Resting sites,edge effects and dispersion of a polyphagous Bactrocera fruit fly within crops of different architecture

The spot or strip application of poisoned protein bait is a lure‐and‐kill technique used for the management of fruit flies. Knowledge of where flies occur in the crop environment is an important part of maximizing the efficacy of this tool. Bactrocera tryoni is a polyphagous pest of horticulture for which very little is known about its distribution within crops. With particular reference to edge effects, we monitored the abundance of B. tryoni in two crops of different architecture; strawberry and apple. In strawberries, we found more flies on the crop edge early in the fruiting season, which lessened gradually and eventually disappeared as the season progressed. In apple orchards, no such edge effect was observed and flies were found equally throughout the orchard. We postulated these differences may be due to differences in crop height (high vs. short) and/or crop canopy architecture (opened and branched in apple, dense and closed in strawberry). In a field cage trial, we tested these predictions using artificial plants of different height and canopy condition. Height and canopy structure type had no significant effects on fly oviposition and protein feeding, but the ‘apple’ type canopy significantly influenced resting. We thus postulate that there was an edge effect in strawberry because the crop was not providing resting sites and flies were doing so in vegetation around the field margins. The finding that B. tryoni shows different resting site preferences based on plant architecture offers the potential for strategic manipulation of the fly through specific border or inter‐row plantings.     

γ‐Octalactone,an effective oviposition stimulant of Bactrocera tryoni

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.     

CRISPR/Cas9‐mediated mutagenesis of the white gene in the tephritid pest Bactrocera tryoni

The Queensland fruit fly, Bactrocera tryoni (Froggatt), is a polyphagous horticultural pest in Australia that is capable of causing significant damage to more than 100 different host fruits and vegetables. Chemical applications and ecological control strategies, such as the sterile insect technique (SIT), are commonly used to suppress established populations and eradicate invasive outbreaks following migration. The recently published B. tryoni draft genome provides new opportunities to identify candidate genes for targeted genome modification in order to generate advanced genetic strains for management using sterile insect strategies. Here, we demonstrate CRISPR/Cas‐mediated mutagenesis in B. tryoni through generating a series of frame‐shift mutations in the ATP‐dependent binding cassette transporter, white, causing a classic white‐eye phenotype. This work establishes methods for CRISPR/Cas genome editing in tephritids and demonstrates its potential for developing genetic sexing strains which could be used for SIT‐based pest control.     

Eco‐evolutionary responses of Bromus tectorum to climate change: implications for biological invasions

How plant populations, communities, and ecosystems respond to climate change is a critical focus in ecology today. The responses of introduced species may be especially rapid. Current models that incorporate temperature and precipitation suggest that future Bromus tectorum invasion risk is low for the Colorado Plateau. With a field warming experiment at two sites in southeastern Utah, we tested this prediction over 4 years, measuring B. tectorum phenology, biomass, and reproduction. In a complimentary greenhouse study, we assessed whether changes in field B. tectorum biomass and reproductive output influence offspring performance. We found that following a wet winter and early spring, the timing of spring growth initiation, flowering, and summer senescence all advanced in warmed plots at both field sites and the shift in phenology was progressively larger with greater warming. Earlier green‐up and development was associated with increases in B. tectorum biomass and reproductive output, likely due early spring growth, when soil moisture was not limiting, and a lengthened growing season. Seeds collected from plants grown in warmed plots had higher biomass and germination rates and lower mortality than seeds from ambient plots. However, in the following two dry years, we observed no differences in phenology between warmed and ambient plots. In addition, warming had a generally negative effect on B. tectorum biomass and reproduction in dry years and this negative effect was significant in the plots that received the highest warming treatment. In contrast to models that predict negative responses of B. tectorum to warmer climate on the Colorado Plateau, the effects of warming were more nuanced, relied on background climate, and differed between the two field sites. Our results highlight the importance of considering the interacting effects of temperature, precipitation, and site‐specific characteristics such as soil texture, on plant demography and have direct implications for B. tectorum invasion dynamics on the Colorado Plateau.     

Wild bacterial probiotics fed to larvae of mass‐reared Queensland fruit fly [Bactrocera tryoni (Froggatt)] do not impact long‐term survival,mate selection,or locomotor activity

Queensland fruit fly [Bactrocera tryoni (Froggatt), Diptera, Tephritidae] is the most devastating insect pest impacting Australian horticulture. The Sterile Insect Technique (SIT) is an important component of tephritid pest management programs. However, mass‐rearing and irradiation (to render insects sterile) may reduce the fitness and performance of the insect, including the ability of sterile males to successfully compete for wild females. Manipulation of the gut microbiome, including the supplementation with bacterial probiotics shows promise for enhancing the quality of mass‐reared sterile flies, however there are fewer published studies targeting the larval stage. In this study, we supplemented the larval stage of mass‐reared B. tryoni with bacterial probiotics. We tested several individual bacteria that had been previously isolated and characterized from the gut of wild B. tryoni larvae including Asaia sp., Enterobacter sp., Lactobacillus sp., Leuconostoc sp. We also tested a consortium of all four of these bacterial isolates. The fitness parameters tested included adult survival in field cages, laboratory mate selection of bacteria supplemented males by bacteria nonsupplemented females, and laboratory locomotor activity of adult flies. None of the bacterial probiotic treatments in the current study was significantly different to the control for field survival, mate selection or locomotor activity of adult B. tryoni, which agree with some of the other studies regarding bacterial probiotics fed to the larval stage of tephritids. Future work is needed to determine if feeding the same, and/or other probiotics to adults, as opposed to larvae can positively impact survival, mating performance, mating competitiveness and locomotor activity of B. tryoni. The bacterial group(s) and function of bacterial species that increase fitness and competitiveness is also of interest to tephritid mass‐rearing programs.     

Flowering and Fruiting Patterns in a Subtropical Rain Forest,Taiwan

Reproductive patterns of tropical and temperate plants are usually associated with climatic seasonality, such as rainfall or temperature, and with their phylogeny. It is still unclear, however, whether plant reproductive phenology is influenced by climatic factors and/or phylogeny in aseasonal subtropical regions. The plant reproductive phenology of a subtropical rain forest in northern Taiwan (24°45′ N, 121°35′ E) was monitored at weekly intervals during a 7‐yr period (2002–2009). The flowering patterns of 46 taxa and fruiting patterns of 26 taxa were examined and evaluated in relation to climatic seasonality, phylogenetic constraints, and different phenophases. Our results indicated that most of the studied species reproduced annually. Additionally, both community‐wide flowering and fruiting patterns exhibited distinct annual rhythms and varied little among years. The community flowering peak matched seasonal changes in day length, temperature, and irradiance; while the community fruiting peak coincided with an increase in bird richness and the diet‐switching of resident omnivorous birds. In addition, phylogenetically closely related species tended to reproduce during the same periods of a year. Neither the mean flowering dates nor seasonal variation in solar radiation, however, was related to the fruit development times. Our results indicate the importance of abiotic, biotic, and evolutionary factors in determining the reproductive phenology in this subtropical forest.     

Host location by the fruit fly parasitoid Diachasmimorpha krausii: role of fruit fly species,life stage and host plant

• 1 Diachasmimorpha krausii is a braconid parasitoid of larval tephritid fruit flies, which feed cryptically within host fruit. At the ovipositor probing stage, the wasp cannot discriminate between hosts that are physiologically suitable or unsuitable for offspring development and must use other cues to locate suitable hosts.
• 2 To identify the cues used by the parasitoid to find suitable hosts, we offered, to free flying wasps, different combinations of three fruit fly species (Bactrocera tryoni, Bactrocera cacuminata, Bactrocera cucumis), different life stages of those flies (adults and larvae) and different host plants (Solanum lycopersicon, Solanum mauritianum, Cucurbita pepo). In the laboratory, the wasp will readily oviposit into larvae of all three flies but successfully develops only in B. tryoni. Bactrocera tryoni commonly infests S. lycopersicon (tomato), rarely S. mauritianum (wild tobacco) but never C. pepo (zucchini). The latter two plant species are common hosts for B. cacuminata and B. cucumis, respectively.
• 3 The parasitoid showed little or no response to uninfested plants of any of the test species. The presence of adult B. tryoni, however, increased parasitoid residency time on uninfested tomato.
• 4 When the three fruit types were all infested with larvae, parasitoid response was strongest to tomato, regardless of whether the larvae were physiologically suitable or unsuitable for offspring development. By contrast, zucchini was rarely visited by the wasp, even when infested with B. tryoni larvae.
• 5 Wild tobacco was infrequently visited when infested with B. cacuminata larvae but was more frequently visited, with greater parasitoid residency time and probing, when adult flies (either B. cacuminata or B. tryoni) were also present.
• 6 We conclude that herbivore‐induced, nonspecific host fruit wound volatiles were the major cue used by foraging D. krausii. Although positive orientation to infested host plants is well known from previous studies on opiine braconids, the failure of the wasp to orientate to some plants even when infested with physiologically suitable larvae, and the secondary role played by adult fruit flies in wasp host searching, are newly‐identified mechanisms that may aid parasitoid host location in environments where both physiologically suitable and unsuitable hosts occur.

     

Dispersal of mass‐reared sterile,laboratory‐domesticated and wild male Queensland fruit flies

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 <500 m from the release point. Comparison of gamma‐irradiated (sterile), laboratory‐adapted and wild male Q‐flies indicated that dispersal distance was not significantly affected by fly type. There was no significant correlation between temperature and mean dispersal distance, but total recaptures were significantly negatively correlated with increasing daily maximum, minimum and average temperature.     

Predicting bird phenology from space: satellite‐derived vegetation green‐up signal uncovers spatial variation in phenological synchrony between birds and their environment

Population‐level studies of how tit species (Parus spp.) track the changing phenology of their caterpillar food source have provided a model system allowing inference into how populations can adjust to changing climates, but are often limited because they implicitly assume all individuals experience similar environments. Ecologists are increasingly using satellite‐derived data to quantify aspects of animals' environments, but so far studies examining phenology have generally done so at large spatial scales. Considering the scale at which individuals experience their environment is likely to be key if we are to understand the ecological and evolutionary processes acting on reproductive phenology within populations. Here, we use time series of satellite images, with a resolution of 240 m, to quantify spatial variation in vegetation green‐up for a 385‐ha mixed‐deciduous woodland. Using data spanning 13 years, we demonstrate that annual population‐level measures of the timing of peak abundance of winter moth larvae (Operophtera brumata) and the timing of egg laying in great tits (Parus major) and blue tits (Cyanistes caeruleus) is related to satellite‐derived spring vegetation phenology. We go on to show that timing of local vegetation green‐up significantly explained individual differences in tit reproductive phenology within the population, and that the degree of synchrony between bird and vegetation phenology showed marked spatial variation across the woodland. Areas of high oak tree (Quercus robur) and hazel (Corylus avellana) density showed the strongest match between remote‐sensed vegetation phenology and reproductive phenology in both species. Marked within‐population variation in the extent to which phenology of different trophic levels match suggests that more attention should be given to small‐scale processes when exploring the causes and consequences of phenological matching. We discuss how use of remotely sensed data to study within‐population variation could broaden the scale and scope of studies exploring phenological synchrony between organisms and their environment.     

Population dynamics of the oriental fruit fly, Bactrocera dorsalis （Diptera： Tephritidae） in the Kunming area,southwestern China

Population dynamics of Bactrocera dorsalis Hendel （Diptera： Tephritidae） were studied through pheromone trapping over 4 years （1997, 1999, 2000, 2003） in the Kunming region, a high plateau area in southwestern China. B. dorsalis immigrates from southern Yunnan to Kunming each year, and occurs during early May through November. Annual trap captures recorded an increase in the B. dorsalis populations from May to July, when they peaked in abundance, and a decline until November. No flies were detected from November to April. The fruit flies had two generations. There was considerable overlapping due to the continuous arrival of immigrating flies during the summer months. Annual capture rates were significantly related to numbers of flies caught in July when peak captures were recorded; whereas the peak captures, in turn, positively depended on numbers of flies recorded in May, the first month of fly appearance in the current year. It suggested that the annual population abundance was mainly dependent on the size of the initial emigrating population. A daily average temperature of 18℃ was probably the threshold temperature required for the flies to undertake long-range dispersal, which partially explained the start of the fly in May each year on this high plateau. Under field conditions, the fruit flies can withstand 13℃ as a daily average temperature. No flies were recorded in any of the study years at a daily temperature colder than 10 ℃.     

Mechanism and effectiveness of safflower oil against female Queensland fruit fly Bactrocera tryoni

Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), infests many horticultural fruit crops in the eastern part of Australia. Farmers usually apply synthetic insecticides to control this pest. Little is known on the use of plant products especially vegetable oils for fruit fly control although they are considered to be safer than synthetic insecticides. In this study, safflower oil was investigated for its mechanism and effectiveness against female B. tryoni. In a laboratory test, safflower oil treatments (2.5 and 5.0 ml l^?1) reduced the number of fly punctures on treated artificial fruits, no matter whether pre‐punctures were present or absent. Safflower oil treatments also reduced the number of fly landings and eggs laid, but only when the treated artificial fruits were without pre‐punctures. These results confirmed that safflower oil is active against female B. tryoni mainly by preventing this fruit fly from making oviposition punctures, not by discouraging them from depositing eggs or by repelling them. The slippery nature of safflower oil is considered to be responsible for a reduction in the susceptibility of artificial fruit to fruit fly punctures. Further investigation using fruit‐bearing tomato plants (a no‐choice test) in a glasshouse situation revealed that safflower oil application at concentrations of 10 and 15 ml l^?1 reduced the number of oviposition punctures but failed to reduce the number of eggs laid. To increase efficacy of safflower oil under field conditions, multiple tools may be needed to reduce fruit fly populations and oviposition behaviour, such as the addition of trap‐crops, provision of artificial oviposition sites, or mixing the insecticides with the oil.     

Drastic post‐LGM expansion and lack of historical genetic structure of a subtropical fig‐pollinating wasp (Ceratosolen sp. 1) of Ficus septica in Taiwan

The climatic oscillations of the last glacial period have had profound influences on the demography and levels of genetic diversity of extant species. Molecular evidence of glacial effects on temperate species has been well documented, whereas little is known regarding that on subtropical species. Here we present analyses based on partial sequences of the mitochondrial cytochrome c oxidase subunit I (COI) gene (1052 bp) and genotypes at 15 microsatellite loci to investigate the historical demography, population structure and ongoing gene flow of an undescribed fig‐pollinating wasp (Ceratosolen sp. 1) of Ficus septica in subtropical Taiwan. Reconstructed historical demography based on the coalescent tree of COI sequences suggests that C. sp. 1 has undergone a drastic population expansion which was tightly coupled with climatic changes since the last glacial maximum (LGM). The magnitude of the population size change was approximately 500‐fold, indicating that the population of this wasp and its host was likely highly compressed during the last glacial period. The lack of significant population differentiation (F_ST < 0.02, for all pairwise F_ST values) may be due to rapid postglacial expansion facilitated by long‐distance dispersal, although a low frequency of first‐generation migrants was detected. Our results clearly demonstrate how recent climatic changes since the LGM and dispersal ability have jointly shaped the genetic composition of a subtropical fig‐pollinating wasp.     

The ecology of Bactrocera tryoni (Diptera: Tephritidae): what do we know to assist pest management?

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.     

Effects of field cage colour and supplementary shade on environmental conditions and mating behaviour of Queensland fruit flies,Bactrocera tryoni

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.     

Strong “bottom‐up” influences on small mammal populations: State‐space model analyses from long‐term studies

“Bottom‐up” influences, that is, masting, plus population density and climate, commonly influence woodland rodent demography. However, “top‐down” influences (predation) also intervene. Here, we assess the impacts of masting, climate, and density on rodent populations placed in the context of what is known about “top‐down” influences. To explain between‐year variations in bank vole Myodes glareolus and wood mouse Apodemus sylvaticus population demography, we applied a state‐space model to 33 years of catch‐mark‐release live‐trapping, winter temperature, and precise mast‐collection data. Experimental mast additions aided interpretation. Rodent numbers in European ash Fraxinus excelsior woodland were estimated (May/June, November/December). December–March mean minimum daily temperature represented winter severity. Total marked adult mice/voles (and juveniles in May/June) provided density indices validated against a model‐generated population estimate; this allowed estimation of the structure of a time‐series model and the demographic impacts of the climatic/biological variables. During two winters of insignificant fruit‐fall, 6.79 g/m² sterilized ash seed (as fruit) was distributed over an equivalent woodland similarly live‐trapped. September–March fruit‐fall strongly increased bank vole spring reproductive rate and winter and summer population growth rates; colder winters weakly reduced winter population growth. September–March fruit‐fall and warmer winters marginally increased wood mouse spring reproductive rate and September–December fruit‐fall weakly elevated summer population growth. Density dependence significantly reduced both species' population growth. Fruit‐fall impacts on demography still appeared after a year. Experimental ash fruit addition confirmed its positive influence on bank vole winter population growth with probable moderation by colder temperatures. The models show the strong impact of masting as a “bottom‐up” influence on rodent demography, emphasizing independent masting and weather influences; delayed effects of masting; and the importance of density dependence and its interaction with masting. We conclude that these rodents show strong “bottom‐up” and density‐dependent influences on demography moderated by winter temperature. “Top‐down” influences appear weak and need further investigation.     

Variation of life‐history traits of the Asian corn borer,Ostrinia furnacalis in relation to temperature and geographical latitude

Life‐history traits from four geographical populations (tropical Ledong population [LD], subtropical Guangzhou [GZ] and Yongxiu populations, and temperate Langfang population [LF]) of the Asian corn borer, Ostrinia furnacalis were investigated at a wide range of temperatures (20–32°C). The larval and pupal times were significantly decreased with increasing rearing temperature, and growth rate was positively correlated with temperature. The relationship between body weight and rearing temperature in O. furnacalis did not follow the temperature–size rule (TSR); all populations exhibited the highest pupal and adult weights at high temperatures or intermediate temperatures. However, development time, growth rate, and body weight did not show a constant latitudinal gradient. Across all populations at each temperature, female were significantly bigger than males, showing a female‐biased sexual size dimorphism (SSD). Contrary to Rensch's rule, the SSD tended to increase with rising temperature. The subtropical GZ population exhibited the largest degree of dimorphism while the temperate LF exhibited the smallest. Male pupae lose significantly more weight at metamorphosis compared to females. The proportionate weight losses of different populations were significantly different. Adult longevity was significantly decreased with increasing temperature. Between sexes, all populations exhibit a rather female‐biased adult longevity. Finally, we discuss the adaptive significance of higher temperature‐inducing high body weight in the moth's life history and why the moth exhibits the reverse TSR.     

Evaluating Drosophila suzukii immunomarking for mark‐capture research

Drosophila suzukii Matsumura (Diptera: Drosophilidae) utilizes ‘Himalaya’ blackberry, Rubus armeniacus Focke (Rosaceae), as a host and may invade berry and stone fruit crops from field margins containing this invasive weed. Laboratory and semi‐field studies were conducted to determine (1) the persistence of protein marks including 10% chicken egg whites (egg albumin protein), 20% bovine milk (milk casein protein), and 20% soy milk (soy trypsin inhibitor protein) on topically sprayed D. suzukii, (2) protein retention on blackberry leaves, and (3) D. suzukii acquisition of protein after exposure to marked blackberry leaves for up to 14 days after application. All flies and leaves were assayed for the presence of the protein marks using protein‐specific enzyme‐linked immunosorbent assays. Egg albumin, milk casein, and soy trypsin proteins persisted on 94, 49, and 25% of the topically marked D. suzukii, respectively, throughout the 14‐day study period. Egg albumin was retained on 100% of treated leaves for 14 days, regardless of environmental conditions. At least 50% of flies exposed residually to egg albumin‐treated leaves were marked for 3 days, regardless of exposure time and environmental conditions. However, increasing fly exposure time to treated leaves in April and June appeared to improve protein mark acquisition. Acquisition of protein by flies from treated leaves for milk casein was inconsistent, and poor for soy trypsin, despite detectable levels on treated leaves. Egg albumin had the longest and most consistent persistence on flies, leaves, and flies exposed to leaves in laboratory and semi‐field studies, under a variety of environmental conditions and exposure times.     

The mating system of the true fruit fly Bactrocera tryoni and its sister species,Bactrocera neohumeralis

The frugivorous “true” fruit fly, Bactrocera tryoni (Queensland fruit fly), is presumed to have a nonresourced‐based lek mating system. This is largely untested, and contrary data exists to suggest Bactrocera tryoni may have a resource‐based mating system focused on fruiting host plants. We tested the mating system of Bactrocera tryoni, and its close sibling Bactrocera neohumeralis, in large field cages using laboratory reared flies. We used observational experiments that allowed us to determine if: (i) mating pairs were aggregated or nonaggregated; (ii) mating system was resource or nonresource based; (iii) flies utilized possible landmarks (tall trees over short) as mate‐rendezvous sites; and (iv) males called females from male‐dominated leks. We recorded nearly 250 Bactrocera tryoni mating pairs across all experiments, revealing that: (i) mating pairs were aggregated; (ii) mating nearly always occurred in tall trees over short; (iii) mating was nonresource based; and (iv) that males and females arrived at the mate‐rendezvous site together with no evidence that males preceded females. Bactrocera neohumeralis copulations were much more infrequent (only 30 mating pairs in total), but for those pairs there was a similar preference for tall trees and no evidence of a resource‐based mating system. Some aspects of Bactrocera tryoni mating behavior align with theoretical expectations of a lekking system, but others do not. Until evidence for unequivocal female choice can be provided (as predicted under a true lek), the mating system of Bactrocera tryoni is best described as a nonresource based, aggregation system for which we also have evidence that land‐marking may be involved.     

Factors affecting the dispersal of large‐scale releases of the Queensland fruit fly,Bactrocera tryoni

This study investigated two factors potentially affecting the spatial distribution of Queensland fruit fly Bactrocera tryoni (Froggatt) after release from a single point. First, the effect of age at release was investigated using a single cohort of 205 000 males from a mass‐rearing strain used for sterile insect releases. Approximately half were released as immature males and the remainder as sexually mature males (1 week later). Males were collected over 3 weeks from a grid of 135 traps, each containing a pheromone/insecticide bait, positioned between 4 and 500 m from the release point. Variation in the distribution of fly density around the release point was assessed by regressing trapped fly counts against distance. Unexpectedly, no significant differences were found in the spatial distribution of the flies. Second, the effect of inbreeding on spatial distribution was investigated using replicated simultaneous releases of two strains of B. tryoni. One strain was the existing (inbred) mass‐rearing strain that has been selected for high productivity in a mass‐rearing facility. The second strain was deliberately outbred but also selected for high productivity. Almost 100 000 males of each strain were released over the two experiments. Regression of trappings against distance differed significantly between strains in only one of five releases, but in all cases the outbred strain had a greater dispersal distance. As our trapping grid was not regular but contained gaps of up to 100 m, a small preliminary experiment investigated whether flies move faster along tree rows or across open fields. At distances up to 100 m, we found no detectable difference in fly distributions. These results are primarily relevant to the large‐scale point releases carried out as part of an existing B. tryoni sterile insect programme and are discussed in that context.     

Effect of conditions in sealed plastic bags on eclosion of mass‐reared Queensland fruit fly,Bactrocera tryoni

The sterile insect technique has been used for more than 50 years to control a range of insects around the world. Sterile insect technique is rapidly becoming a major component of many area‐wide fruit fly management programmes. Irradiation of immature life stages induces sterility in adults, which are then distributed over large areas to mate with wild flies, resulting in no viable offspring. However, irradiation in normal air results in declining adult quality. To optimize the quality of sterile adult flies, several techniques are available to lower the levels of oxygen in fruit fly tissues prior to irradiation. The simplest method is to seal pupae in plastic bags and allow the oxygen consumption of pupae to minimize oxygen in both the air and pupal tissue. Some fruit fly species have rapid decreases in eclosion as a result of low oxygen atmospheres. We tested the tolerance of Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera: Tephritidae), to low oxygen for the first time. In the first two experiments, unirradiated B. tryoni pupae were tested for different periods in sealed plastic bags at 17, 21, and 26 °C. Optimum eclosion occurred at 21 °C with the lowest eclosion at 26 °C. In general, mean full eclosion declined at ca. 0.1% eclosion per hour sealed in plastic bags during the first 96 h for all temperatures. In the third and fourth experiments at 17 °C, there was a decline in average eclosion for irradiated and unirradiated pupae of about 13.4% after they were sealed in plastic bags for 192 h. In general, B. tryoni eclosion declined at 0.1% per hour inside sealed plastic bags for periods up to 192 h at 17 °C. Queensland fruit flies can tolerate long periods of conditions found inside sealed plastic bags and current practices for sterile B. tryoni release programmes will result in minimum decrease in eclosion. The possible evolution of tolerance of these conditions is discussed.