Metagenomic Survey of the Highly Polyphagous Anastrepha ludens Developing in Ancestral and Exotic Hosts Reveals the Lack of a Stable Microbiota in Larvae and the Strong Influence of Metamorphosis on Adult Gut Microbiota

Evaluating impacts of radiation-induced sterilization on the performance and gut microbiome of mass-reared Mediterranean fruit fly (Ceratitis capitata) in Hawai'i

Sterile insect technique (SIT) is a useful strategy for preventing and mitigative establishment of invasive insect species. SIT of the pest tephritid Mediterranean fruit fly, Ceratitis capitata (Wiedemann, 1824)WiedemannWiedemann, has been effective in preventing population establishment in vulnerable agricultural areas of the United States. However, irradiation-induced sterilization can have detrimental impacts resulting in reduced performance metrics. Mediterranean fruit fly males reared for SIT have been shown to have differences in their microbiomes relative to other population sources, which has been postulated to be a factor in how well flies compete with wild conspecifics. To identify baseline performance metrics on the effects of irradiation on the gut microbiome of mass-reared flies in Hawai'i, a study was performed to assess performance metrics and microbiome (bacterial 16S rRNA) variation across multiple timepoints. Mediterranean fruit fly pupae were selected from mass-reared trays intended for release, and paired samples were either irradiated or remained as controls and transported to the laboratory for evaluation. Irradiated flies exhibited fewer successful fliers, more rapid mortality rates, and were less active relative to control nonirradiated flies. Contrary to initial expectations, irradiation did not exert substantial impacts on the composition or diversity of bacterial reads. Samples were primarily comprised of sequences classified as Klebsiella and there were low levels of both read and taxonomic diversity relative to other 16S surveys of medfly. Although this study does not demonstrate a strong effect of irradiation alone on the Mediterranean fruit fly microbiome, there are several explanations for this discrepancy.

Safety Assessment of the Potential Probiotic Bacterium Limosilactobacillus fermentum J23 Using the Mexican Fruit Fly (Anastrepha ludens Loew, Diptera: Tephritidae) as a Novel In Vivo Model

Safety assessment of probiotics is difficult but essential. In this work, the Mexican fruit fly, Anastrepha ludens (Loew) (Diptera: Tephritidae), was used as in vivo model to assess the biosafety of Limosilactobacillus fermentum J23. In the first set of experiments, the strain was orally administered to adult flies through direct feeding, whereas in the second set of experiments, it was supplemented through the larval rearing medium. Data showed that L. fermentum J23 did not lead to increased mortality or treatment-related toxicity signs in adult female and male flies. Ingestion of L. fermentum J23 by adult female flies led to a statistically significant improvement in locomotor activity compared to the control groups (ca. 59% decrease in climbing time, p < 0.0001). A positive trend in lifespan extension under stress (maximum lifespan = 144 h) was also observed. When L. fermentum J23 was administered to the larvae, the adult emergence (p = 0.0099), sex ratio (p = 0.0043), and flight ability (p = 0.0009) increased significantly by 7%, 31%, and 8%, respectively, compared to the control diet. No statistical effect between the control diet and the L. fermentum J23-based diet for the number of pupae recovered, pupal weight, duration of the pupal stage, lifespan under stress, and morphological development was observed. We conclude that feeding L. fermentum J23 to the novel experimental model A. ludens had no toxic effects and could be safely considered a potential probiotic for food supplements; however, further studies are still needed to establish its biosafety in humans.

Gut bacterial population and community dynamics following adult emergence in pest tephritid fruit flies

Gut microbiota are important contributors to insect success. Host-microbe interactions are dynamic and can change as hosts age and/or encounter different environments. A turning point in these relationships the transition from immature to adult life stages, particularly for holometabolous insects where there is radical restructuring of the gut. Improved knowledge of population and community dynamics of gut microbiomes upon adult emergence inform drivers of community assembly and physiological aspects of host-microbe interactions. Here, we evaluated the bacterial communities of the pest tephritid species melon fly (Zeugodacus cucurbitae) and Medditeranean fruit fly (medfly, Ceratitis capitata) associated with the pupae life stage and timepoints immediately following adult eclosion. We used a combination of culturing to determine cultivatable bacterial titers, qPCR to determine 16S-rRNA SSU copy numbers, and 16S V4 sequencing to determine changes in communities. Both culturing and qPCR revealed that fly bacterial populations declined upon adult emergence by 10 to 100-fold followed by recovery within 24 h following eclosion. Titers reached ~ 107 CFUs (~ 108 16S rRNA copies) within a week post-emergence. We also observed concurrent changes in amplicon sequence variance (ASVs), where the ASV composition differed overtime for both melon fly and medfly adults at different timepoints. Medfly, in particular, had different microbiome compositions at each timepoint, indicating greater levels of variation before stabilization. These results demonstrate that tephritid microbiomes experience a period of flux following adult emergence, where both biomass and the makeup of the community undergoes dramatic shifts. The host-microbe dynamics we document suggest plasticity in the community and that there may be specific periods where the tephritid gut microbiome may be pliable to introduce and establish new microbial strains in the host.

How Rearing Systems for Various Species of Flies Benefit Humanity

Flies (Diptera) have played a prominent role in human history, and several fly species are reared at different scales and for different beneficial purposes worldwide. Here, we review the historical importance of fly rearing as a foundation for insect rearing science and technology and synthesize information on the uses and rearing diets of more than 50 fly species in the families Asilidae, Calliphoridae, Coelopidae, Drosophilidae, Ephydridae, Muscidae, Sarcophagidae, Stratiomyidae, Syrphidae, Tachinidae, Tephritidae, and Tipulidae. We report more than 10 uses and applications of reared flies to the well-being and progress of humanity. We focus on the fields of animal feed and human food products, pest control and pollination services, medical wound therapy treatments, criminal investigations, and on the development of several branches of biology using flies as model organisms. We highlight the relevance of laboratory-reared Drosophila melanogaster Meigen as a vehicle of great scientific discoveries that have shaped our understanding of many biological systems, including the genetic basis of heredity and of terrible diseases such as cancer. We point out key areas of fly-rearing research such as nutrition, physiology, anatomy/morphology, genetics, genetic pest management, cryopreservation, and ecology. We conclude that fly rearing is an activity with great benefits for human well-being and should be promoted for future advancement in diverse and innovative methods of improving existing and emerging problems to humanity.

Feeding on the Fruit Waste Orange Bagasse Modifies Immature Protein Content, Body Weight, Scent Bouquet Composition, and Copula Duration in Males of a Tephritid Frugivorous Fly

Anastrepha ludens is a polyphagous frugivorous tephritid that infests citrus and mango. Here, we report the establishment of a laboratory colony of A. ludens reared on a larval medium that is a waste for the citrus industry, specifically, orange (Citrus × sinensis) fruit bagasse. After 24 generations of rearing on a nutritionally poor orange bagasse diet, pupae weighed 41.1% less than pupae from a colony reared on a nutritionally rich artificial diet. Larvae from the orange bagasse diet had 6.94% less protein content than larvae from the artificial diet, although their pupation rate was similar. Males from the orange bagasse diet produced a scent bouquet with 21 chemical compounds and were sexually competitive, but they had significantly shorter copulations when compared to males from the artificial diet and from the wild host, Casimiroa edulis, which had relatively simple scent bouquets. The chemical complexity in the odors of males from the orange bagasse diet might initially have attracted females to novel scent combinations, but, once in the copula, they may have been able to sense negative characteristics in males, leading them to terminate copulations soon after they began. We conclude that A. ludens can adjust morphological, life history, nutritional, and chemical traits when adapted to a larval environment consisting of fruit bagasse.

Pathogenicity of multiple Providencia species (Enterobacteriales: Morganellaceae) to the mass-reared Mexican fruit fly (Diptera: Tephritidae)

Mexican fruit fly (Anastrepha ludens (Loew)) (Diptera: Tephritidae) represents a major threat to fruit production in the Western Hemisphere. Sterile insect technique is used to suppress and eradicate wild populations. Success of this control method necessitates weekly production of hundreds of millions of flies, their sterilization by irradiation, and their aerial release. Diet needed to produce large fly numbers are conducive to the spread of bacteria. Pathogenic bacteria were isolated from 3 rearing facilities and from multiple sources: eggs, larvae, pupae and spent diet, and were found to include some isolates identified to the genus Providencia (Enterobacteriales: Morganellaceae). We identified 41 Providencia isolates and tested their pathogenicity to A. ludens. Based on 16s rRNA sequences, 3 groups were clustered into several species of Providencia with varying capacities to affect the Mexican fruit fly production. Isolates putatively identified as P. alcalifaciens/P. rustigianii were all pathogenic causing larval and pupal yield reduction of 46-64% and 37-57%, respectively. Among them, Providencia isolate 3006 was the most pathogenic reducing larval and pupae yield by 73 and 81%, respectively. Isolates identified as P. sneebia were not pathogenic. The final cluster, P. rettgeri/P. vermicola, were variable in pathogenicity with 3 isolates yielding like the control and the rest causing larval and pupal yield reduction of 26-53% and 23-51%, respectively. Isolates putatively identified as P. alcalifaciens/P. rustigianii were more virulent than P. rettgeri/P. vermicola. Accurate identification of species is needed to diagnose and monitor pathogenic versus nonpathogenic Providencia strains.

Effect of a Probiotic-Enriched Diet on Sexual Competitiveness, Pheromone Emission, and Cuticular Hydrocarbons of Sterile and Fertile Anastrepha ludens (Diptera: Tephritidae)

The sterile insect technique has been used for the eradication or control of numerous tephritid fruit flies. However, mass-rearing and sterilization can affect the microbiota and sexual performance of male tephritid fruit flies. Despite the addition of postteneral protein food which contributes to the enhancement of the sexual performance of mass-reared males, in some cases, they are less competitive than their wild counterparts. Alternatively, the addition of probiotics may improve the sexual performance of mass-reared sterile males. In this study, we evaluated the effect of a postteneral Lactobacillus casei-enriched diet on the sexual competitivity, pheromone emission, and cuticular hydrocarbons of mass-reared sterile and fertile Anastrepha ludens (Loew) (Diptera: Tephritidae) males. Flies were fed either with sugar, standard diet (sugar and protein, 3:1), sugar + probiotic, or standard diet + probiotic. The addition of the probiotic improved the sexual competitivity of fertile and sterile males that were devoid of protein but led to a negative effect on males fed with a standard diet. As compared to males that were fed with the standard diet + probiotic/only sugar, the males fed with the standard diet or those fed on sugar + probiotic displayed a higher number of mating instances. Sterile males that fed on sugar + probiotic had a higher relative amount of anastrephine, epianastrephine, n-methyl octacosane, and 2-methyl triacontane than those fed on sugar only. Overall, these compounds were common in the treatments where males had the best sexual performance. Our results suggest that the probiotics offer nutritional advantages to males whose food lacks protein.

Bitter friends are not always toxic: The loss of acetic acid bacteria and the absence of Komagataeibacter in the gut microbiota of the polyphagous fly Anastrepha ludens could inhibit its development in Psidium guajava in contrast to A. striata and A. fraterculus that flourish in this host

The gut microbiota is key for the homeostasis of many phytophagous insects, but there are few studies comparing its role on host use by stenophagous or polyphagous frugivores. Guava (Psidium guajava) is a fruit infested in nature by the tephritids Anastrepha striata and A. fraterculus. In contrast, the extremely polyphagous A. ludens infests guava only under artificial conditions, but unlike A. striata and the Mexican A. fraterculus, it infests bitter oranges (Citrus x aurantium). We used these models to analyze whether the gut microbiota could explain the differences in host use observed in these flies. We compared the gut microbiota of the larvae of the three species when they developed in guava and the microbiota of the fruit pulp larvae fed on. We also compared the gut microbiota of A. ludens developing in C. x aurantium with the pulp microbiota of this widely used host. The three flies modified the composition of the host pulp microbiota (i.e., pulp the larvae fed on). We observed a depletion of Acetic Acid Bacteria (AAB) associated with a deleterious phenotype in A. ludens when infesting P. guajava. In contrast, the ability of A. striata and A. fraterculus to infest this fruit is likely associated to a symbiotic interaction with species of the Komagataeibacter genus, which are known to degrade a wide spectrum of tannins and polyphenols. The three flies establish genera specific symbiotic associations with AABs. In the case of A. ludens, the association is with Gluconobacter and Acetobacter, but importantly, it cannot be colonized by Komagataeibacter, a factor likely inhibiting its development in guava.