Queensland Fruit Fly Bactrocera Tryoni Research Articles

An analysis of fruit carried into a quarantine area and an evaluation of infestation rate by Queensland fruit fly Bactrocera tryoni (Froggatt) (Diptera: Tephritidae)

The risk of new establishments of Queensland fruit fly (Qfly), Bactrocera tryoni, in pest-free areas is linked to the fruit carried by road travellers. However, there is little information on what proportion of carried fruit is infested. Previous studies examined the numbers of fruits carried by travellers but not if the fruits were infested. Here, we report on the results of 989 fruit consignments seized on three main entry roads into the Fruit Fly Exclusion Zone and assessed for infestation. We found 1.01% of consignments were infested with tephritids. However, only 0.2% were infested with sufficient Qfly to potentially result in a new establishment. Within the main fruit groups carried, we detected stone fruit, tomatoes, pome fruit, citrus, bananas and tropical fruit in that order. Based on our data and previously published figures, we estimated that there were 1148 consignments infested with tephritids that entered the zone annually. Additionally, we estimated that 227 vehicles carried Qfly-infested fruit consignments into the quarantine zone annually and each of these had the potential to start a new establishment. Our results will help inform managers of quarantine zones.

Evaluating trap and lure combinations using Biotraps and Lynfield traps for the surveillance of Queensland fruit fly Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) and other tephritids in southern New South Wales, Australia

Fruit fly surveillance remains essential for international and domestic trade. The dry cuelure baited Lynfield trap has been the Australian standard since the early 1990s. Here, we tested the two versions of Biotraps against the Lynfield traps in the Riverina area of New South Wales. The Biotraps using a protein gel performed significantly better in trapping Island fly and female Queensland fruit fly. Also, Biotraps were assessed as at least equal to or superior to Lynfield traps for trapping male Queensland fruit fly. However, the number of Newman fly trapped exhibited no significant difference between the two trap types in both time periods A and B. We discuss differences in trap architecture, toxicants and lures between the two traps, along with benefits for storage and transport.

Electrophysiological and Behavioral Responses of Virgin Female Bactrocera tryoni to Microbial Volatiles from Enterobacteriaceae.

The Queensland fruit fly (Bactrocera tryoni) is a major polyphagous pest widespread in Australia and several Pacific Islands. Bacteria present on the host plant phyllosphere supply proteins, essential for egg development and female sexual maturity. We investigated the role of microbial volatile organic compounds (MVOCs) emitted by Enterobacteriaceae commonly found on the host plant and in the fly gut in attracting virgin females. Bacteria were cultured on artificial media and natural fruits, at various pH, and MVOCs were collected using different headspace volatile absorbent materials. The olfactory responses of virgin females to bacterial MVOCs were assessed via electrophysiology and behavioral assays. The production of MVOCs was strongly influenced qualitatively by the bacterial strain and the type of media, and it semi-quantitatively varied with pH and time. MVOCs emitted by Klebsiella oxytoca invoked the strongest antennal response and were the most attractive. Among the identified compounds triggering an olfactory response, D-limonene and 2-nonanone were both significantly behaviorally attractive, whereas phenol, nonanal, isoamyl alcohol, and some pyrazines appeared to be repulsive. This study deepens our understanding of the chemical ecology between fruit flies and their bacterial symbionts and paves the way for novel synthetic lures based on specifically MVOCs targeting virgin females.

Transmission modes and efficiency of iflavirus and cripavirus in Queensland fruit fly, Bactrocera tryoni

Infections of insects with insect-specific RNA viruses are common and can affect host fitness and health. Previously, persistent RNA virus infections were detected in tephritid fruit flies, including the Queensland fruit fly (Bactrocera tryoni), Australia’s most significant horticultural pest. Their transmission modes and efficiency are unclear yet may influence virus epidemiology in field and laboratory populations. Using standard RT-PCR and RT-qPCR we detected iflavirus, cripavirus and sigmavirus in five laboratory populations recently established with field-collected B.tryoni. Virus absence in some individuals suggested that virus transmission is incomplete. Random virus segregation in an isofemale experiment resulted in the establishment of isofemale lines with and without iflavirus and cripavirus. In infected lines, viral loads normalised against host gene transcripts were variable, but did not differ between pupae and adults. Iflavirus and cripavirus were transmitted horizontally, with viruses detected (including at low viral loads) in many previously uninfected individuals after four days, and in most after 12 days cohabitation with infected flies. Iflavirus, but not cripavirus, was transmitted vertically, and surface-sterilised embryos contained high loads. Furthermore, high iflavirus loads in individual females resulted in high loads in their offspring. We demonstrated that viruses are highly prevalent in laboratory populations and that it is possible to establish and maintain uninfected fly lines for the assessment of virus transmission and host effects. This is important for pest management strategies such as the sterile insect technique which requires the mass-rearing of flies, as their fitness and performance may be affected by covert virus infections.

Predicting point-source invasion success in the Queensland fruit fly (Bactrocera tryoni): An individual-based modelling approach

Fruit flies are a major pest worldwide for fruit producing industries. Incursions into fly free areas usually occurs via infested fruit; however, little is reported about the size of a propagule to start a new establishment. Propagule pressure is an important predictor of the probability that an invasive species will establish a breeding population. Recently, individual-based model (IBM) became a valuable modelling tool for exploring invasive species. Here, we developed a spatially-explicit individual-based model (IBM) specifically parameterized for the Queensland fruit fly (Qfly) (Bactrocera tryoni Froggatt), a major horticultural pest species in Australia and a major quarantine concern worldwide. Usually, new establishments or incursions originate from the introduction of infested fruit and larvae must progress through several stages to become sexually mature adults. For a Qfly incursion to establish a breeding population, flies must avoid predators and survive long enough to become reproductively mature, find a mate, and find ripening fruit. Additionally, their offspring must survive and successfully reproduce. The IBM model simulated release of a fixed number of flies into a heterogeneous environment of varying suitability. We conducted simulations to delineate the contributions of demographic stochasticity and Allee effects (finding a mate in a spatial environment) on establishment probability. Our model delineated several key influential factors, especially tree density, extrinsic mortality and mating range. We performed sensitivity analyses to identity which biological and ecological mechanisms strongly affect establishment probability. Integrating the model's findings with information on transport of infested fruit helps explain why Qfly incursions are common, but yet most fail to establish. Our model predicted that circa 16 and 50 flies were required for a 50% and 99% chance of establishment respectively. Additionally, our model predicted the mating distance for Qfly was 16.1 m. The mean daily dispersal distance was 30 m. We discuss how this knowledge might be used to better manage Qfly by alterations in surveillance and male annihilation technique.

Analysis of components in male annihilation blocks used to manage Queensland fruit fly Bactrocera tryoni (Froggatt)

The male annihilation technique (MAT) is used throughout the world to assist in the management and eradication of fruit flies. In Australia, often MAT was deployed using particle board blocks (50 × 50 mm) and was used in southern New South Wales to manage Queensland fruit fly Bactrocera tryoni. We sampled 120 MAT blocks over two years which were newly manufactured, new and stored (for later use), exposed for a four or twelve months period and analysed them for the effects of environmental exposure on chemical contents and the weight of blocks. Chemicals present in the blocks were malathion (toxicant), cuelure (male lure) and raspberry ketone (male lure). Total weight of the blocks and the weight of the chemicals from the block's central core and edge components were recorded separately. We found that the storage of newly manufactured blocks did not prevent chemical degradation; cuelure and malathion contents were reduced by 25% and 16%, respectively, in a stored block when compared to a new block. Most changes in the chemical contents of the blocks occurred in the first four months of field deployment, with 56% and 35% reduction analysed in cuelure and malathion contents, respectively. Loss in chemical contents and weight of blocks continued with long-term exposure of blocks from four to twelve months. Edges were found to degrade more as compared to the central core of the used blocks. Managers need to be aware of chemical degradation patterns if particle board is to be used in future MAT programs.

Diversity and sex differences in rectal gland volatiles of Queensland fruit fly, Bactrocera tryoni (Diptera: Tephritidae).

Rectal gland volatiles are key mediators of sexual interactions in tephritid fruit flies. We used solid-phase microextraction (SPME) plus gas chromatography-mass spectrometry (GC-MS) and gas chromatography-flame ionization detection (GC-FID) to substantially expand rectal gland chemical characterisation of the Queensland fruit fly (Bactrocera tryoni (Diptera: Tephritidae); Qfly). The SPME GC-MS analysis identified 24 of the 30 compounds previously recorded from Qfly rectal glands, plus another 21 compounds that had not previously been reported. A few amides and fatty acid esters dominated the chromatograms of males and females respectively, but we also found other esters, alcohols and aldehydes and a ketone. The GC-FID analyses also revealed over 150 others, as yet unidentified, volatiles, generally in lesser amounts. The GC-FID analyses also showed 49 and 12 compounds were male- and female-specific, respectively, both in single sex (virgin) and mixed sex (mostly mated) groups. Another ten compounds were male-specific among virgins but undetected in mixed sex groups, and 29 were undetected in virgins but male-specific in mixed sex groups. The corresponding figures for females were four and zero, respectively. Most short retention time peaks (including a ketone and an ester) were male-specific, whereas most female-biased peaks (including five fatty acid esters) had long retention times. Our results indicate previously unsuspected diversity of rectal gland volatiles that might have pheromone functions in males, but far fewer in females.

Virulence, penetration rate and reproductive potential of entomopathogenic nematodes from eastern Australia in Queensland fruit fly, Bactrocera tryoni

Queensland fruit fly (Bactrocera tryoni) is Australia’s most significant horticultural pest, yet limited options are available for its biological control. Here, we assessed the virulence and reproductive potential of 32 newly isolated Australian entomopathogenic nematode (EPN) strains of Heterorhabditis bacteriophora, Heterorhabditis indica, Heterorhabditis marelatus, Heterorhabditis zealandica and Steinernema feltiae against the late third larval instar and pupal stages of B. tryoni under laboratory conditions, and compared their performance with four commercially available strains of H. bacteriophora, H. zealandica, S. feltiae and S. carpocapsae. All EPN strains caused significant larval mortality, and, remarkably, 29 also pupal mortality. Among the EPN strains the mean LD50 value, presented as the number of infective juveniles (IJs) per B. tryoni individual, ranged from 25 to 114 IJs per larva, and from 114 to 360 per pupa; therefore, 3.2 to 4.6× more IJs were required to kill pupae. The penetration rates of IJs in B. tryoni larvae varied from 2 to 6.8%, and the number of IJs recovered per larva varied between 2,100 to 5,683. Our findings highlight the potential of Australian EPN strains for controlling larval and pupal stages of B. tryoni. Overall, based on the three tested traits, one H. zealandica strain (Hz.NAR1), three H. indica strains (Hi.ECCH, Hi.HRN and Hi.HIE2), one H. bacteriophora strain (Hb.HIE), one H. marelatus strain (Hm.ENCBF2) and one S. feltiae strain (Sf.Y13) were found the most promising candidates as potential biological control agents against the soil inhabiting stages of B. tryoni. Further laboratory testing is required to assess their persistence under a broader range of environmental conditions before their biological control efficacy can be trialled under field conditions.

An Integrated Biosecurity Risk Assessment Model (IBRAM) For Evaluating the Risk of Import Pathways for the Establishment of Invasive Species.

An important aspect of analyzing the risk of unwanted organisms establishing in an area is understanding the pathways by which they arrive. Evaluating the risks of these pathways requires use of data from multiple sources, which frequently are uncertain. To address the needs of agencies responsible for biosecurity operations, we present an Integrated Biosecurity Risk Assessment Model (IBRAM) for evaluating the risk of establishment and dispersal of invasive species along trade pathways. The IBRAM framework consists of multiple linked models which describe pest entry into the country, escape along trade pathways, initial dispersal into the environment, habitat suitability, probabilities of establishment and spread, and the consequences of these invasions. Bayesian networks (BN) are used extensively to model these processes. The model includes dynamic BN components and geographic data, resulting in distributions of output parameters over spatial and temporal axes. IBRAM is supported by a web-based tool that allows users to run the model on real-world pest examples and investigate the impact of alternative risk management scenarios, to explore the effect of various interventions and resource allocations. Two case studies are provided as examples of how IBRAM may be used: Queensland fruit fly (Bactrocera tryoni) (Diptera: Tephritidae) and brown marmorated stink bug (Halyomorpha halys) (Hemiptera: Pentatomidae) are unwanted organisms with the potential to invade Aotearoa New Zealand, and IBRAM has been influential in evaluating the efficacy of pathway management to mitigate the risk of their establishment in the country.

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.

Seasonal weight fluctuations in wild Queensland fruit fly Bactrocera tryoni (Froggatt) (Diptera: Tephritidae) may be a survival mechanism

We wanted to evaluate if the body weight of wild adult Queensland fruit fly Bactrocera tryoni changed in response to season or months to confirm results reported in the mass rearing facility. Also, this will provide insights into survival mechanisms in wild flies. We analysed 34,924 flies from the Sydney surveillance array and measured dry and fresh weight across time (months and seasons). We used results from sterile fly production to extrapolate survival traits based on adult fly weights. We found the heaviest flies were collected in late winter (August) and early spring (September and October) and heavier weights are indicative of higher eclosion and flight ability. On the other hand, lighter flies were collected in May, June and July, followed by the other autumn months. We suspect this is associated with longevity and winter survival. We conclude that fly weights vary according to months and seasons and these variations may confer different survival traits for each season.

Tracing the origins of recent Queensland fruit fly incursions into South Australia, Tasmania and New Zealand

Incursions of the Queensland fruit fly Bactrocera tryoni (Qfly) into areas without permanent Qfly populations present serious threats to the Australian and New Zealand horticultural industries. Identifying the origins of recent incursions will help reduce future threats by enabling the targeting of problematic incursion routes for more stringent quarantine protocols. Here we present an analytical framework based on supervised and unsupervised machine learning to identify the origins and recent population history of incursion individuals. Our framework is based on a recently developed reference dataset of genome-wide markers for 35 Qfly populations from across the ranges of Qfly and the related taxon Bactrocera aquilonis (NTfly). We apply our framework to recent incursions into New Zealand, Tasmania and South Australia. Two distinct Qfly sources were identified for incursions into New Zealand (total 18 individuals), one from the east coast of Australia and one from New Caledonia. All eight recent incursion collections analysed (total 85 individuals) from South Australia and Tasmania most likely originated from just one of six clusters of populations in our reference database, Qfly from the east coast of Australia. None were found to originate from clusters containing NTfly or Qfly/NTfly hybrids in the Northern Territory or north Western Australia. Several, but not all, of the collections showed signals of small founding population size and two Tasmanian collections each included individuals apparently derived from three different sources within the east coast of Australia. In total, several more incursion events were detected than previously known, although some were founded by relatively few individuals.

Climate stress resistance in male Queensland fruit fly varies among populations of diverse geographic origins and changes during domestication

BackgroundThe highly polyphagous Queensland fruit fly (Bactrocera tryoni Froggatt) expanded its range substantially during the twentieth century and is now the most economically important insect pest of Australian horticulture, prompting intensive efforts to develop a Sterile Insect Technique (SIT) control program. Using a “common garden” approach, we have screened for natural genetic variation in key environmental fitness traits among populations from across the geographic range of this species and monitored changes in those traits induced during domestication.ResultsSignificant variation was detected between the populations for heat, desiccation and starvation resistance and wing length (as a measure of body size). Desiccation resistance was correlated with both starvation resistance and wing length. Bioassay data for three resampled populations indicate that much of the variation in desiccation resistance reflects persistent, inherited differences among the populations. No latitudinal cline was detected for any of the traits and only weak correlations were found with climatic variables for heat resistance and wing length. All three stress resistance phenotypes and wing length changed significantly in certain populations with ongoing domestication but there was also a strong population by domestication interaction effect for each trait.ConclusionsEcotypic variation in heat, starvation and desiccation resistance was detected in Australian Qfly populations, and these stress resistances diminished rapidly during domestication. Our results indicate a need to select source populations for SIT strains which have relatively high climatic stress resistance and to minimise loss of that resistance during domestication.

Disruption of duplicated yellow genes in Bactrocera tryoni modifies pigmentation colouration and impacts behaviour

Irradiated Queensland fruit flies (Bactrocera tryoni) used in Sterile Insect Technique (SIT) programmes are marked with fluorescent dyes to distinguish them from wild flies when recaptured in monitoring traps. However, coating sterile pupae with powdered dyes can reduce emergence rates and fly quality and can sometimes produce insufficiently certain discrimination through inadequate coating or because the dye is transferred to wild flies through contact. Here we created a phenotypically distinct B. tryoni strain that lacks typical melanisation patterns through CRISPR/Cas9-mediated mutagenesis of tandemly duplicated yellow-y genes and then assessed effects of this visible trait on fly performance. Recessive mutations are only required in one of these copies to restrict melanisation and generate a phenotype clearly distinguished from wild type. The yellow strain showed significant declines in eclosion rates and in the percentage of fliers directly after emergence. Locomotor activity was greater in the yellow strain, and these mutations did not generally affect mating probability, copula latency, or copula duration. The longevity of yellow flies was approximately 10 days shorter than wild-type flies in both sexes. Overall, replacing dyes with yellow body marker for SIT can simplify production, eliminate a step that is known to reduce fly quality, remove potentially hazardous dyes from production, enable accurate discrimination from wild flies, and improve cost-effectiveness; however, direct comparisons of the decrements in performance associated with dyes on mass-reared wild-type flies and disruption of yellow-y genes are now required to determine the relative suitability of these marking methods for B. tryoni SIT.

Visibility and Persistence of Fluorescent Dyes, and Impacts on Emergence, Quality, and Survival of Sterile Queensland Fruit Fly Bactrocera tryoni (Diptera: Tephritidae).

Tephritid flies released in sterile insect technique pest management programs are usually marked with fluorescent dyes so that they can be distinguished from wild flies in monitoring traps. Dyes can have adverse effects on emergence, quality, and survival, which can impact sterile insect technique (SIT) success, and so it is important to identify dyes and doses that maximize marking efficacy while minimizing deleterious effects on fly quality. This study examines the effects of five fluorescent dye products, Fluoro Pink, Fluoro Orange, Stella Green, Arc Chrome, and Astral Pink applied at four dose levels (1, 2, 3, and 4 g/liter) on Queensland fruit fly. All dye products caused a similar dose-dependent reduction in percentage of adult emergence. Incidence of morphological deformity of emerged adults increased with dose, and this trend was similar for all dye products. No effects of dye product or dose were found on survival rates over the first 35 d of adulthood, although females tended to have higher survival than males. Visibility varied with dose and dye product; 1 g/liter dye was less visible than 2, 3, or 4 g/liter, and Stella green had lower visibility than other dyes. All of the tested dyes except for Stella green were similar in all assessed metrics of fly performance and are recommended for use in SIT programs.

Caffeine as a promotor of sexual development in sterile Queensland fruit fly males

Sterile insect technique (SIT) is an environmentally benign pest management technique that involves releasing millions of sterile insects to suppress reproduction of pest populations. Many fruit flies, including Queensland fruit fly (Bactrocera tryoni Froggatt, ‘Q-fly’), have long adult maturation periods such that pre-maturation mortality can greatly reduce abundance of sexually active sterile males and impede SIT efficacy. Q-fly is the most difficult and costly challenge to market access for Australia’s horticulture industries, and has been targeted for intensive use of SIT program. We here demonstrate potential of pre-release caffeine supplements as a novel means to accelerate sexual maturation in male Q-fly. In mating trials, analytical caffeine was very effective at accelerating sexual maturation, while no positive effects of caffeine-containing instant coffee or guarana supplements were detected. In parallel, development of testes and ejaculatory apodemes was accelerated in males provided analytical caffeine but not instant coffee or guarana. High doses of guarana and instant coffee reduced longevity while even the highest doses of analytical caffeine did not affect longevity. Pre-release caffeine supplements promote sexual maturation in Q-flies, and similar benefits are expected in other fruit flies having long adult maturation periods.

Dietary methoprene treatment promotes rapid development of reproductive organs in male Queensland fruit fly

Methoprene supplements added to diets of yeast hydrolysate and sugar promote early expression of sexual behaviour and mating in male Queensland fruit fly (Bactrocera tryoni; ‘Q-fly’) and show promise as a pre-release treatment for sterile insect technique programs. Currently it is not known whether the early mating behaviour of methoprene-treated male Q-flies is only behavioural or is coupled with accelerated development of reproductive organs. Accordingly, the present study investigates whether incorporation of methoprene into diets of yeast hydrolysate and sugar (1:3) or sugar alone, accelerate development of testes, ejaculatory apodeme, and accessory glands in male Q-flies and ovaries in females. All organs increased in size as the flies aged and matured, and development rate of all organs was far greater when the flies were provided yeast hydrolysate in addition to sugar. Incorporation of methoprene into diets containing yeast hydrolysate was found to strongly accelerate development of testes and ejaculatory apodeme, but not accessory glands, in males. In the absence of yeast hydrolysate, methoprene treatment had only a modest effect on male organ development. In contrast to males, development of ovaries in female Q-flies did not respond to dietary methoprene supplements, regardless of whether they were fed yeast hydrolysate and sugar or sugar alone. These findings of diet-dependent effects of methoprene supplements on reproductive organs are a close match to previous studies investigating effects of methoprene supplements on mating behaviour. Overall, methoprene supplements substantially enhance the positive effects of protein rich adult diet on the early expression of sexual behaviour and accelerate development of reproductive organs in male, but not female, Q-flies. Methoprene supplements added to pre-release diets of yeast hydrolysate and sugar show promise as a means of accelerating reproductive development of Q-flies released in sterile insect technique programs, and may also bias operational sex ratio in favour of males.

Current quarantine and suspension distances are excessive for incipient populations of Queensland fruit fly (Bactrocera tryoni (Froggatt)) (Diptera: Tephritidae) in southern New South Wales, Australia

The Queensland fruit fly (Qfly; Bactrocera tryoni Froggatt) is a major horticultural pest species in Australia and considered a serious quarantine concern, both domestically and internationally. When a Qfly outbreak is declared in the main horticultural regions of southeast Australia, a 15 km radius suspension zone is established (area of 707 km2) around the epicentre of the outbreak. This suspension radius was originally adopted in the early 1990s. Here, we analysed trapping data in New South Wales (Australia) from 2002 to 2010 to evaluate the suitability of the 15 km suspension radius. There were 439 Qfly incursions recorded in Qfly-free zones, but only 9.9% of these incursions resulted in a declared outbreak. For these outbreaks, we conducted two distinct analyses. First, we modelled the distribution of infestation radii from the outbreaks and predicted the suspension distance using multiple levels of risk protection (e.g. probit 8.7, probit 9). Second, we fitted various probability distributions to individual fly trapping data and then estimated upper confidence limits for suspension distances, based on dispersal patterns of Qfly. Overall, the predicted suspension radii were substantially smaller than the current 15 km radius. Our results concur with other studies suggesting that Qfly are relatively poor colonisers. We propose that the current 15 km could be reduced substantially to 3 or 4 km.

Ecological Drivers and Sex-Based Variation in Body Size and Shape in the Queensland Fruit Fly, Bactrocera tryoni (Diptera: Tephritidae).

The Queensland fruit fly (Bactrocera tryoni; Q-fly) is an Australian endemic horticultural pest species, which has caused enormous economic losses. It has the potential to expand its range to currently Q-fly-free areas and poses a serious threat to the Australian horticultural industry. A large number of studies have investigated the correlation between environmental factors and Q-fly development, reproduction, and expansion. However, it is still not clear how Q-fly morphological traits vary with the environment. Our study focused on three morphological traits (body size, wing shape, and fluctuating asymmetry) in Q-fly samples collected from 1955 to 1965. We assessed how these traits vary by sex, and in response to latitude, environmental variables, and geographic distance. First, we found sexual dimorphism in body size and wing shape, but not in fluctuating asymmetry. Females had a larger body size but shorter and wider wings than males, which may be due to reproductive and/or locomotion differences between females and males. Secondly, the body size of Q-flies varied with latitude, which conforms to Bergmann’s rule. Finally, we found Q-fly wing shape was more closely related to temperature rather than aridity, and low temperature and high aridity may lead to high asymmetry in Q-fly populations.

Forewarned is forearmed: Queensland fruit flies detect olfactory cues from predators and respond with predator-specific behaviour

Animals can gain significant advantages from abilities to detect cues from predators, assess risks, and respond adaptively to reduce the likelihood of injurious interactions. In contrast, predator cue-induced changes in behaviour may interfere with fitness-associated activities such as exploration, foraging and reproduction. Despite the ecological importance of predator-prey interactions in insects, remarkably little is known about the abilities of insects to detect and respond to olfactory cues from predators, or the potential costs of such responses. We here demonstrate that a tephritid fruit fly, the Queensland fruit fly Bactrocera tryoni, is able to detect and respond differentially to volatile olfactory cues from four potential predators (three spiders and an ant) that vary in prevalence and diurnal activity. Male and female flies increased or decreased motility (velocity, active time, distance moved), or exhibited no change in motility, depending on which predator volatiles they encountered. Further, flies significantly reduced foraging, oviposition and mating propensity in the presence of volatiles from any of the predators. This study is the first report of predator-specific responses to olfactory cues in a tephritid fruit fly, and highlights that such anti-predator responses can impose costs on general activity and reproductive behaviour.