The microbiota of Drosophila suzukii influences the larval development of Drosophila melanogaster

The influence of Acetobacter pomorum bacteria on the developmental progression of Drosophila suzukii via gluconic acid secretion

Insects are rich in various microorganisms, which play diverse roles in affecting host biology. Although most Drosophila species prefer rotten fruits, the agricultural pest Drosophila suzukii attacks ripening fruits before they are harvested. We have reported that the microbiota has positive and negative impacts on the agricultural pest D. suzukii on nutrient-poor and -rich diets, respectively. On nutrient-poor diets, microbes provide protein to facilitate larval development. But how they impede D. suzukii development on nutrient-rich diets is unknown. Here we report that Acetobacter pomorum (Apo), a commensal bacterium in many Drosophila species and rotting fruit, has several detrimental effects in D. suzukii. Feeding D. suzukii larvae nutrient-rich diets containing live Apo significantly delayed larval development and reduced the body weight of emerged adults. Apo induced larval immune responses and downregulated genes of digestion and juvenile hormone metabolism. Knockdown of these genes in germ-free larvae reproduced Apo-like weakened phenotypes. Apo was confirmed to secrete substantial amounts of gluconic acid. Adding gluconic acid to the D. suzukii larval diet hindered larval growth and decreased adult body weight. Moreover, the dose of gluconic acid that adversely affected D. suzukii did not negatively affect Drosophila melanogaster, suggesting that D. suzukii is less tolerant to acid than D. melanogaster. Taken together, these findings indicate that D. suzukii is negatively affected by gluconic acid, which may explain why it prefers ripening fruit over Apo-rich rotting fruit. These results show an insect's tolerance to microbes can influence its ecological niche.

Identification of key yeast species and microbe-microbe interactions impacting larval growth of Drosophila in the wild

Microbiota consisting of various fungi and bacteria have a significant impact on the physiological functions of the host. However, it is unclear which species are essential to this impact and how they affect the host. This study analyzed and isolated microbes from natural food sources of Drosophila larvae, and investigated their functions. Hanseniaspora uvarum is the predominant yeast responsible for larval growth in the earlier stage of fermentation. As fermentation progresses, Acetobacter orientalis emerges as the key bacterium responsible for larval growth, although yeasts and lactic acid bacteria must coexist along with the bacterium to stabilize this host-bacterial association. By providing nutrients to the larvae in an accessible form, the microbiota contributes to the upregulation of various genes that function in larval cell growth and metabolism. Thus, this study elucidates the key microbial species that support animal growth under microbial transition.

Recent trends in insect gut immunity

The gut is a crucial organ in insect defense against various pathogens and harmful substances in their environment and diet. Distinct insect gut compartments possess unique functionalities contributing to their physiological processes, including immunity. The insect gut's cellular composition is vital for cellular and humoral immunity. The peritrophic membrane, mucus layer, lumen, microvilli, and various gut cells provide essential support for activating and regulating immune defense mechanisms. These components also secrete molecules and enzymes that are imperative in physiological activities. Additionally, the gut microbiota initiates various signaling pathways and produces vitamins and minerals that help maintain gut homeostasis. Distinct immune signaling pathways are activated within the gut when insects ingest pathogens or hazardous materials. The pathway induced depends on the infection or pathogen type; include immune deficiency (imd), Toll, JAK/STAT, Duox-ROS, and JNK/FOXO regulatory pathways. These pathways produce different antimicrobial peptides (AMPs) and maintain gut homeostasis. Furthermore, various signaling mechanisms within gut cells regulate insect gut recovery following infection. Although some questions regarding insect gut immunity in different species require additional study, this review provides insights into the insect gut's structure and composition, commensal microorganism roles in Drosophila melanogaster and Tenebrio molitor life cycles, different signaling pathways involved in gut immune systems, and the insect gut post-infection recovery through various signaling mechanisms.

Factors influencing oviposition behaviour of the invasive pest, Drosophila suzukii, derived from interactions with other Drosophila species: potential applications for control

Drosophila suzukii (Matsumura) or spotted wing Drosophila is a worldwide invasive pest of soft- and stone-fruit production. Female D. suzukii lay their eggs in ripening fruit and the hatched larvae damage fruit from the inside, rendering it unmarketable and causing significant economic loss. Current methods to reduce D. suzukii population in the field primarily rely on chemical insecticides which are not a sustainable long-term solution and increase the risk of resistance developing. Several studies demonstrate that when D. suzukii encounter or coexist with other Drosophila on a food source, this is usually a disadvantage to D. suzukii, leading to reduced oviposition and increased larval mortality. These effects have potential to be exploited from a pest management perspective. In this review we summarise recent research articles focusing on the interspecific interactions between D. suzukii and other Drosophila species aimed at understanding how this drives D. suzukii behaviour. Potential semiochemical and microbiome impacts are postulated as determinants of D. suzukii behaviour. Development of control practices focusing on reducing D. suzukii populations and deterring them from laying eggs by utilising factors that drive their behaviour are discussed. © 2023 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Microbiome Structure of a Wild Drosophila Community along Tropical Elevational Gradients and Comparison to Laboratory Lines

Variation along environmental gradients in host-associated microbial communities is not well understood compared to free-living microbial communities. Because elevational gradients may serve as natural proxies for climate change, understanding patterns along these gradients can inform our understanding of the threats hosts and their symbiotic microbes face in a warming world. In this study, we analyzed bacterial microbiomes from pupae and adults of four Drosophila species native to Australian tropical rainforests. We sampled wild individuals at high and low elevations along two mountain gradients to determine natural diversity patterns. Further, we sampled laboratory-reared individuals from isofemale lines established from the same localities to see if any natural patterns are retained in the lab. In both environments, we controlled for diet to help elucidate other deterministic patterns of microbiome composition. We found small but significant differences in Drosophila bacterial community composition across elevation, with some notable taxonomic differences between different Drosophila species and sites. Further, we found that field-collected fly pupae had significantly richer microbiomes than laboratory-reared pupae. We also found similar microbiome composition in both types of provided diet, suggesting that the significant differences found among Drosophila microbiomes are the products of surrounding environments with different bacterial species pools, possibly bound to elevational differences in temperature. Our results suggest that comparative studies between lab and field specimens help reveal the true variability in microbiome communities that can exist within a single species. IMPORTANCE Bacteria form microbial communities inside most higher-level organisms, but we know little about how the microbiome varies along environmental gradients and between natural host populations and laboratory colonies. To explore such effects on insect-associated microbiomes, we studied the gut microbiome in four Drosophila species over two mountain gradients in tropical Australia. We also compared these data to individuals kept in the laboratory to understand how different settings changed microbiome communities. We found that field-sampled individuals had significantly higher microbiome diversity than those from the lab. In wild Drosophila populations, elevation explains a small but significant amount of the variation in their microbial communities. Our study highlights the importance of environmental bacterial sources for Drosophila microbiome composition across elevational gradients and shows how comparative studies help reveal the true flexibility in microbiome communities that can exist within a species.

Selection and Comparative Gene Expression of Midgut-Specific Targets for Drosophila suzukii

Spotted-wing drosophila (SWD), Drosophila suzukii, is a destructive and invasive pest that attacks most small fruits and cherries. The current management for SWD involves the use of conventional insecticides. In an effort to develop a biologically based control option, the application of RNA interference (RNAi) has been investigated. To develop an RNAi approach, suitable targets must be identified, and an efficient delivery method must be developed for introducing the double-stranded RNA (dsRNA) in the midgut. In D. suzukii, we previously found that dsRNA nucleases actively degrade dsRNA molecules in the midgut. In this study, we focused on identifying biological targets focused on the midgut membrane. The profile of midgut-specific genes was analyzed and compared with the genes expressed in the whole-body using transcriptome analysis. Differential gene expression analysis revealed that 1921 contigs were upregulated and 1834 contigs were downregulated in the midgut when compared to genes from other body tissues. We chose ten midgut-specifically upregulated genes and empirically confirmed their expressions. We are particularly interested in the midgut membrane proteins, including G protein-coupled receptors (GPCRs) such as diuretic hormone 31 (DH31) receptor, neuropeptide F (NPF) recepror, toll-9, adhesion receptors, methuselah (mth), and gustatory receptor, because insect GPCRs have been offered great potential for next-generation pest management.

Gut fungal community and its probiotic effect on Bactrocera dorsalis

The oriental fruit fly, Bactrocera dorsalis (Diptera: Tephritidae) is a destructive horticultural pest which causes considerable economic losses every year. A collection of microorganisms live within the B. dorsalis gut, and they are involved in its development, physiology, and behavior. However, knowledge regarding the composition and function of the gut mycobiota in B. dorsalis are still limited. Here, we comprehensively characterized the gut mycobiota in B. dorsalis across different developmental stages. High-throughput sequencing results showed a significant difference in fungal species abundance and diversity among different developmental stages of B. dorsalis. Quantitative polymerase chain reaction and culture-dependent methods showed that yeast species was the dominant group in the larval stage. We isolated 13 strains of yeast from the larval gut, and found that GF (germ-free) larvae mono-associated with strain Hanseniaspora uvarum developed faster than those mono-associated with other tested fungal strains. Supplementing the larval diet with H. uvarum fully rescued B. dorsalis development, shortened the larval developmental time, and increased adult wing lengths, as well as the body sizes and weights of both pupae and adults. Thus, our study highlights the close interactions between gut fungi, especially H. uvarum, and B. dorsalis. These findings can be applied to the sterile insect technique program to promote host development during mass insect rearing.

Beyond canonical models: why a broader understanding of Diptera-microbiota interactions is essential for vector-borne disease control

Vector-borne diseases constitute a major global public health threat. The most significant arthropod disease vectors are predominantly comprised of members of the insect order Diptera (true flies), which have long been the focus of research into host-pathogen dynamics. Recent studies have revealed the underappreciated diversity and function of dipteran-associated gut microbial communities, with important implications for dipteran physiology, ecology, and pathogen transmission. However, the effective parameterization of these aspects into epidemiological models will require a comprehensive study of microbe-dipteran interactions across vectors and related species. Here, we synthesize recent research into microbial communities associated with major families of dipteran vectors and highlight the importance of development and expansion of experimentally tractable models across Diptera towards understanding the functional roles of the gut microbiota in modulating disease transmission. We then posit why further study of these and other dipteran insects is not only essential to a comprehensive understanding of how to integrate vector-microbiota interactions into existing epidemiological frameworks, but our understanding of the ecology and evolution of animal-microbe symbiosis more broadly.

A Functional Analysis of the Purine Salvage Pathway in Acetobacter fabarum

Acetobacter species are a major component of the gut microbiome of the fruit fly Drosophila melanogaster, a widely used model organism. While a range of studies have illuminated impacts of Acetobacter on their hosts, less is known about how association with the host impacts bacteria. A previous study identified that a purine salvage locus was commonly found in Acetobacter associated with Drosophila. In this study, we sought to verify the functions of predicted purine salvage genes in Acetobacter fabarum DsW_054 and to test the hypothesis that these bacteria can utilize host metabolites as a sole source of nitrogen. Targeted gene deletion and complementation experiments confirmed that genes encoding xanthine dehydrogenase (xdhB), urate hydroxylase (urhA), and allantoinase (puuE) were required for growth on their respective substrates as the sole source of nitrogen. Utilization of urate by Acetobacter is significant because this substrate is the major nitrogenous waste product of Drosophila, and its accumulation in the excretory system is detrimental to both flies and humans. The potential significance of our findings for host purine homeostasis and health are discussed, as are the implications for interactions among microbiota members, which differ in their capacity to utilize host metabolites for nitrogen. IMPORTANCEAcetobacter are commonly found in the gut microbiota of fruit flies, including Drosophila melanogaster. We evaluated the function of purine salvage genes in Acetobacter fabarum to test the hypothesis that this bacterium can utilize host metabolites as a source of nitrogen. Our results identify functions for three genes required for growth on urate, a major host waste product. The utilization of this and other Drosophila metabolites by gut bacteria may play a role in their survival in the host environment. Future research into how microbial metabolism impacts host purine homeostasis may lead to therapies because urate accumulation in the excretory system is detrimental to flies and humans.

Isolation and Identification of Wild Yeast from Malaysian Grapevine and Evaluation of Their Potential Antimicrobial Activity against Grapevine Fungal Pathogens

Pathogenic fungi belonging to the genera Botrytis, Phaeomoniella, Fusarium, Alternaria and Aspergillus are responsible for vines diseases that affect the growth, grapevine yield and organoleptic quality. Among innovative strategies for in-field plant disease control, one of the most promising is represented by biocontrol agents, including wild epiphytic yeast strains of grapevine berries. Twenty wild yeast, isolated and molecularly identified from three different Malaysian regions (Perlis, Perak and Pahang), were evaluated in a preliminary screening test on agar to select isolates with inhibition against Botrytis cinerea. On the basis of the results, nine yeasts belonging to genera Hanseniaspora, Starmerella, Metschnikowia, Candida were selected and then tested against five grape berry pathogens: Aspergillus carbonarius, Aspergillus ochraceus, Fusarium oxysporum, Alternaria alternata and Phaeomoniella chlamydospora.Starmerella bacillaris FE08.05 and Metschnikowia pulcherrima GP8 and Hanseniaspora uvarum GM19 showed the highest effect on inhibiting mycelial growth, which ranged between 15.1 and 4.3 mm for the inhibition ring. The quantitative analysis of the volatile organic compound profiles highlighted the presence of isoamyl and phenylethyl alcohols and an overall higher presence of low-chain fatty acids and volatile ethyl esters. The results of this study suggest that antagonist yeasts, potentially effective for the biological control of pathogenic moulds, can be found among the epiphytic microbiota associated with grape berries.

Enterobacter sp. AA26 as a Protein Source in the Larval Diet of Drosophila suzukii

The Spotted-Wing Drosophila fly, Drosophila suzukii, is an invasive pest species infesting major agricultural soft fruits. Drosophila suzukii management is currently based on insecticide applications that bear major concerns regarding their efficiency, safety and environmental sustainability. The sterile insect technique (SIT) is an efficient and friendly to the environment pest control method that has been suggested for the D. suzukii population control. Successful SIT applications require mass-rearing of the strain to produce competitive and of high biological quality males that will be sterilized and consequently released in the wild. Recent studies have suggested that insect gut symbionts can be used as a protein source for Ceratitis capitata larval diet and replace the expensive brewer's yeast. In this study, we exploited Enterobacter sp. AA26 as partial and full replacement of inactive brewer's yeast in the D. suzukii larval diet and assessed several fitness parameters. Enterobacter sp. AA26 dry biomass proved to be an inadequate nutritional source in the absence of brewer's yeast and resulted in significant decrease in pupal weight, survival under food and water starvation, fecundity, and adult recovery.

Physicochemical Characteristics and Superficial Damage Modulate Persimmon Infestation by Drosophila suzukii (Diptera: Drosophilidae) and Zaprionus indianus

Drosophila suzukii (Matsumura) (Diptera: Drosophilidae) and Zaprionus indianus Gupta (Diptera: Drosophilidae) were recently observed co-infesting persimmons in Brazil. We evaluate the infestation susceptibility of persimmons at different ripening stages (unripe, UN; early ripe, ER; orange ripe, OR, and overripe, OV) by D. suzukii and Z. indianus in the field and laboratory conditions. Additionally, we determined the influence of physicochemical characteristics (e.g., resistance to penetration force, fruit skin color, acidity (pH), TSS concentration, total titratable acidity [TTA]) and the type of damage that facilitates infestation by D. suzukii or Z. indianus. In the field, the natural infestation capacity and biological development of D. suzukii and Z. indianus were verified in whole fruits at the ripening stages ER, OR, and OV. The natural infestation was directly related to the physicochemical characteristics of the fruits (resistance to penetration force, pH, and total soluble solids). In the no-choice bioassay, the oviposition rate of D. suzukii did not differ between the ripening stages of the fruit. However, in the choice bioassay, there was a higher preference for oviposition in OV fruits. Regarding Z. indianus, the highest preference for oviposition was observed in OR and OV fruits in both bioassays. The presence of mechanical damage did not increase the susceptibility of the fruits to D. suzukii. However, it favored the oviposition of Z. indianus in OR and OV fruits. The damage caused by D. suzukii or mechanical damage favored the infestation by Z. indianus. This is the first report of the capacity of D. suzukii to infest whole persimmons in Brazil.

How gut microbiome interactions affect nutritional traits of Drosophila melanogaster

Most research on the impact of the gut microbiome on animal nutrition is designed to identify the effects of single microbial taxa and single metabolites of microbial origin, without considering the potentially complex network of interactions among co-occurring microorganisms. Here, we investigated how different microbial associations and their fermentation products affect host nutrition, using Drosophila melanogaster colonized with three gut microorganisms (the bacteria Acetobacter fabarum and Lactobacillus brevis, and the yeast Hanseniaspora uvarum) in all seven possible combinations. Some microbial effects on host traits could be attributed to single taxa (e.g. yeast-mediated reduction of insect development time), while other effects were sex specific and driven by among-microbe interactions (e.g. male lipid content determined by interactions between the yeast and both bacteria). Parallel analysis of nutritional indices of microbe-free flies administered different microbial fermentation products (acetic acid, acetoin, ethanol and lactic acid) revealed a single consistent effect: that the lipid content of both male and female flies is reduced by acetic acid. This effect was recapitulated in male flies colonized with both yeast and A. fabarum, but not for any microbial treatment in females or males with other microbial complements. These data suggest that the effect of microbial fermentation products on host nutritional status is strongly context dependent, with respect to both the combination of associated microorganisms and host sex. Taken together, our findings demonstrate that among-microbe interactions can play a critically important role in determining the physiological outcome of host-microbiome interactions in Drosophila and, likely, in other animal hosts.