Diet quality mediates activity patterns in adult Queensland fruit fly (Bactrocera tryoni)

Effects of Physiological Status and Environmental Factors on the Lure Responses of Three Pest Fruit Fly Species (Diptera: Tephritidae)

Biotic and abiotic factors influence how insects respond to stimuli. This can make it challenging to interpret captures in traps used to monitor pest abundance in management programmes. To address this, the lure response of three pest fruit flies (Diptera: Tephritidae) was evaluated in a semi-field setting with respect to several physiological and environmental factors. Using standardised methods with known fly numbers in field cages, the response to Biolure (food-based lure) was evaluated for Ceratitis capitata, Ceratitis cosyra and Bactrocera dorsalis. Response to the male lures was tested: E.G.O PheroLure for C. capitata and C. cosyra, Trimedlure for C. capitata, and methyl eugenol for B. dorsalis. The physiological variables evaluated were fly age, sex, weight, and total body nutritional composition. The environmental effects of temperature, relative humidity and light intensity were also assessed. Protein-deprived adults responded more strongly to Biolure. The response to Biolure was not sex-specific. Fly age influenced the response of all species to all tested lures. However, this effect was species and lure specific. Temperature was the most influential environmental factor, with response generally increasing with temperature. Lower thresholds for lure response, despite the proximity of responsive flies, range from 12.21 to 22.95 °C depending on the species and lure tested. These results indicate that trapping systems and management activity thresholds must take physiological and environmental variation into account to increase their accuracy.

Daily activity profiles over the lifespan of female medflies as biomarkers of aging and longevity

The relationship between the early-age activity of Mediterranean fruit flies (medflies) or other fruit flies and their lifespan has not been much studied, in contrast to the connections between lifespan and diet, sexual signaling, and reproduction. The objective of this study is to assess intra-day and day-to-day activity profiles of female Mediterranean fruit flies and their role as biomarker of longevity as well as to explore the relationships between these activity profiles, diet, and age-at-death throughout the lifespan. We use advanced statistical methods from functional data analysis (FDA). Three distinct patterns of activity variations in early-age activity profiles can be distinguished. A low-caloric diet is associated with a delayed activity peak, while a high-caloric diet is linked with an earlier activity peak. We find that age-at-death of individual medflies is connected to their activity profiles in early life. An increased risk of mortality is associated with increased activity in early age, as well as with a higher contrast between daytime and nighttime activity. Conversely, medflies are more likely to have a longer lifespan when they are fed a medium-caloric diet and when their daily activity is more evenly distributed across the early-age span and between daytime and nighttime. The before-death activity profile of medflies displays two characteristic before-death patterns, where one pattern is characterized by slowly declining daily activity and the other by a sudden decline in activity that is followed by death.

Electronic recording of lifetime locomotory activity patterns of adult medflies

Age-specific and diurnal patterns of locomotory activity, can be considered as biomarkers of aging in model organisms and vary across the lifetime of individuals. Τhe Mediterranean fruit fly (medfly), Ceratitis capitata, is a commonly used model-species in studies regarding demography and aging. In the present study, we introduce a modification of the automated locomotory activity electronic device LAM25system (Locomotory Activity Monitor)-Trikinetics, commonly used in short time studies, to record the daily locomotory activity patterns of adult medflies throughout the life. Additionally, fecundity rates and survival of adult medflies were recorded. Male and female medflies were kept in the system tubes and had access to an agar-based gel diet, which provided water and nutrients. The locomotory activity was recorded at every minute by three monitors in the electronic device. The locomotory activity of females was higher than that of males across the different ages. For both sexes locomotory rates were high during the first 20 days of the adult life and decreased in older ages. The activity of males was high in the morning and late afternoon hours, while that of females was constantly high throughout the photophase. Negligible locomotory activity was recorded for both sexes during the nighttime. Males outlived females. Fecundity of females was higher in younger ages. Our results support the adoption of LAM25system in studies addressing aging of insects using medfly as a model organism.

Methoprene treatment increases activity, starvation and desiccation risk of Queensland fruit fly

Juvenile hormone is an important regulator of sexual development in insects, and application of methoprene, a juvenile hormone analogue, together with access to a protein-rich diet, has been found to accelerate sexual maturation of several tephritid fruit fly species including Queensland fruit fly Bactrocera tryoni ('Q-fly'). Such accelerated development is a potentially valuable means to increase participation of released males in sterile insect technique programs. However, there is a risk that benefits of accelerated maturation might be countered by increased vulnerability to starvation and desiccation. The present study investigates this possibility. After emergence, flies were treated with three levels of methoprene (0, 0.05%, and 0.5%) incorporated into a diet of sugar and yeast hydrolysate for two days after emergence. Survival of groups and individual flies was assessed under conditions of food stress, food and water stress, and ad libitum access to diet, and survival of individual flies was also assessed under desiccation stress. Most flies provided ad libitum access to diet were still alive at 7 days, whereas all stressed flies died within 4 days. Desiccation stressed flies had the shortest survival followed by food and water stress, and then food stress. Methoprene supplements increased susceptibility of flies to each stress. Flies subjected to food and water stress had the least lipid reserves at death, whereas flies subjected to desiccation stress retained the least water reserves. To investigate mechanisms that might underlie reduced survival under stress; we also quantified activity level of flies that were subjected to food and water stress and desiccation stress. Activity level was greater for flies provided methoprene, but did not vary with stress type or sex, suggesting that increased vulnerability of flies to stress is related to elevated metabolism associated with elevated activity. Deleterious effects of methoprene supplements on stress tolerance indicate a need for careful consideration of the conditions that will be encountered by flies in the field before deploying methoprene as a pre-release treatment in Q-fly sterile insect technique programs.

Light Conditions After Emergence Affect Food Consumption and Survival of Ceratitis capitata (Diptera: Tephritidae) Sterile Males

To favor and standardize fruit fly production, many environmental factors are regulated in a mass-rearing facility. Specifically, in the holding rooms where sterile fruit flies are kept before releasing, they are exposed to constant darkness in order to reduce aggressive interactions and depletion of energy resources. However, such light conditions could negatively affect the quality traits and male mating performance. The objective of this study was to determine whether light conditions have an effect on quality traits in mass-reared 'Mediterranean fruit flies' Ceratitis capitata (Wiedemann) (Diptera: Tephritidae). Under laboratory conditions and in two sequential experiments, we studied the effect of 1) different light intensities and 2) photoperiods, on adult food consumption, adult body weight, survival, and percent of flying and calling males. In the first experiment, sterile male flies were exposed to different light intensities during 3 d after emergence: 1000, 500, or 250 lux, with a 12:12 photoperiod. Complete darkness was used as a control. In the second experiment, adult flies were exposed to the following photoperiods (L(1000 lux)-D): 14-10, 12-12, 8-16, 4-20, and 0-24 as a control. Our results showed that flies under darkness ingested less food, were heavier, and exhibited higher survival than flies under any treatment of light intensity or photoperiod. Furthermore, the percentage of fliers and number of calling males did not differ among treatments. We conclude that holding males for 3 d under darkness do not affect their quality; indeed, emerging under this condition appears to favor them. The implications of these findings for SIT programs are discussed.

Nutritional ecology and foraging theory

Historically, two fields of research have developed theory around foraging and feeding that have influenced biology more broadly, optimal foraging theory and nutritional ecology. While these fields have developed largely in parallel, they are complementary with each offering particular strengths. Here we show how an approach developed in the study of insect nutrition, called nutritional geometry, has provided a framework for incorporating key aspects of optimal foraging theory into nutritional ecology. This synthesis provides a basis for integrating with foraging and feeding the many facets of biology that are linked to nutrition and is now influencing diverse areas of the biological and biomedical sciences.

The odor of a plant metabolite affects life history traits in dietary restricted adult olive flies

Food quality shapes life history traits either directly or through response of individuals to additional environmental factors, such as chemical cues. Plant extracts used as food additives modulate key life history traits; however little is known regarding such effects for olfactory chemical cues. Exploiting an interesting experimental system that involves the olive fly (Bactrocera oleae) and the plant metabolite α-pinene we asked whether exposure of adults to this compound modulates adult longevity and female reproduction in similar manner in a stressful - dietary (protein) restricted (DR) and in a relaxed- full diet (FD) feeding environment. Accordingly, we exposed males and females to the aroma of α-pinene and measured lifespan and age-specific fecundity in the above two dietary contexts. Our results demonstrate that exposure to α-pinene increased longevity in males and fecundity in females only under dietary restricted conditions. In relaxed food conditions, females exposed to α-pinene shifted high egg-laying towards younger ages compared to non-exposed ones. This is the first report demonstrating that a plant compound affects key life history traits of adult olive flies through olfaction. These effects are sex-specific and more pronounced in dietary restricted adults. Possible underlying mechanisms and the ecological significance are discussed.

Diet dependent experience and physiological state shape the behavior of a generalist herbivore

The performance of herbivorous insects depends on a balance of nutrient uptake and toxin avoidance. Whereas high concentrations of defensive plant metabolites impair both generalists and specialists, generalists are likely less adapted to particular hosts and thus more negatively affected by plant defense traits. Furthermore, resulting diet-dependent differences in the physiological state and the gained experience of an animal may shape its behavior. Here, we investigated the effects of life-long experience with leaves of different quality on the performance and various behavioral traits of the generalist leaf beetle Galeruca tanaceti. Rearing individuals continuously on three different diets [young leaves, old leaves, or leaves of different age of cabbage (Brassicaceae) in alternating order every other day], we found that relative growth rates (RGRs) of the larvae were higher when feeding on young leaves than when feeding on the other diets. Feeding on leaves of different age in alternating order reduced the performance of G. tanaceti, indicating costs involved in diet mixing. The experience gained by the respective food qualities shaped the preference behavior in adult beetles. Positive and negative feedbacks of animals reared on young or old leaves, respectively, led to a preference towards young leaves. In contrast, feedback was probably prevented for animals reared on alternating diet, which did not exhibit any preferences. Older adults did not show any diet-dependent differences in body mass due to physiological changes during adult development. A battery of behavioral tests with the older adults revealed that the behavior was consistent over context and partially over time but behaviors did not differ in dependence of the diet experience. We retrieved three personality dimensions for this species, namely boldness, activity, and exploration. The behavioral structure was very similar to earlier findings for another chrysomelid species, indicating a broader validity of the concept of personality dimensions in insects. Our results demonstrate the importance of both experience- and state-dependence when investigating behavioral phenotypes.