Effective trapping of fruit flies with cultures of metabolically modified acetic acid bacteria

Axenic and gnotobiotic insect technologies in research on host-microbiota interactions

Insects are one of the most important animal life forms on earth. Symbiotic microbes are closely related to the growth and development of the host insects and can affect pathogen transmission. For decades, various axenic insect-rearing systems have been developed, allowing further manipulation of symbiotic microbiota composition. Here we review the historical development of axenic rearing systems and the latest progress in using axenic and gnotobiotic approaches to study insect-microbe interactions. We also discuss the challenges of these emerging technologies, possible solutions to address these challenges, and future research directions that can contribute to a more comprehensive understanding of insect-microbe interactions.

Effect of Aging on Three Lures Used for Monitoring Ceratitis capitata (Diptera: Tephritidae): Release Rate, Volatile Composition, and Fly Recaptures

Prevention and control programs for Ceratitis capitata require a large supply of lures and traps for use in established trapping networks and mass-trapping suppression measures. The main lures currently used are: Trimedure (TML), three-component Biolure (BL), and Ceratrap (CT). The aim of this study was to determine the release rates of these lures, the chemical composition of their volatiles, and how these parameters change with exposure time. Tests were conducted under field conditions at three different elevations (25, 500, and 1,300 masl) during the dry and rainy seasons in Chiapas, Mexico. We found that for TML and BL, the release rate was similar in both seasons and at all three elevations. In the case of CT, the release rate was greater during the dry season and at the lowest elevation during the rainy season. With the caveat of using solid-phase microextraction technique for identification of lure compounds in this study, we found that the volatile compounds of TML were maintained throughout the rainy season, however, in the dry season, some compounds could not be detected. The volatile compounds emitted by BL were trimethylamine, ammonium acetate, and acetamide. Among volatile compounds of CT, acetic acid was the most abundant in the rainy season, while minor compounds were only detected during the first five weeks. Recapture rates were affected by elevation in the three lures tested and there was a significant interaction between elevation in exposure time for TML and BL.

Brown Rice Vinegar as an Olfactory Field Attractant for Drosophila suzukii (Matsumura) and Zaprionus indianus Gupta (Diptera: Drosophilidae) in Cherimoya in Maui, Hawaii, with Implications for Attractant Specificity between Species and Estimation of Relative Abundance

Drosophila suzukii (Matsumura) is an agricultural pest that has been observed co-infesting soft-skinned fruits with Zaprionus indianus Gupta. The characterization of olfactory preferences by species is a necessary step towards the development of species-specific attractants. Five olfactory attractants were used to survey the populations of two invasive drosophilids in cherimoya in Maui, Hawaii. The attractants used were apple cider vinegar (ACV), brown rice vinegar (BRV), red wine (RW), apple cider vinegar and red wine (ACV+RW; 60/40), and brown rice vinegar and red wine (BRV+RW; 60/40). For D. suzukii, BRV+RW resulted in more captures than BRV, ACV, and RW, while ACV+RW resulted in more captures than ACV. No differences were observed between BRV+RW and ACV+RW. BRV had greater specificity in attracting D. suzukii compared to ACV, ACV+RW, and RW. For Z. indianus, no significant differences were observed in either the mean captures or specificity for any attractant used. Collectively, these findings demonstrate that (1) BRV and BRV+RW are effective field attractants and (2) D. suzukii has unique olfactory preferences compared to non-target drosophilids, while (3) Z. indianus’ preferences do not appear to vary from non-target drosophilids, and (4) the accuracy of relative abundance is impacted by the specificity of the attractants.

Agmatine Production by Aspergillus oryzae Is Elevated by Low pH during Solid-State Cultivation

Sake (rice wine) produced by multiple parallel fermentation (MPF) involving Aspergillus oryzae (strain RW) and Saccharomyces cerevisiae under solid-state cultivation conditions contained 3.5 mM agmatine, while that produced from enzymatically saccharified rice syrup by S. cerevisiae contained <0.01 mM agmatine. Agmatine was also produced in ethanol-free rice syrup prepared with A. oryzae under solid-state cultivation (3.1 mM) but not under submerged cultivation, demonstrating that A. oryzae in solid-state culture produces agmatine. The effect of cultivation conditions on agmatine production was examined. Agmatine production was boosted at 30°C and reached the highest level (6.3 mM) at pH 5.3. The addition of l-lactic, succinic, and citric acids reduced the initial culture pHs to 3.0, 3.5, and 3.2, respectively, resulting in a further increase in agmatine accumulation (8.2, 8.7, and 8.3 mM, respectively). Homogenate from a solid-state culture exhibited a maximum l-arginine decarboxylase (ADC) activity (74 pmol · min^-1 · μg^-1) at pH 3.0 at 30°C; homogenate from a submerged culture exhibited an extremely low activity (<0.3 pmol · min^-1 · μg^-1) under all conditions tested. These observations indicated that efficient agmatine production in ethanol-free rice syrup is achieved by an unidentified low-pH-dependent ADC induced during solid-state cultivation of A. oryzae, even though A. oryzae lacks ADC orthologs and instead possesses four ornithine decarboxylases (ODC1 to ODC4). Recombinant ODC1 and ODC2 exhibited no ADC activity at acidic pH (pH < 4.0), suggesting that other decarboxylases or an unidentified ADC is involved in agmatine production.IMPORTANCE It has been speculated that, in general, fungi do not synthesize agmatine from l-arginine because they do not possess genes encoding arginine decarboxylase. Numerous preclinical studies have shown that agmatine exerts pleiotropic effects on various molecular targets, leading to an improved quality of life. In the present study, we first demonstrated that l-arginine was a feasible substrate for agmatine production by the fungus Aspergillus oryzae RW. We observed that the productivity of agmatine by A. oryzae RW was elevated at low pH only during solid-state cultivation. A. oryzae is utilized in the production of various Asian fermented foods. The saccharification conditions optimized in the current study could be employed not only in the production of an agmatine-containing ethanol-free rice syrup but also in the production of many types of fermented foods, such as soy sauce (shoyu), rice vinegar, etc., as well as for use as novel therapeutic agents and nutraceuticals.

Polyamines in brown rice vinegar function as potent attractants for the spotted wing drosophila

Vinegar produced by acetic acid bacteria is used as an attractant for fruit flies. Apple cider vinegar (ACV) and brown rice vinegar (BRV) are used as lures to detect Drosophila suzukii (also known as the spotted wing drosophila [SWD], a newly emerging invasive pest of soft-skinned fruits) and to capture Drosophila melanogaster, respectively. In the present study, we evaluated the attractiveness of BRV and ACV to SWD in laboratory trapping experiments using an upturned microcentrifuge tube with a pipette tip as a trap. We transferred SWD (approximately 20, 7-10 days old) to a glass vial containing a trap baited with BRV or ACV and counted the captured flies. BRV attracted more flies (52.88 ± 9.75%) than ACV (35.78 ± 7.47%) in 6 h. Based on high-performance liquid chromatography, we found that BRV contained greater amounts of putrescine (12.36 ± 0.44 μM) and spermidine (35.08 ± 4.34 μM) than ACV (putrescine, 0.31 ± 0.067 μM; spermidine, not detected). The attractiveness of ACV supplemented with putrescine (12 μM) and spermidine (35 μM) (68.56 ± 4.69%) was significantly higher than that of ACV, indicating that the enhanced attractiveness of BRV to SWD was accomplished by the additive effects of polyamines and other known attractive volatiles, such as acetic acid and acetoin. BRV is expected to be a powerful tool for the efficient management of SWD.