability of sperm storage, number of sperm stored, female remating tendency and longevity of male Q-flies. 3 Protein-fed males were more likely to mate than males fed only sucrose, especially when young. Protein-fed males also had shorter mating latencies and longer copulations than protein-deprived males. 4 Females mated by protein-fed males were more likely to store sperm, stored more sperm and were less likely to remate than were females mated by proteindeprived males. Females were also less likely to remate if their first mate had been large. 5 Overall, providing male Q-flies access to a protein source for a 24-or 48-h window early on in their adult life was sufficient to greatly enhance all assessed measures of performance. Although 24-h access was sufficient for a notable enhancement, further benefits were evident in males provided 48-h access. 6 The results are discussed in terms of the practical implications for Sterile Insect Technique programs used to eradicate or suppress wild Q-fly populations.

Nutrition is commonly a powerful determinant of sexual performance in insects, and recent studies have found this to be the case in Queensland fruit flies (Tephritidae: Bactrocera tryoni Froggatt; ‘Q‐flies’); male Q‐flies allowed to self‐regulate intake of yeast hydrolysate, a rich source of amino acids and vitamins used in most mass‐rearing programmes (protein) and sucrose (carbohydrate), had greatly enhanced sexual performance compared with males provided only sucrose. While some yeast hydrolysate is clearly beneficial for the sexual performance of adult male Q‐flies, the questions of what proportion of yeast hydrolysate in the diet is sufficient to yield full benefits, or is too much, have not yet been addressed. To address these questions, the present study assessed sexual performance and longevity of adult male Q‐flies maintained on diets containing various proportions of yeast hydrolysate and sucrose. Male Q‐flies maintained as adults on dry mixtures containing 9%, 17% or 25% yeast hydrolysate had mating probability, mating latency, copula duration and longevity similar to those provided yeast hydrolysate and sucrose in separate dishes and allowed to self‐regulate intake. As in previous studies, while longevity was unaffected we found a marked reduction in sexual performance when the flies were completely denied access to yeast hydrolysate, and the few that did mate had relatively short copulations. At the other extreme, flies receiving diets with high levels of yeast hydrolysate (50%, 75%, 83% and 91%) suffered marked reductions both in longevity and in mating performance.

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