Queensland fruit fly, Bactrocera tryoni (Froggatt), is the most significant pest of Australia’s $9 billion horticulture industry. The sterile insect technique (SIT) and cue-lure (a synthetic analogue of raspberry ketone (RK))-based male annihilation technique (MAT) are two of the most effective management tools against this pest. However, combining these two approaches is considered incompatible as MAT kills sterile and ‘wild’ males indiscriminately. In the present study we tested the effect of pre-release feeding of B. tryoni on RK on their post-release survival and response to MAT in field cages and in a commercial orchard. In both settings, survival was higher for RK supplemented adults compared to control (i.e. RK denied) adults. A lower number of RK supplemented sterile males were recaptured in MAT baited traps in both the field cages and orchard trials compared to RK denied sterile males. The advantage of this novel “male replacement” approach (relatively selective mortality of wild males at lure-baited traps while simultaneously releasing sterile males) is increasing the ratio of sterile to wild males in the field population, with potential for reducing the number of sterile males to be released.

BackgroundThe Queensland fruit fly, Bactrocera tryoni (Froggatt) (Diptera, Tephritidae) is the most significant insect pest of Australian horticulture. Bactrocera tryoni is controlled using a range of tools including the Sterile Insect Technique (SIT). Mass-rearing and irradiation of pupae in SIT can reduce the fitness and quality of the released sterile insects. Studies have also showed reduced microbial gut diversity in domesticated versus wild tephritids.ResultsTransmission electron microscopy confirmed the presence of the bacterial isolates in the mid-gut of mass-reared larvae, and plate counts from individual larval guts showed increased numbers of bacteria in supplemented larvae. Several developmental and fitness parameters were tested including larval development time (egg-hatch to pupation), pupal weight, emergence, flight ability, sex-ratio, and time to adult eclosion (egg-hatch to adult eclosion). Enterobacter sp. and Asaia sp. shortened larval development time, while this was delayed by Lactobacillus sp., Leuconostoc sp. and a blend of all four bacteria. The mean time from egg hatch to adult eclosion was significantly reduced by Leuconostoc sp. and the blend for males and females, indicating that the individual bacterium and consortium affect flies differently depending on the life stage (larval or pupal). There was no impact of bacterial supplemented larvae on pupal weight, emergence, flight ability, or sex ratio.ConclusionsOur findings show that bacteria fed to the larval stage of B. tryoni can impart fitness advantages, but the selection of probiotic strains (individual or a consortium) is key, as each have varying effects on the host. Bacteria added to the larval diet particularly Leuconostoc sp. and the blend have the capacity to reduce costs and increase the number of flies produced in mass-rearing facilities by reducing time to adult eclosion by 1.3 and 0.8 mean days for males, and 1.2 and 0.8 mean days for females.

This study investigated alternative in-field chemical controls against Bactrocera tryoni (Froggatt). Bioassay 1 tested the mortality of adults exposed to fruit and filter paper dipped in insecticide, and the topical application of insecticide to adults/fruit. Bioassay 2 measured the mortality of adults permitted to oviposit on fruit dipped in insecticide and aged 0, 1, 3, or 5 days, plus the production of offspring. Bioassay 3 tested infested fruit sprayed with insecticide. The field bioassay trialed the mortality of adults exposed to one- and five-day insecticide residues on peaches, and subsequent offspring. Abamectin, alpha-cypermethrin, clothianidin, dimethoate (half-label rate), emamectin benzoate, fenthion (half- and full-label rate), and trichlorfon were the most efficacious in bioassay 1, across 18 tested insecticide treatments. Overall, the LT50 value was lowest for fenthion (full-label rate), clothianidin, and alpha-cypermethrin. Fenthion, emamectin benzoate, and abamectin had the greatest effect on adult mortality and offspring production. Infested fruit treated with acetamiprid, fenthion, and thiacloprid produced no/very few offspring. Alpha-cypermethrin demonstrated good field efficacy against adults (one day post treatment: 97.2% mortality, five day post treatment: 98.8% mortality) and subsequent offspring (100% across one and five day post treatments), comparable to that of fenthion (full-label rate) (100% mortality for offspring and adults across both post treatments). Alpha-cypermethrin is a possible alternative to fenthion against B. tryoni; as a pyrethroid, it may not be desirable if adjunct biological control is imperative. Thiacloprid and Acetamiprid may be useful as a post-harvest treatment.

BACKGROUND: Tephritid fruit flies are recognized as the most economically important insect pest group, causing significant losses to horticultural crops globally. The sterile insect technique (SIT) is used to suppress or eradicate pest fruit flies in many countries. The provisioning of adult dietary or olfactory supplementation pre-release is commonly used to improve the mating performance of sterile male flies in SIT. This study on a major pest species, Queensland fruit fly, Bactrocera tryoni (Froggatt), focused on improving mating performance by providing a semiochemical, raspberry ketone (RK), in the pre-release adult diet. RESULTS: Survival was numerically higher for RK-supplemented males. Sexual maturity occurred 1 day earlier (from 7 to 6 days) in RK-supplemented sterile males. The mating latency period decreased with maturation age and was lower for RK-fed males. RK-supplemented sterile males increasingly mated with fertile females as they aged (10-19 days). The mating competitiveness of both RK-supplemented sterile males and RK-denied sterile males was greater than that of wild males. CONCLUSION: The early sexual maturity and increased mating performance of RK-supplemented sterile males indicate that the effectiveness of SIT programmes can be increased through dietary supplementation with RK during the pre-release period.

The results of this study suggest that a novel male annihilation technique (specialized pheromone and lure application technology [SPLAT] incorporating cue-lure [CL] plus spinosad) is as effective as industry standard male annihilation controls, and is worth exploring further to manageBactrocera tryoni(Froggatt) populations. Three lures were evaluated in a contact and feeding bioassay and a cage attractancy trial: 1) SPLAT-CL + spinosad; 2) SPLAT-CL without spinosad; and 3) wick-CL + malathion. In a field attraction trial, lures (1) and (3) were evaluated with a third treatment, caneite blocks-CL + malathion. Lures were weathered for 0, 1, 2, 4, or 8 wk, with an additional weathering treatment of 12 wk included in the field trial. In the contact and feeding bioassay, lures with SPLAT-CL + spinosad were >97% effective at 48 h for up to 2 wk weathering; however, wicks-CL + malathion killedB. tryoniwithin 2 h of exposure under all weathering periods. In the cage attractancy trial, SPLAT-CL + spinosad was as effective as, or performed better than, wicks-CL + malathion under all weathering treatments. The field study trap catches were similar for SPLAT-CL + spinosad and blocks-CL + malathion, and both had higher trap catches than wicks-CL + malathion at all weathering periods, except week 12. Overall, SPLAT-CL + spinosad compared favorably with current standard techniques for male annihilation and warrants further research. SPLAT-CL + spinosad may be a reduced-risk alternative for wicks-CL + malathion or blocks-CL + malathion forB. tryoniand other CL-responding fruit flies, such asBactrocera cucurbitaeCoquillett, because it contains a reduced-risk insecticide that poses a lower risk to humans and the environment and does not require labor-intensive handling and placement.

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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.

Global markets do not tolerate the presence of fruit fly (Tephritidae) in horticultural produce. A key method of control for tephritidae pests, is the sterile insect technique (SIT). Several countries release a bisex strain, i.e., males and females, however the sterile male is the only sex which contributes to wild population declines when released en masse. In commercial orchards, there are concerns that sterile females released as part of bisex strains, may oviposit, i.e., ‘sting’ and cause damage to fruit, rendering it unmarketable. Australia has released a bisex strain of sterile Queensland fruit fly, Bactrocera tryoni Froggatt, for several decades to suppress wild pest populations, particularly in peri-urban and urban environments. Here, we assessed fruit damage in two commercially grown stone fruit orchards where bisex sterile B. tryoni were released, and in an orchard that did not receive sterile flies. The number of detected stings were higher in only one SIT release orchard, compared with the control; however, there was no difference between SIT and control orchards in the number of larvae detected. We showed that there is no evidence that sterile female B. tryoni released in large numbers caused stings, or damage that led to downgraded or unsaleable fruit. The bisex strain of sterile B. tryoni is recommended for use in commercial stone-fruit orchards, under the conditions in which this trial was conducted.