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Floral constituents of the Australian tar tree, Semecarpus australiensis, distributed in Melanesia and Northern Australia, were extracted with solvent, and analyzed by gas chromatography-mass spectrometry. The main constituents were 16- and 18-carbon fatty acids and their ethyl esters. Amongst the 67 identified compounds, zingerone was detected in minute quantity, providing the chemical basis for previous observations of fruit fly attraction to the flowers. The present study is the first to report the chemical profile of tar tree flowers.

Queensland fruit fly (Q-fly), Bactrocera tryoni (Froggatt), is a significant pest of horticultural crops in Australia. The sterile insect technique (SIT) is currently employed to eradicate outbreaks in fruit fly free regions and may also be used to suppress populations in endemic regions. For SIT to succeed, it is imperative that the released sterile males survive, disperse, attain sexual maturity, and are sexually competitive against their wild rivals. Q-fly SIT programmes have conventionally held adult flies for two to three days and have sometimes fed them only sugar before release, providing little time or nutrition for development prior to release. We investigated whether a 5-d pre-release holding period and provision of yeast hydrolysate (YH) together with sugar in the pre-release diet increase abundance of mature male Q-fly in the field. Indicating increased survivorship and/or maturation, the combination of YH feeding and 5-d pre-release holding period resulted in 6–8 times more recaptures of mature male flies in cuelure traps than was the case for flies released at 2 d with or without YH and for flies released at 5 d without YH. Flies held for 5 d and fed YH were relatively more abundant than flies from other treatments in traps close to the release point and were as abundant as other treatments in traps at the greatest assessed distances. These findings strongly support a recommendation that sterile Q-flies be provided a pre-release diet of YH and sugar and be held for 5-d post-eclosion before release.

Queensland fruit fly (Q-fly), Bactrocera tryoni (Froggatt), presents a major threat to Australian fruit production and trade. The sterile insect technique (SIT) is increasingly employed to manage Q-fly. Quality of sterile males released in SIT programs, and hence program efficacy, can be affected by pre- and post-production processes, such as mass rearing, packing, irradiation, transportation, and release. Given long distances from rear-out facilities to release sites, adult flies are usually chilled to reduce metabolism and stress during transportation. To guide SIT procedures, it is important to understand the impact of such practices on performance of sterile Q-fly. The present study assesses the effect of chilling temperature and exposure period on quality parameters of sterile Q-fly. We considered the effects of two temperature regimes (4 and 6°C) and six exposure periods (0, 1, 2, 4, 6, and 12 h) on chill-coma recovery time, flight ability, survival under nutritional stress, and longevity of both males and females. Flies chilled at 4°C took longer to recover than that those chilled at 6°C. Flight ability, survival under nutritional stress, and longevity all decreased as chilling period increased but did not differ between the two tested temperatures. We recommend that periods of chilling during transportation from rear-out facilities to release sites be minimized in order to retain quality of sterile Q-fly and that increased release rates be considered when longer chilling periods are required.

Queensland fruit fly is one of the most economically important horticultural pests in Australia. Sterile insect technique (SIT) is now being reconsidered and upscaled to combat this pest so reliable discrimination of released sterile Q-flies from wild flies in monitoring traps is important for effective SIT operations. Stable isotopes provide a permanent chemical marker to discriminate sterile and wild flies when dye marking is unclear. In this study, we compared the isotopic ratios of carbon and nitrogen between Q-flies reared on different larval diets and wild flies collected from diverse locations in Australia and New Caledonia. Finally, we conducted a release–recapture study to corroborate differences in stable isotope C and N ratios in laboratory-reared and wild Q-flies. The δ15N values obtained from wild and laboratory Q-flies showed high variability that is likely related to the food source of the larval and/or adult stage and do not offer an effective means to discriminate between sterile and wild Q-flies. The δ13C values of examined wild Q-flies ranged from − 27.46 to − 24.37‰ VPDB, whereas those from laboratory-reared, released and recaptured Q-flies ranged from − 25.73 to − 19.26‰ VPDB. Differences in δ13C values resulted in 100% correct classification of wild flies and 96.88% correct classification of released flies. Measurements of intrinsic δ13C values offer a precise tool to discriminate between sterile and wild Q-flies in SIT programs, regardless of the composition of the larval or adult pre-release diets.

Studies of reproductive biology in insects often require quantification of sperm production, transfer or storage. Here, we develop a quantitative real-time PCR-based assay using a Y-specific marker for quantification of sperm from spermathecae of female Queensland fruit fly ('Q-fly'), overcoming constraints typical of traditional sperm quantification methods. The assay enables accurate and reliable quantification of as few as 50 sperm and provides a means to analyse large numbers of samples with flexible timing. The real-time PCR method enables revised understanding of how many sperm are stored by female Q-flies, the distribution of storage between the two spermathecae, and the relationship between copula duration and sperm storage. Real-time PCR assays based on Y-specific markers provide an effective solution for sperm quantification in tephritid flies, as well as in other insects and potentially other animals with sperm storage organs. This article is protected by copyright. All rights reserved.

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.

Divergence between populations in mating behaviour can function as a potent premating isolating mechanism and promote speciation. However, very few cases of inherited intraspecific variation in sexual signalling have been reported in tephritid fruit flies, despite them being a highly speciose family. We tested for such variation in one tephritid, the Queensland fruit fly, Bactrocera tryoni (Qfly). Qfly mating behaviour depends on volatiles secreted from male rectal glands but no role for the volatiles from female rectal glands has yet been reported. We previously detected over 100 volatile compounds in male rectal glands and identified over 30 of them. Similar numbers were recorded in females. However, many compounds showed presence/absence differences between the sexes and many others showed quantitative differences between them. Here we report inherited variation among 24 Qfly lines (23 isofemale lines established from recent field collections and one domesticated line) in the abundance of three esters, two alcohols, two amides, an aldehyde and 18 unidentified volatiles in male rectal glands. We did not find any compounds in female rectal glands that varied significantly among the lines, although this may at least partly reflect lower female sample numbers. Most of the 26 male compounds that differed between lines were more abundant in the domesticated line than any of the recently established isofemale lines, which concurs with other evidence for changes in mating behaviour during domestication of this species. There were also large differences in several of the 26 compounds among the isofemale lines, and some of these differences were associated with the regions from which the lines were collected. While some of the variation in different compounds was correlated across lines, much of it was not, implicating involvement of multiple genes. Our findings parallel reports of geographic variation in other Qfly traits and point to inherited differences in reproductive physiology that could provide a basis for evolution of premating isolation between ecotypes.

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.

Bactrocera bryoniae is a polyphagous and economically significant fruit fly found in Indonesia, Papua New Guinea and Australia. To understand chemical-mediated sexual communication, and the potential for novel pheromone-based attractants for monitoring and mass-trapping of B. bryoniae, rectal gland exudates and emissions from sexually mature males and females were investigated. Gas chromatography–mass spectrometry showed that male rectal glands contained six compounds, of which 1,7-dioxaspiro[5,5]undecane elicited electroantennographic (EAD) and electropalpographic (EPD) responses in both sexes, ethyl 3-acetoxybutanoate elicited EPD responses in both sexes, N-(3-methylbutyl)acetamide elicited EAD response from males and 4-hydroxy-1,7-dioxaspiro[5.5]undecane elicited EAD responses in males and females and EPD responses in females. Female rectal glands contained 23 compounds with the esters ethyl laurate and ethyl myristate as major components. Amongst the female rectal gland constituents, ethyl laurate, ethyl myristate and ethyl palmitate elicited EAD responses in males and females, N-(3-methylbutyl)acetamide elicited EAD responses in males only, (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane elicited EAD responses in males and EPD responses in females, and 2,7-dimethyl-1,6-dioxaspiro[4.5]decane, (E,E)-2-ethyl-7-methyl-1,6-dioxaspiro[4.5]decane, (E,E)-2-ethyl-8-methyl-1,7-dioxaspiro[5.5]undecane, (Z,Z)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, (E,E)-2-propyl-8-methyl-1,7-dioxaspiro[5.5]undecane and ethyl caprate elicited EPD responses in females only. Y-tube bioassays indicated that male rectal gland extracts and headspace volatiles attracted females and males, while female rectal gland extracts and headspace volatiles only attracted males. The results suggest that ethyl 3-acetoxybutanoate, 1,7-dioxaspiro[5,5]undecane and 4-hydroxy-1,7-dioxaspiro[5.5]undecane may be components of male-produced sex pheromone in B. bryoniae while (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, N-(3-methylbutyl)acetamide, ethyl laurate, ethyl myristate and ethyl palmitate may be components of female-produced sex pheromone. Ethyl 3-acetoxybutanoate, N-(3-methylbutyl) acetamide, 1,7-dioxaspiro[5,5]undecane and 4-hydroxy-1,7-dioxaspiro[5.5]undecane may be components of male aggregation pheromone. These findings contribute to the understanding of pheromone communication in B. bryoniae and provide a foundation for developing pheromone-based monitoring and control methods.

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.

Diverse methods have been used to sample insect semiochemicals. Sampling methods can differ in efficiency and affinity and this can introduce significant biases when interpreting biological patterns. We compare common methods used to sample tephritid fruit fly rectal gland volatiles (‘pheromones’), focusing on Queensland fruit fly, Bactrocera tryoni. Solvents of different polarity, n-hexane, dichloromethane and ethanol, were compared using intact and crushed glands. Polydimethylsiloxane, polydimethylsiloxane/divinylbenzene and polyacrylate were compared as adsorbents for solid phase microextraction. Tenax-GR and Porapak Q were compared as adsorbents for dynamic headspace sampling. Along with compounds previously reported for B. tryoni, we detected five previously unreported compounds in males, and three in females. Dichloromethane extracted more amides while there was no significant difference between the three solvents in extraction of spiroacetals except for (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane for which n-hexane extracted higher amount than both dichloromethane and ethanol. Ethanol failed to contain many of the more volatile compounds. Crushed rectal gland samples provided higher concentrations of extracted compounds than intact rectal gland samples, but no compounds were missed in intact samples. Of solid phase microextraction fibers, polyacrylate had low affinity for spiroacetals, ethyl isobutyrate and ethyl-2-methylbutanoate. Polydimethylsiloxane was more efficient for spiroacetals while type of fiber did not affect the amounts of amides and esters. In dynamic headspace sampling, Porapak was more efficient for ethyl isobutyrate and spiroacetals, while Tenax was more efficient for other esters and amides, and sampling time was a critical factor. Biases that can be introduced by sampling methods are important considerations when collecting and interpreting insect semiochemical profiles.

Humans have used weaver ants, Oecophylla smaragdina, as biological control agents to control insect pests in orchards for many centuries. Over recent decades, the effectiveness of weaver ants as biological control agents has been attributed in part to kairomones produced by the ants, but the chemical identity of these kairomones has remained unknown. We have identified the kairomone responsible for deterrence by O. smaragdina, providing a significant advance in understanding the chemical basis of their predator/prey interactions. Olfactometer assays with extracts from weaver ants demonstrated headspace volatiles to be highly repellent to Queensland fruit fly, Bactrocera tryoni. Using electrophysiology and bioassays, we demonstrate that this repellence is induced by a single compound, 1-octanol. Of 16 compounds identified in O. smaragdina headspace, only 1-octanol evoked an electrophysiological response from B. tryoni antennae. Flies had greatly reduced oviposition and spent significantly less time in an olfactometer arm in the presence of 1-octanol or a synthetic blend of headspace volatiles containing 1-octanol than in the presence of a synthetic blend of headspace volatiles without 1-octanol, or clean air. Taken together, our results demonstrate that 1-octanol is the functional kairomone component of O. smaragdina headspace that explains repellence and oviposition deterrence, and is hence an important contributor to the effectiveness of these ants as biological control agents.

The sterile insect technique (SIT), a benign pest control strategy, is currently undergoing a substantial renewal for controlling the Queensland fruit fly (Q-fly), a major horticultural pest in Australia. Production and delivery of high-quality flies is fundamental to effective SIT. While efforts are commonly made to improve production at a factory level (both quantity and quality), the methods and conditions during post-production operations also need to be tuned to minimize reductions in fly quality. Hypoxia, irradiation and vibration are important stressors that are experienced by pupae during production, packing and transportation. However, little is known about the impacts of such stressors on Q-fly quality. We conducted two laboratory experiments to investigate the response of Q-fly to such post-production stressors, with the aim of then developing guidelines that minimize quality reductions for SIT programs. In Experiment 1, Q-fly pupae of different ages (3, 6 or 9-day old) were exposed to vibrations for 5, 30, 60 and 300 s. Flight ability tests revealed that 6- and 9-day-old pupae were the most sensitive to vibration, with significant reduction in emergence and percentage of fliers. In Experiment 2, the effect of hypoxia, irradiation and vibration, in isolation or in combination, was evaluated on 9-day-old pupae. Irradiation and vibration exhibited a multiplicative negative effect on flight ability parameters. It is recommended not to subject pupae to intense or extensive vibration during the late pupal stage and to avoid prolonged periods of hypoxia.

We report on the vapor pressures at ambient temperatures of seven attractants of Bactrocera, Dacus, and Zeugodacus fruit flies—raspberry ketone, cuelure, raspberry ketone trifluoroacetate, methyl e...

Insecticides used to control fruit fly pests have been implicated in negative effects on natural enemies, human health and the environment. As potential ‘softer’ insecticides, natural compounds such as essential oils and their constituents have received increased attention as insecticide candidates. Queensland fruit fly (Q-fly), Bactrocera tryoni (Froggatt), is the most economically damaging fruit fly species in Australia. Cuelure and melolure are plant-based attractants of males in Q-fly and many other dacine fruit flies and are structurally similar to benzyl acetone. We hypothesized that fluorination of benzyl acetone would introduce toxicity that could be exploited for insecticidal applications. Toxicity to Q-fly of nine fluorinated analogs of benzyl acetone as well as the known attractants cuelure and melolure was investigated. LC50 and LC90 values of the compounds were obtained using a surface-film assay method. Fluorination at the meta and/or para-position of benzene ring was found to increase toxicity to both Q-fly sexes. We further examined toxicity and short-range attraction to Q-fly using traps in outdoor cages. The nine fluorinated analogs of benzyl acetone were all highly toxic to male Q-flies, whereas cuelure and melolure were not. Some analogs were attractive to male Q-flies. None of the nine analogs, cuelure or melolure had an inhibitory effect on the proliferation of BEAS-2B human bronchial epithelial cells, suggesting very low or negligible mammalian toxicity. Fluorinated analogs of benzyl acetone have potential as new toxicants for Q-fly, and likely other insects, and some may also have attractive properties for cuelure-responding fruit flies.

Pre‐release dietary treatment with methoprene, a juvenile hormone analogue, decreases the age at which male Queensland fruit flies mature and hence may decrease the post‐release delay until released sterile flies participate in sterile insect technique (SIT) programmes. However, if matings of young methoprene‐treated males are not effective at inducing sexual inhibition in their mates, then this treatment may not enhance SIT. The present study investigates efficacy of matings of methoprene‐treated males at inducing sexual inhibition in their mates. Methoprene incorporated into a diet of sugar and yeast hydrolysate (w/w 3:1) for 48 hr after emergence resulted in significantly increased male mating propensity when flies were

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.

Multiple mating by females, polyandry, is common in insects, including in tephritid fruit flies. Female insects that remate commonly store sperm of multiple males. How the sperm of different males contribute to paternity is an important element of sexual selection. Sexual behavior and reproduction of the Queensland fruit fly (Qfly), Bactrocera tryoni, has been extensively investigated both in relation to understanding this economically important species' reproductive biology and in relation to implications for Sterile Insect Technique (SIT), whereby sterile flies are released to constrain reproduction of pest populations. Despite numerous studies of pre- and postcopulatory sexual selection in Qfly, there have been no direct studies of paternity patterns in polyandrous female Qflies. We used two morphologically distinguishable lines to investigate patterns of sperm use in Qfly. The two lines showed comparable mating performance evidenced by similar mating and remating frequency, copula duration, and proportion of second mate paternity (P2) between reciprocal crosses. The mechanism of sperm usage, with P2 close to 0.5 immediately after the second mating followed by gradual decrease of P2 as females aged, is most consistent with stratification or repositioning of sperm. Patterns observed in the present study are compared with the available information from other tephritid fruit flies, and are discussed in relation to this species' reproductive biology, known patterns of sperm storage, and SIT.

Pheromones are biologically important in fruit fly mating systems, and also have potential applications as attractants or mating disrupters for pest management. Bactrocera kraussi (Hardy) (Diptera: Tephritidae) is a polyphagous pest fruit fly for which the chemical profile of rectal glands is available for males but not for females. There have been no studies of the volatile emissions of either sex or of electrophysiological responses to these compounds. The present study (i) establishes the chemical profiles of rectal gland contents and volatiles emitted by both sexes of B. kraussi by gas chromatography–mass spectrometry (GC–MS) and (ii) evaluates the detection of the identified compounds by gas chromatography–electroantennogram detection (GC–EAD) and –electropalpogram detection (GC–EPD). Sixteen compounds are identified in the rectal glands of male B. kraussi and 29 compounds are identified in the rectal glands of females. Of these compounds, 5 were detected in the headspace of males and 13 were detected in the headspace of females. GC–EPD assays recorded strong signals in both sexes against (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, 2-ethyl-7-mehtyl-1,6-dioxaspiro[4.5]decane isomer 2, (E,Z)/(Z,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, and (Z,Z)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane. Male antennae responded to (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane, 2-methyl-6-pentyl-3,4-dihydro-2H-pyran, 6-hexyl-2-methyl-3,4-dihydro-2H-pyran, 6-oxononan-1-ol, ethyl dodecanoate, ethyl tetradecanoate and ethyl (Z)-hexadec-9-enoate, whereas female antennae responded to (E,E)-2,8-dimethyl-1,7-dioxaspiro[5.5]undecane and 2-methyl-6-pentyl-3,4-dihydro-2H-pyran only. These compounds are candidates as pheromones mediating sexual interactions in B. kraussi.

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.

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.

Queensland fruit flies Bactrocera tryoni (Froggatt) have a long adult maturation phase which, together with high mortality rates, can substantially reduce number of released flies that survive to mature and contribute to sterile insect technique (SIT) programmes. This constraint on SIT can potentially be addressed by incorporating methoprene, a juvenile hormone analogue, into an adult diet of sugar and yeast hydrolysate for 2 days after emergence. Methoprene treatments have been found to accelerate sexual development of male Queensland fruit fly, resulting in increased mating propensity of 5–7-day-old males in no-choice laboratory trials. Before considering deployment of methoprene as a pre-release treatment in SIT, it is necessary to demonstrate mating competitiveness and compatibility of methoprene-treated flies under field-like conditions. In the present study, we assessed whether methoprene treatment increases ability of sterile males (5 and 7 days old) to compete with mature (wild or laboratory) males for matings with mature (wild or laboratory) females in field cages. We also investigated mating compatibility to test for sexual isolation between sterile flies and mature (wild or laboratory) fertile flies. In mating competitiveness tests, methoprene-treated males of either age outperformed mature wild or laboratory males for matings with mature wild or laboratory females, respectively. Untreated 5- and 7-day-old males were less competitive than mature wild or laboratory mature males and hence had lower relative sterility indexes. Methoprene-treated males mated earlier in the evening and continued mating for longer than untreated sterile males and mature wild or laboratory males. In mating compatibility trials, methoprene-treated males mated equally with methoprene-treated females and mature females, whereas methoprene-treated females tended to mate more often with mature males than with methoprene-treated males. However, untreated flies of both sexes exhibited substantial sexual isolation. Pairings that comprised methoprene-treated males and mature females had shorter mating latency and longer copulations than other pairings. Unlike males, methoprene-treated females did not exhibit changes in mating latency or duration. Overall, the present study supports the use of pre-release dietary methoprene treatment in Queensland fruit fly SIT.

Insects commonly rely on olfactory, gustatory and visual cues when deciding where to lay eggs. The olfactory cues that stimulate oviposition in the Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), are not well understood. Here, we show that two known oviposition stimulants of the Oriental fruit fly, Bactrocera dorsalis (Hendel) (Diptera: Tephritidae)—γ‐octalactone and benzothiazole—strongly elicit aggregation and oviposition in B. tryoni. Two other known oviposition stimulants of B. dorsalis—ethyl tiglate and 1‐octen‐3‐ol—elicit aggregation but not oviposition. Highlighting species overlap, but also differences, in oviposition stimulants, these findings have practical application for mass‐rearing in which vast numbers of flies are reared for sterile insect technique programs and may also have practical application in the development of pest management and monitoring tools.

Sterile insect technique (SIT) for Queensland fruit fly, Bactrocera tryoni Froggatt, Australia’s most economically damaging fruit fly species, is currently undergoing a major renewal and expansion. SIT relies on efficient and economical mass-rearing procedures that produce high-quality flies. Two solid larval diets, carrot and lucerne chaff, have traditionally been used to rear Queensland fruit fly. Recently, a gel larval diet has been developed to eliminate biological bulking agents from the mass-rearing process, but to date, there has been no direct comparison of gel larval diet with traditional solid diets. In the present study, the performance of flies reared on gel larval diet was compared with the performance of flies reared on carrot and lucerne chaff diets. In addition, to investigate whether the performance of reared flies depends on ancestral diet as well as tested diet, we sourced eggs from a colony maintained on carrot diet and from a colony maintained on a lucerne chaff diet. Overall, the gel diet was as good or better than the solid diets in all quality control parameters, including, egg–larval duration, pupal number, pupal recovery, adult emergence, percentage of fliers, and rate of fliers. Of note, larvae developed faster and pupated more synchronously on the gel diet than on either of the solid diets. At the loading densities used, gel and carrot diets produced less waste than lucerne chaff diet. Gel diets offer a rearing solution for Queensland fruit fly that eliminates biological bulking agents and yields faster and more synchronous larval development without compromising productivity or quality.

Background Cool storage is a valuable means of manipulating insect development time. The Queensland fruit fly (Q-fly) is Australia's most economically significant pest of fruit crops. The present study investigates cool storage of Q-fly pupae for increasing production flexibility for sterile insect technique programs. Development time, survival and fly quality were assessed following continuous storage of 1-day-old pupae at temperatures ranging from 13 to 25 °C. Results Survival was reduced almost to zero by pupal storage at 13 and 15 °C, was greatly reduced by storage at 17 °C, and was modestly reduced by storage at 19 °C. Pupal development time was extended by 16 days at 17 °C and by 9 days at 19 °C. Cool storage negatively affected flight ability and depleted lipid reserves. Cool storage at 19 °C enhanced the ability of 3-day-old adults to recover from chill-coma compared to control flies, indicating cold acclimation. Conclusion There is potential for use of cool storage in Q-fly mass rearing, especially to improve alignment between production and field releases. For the purpose of delaying the development time of Q-fly pupae with minimal quality reduction, storage at 23 °C is recommended for 1-day-old pupae. © 2019 Society of Chemical Industry.

Insects commonly undergo substantial changes during adaptation for laboratory or mass-rearing environments (‘domestication’) that may have significant implications for inferences from laboratory studies and utility for biological control. We assessed the effect of domestication on the amount and blend of volatiles released during sexual calling by laboratory-reared Bactrocera tryoni males using colonies from three regions of Australia: Brisbane, Cairns and Sydney. For each region, volatiles released by males from a young colony (five or fewer generations) and an old colony (20+ generations) during sexual calling was compared. Males from old colonies released more volatiles than males from young colonies. All components of the blend were more abundant in one or more of the older colonies, although differences varied by compound and by region. To assess changes over generations, the young and old colonies obtained from Brisbane were sampled at 5, 12 and 15 generations (young colony) and 25, 35 and 38 generations (old colony). While the old colony remained unchanged, flies from the young colony released more volatiles at each sequential sampling episode, and became increasingly similar to the old colony. Increased volatile production during domestication may be an adaptive response to crowded rearing conditions in which males need to overcome a chemically noisy environment to be sexually successful.

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