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1. Aphid facultative symbionts confer no protection against the fungal entomopathogen Batkoa apiculata

   https://doi.org/10.1371/journal.pone.0286095  

   Inchauregui, Rose A.; Tallapragada, Keertana; Parker, Benjamin J. (May 2023, PLOS ONE)

   Sanda, Nafiu Bala (Ed.)

   Fungi in the familyEntomophthoraceaeare prevalent pathogens of aphids. Facultative symbiotic bacteria harbored by aphids, includingSpiroplasma sp. andRegiella insecticola, have been shown to make their hosts more resistant to infection with the fungal pathogenPandora neoaphidis. How far this protection extends against other species of fungi in the familyEntomophthoraceaeis unknown. Here we isolated a strain of the fungal pathogenBatkoa apiculatainfecting a natural population of pea aphids (Acyrthosiphon pisum) and confirmed its identity by sequencing the 28S rRNA gene. We then infected a panel of aphids each harboring a different species or strain of endosymbiotic bacteria to test whether aphid symbionts protect againstB.apiculata. We found no evidence of symbiont-mediated protection against this pathogen, and our data suggest that some symbionts make aphids more susceptible to infection. This finding is relevant to our understanding of this important model of host-microbe interactions, and we discuss our results in the context of aphid-microbe ecological and evolutionary dynamics. 

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2. A novel mitovirus associated with the fungal entomopathogen Zoophthora radicans

   https://doi.org/10.1371/journal.pone.0331239  

   Adler, Meaghan J; Martin, McKayla M; Rozo-Lopez, Paula; Parker, Benjamin J (September 2025, PLOS One)

   Debat, Humberto Julio (Ed.)

   Metatranscriptome sequencing has emerged as a powerful tool for uncovering viral diversity in insects and their associated microbes. To explore viruses linked to the pea aphid (Acyrthosiphon pisum), we performed metatranscriptome sequencing on field-collected samples. In addition to several known plant viruses, we assembled the genome of a new virus homologous to species in the familyMitoviridae, which are positive-sense single-stranded RNA viruses that encode only an RNA-dependent RNA polymerase and typically replicate in mitochondria. Given the frequent association of mitoviruses with fungi and the presence of entomopathogenic fungal reads in our dataset, we conducted 18S amplicon sequencing and PCR screening on individual aphids. These analyses identified two fungal entomopathogens and uncovered an association between the mitovirus andZoophthora radicans, a generalist aphid pathogen. Our findings shed light on the hidden microbial diversity in natural pea aphid populations and emphasize the utility of metatranscriptomics in identifying novel virus-host associations. 

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3. Heritable viral symbionts in the family Iflaviridae are widespread among aphids

   https://doi.org/10.1128/aem.01606-25  

   Rozo-Lopez, Paula; Torres, Vanesa; Torres, Joseph; Drolet, Barbara S; Käfer, Simon; Parker, Benjamin J (November 2025, Applied and Environmental Microbiology)

   Rudi, Knut (Ed.)

   ABSTRACT Heritable microbes shape host phenotypes and serve as important drivers of evolution. While interactions between insects and bacterial symbionts have been extensively studied, the prevalence and evolution of insect-viral symbioses remain poorly understood. We discovered multiple new species of iflaviruses in aphids, an important model for research on symbiosis, and found these microbes to be widespread across aphid species. We show that iflaviruses are persistently maintained in asexual host lines without apparent fitness costs while being transmitted vertically from mothers to offspring. Using field data and phylogenetic evidence, we found that aphid iflaviruses move horizontally among host species, but laboratory experiments showed that horizontal transmission does not result in persistent infections. Using quantitative PCR and immunohistochemistry, we discovered that viral infections localize in the host fat bodies and developing embryos. Surprisingly, we also found viral infections inside bacteria-housing cells called bacteriocytes, along with a positive correlation between viral and bacterial symbiont density. Together, our work suggests that iflaviruses are widespread heritable symbionts in aphids. IMPORTANCEIn recent years, the rise of metatranscriptome sequencing has led to the rapid discovery of novel viral sequences in insects. However, few studies have carefully investigated the dynamics of insect-virus interactions to produce a general understanding of viral symbiosis. Aphids are an important model for understanding the evolution and molecular basis of symbiosis, but whether viruses are forming persistent symbiotic relationships with aphids remains unclear. Here, we show that heritable iflaviruses are a widespread but previously unrecognized part of the aphid heritable microbiome. Aphid iflaviruses are transmitted alongside bacteria from mothers to offspring, potentially via specialized bacteriocytes that house symbiotic microbes. Our findings suggest that aphids establish persistent relationships with iflaviruses and are likely coevolving with these viral symbionts. 

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4. An aphid symbiont confers protection against a specialized RNA virus, another increases vulnerability to the same pathogen

   https://doi.org/10.1111/mec.16801  

   Higashi, Clesson H.; Nichols, William L.; Chevignon, Germain; Patel, Vilas; Allison, Suzanne E.; Kim, Kyungsun Lee; Strand, Michael R.; Oliver, Kerry M. (February 2023, Molecular Ecology)

   Abstract Insects often harbour heritable symbionts that provide defence against specialized natural enemies, yet little is known about symbiont protection when hosts face simultaneous threats. In pea aphids (Acyrthosiphon pisum), the facultative endosymbiontHamiltonella defensaconfers protection against the parasitoid,Aphidius ervi, andRegiella insecticolaprotects against aphid‐specific fungal pathogens, includingPandora neoaphidis. Here, we investigated whether these two common aphid symbionts protect against a specialized virusA. pisum virus(APV), and whether their antifungal and antiparasitoid services are impacted by APV infection. We found that APV imposed large fitness costs on symbiont‐free aphids and these costs were elevated in aphids also housingH. defensa. In contrast, APV titres were significantly reduced and costs to APV infection were largely eliminated in aphids withR. insecticola. To our knowledge,R. insecticolais the first aphid symbiont shown to protect against a viral pathogen, and only the second arthropod symbiont reported to do so. In contrast, APV infection did not impact the protective services of eitherR. insecticolaorH. defensa. To better understand APV biology, we produced five genomes and examined transmission routes. We found that moderate rates of vertical transmission, combined with horizontal transfer through food plants, were the major route of APV spread, although lateral transfer by parasitoids also occurred. Transmission was unaffected by facultative symbionts. In summary, the presence and species identity of facultative symbionts resulted in highly divergent outcomes for aphids infected with APV, while not impacting defensive services that target other enemies. These findings add to the diverse phenotypes conferred by aphid symbionts, and to the growing body of work highlighting extensive variation in symbiont‐mediated interactions. 

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5. Bacterial and fungal components of the gut microbiome have distinct, sex-specific roles in Hawaiian Drosophila reproduction

   https://doi.org/10.1101/2023.07.14.549088  

   Medeiros, Matthew J; Seo, Laura; Macias, Aziel; Price, Donald K; Yew, Joanne Y (July 2023, bioRxiv)

   Abstract Gut microbiomes provide numerous physiological benefits for host animals. The role of bacterial members of microbiomes in host physiology is well-documented. However, much less is known about the contributions and interactions of fungal members of the microbiome even though fungi are significant components of many microbiomes, including those of humans and insects. Here, we used antibacterial and antifungal drugs to manipulate the gut microbiome of a Hawaiian picture-wingDrosophilaspecies,D. grimshawi, and identified distinct, sex-specific roles for the bacteria and fungi in microbiome community stability and reproduction. Female oogenesis, fecundity and mating drive were significantly diminished when fungal communities were suppressed. By contrast, male fecundity was more strongly affected by bacterial but not fungal populations. For males and females, suppression of both bacteria and fungi severely reduced fecundity and altered fatty acid levels and composition, implicating the importance of interkingdom interactions on reproduction and lipid metabolism. Overall, our results reveal that bacteria and fungi have distinct, sexually-dimorphic effects on host physiology and interkingdom dynamics in the gut help to maintain microbiome community stability and enhance reproduction. 

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