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BACKGROUND The sterile insect technique (SIT) is used in Australia to contain and eradicate outbreaks of Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) in fruit-fly-free regions, and to manage populations in some endemic regions. To assess the likely impact of SIT on wild B. tryoni populations it is important to assess the colocation and synchrony of male calling between sterile and wild flies. We observed the location and timing of calling behaviours of marked mass-reared (fertile and sterile) and wild B. tryoni males in walk-in field cages. RESULTS We found that wild males called further from the canopy centre than mass-reared (fertile or sterile) males. Mass-reared (fertile or sterile) males called earlier in the evening than wild males and, consequently, mass-reared males called when temperature and light intensity were higher than when wild males called. CONCLUSION Male calling is a prerequisite to mating among dacine fruit flies. Therefore, our observations of spatio-temporal divergence in male calling behaviour may lead to assortative mating between mass-reared and wild B. tryoni in SIT applications. The importance of these spatio-temporal differences warrants further inquiry, with particular focus on how environmental conditions modify calling behaviour and avenues to ameliorate differences between sterile and wild flies. © 2021 Society of Chemical Industry.

Citrus Research International; Hortgro Science; South African Table Grape Industry and National Research Foundation.

Insects tend to live within well-defined habitats, and at smaller scales can have distinct microhabitat preferences. These preferences are important, but often overlooked, in applications of the sterile insect technique. Different microhabitat preferences of sterile and wild insects may reflect differences in environmental tolerance and may lead to spatial separation in the field, both of which may reduce the control program efficiency. In this study, we compared the diurnal microhabitat distributions of mass-reared (fertile and sterile) and wild Queensland fruit flies, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae). Flies were individually tagged and released into field cages containing citrus trees. We recorded their locations in the canopies (height from ground, distance from canopy center), behavior (resting, grooming, walking, feeding), and the abiotic conditions on occupied leaves (temperature, humidity, light intensity) throughout the day. Flies from all groups moved lower in the canopy when temperature and light intensity were high, and humidity was low; lower canopy regions provided shelter from these conditions. Fertile and sterile mass-reared flies of both sexes were generally lower in the canopies than wild flies. Flies generally fed from the top sides of leaves that were lower in the canopy, suggesting food sources in these locations. Our observations suggest that mass-reared and wild B. tryoni occupy different locations in tree canopies, which could indicate different tolerances to environmental extremes and may result in spatial separation of sterile and wild flies when assessed at a landscape scale.

The oxidative damage caused to cells by reactive oxygen species (ROS) is one of several factors implicated in causing ageing. Oxidative damage may also be a proximate cost of reproductive effort that mediates the trade-off often observed between reproduction and survival. However, how the balance between oxidative damage and antioxidant protection affects life-history strategies is not fully understood. To improve our understanding, we selected on female reproductive age in the marula fruit fly, Ceratitis cosyra, and quantified the impact of selection on female and male age-dependent mortality, female fecundity, male sperm transfer, calling and mating. Against expectations, upward-selected lines lived shorter lives and experienced some reductions in reproductive performance. Selection affected oxidative damage to lipids and total antioxidant protection, but not in the direction predicted; longer lives were associated with elevated oxidative damage, arguing against the idea that accumulated oxidative damage reduces lifespan. Greater reproductive effort was also associated with elevated oxidative damage, suggesting that oxidative damage may be a cost of reproduction, although one that did not affect survival. Our results add to a body of data showing that the relationship between lifespan, reproduction and oxidative damage is more complex than predicted by existing theories.

In herbivorous insects, the degree of host specialisation may be one ecological factor that shapes lifespan. Because host specialists can only exploit a limited number of plants, their lifecycle should be synchronised with host phenology to allow reproduction when suitable hosts are available. For species not undergoing diapause or dormancy, one strategy to achieve this could be evolving long lifespans. From a physiological perspective, oxidative stress could explain how lifespan is related to degree of host specialisation. Oxidative stress caused by Reactive Oxygen Species (ROS) might help underpin ageing (the Free Radical Theory of Aging (FRTA)) and mediate differences in lifespan. Here, we investigated how lifespan is shaped by the degree of host specialisation, phylogeny, oxidative damage accumulation and antioxidant protection in eight species of true fruit flies (Diptera: Tephritidae). We found that lifespan was not constrained by species relatedness or oxidative damage (arguing against the FRTA); nevertheless, average lifespan was positively associated with antioxidant protection. There was no lifespan difference between generalist and specialist species, but most of the tephritids studied had long lifespans in comparison with other dipterans. Long lifespan may be a trait under selection in fruit-feeding insects that do not use diapause.

Markets importing citrus fruit including lemons, Citrus limon (L.) Burman f., from South Africa require that the fruit be free of fruit fly pests (Diptera: Tephritidae). Historically there has been no fruit fly infestation recorded on lemons destined for export from South Africa. In this study, we assessed the host status of commercial export grade Eureka lemons, Citrus limon (L.) Burmanf. cv. Eureka, for four fruit fly pest species of economic importance in South Africa: Ceratitis capitata (Wiedemann), Ceratitis rosa Karsch, Ceratitis quilicii De Meyer, Mwatawala & Virgilio, and Bactrocera dorsalis (Hendel). Trapping was conducted in 10 Eureka lemon orchards in two major citrus production regions over two citrus seasons between 2016 and 2017 to determine the level of fruit fly abundance in the sampled orchards. Lemons were collected at harvest over the two seasons in the same orchards where trapping was conducted. Fruit fly infestation of the sampled lemons was determined by dissection. Additionally, infestation of lemons was determined under forced exposure to mature mated females of C. capitata and B. dorsalis. Trapping data showed the presence of adults of all four fruit fly species in the sampled lemon orchards. No fruit fly infestation was detected in 43 222 Eureka lemons sampled at harvest. There was also no infestation of lemons under forced exposure conditions. The results of this study provide evidence with 99.99 % efficacy and a 99%confidence level that SouthAfrican commercial export grade Eureka lemon fruit is not a host for C. capitata, C. rosa, C. quilicii or B. dorsalis.

The highly invasive oriental fruit fly, Bactrocera dorsalis (Hendel), has been declared present in the northern parts of South Africa since 2013. A study was thus initiated in July 2014 to determine the host range and field population of the pest species in the region. Fruit were collected from commercial fruit production, interface (smaller commercial blocks surrounded by natural savannah vegetation) and natural areas (savannah vegetation) throughout Limpopo and Mpumalanga provinces, South Africa. Field sites consisted of five commercial fruit production sites, two interface sites and two natural areas. Fruit samples from the tree and the ground were collected and incubated separately to determine infesting fruit fly species and the degree of infestation. Adult B. dorsalis populations were monitored at each field site using three methyl eugenol-baited bucket traps to estimate population pressure and to determine with the use of time series analysis if monthly trap captures were correlated with fruit infestation. Bactrocera dorsalis was reared from seven plant species: two from commercial orchards (Mangifera indica cv. [Tommy Atkins, Sensation], Citrus sinensis cv. [Valencia]), and five from other plant species (Psidium guajava, Anacardium occidentale, Solanum mauritianum, Xylotheca kraussiana, Vangueria infausta). Fruit utilized by B. dorsalis was also infested or damaged by other species, which may indicate opportunism by the pest, and the potential for competitive interactions. Time series analyses show adult population increased 2 months after an increase in mean temperature in all sites, 4 months after rainfall in natural and interface sites, and 1 month and 3 months after fruit infestation in commercial and natural and interface sites, respectively. This study shows B. dorsalis utilizing a limited range of hosts in South Africa. However, the host range of B. dorsalis may expand as it may not yet have encountered all potential hosts.

Daylight fluorescent pigment powders are frequently used to self-mark tephritid flies that are released in sterile insect technique programmes and for studies on their population ecology, movement and behaviour. This study was conducted to determine the effects of pigment colour and dose in marking the Oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae). Six pigment colours (Astral Pink 1, Blaze 5, Stellar Green 8, Lunar Yellow 27, Comet Blue 60 and Invisible Blue 70) were applied to pupae at doses of 0, 2, 4, or 6 g/l. Under laboratory conditions, pigment colour had a small but significant effect on the number of partially emerged and deformed adults; the fewest of these were observed when flies were marked with Astral Pink 1. Pigment concentration, on the other hand, had no effect on adult emergence, partial emergence, deformed adults and mortality on the last day of eclosion. There was no significant effect of pigment colour on adult survival under laboratory and semi-field conditions. Under laboratory conditions, however, there was an effect of pigment concentration on adult survival depending on pigment colour. Visibility under an ultraviolet light and persistence of marks was significantly affected by pigment colour and concentration when observed under laboratory conditions, but not under semi-field conditions. Regardless of colour or dose, pigments used in the study were visible for at least 14 days, but began to fade by 21 days after adult eclosion. To mark B. dorsalis under temperate, warmsummer African conditions, all pigment colours tested in this study may be applied at 2–4 g/l pupae. Recaptures of marked and released flies may be underestimated as the flies age.

The five-spotted fruit fly, Ceratitis quinaria (Bezzi) (Diptera: Tephritidae), is distributed in parts of eastern and western Africa, northern Africa and southern Africa (including South Africa). The species also occurs outside of Africa, in Yemen. The host range of C. quinaria is narrow, with Mangifera indica L. being the main host of commercial importance. Ceratitis quinaria was claimed to be associated with citrus in Sudan although this claim was never substantiated and there has never been any confirmed reared record of C. quinaria on citrus despite numerous surveys of citrus across Africa. In order to verify the type of association that C. quinaria has with citrus, field surveys were carried out in South Africa to determine the distribution and seasonal occurrence of C. quinaria in commercial citrus orchards and the possible natural infestation of citrus by this species. Surveys on distribution of C. quinaria across South Africa were carried out in 1999 and 2000 by trapping with Ceratitislure (containing protein hydrolysate and β-caryophyllene). The seasonal occurrence of C. quinaria in the northern areas of South Africa was determined over two years between 2015 and 2017 by trapping with Enriched Ginger Oil (EGO), a male lure containing α-copaene. In the same trapping period, citrus and other fruit were sampled to determine infestation by C. quinaria. Additionally between 2009 and 2018, citrus fruit was sampled from the trees and ground in other commercial and non-commercial areas in the north of South Africa. All fruit samples collected were incubated for at least five weeks to allow rearing of flies to the pupal and adult stages. Trapping surveys conducted between 1999 and 2000 showed the presence of C. quinaria only in the northern areas of South Africa. Catches of C. quinaria males in EGO-baited traps were low in commercial citrus orchards (peak of catches being lower than 0.05 flies/trap/day). Catches of C. quinaria were mainly recorded outside of the citrus ripening period. No C. quinaria was reared from any of the citrus fruit sampled, even in those areas where the presence of the species was demonstrated by catches in EGO-baited traps. The fruit surveys therefore demonstrated the absence of natural infestation of citrus with C. quinaria in South Africa and supported existing biological information that citrus is not a host for C. quinaria.

In pest management programmes that incorporate the sterile insect technique (SIT), the ability of mass-reared insects to tolerate dry conditions may influence their survival after release in the field. In the present study, desiccation resistance of adult mass-reared Queensland fruit flies,Bactrocera tryoni(Frogatt) (Diptera: Tephritidae), that are routinely released in SIT programmes was compared with that of wild flies at 1, 10 and 20 days after adult eclosion. Under dry conditions without access to food or water, longevity of mass-rearedB. tryoniwas significantly less than that of their wild counterparts. Desiccation resistance of mass-reared flies declined monotonically with age, but this was not the case for wild flies. The sharp decline in desiccation resistance of mass-reared flies as they aged was likely explained by decreased dehydration tolerance. As in an earlier study, desiccation resistance of females was significantly lower than that of males but this was particularly pronounced in mass-reared females. Female susceptibility to dry conditions corresponded with declining dehydration tolerance with age and associated patterns of reproductive development, which suggests that water content of their oocyte load is not available for survival during periods of water stress.

Acclimation in the thermal tolerance range of insects occurs when they are exposed to novel temperatures in the laboratory. In contrast to the large number of studies that have tested for the ability of insects to acclimate, relatively few have sought to determine the time-course for attainment and reversal of thermal acclimation. In this study the time required for the Mediterranean fruit fly, Ceratitis capitata Wiedemann, and the Natal fruit fly, Ceratitis rosa Karsch, to acclimate to a range of constant temperatures was tested by determining the chill-coma recovery time and heat knock-down time of flies that had been exposed to novel benign temperatures for different durations. The time required for reversal of acclimation for both Ceratitis species was also determined after flies had been returned to the control temperature. Acclimation to 31 °C for only one day significantly improved the heat knock-down time of C. capitata, but also led to slower recovery from chill-coma. Heat knock-down time indicated that acclimation was achieved after only one day in C. rosa, but it took three days for C. rosa to exhibit a significant acclimation response to a novel temperature of 33 °C when measured using chill-coma recovery time. Reversal of acclimation after return to initial temperature conditions was achieved after only one day in both C. capitata and C. rosa. Adult C. capitata held at 31.5 °C initially exhibited improved heat knock-down times but after 9 days the heat knock-down time of these flies had declined to levels not significantly different from that of control flies held at the baseline temperature of 24 °C. In both Ceratitis species, heat knock-down time declined with age whereas chill-coma recovery time increased with age, indicating an increased susceptibility to high and low temperatures, respectively.

Post-teneral dietary supplements have been found to improve mating performance of male Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) (Q-fly) and show considerable promise for enhancement of sterile insect technique (SIT) programmes even when applied within the current 48 h pre-release holding period. However, Q-flies are released as a bisexual strain, and the positive effects of a diet including yeast hydrolysate for males may also boost reproductive development and sexual performance of females. Increased prevalence of mature sterile females can substantially dilute SIT efficacy as mating capacity of sterile males is largely depleted by sterile females rather than the relatively rare wild females. Here, we demonstrate that providing yeast hydrolysate for 48 h after adult emergence, emulating the current pre-release holding period of Q-fly SIT, leads to a significant increase in reproductive development and sexual performance in male Q-flies. In contrast, female Q-flies with access to yeast hydrolysate for 48 h had ovaries that were poorly developed and, particularly at younger ages, were less likely to mate and remate than females with continuous, ad libitum access to yeast hydrolysate. Our findings suggest that addition of yeast hydrolysate into the pre-release diet of Q-flies could be a cost-effective means of releasing a bisexual strain with competitive males but with sexually immature females, thereby rendering it operationally more similar to a unisexual strain.

Diet has a profound influence on the fitness of adult tephritid flies. Mass-reared flies are provided yeast hydrolysate as a rich source of nutrition that supports rapid sexual development and mating success. In contrast, wild tephritid flies often live in environments where food may be hard to find, and these are the conditions that sexually immature mass-reared sterile males encounter when released into the field during sterile insect technique campaigns. The effect of natural food sources (bat guano, bird droppings, citrus pollen, and wheat pollen) on the sexual development of adult mass-reared fertile, mass-reared sterile, and wild male Queensland fruit flies, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), was determined by measuring ejaculatory apodeme size. Inclusion of yeast hydrolysate in the adult diet was associated with faster growth of the ejaculatory apodeme in comparison with all other diets. Effects of diet were far less pronounced in mass-reared males, which may indicate reduced nutritional requirements, whereas the ejaculatory apodeme of wild males fed on natural sources of food or sucrose alone did not increase in size over the first 20 days of adult life.

Desiccation resistance is important for the survival of adult insects, although this key physiological trait has rarely been studied in tephritid flies. In the present study, desiccation resistance of female and male adult Queensland fruit flies Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) is determined with respect to age after adult eclosion. Resistance to acute starvation is measured over the same period to disentangle the competing roles of water loss and food deprivation. Survival of adult B. tryoni subjected to conditions of low humidity and starvation is reduced considerably compared with adults that are subjected to starvation alone. Desiccation resistance of adult female B. tryoni is generally lower than that of adult males. Desiccation resistance of adult B. tryoni declines in a continuous and regular manner over the first 20 days after adult eclosion. The regular pattern of declining resistance to desiccation with age in B. tryoni indicates that this reduction is not associated with the onset of maturity and maintenance of reproductive structures, nor with sexual activity. By contrast, resistance to starvation is similar at 0 and 6 days after adult eclosion, and declines thereafter. Survival under starvation and water stress is not related to wing length, which is a standard measure of fly size.

The distribution, systematics and ecology of Bactrocera tryoni, the Queensland fruit fly, are reviewed. Bactrocera tryoni is a member of the B. tryoni complex of species, which currently includes four named species, viz. B. tryoni ssp., B. neohumeralis, B. melas and B. aquilonis. The species status of B. melas and B. aquilonis is unclear (they may be junior synonyms of B. tryoni) and their validity, or otherwise, needs to be confirmed as a matter of urgency. While Queensland fruit fly is regarded as a tropical species, it cannot be assumed that its distribution will spread further south under climate change scenarios. Increasing aridity and hot dry summers, as well as more complex, indirect interactions resulting from elevated CO2, make predicting the future distribution and abundance of B. tryoni difficult. The ecology of B. tryoni is reviewed with respect to current control approaches (with the exception of sterile insect technique (SIT) which is covered in a companion paper). We conclude that there are major gaps in the knowledge required to implement most noninsecticide-based management approaches. Priority areas for future research include host–plant interactions, protein and cue-lure foraging and use, spatial dynamics, development of new monitoring tools, investigating the use of natural enemies and better integration of fruit flies into general horticultural IPM systems.

Mass-reared sterile tephritid flies released in sterile insect technique (SIT) programmes exhibit behaviour, physiology and longevity that often differ from their wild counterparts. In the present study, video recordings of flies in laboratory cages are used to determine whether the sequential processes of mass-rearing and sterilization (using gamma radiation) that are integral to SIT affect general activity patterns of male and female Queensland fruit flies Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) (‘Q-flies'). Compared with wild flies, mass-reared flies exhibit a marked reduction in overall activity, and further reduction is found after sterilization. In terms of the frequency of activities, both fertile and sterile mass-reared Q-flies fly less often and exhibit more bouts of inactivity and grooming than wild Q-flies. In addition, in terms of the duration of activities, fertile and sterile mass-reared Q-flies spend less time flying and more time walking, grooming and being inactive than wild Q-flies. Although fertile and sterile mass-reared flies are similar in other regards, sterile mass-reared flies spend more time being inactive than fertile mass-reared flies. These findings raise new questions about how changes in behaviour and activity levels may influence the performance of mass-reared sterile Q-flies in the field, as well as the physiological and metabolic processes that are involved. The frequency and duration of inactivity could provide a simple but powerful and biologically relevant test for quality in mass-rearing and SIT programs.

Queensland fruit flies, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) (‘Q-flies’) were released as sexually immature adults from a point within an orchard. Marked male Q-flies were recaptured in the trap furthest from the release point (1087 m) by 2 weeks after release, although 98.25 ± 1.04% of recaptured males were trapped

Male insects that are unable to replenish sperm supplies between matings can suffer fitness costs either because their mates are more likely to accept subsequent suitors, or because their sperm are outnumbered when females do remate. We assessed the ability of fertile and sterile (irradiated) male Queensland fruit flies, Bactrocera tryoni (‘Q-flies’), to have sperm stored by five sequential mates as well as the association between sperm depletion and female remating tendency. Sequential mates of fertile males stored similar numbers of sperm, indicating ample ability to replenish and maintain constant supplies between their once-daily mating opportunities. In contrast, sequential mates of sterile males stored progressively fewer sperm, with only trivial numbers of sperm stored by females mated by sterile males that had mated with two or more females previously. Despite the massive reduction in sperm storage by sequential mates of sterile males, fertile and sterile males were similar in their ability to induce sexual inhibition in their mates (to at least 30 days) and neither showed any decline in this ability across sequential matings. The ability of multiple-mated sterile males to induce sexual inhibition in their mates despite near or complete absence of sperm provides compelling evidence that sperm abundance plays no role in the induction of sexual inhibition in this species.

The current study is an important step toward calibrating, validating, and improving irradiation methods used for Bactrocera tryoni (Froggatt) sterile insect technique (SIT). We used routine International Atomic Energy Agency/U.S. Department of Agriculture/Food and Agriculture Organization quality control tests assessing percentage of emergence, flight ability, sex ratio, mortality under stress, reproductive sterility, and sexual competitiveness, as well as a nonstandard test of longevity under nutritional stress to assess the impact of a range of target irradiation doses (60, 65, 70, 75, and 80 Gy) on the product quality of mass reared B. tryoni used in SIT. Sterility induction remained adequate (>99.5%) for sterile male-fertile female crosses, and 100% sterility was achieved in fertile male-sterile female crosses and sterile male-sterile female crosses for each irradiation doses tested. There was significant increase in mortality under stress as irradiation dose increased, and reduced participation in mating by males irradiated at higher doses. The current target-sterilizing dose for SIT of 70-75 Gy is associated with significant reduction in fly product "quality". Our data suggest that adequate sterility and improved fly quality could be achieved through a small reduction in target sterilizing dose.

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.

Recent laboratory studies of mass-reared flies in small cages have found that periods of just 24- or 48-h access to yeast hydrolysate can substantially enhance mating performance of mass-reared male Queensland fruit flies, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) ('Q-flies'). Using field cage tests that provide a better approximation of nature, we here investigated whether access to yeast hydrolysate for 48 h after adult emergence improves the ability of male and female mass-reared, sterile Q-flies to compete sexually with wild-type flies that had been provided continuous access to yeast hydrolysate. Mating probability of sterile males was significantly increased by 48-h access to yeast hydrolysate; sterile males provided 48-h access to yeast hydrolysate had mating probability similar to that of wild males provided continuous access to yeast hydrolysate, whereas sterile males deprived of access to yeast hydrolysate had much lower mating probability. Unlike males, access to yeast hydrolysate for 48 h did not increase mating probability of sterile female Q-flies. We instead found that wild females provided continuous access to yeast hydrolysate had higher mating probability than sterile females that did or did not have 48-h access to yeast hydrolysate. This result raises the possibility that a bisexual Q-fly strain might operate essentially as a male-only release when the flies are given access to yeast hydrolysate during a 48-h pre-release holding period. Sterile males given access to yeast hydrolysate for 48 h mated significantly earlier in the evening than wild males and, as in other recent studies, this tendency was associated with an increased tendency to mate on the trees rather than the cage walls. There was no evidence of sexual isolation in this study, as wild and sterile mass-reared flies showed no evidence of preferential mating with their own kind. Further studies are now needed to assess the potential for pre-release access to yeast hydrolysate to improve sexual performance and longevity of sterile, mass-reared, Q-flies in the field.

Feeding on yeast hydrolysate (a source of nitrogen) has a strong influence on the physiology and behaviour of the Queensland fruit fly (Q-fly), Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), affecting longevity, sexual maturation, oogenesis, and mating performance. In this study, we demonstrate that access to yeast hydrolysate also influences the development of attraction to cue-lure in Q-flies. We provided virgin Q-flies various periods of access to yeast hydrolysate (continuous, 48 h, 24 h, or deprived). Attraction of males to cue-lure was increased and occurred at an earlier age when they were fed yeast hydrolysate. Males given continuous access were strongly attracted to cue-lure at a younger age (8 days after emergence), but by 12 days after emergence attraction of males given access to yeast hydrolysate for 48 h did not differ from males given continuous access. Attraction by males deprived or given just 24 h access to yeast hydrolysate was always significantly lower than those of males with continuous access. Male attraction to cue-lure was highest in the early morning. While cue-lure is most often thought of as a male attractant, virgin female Q-flies were caught in cue-lure traps at dusk at ages when they are known to be sexually mature. We suggest that cue-lure or similar natural chemicals play a role in the Q-fly mating system. γ-Irradiation used to induce sterility had no significant effect on attraction to cue-lure by Q-flies.

The mating performance field cage test is a required periodic quality-control assessment for factory-reared fruit flies used for the sterile insect technique. The FAO/IAEA/USDA guidelines for assessing fly quality state that if during tests a large proportion of flies call and mate on cage walls, away from host trees, then environmental conditions within the cage need to be adjusted and tests repeated. Here we test effects of cage design, specifically mesh colour (green, white) and addition of supplementary shade, on the mating behaviour of Queensland fruit fly (Q-fly), Bactrocera tryoni Froggatt (Diptera: Tephritidae). Observations were made over a 4-h period at dusk when these flies mate. Changes in environmental conditions in each cage over the dusk period varied with cage design. We recorded the highest proportion of matings taking place on trees as opposed to cage walls (>90%) in the unshaded white cage, the shaded white and un-shaded green cages being intermediate (ca. 70%), and the shaded green cage had the least (ca. 40%). The effects of field cage colour and supplementary shade on mating behaviour are discussed. We recommend that Q-fly field cage tests should be conducted in cages with a light coloured mesh, and that supplementary shading should only be applied if there is a need to adjust temperature and light within the cage.

Queensland fruit fly (Bactrocera tryoni; Q-fly) pupae are routinely irradiated to induce reproductive sterility in adults released in a sterile insect technique programme. Although there have been some studies of how total dose influences fly quality, dose rate has not been considered. In the present study, pupae were irradiated at a target dose range of 70‐75 Gy at dose rates of approximately 5, 7, 26, 57 and 80 Gy/min and were then subjected to routine IAEA/FAO/USDA quality control tests including emergence, flight ability, mortality under stress and sterility induction. No significant effects of dose rate were found on emergence or flight ability. Sterility induction was also found to be independent of dose rate, a result conforming to a ‘one-hit’ ionizing event hypothesis. Flies irradiated at higher dose rates suffered increased mortality under stress. This appears to stem from an increased tendency to over-shoot the target dose when irradiating at high dose rates. We recommend that, to reduce potential error in total target dose, the lowest practical dose rate be used when irradiating Q-fly pupae for use in the sterile insect technique. J. Appl. Entomol.

Dispersal of immature male and female Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), was assessed over a period of 1 week from a single release point on three separate occasions using an array of Lynfield traps baited with cue-lure and odouriferous yellow or black sticky spheres baited with food lure (protein autolysate). Lynfield traps recaptured males; yellow or black spheres recaptured both sexes in approximately equal proportions, although at a much lower rate. As a percentage of the recapture rate for males by Lynfield traps, the mean recapture rate for yellow spheres ranged from 1.0% to 7.5% for males and 0.7% to 4.0% for females, whereas the recapture rates for black spheres ranged from 0.4% to 3.6% and 0.6% to 1.8%, respectively. The rate of recapture of sterile male flies was greater than that of unsterilised flies; this may have been due to a faster maturation rate in sterile males or because a greater proportion of them remained within the trap array rather than dispersing. There was no significant trend in recapture rate with distance from the release point to the edge of the array (88 m), except in the case of females on sticky traps where no trend was detected between 19 and 88 m. These results lend support to assumptions made about the distribution of males and females with respect to the minimum breeding density of fruit fly propagules invading a fly-free zone, and the method chosen to distribute sterile B. tryoni for the sterile insect technique.

The importance of male aggregation size for female visitation and initiation of male pheromone-calling was investigated in Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) using artificial male aggregations in large laboratory cages. Female B. tryoni visited the largest aggregation more frequently than single males in association with a higher proportion of calling males, but there was no correlation between aggregation size and female visitation. Female B. tryoni had a limited capacity to perceive a difference between the number of calling males. Calling propensity of male B. tryoni was increased by the presence of conspecific males. Increased calling propensity in larger groups of male B. tryoni may be due to social facilitation of male calling behaviour. Female visitation at aggregations was only weakly associated with male calling, suggesting that aggregation size and the number of pheromone-calling males are not the only factors important in locating mates in B. tryoni, and it is possible that low-density populations could persist so long as females can encounter single males.

Background The Mediterranean fruit fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae) is a highly invasive species now with an almost cosmopolitan distribution. Two other damaging, polyphagous and closely-related species, the marula fruit fly, Ceratitis cosyra (Walker), and the Natal fly, Ceratitis rosa Karsch, are not established outside of sub-Saharan Africa. In this study, adult water balance traits and nutritional body composition were measured in all three species at different temperatures and levels of relative humidity to determine whether tolerance of water stress may partially explain their distribution. Results Adult C. capitata exhibited higher desiccation resistance than C. rosa but not C. cosyra. Desiccation resistance of C. capitata was associated with lower rates of water loss under hot and dry conditions, higher dehydration tolerance, and higher lipid reserves that were catabolised during water stress. In comparison with C. capitata, C. cosyra and C. rosa lost water at significantly higher rates under hot, dry conditions, and did not catabolise lipids or other sources of metabolic water during water stress. Conclusions These results suggest that adult physiological traits permitting higher tolerance of water stress play a role in the success of C. capitata, particularly relative to C. rosa. The distribution of C. cosyra is likely determined by the interaction of temperature with water stress, as well as the availability of suitable hosts for larval development. Electronic supplementary material The online version of this article (doi:10.1186/s12983-016-0147-z) contains supplementary material, which is available to authorized users.

The effects of domestication and irradiation on the mating behaviour of males of Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) were investigated by caging wild, laboratory-domesticated and sterile (laboratory-domesticated, gamma-irradiated) males with wild females. Mating behaviour of mass-reared males was different from that of wild males, although behaviour of wild and sterile males was similar. Mass-reared males engaged in mounting of other males much more frequently than wild and sterile males, and began calling significantly earlier before darkness. Unnatural selection pressures imposed in mass-rearing conditions may explain these changes in mass-reared male behaviour. Male calling did not appear to be associated with female choice of mating partners, although this does not exclude the possibility that calling is a cue used by females to discriminate among mating partners. Despite differences in behaviour, frequency of successful copulations and mating success were similar among wild, mass-reared and sterile males.

Copula duration and sperm storage patterns can directly or indirectly affect fitness of male and female insects. Although both sexes have an interest in the outcome, research has tended to focus on males. To investigate female influences, we compared copula duration and sperm storage of Queensland fruit fly females that were intact, or had been incapacitated through decapitation or abdomen isolation. We found that copulations were far longer when females had been incapacitated, indicating that constraints imposed on copula duration by intact females had been relaxed. Repeatability of copula duration for males was very low regardless of female treatment, and this is also consistent with strong female influence. Number of sperm in the spermathecae was not influenced by female treatment, suggesting that female abdominal ganglia control the transport of sperm to these long-term storage organs. However, more sperm were found in the ventral receptacles of incapacitated females compared to intact females. Overall, results implicate cephalic ganglia in regulation of copula duration and short-term sperm storage in the ventral receptacle and abdominal ganglia in regulation of long-term sperm storage in the spermathecae.