Cost of reproduction in the Queensland fruit fly: Y-model versus lethal protein hypothesis

The trade-off between lifespan and reproduction is commonly explained by differential allocation of limited resources. Recent research has shown that the ratio of protein to carbohydrate (P : C) of a fly's diet mediates the lifespan–reproduction trade-off, with higher P : C diets increasing egg production but decreasing lifespan. To test whether this P : C effect is because of changing allocation strategies (Y-model hypothesis) or detrimental effects of protein ingestion on lifespan (lethal protein hypothesis), we measured lifespan and egg production in Queensland fruit flies varying in reproductive status (mated, virgin and sterilized females, virgin males) that were fed one of 18 diets varying in protein and carbohydrate amounts. The Y-model predicts that for sterilized females and for males, which require little protein for reproduction, there will be no effect of P : C ratio on lifespan; the lethal protein hypothesis predicts that the effect of P : C ratio should be similar in all groups. In support of the lethal protein hypothesis, and counter to the Y-model, the P : C ratio of the ingested diets had similar effects for all groups. We conclude that the trade-off between lifespan and reproduction is mediated by the detrimental side-effects of protein ingestion on lifespan.

Nutrients, not caloric restriction, extend lifespan in Queensland fruit flies (Bactrocera tryoni)

Caloric 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.

A review of 16 years of quality control parameters at a mass-rearing facility producing Queensland fruit fly, Bactrocera tryoni

From 1996 to 2012, the mass-rearing facility at Camden (NSW, Australia) has been producing Queensland fruit flies, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae). During this time, the facility has regularly recorded fly quality parameters, creating a unique data set that provides an invaluable opportunity to evaluate the interrelationships among standard quality control (QC) parameters and test for redundant QC variables. Here, we conducted an exploratory data analysis to reveal relationships among the QC parameters. We found that pupal weight, adult lifespan, and longevity under nutritional stress (i.e., survival duration without food or water) had distinct monthly trends, suggesting that these QC parameters are sensitive to seasonal conditions. Furthermore, emergence percentage, flight ability, and adult lifespan were adversely affected by the dyeing/handling/irradiation process associated with sterile insect releases. Using a multivariate approach and controlling for monthly and yearly patterns, we showed that pupal weight and egg hatch are consistently negatively related and that percentage male and emergence rates are consistently negatively related. These results suggest that these correlation pairs measure similar quality information and hence one QC variable from each pair could be dropped. Flight ability was not strongly correlated with any of the QC variables, suggesting that this QC variable remains a useful QC metric. Finally, the longevity under nutritional stress QC appears to be fairly insensitive to QCs and we suggest that it should be replaced by the standard mortality under stress test.

Longitudinal predictors of frequent vegetable and fruit consumption among socio-economically disadvantaged Australian adolescents

Adequate vegetable and fruit consumption is necessary for preventing nutrition-related diseases. Socio-economically disadvantaged adolescents tend to consume relatively few vegetables and fruits. However, despite nutritional challenges associated with socio-economic disadvantage, a minority of adolescents manage to eat vegetables and fruit in quantities that are more in line with dietary recommendations. This investigation aimed to identify predictors of more frequent intakes of fruits and vegetables among adolescents over a 2-year follow-up period. Data were drawn from 521 socio-economically disadvantaged (maternal education ≤Year 10 of secondary school) Australian adolescents aged 12–15 years. Participants were recruited from 37 secondary schools and were asked to complete online surveys in 2004/2005 (baseline) and 2006/2007 (follow-up). Surveys comprised a 38-item FFQ and questions based on Social Ecological models examining intrapersonal, social and environmental influences on diet. At baseline and follow-up, respectively, 29% and 24% of adolescents frequently consumed vegetables (≥2 times/day); 33% and 36% frequently consumed fruit (≥1 time/day). In multivariable logistic regressions, baseline consumption strongly predicted consumption at follow-up. Frequently being served vegetables at dinner predicted frequent vegetable consumption. Female sex, rarely purchasing food or drink from school vending machines, and usually being expected to eat all foods served predicted frequent fruit consumption. Findings suggest nutrition promotion initiatives aimed at improving eating behaviours among this at-risk population and should focus on younger adolescents, particularly boys; improving adolescent eating behaviours at school; and encouraging families to increase home availability of healthy foods and to implement meal time rules.

When nutritional guidelines and life collide: family fruit and vegetable socialisation practices in low socioeconomic communities

Parents play a critical role in promoting fruit and vegetable consumption, for eating patterns established early in life tend to persist into adulthood. Despite this, the factors that facilitate or inhibit parents’ capacity to socialise fruit and vegetable consumption into their children’s daily diets remain poorly defined. Thirty-eight semi-structured interviews with residents, allied healthcare professionals, community leaders, community programme leaders and a local government leader living or working in two low socioeconomic suburbs were consequently conducted to ascertain factors exogenous and endogenous to the family unit that shaped parental food socialisation practices. Budgetary and time constraints emerged as exogenous factors that constrained fruit and vegetable socialisation. Constraining effects were also found for a range of endogenous factors, including commensal experiences, children’s food fussiness and the feeding styles employed by parents. As such, while many caregivers may wish to socialise fruit and vegetable consumption into their children’s daily diets, their capacity to do so is often inhibited by factors beyond their volitional control. Failure to take heed of these factors could therefore result in the development of social marketing campaigns that are ineffective at best or give rise to unintentionally harmful outcomes at worst.

Factors affecting acceptability of an email-based intervention to increase fruit and vegetable consumption

 Background: Fresh Facts is a 30-day email-delivered intervention designed to increase the fruit and vegetable consumption of Australian young adults. This study investigated the extent to which the program was acceptable to members of the target audience and examined the relationships between participant and intervention characteristics, attrition, effectiveness, and acceptability ratings. Methods: Young adults were randomised to two levels of message frequency: high-frequency (n = 102), low-frequency (n = 173). Individuals in the high-frequency group received daily emails while individuals in the low-frequency group received an email every 3 days. Results: Individuals in the high-frequency group were more likely to indicate that they received too many emails than individuals in the low-frequency group. No other differences in acceptability were observed. Baseline beliefs about fruit and vegetables were an important predictor of intervention acceptability. In turn, acceptability was associated with a number of indicators of intervention success, including change in fruit and vegetable consumption. Conclusions: The findings highlight the importance of considering the relationship between these intervention and participant factors and acceptability in intervention design and evaluation. Results support the ongoing use of email-based interventions to target fruit and vegetable consumption within young adults. However, the relationships between beliefs about fruit and vegetable consumption and acceptability suggest that this intervention may be differentially effective depending on individual's existing beliefs about fruit and vegetable consumption. As such, there is a pressing need to consider these factors in future research in order to minimize attrition and maximize intervention effectiveness when interventions are implemented outside of a research context.

Randomized controlled trial of a telephone-based intervention for child fruit and vegetable intake: long-term follow-up

Telephone-based interventions can be effective in increasing child fruit and vegetable intake in the short term (<6 mo). The long-term efficacy of such interventions, however, is unknown.