RNA Viruses Are Prevalent and Active Tenants of the Predatory Mite Phytoseiulus persimilis (Acari: Phytoseiidae).

Many arthropod species harbor a diverse range of viruses. While much is known about pathogenic viruses of some economically important insects and arthropods involved in disease transmission, viruses associated with mites have rarely been studied. The main objective of this study was to characterize the virome of Phytoseiulus persimilis (Phytoseiidae), a predatory mite commercially used worldwide for the biological control of the key pest Tetranychus urticae (Tetranichidae). A combination of de novo transcriptome assembly and virion sequencing, revealed that RNA viruses are highly prevalent and active tenants of commercial populations of P. persimilis, comprising on average 9% of the mite's total mRNA. Seventeen RNA viruses dominated the mite's virome (i.e., were highly transcribed) with over half (n = 10) belonging to the order Picornavirales, + ssRNA viruses that infect a large range of hosts, including arthropods. Screening of the 17 dominant virus sequences in P. persimilis and T. urticae revealed that three viruses (two Picornavirales of the families Iflaviridae and Dicistroviridae, and one unclassified Riboviria) are unique to P. persimilis and three others (two unclassified Picornavirales and one unclassified Riboviria) are present in both mite species. Most of the sequences were related to viruses previously documented in economically important arthropods, while others have rarely been documented before in arthropods. These findings demonstrate that P. persimilis, like many other arthropods, harbors a diverse RNA virome, which might affect the mite's physiology and consequently its efficiency as a biological control agent.

Genomic characterization of viruses associated with the parasitoid Anagyrus vladimiri (Hymenoptera: Encyrtidae).

Knowledge on symbiotic microorganisms of insects has increased dramatically in recent years, yet relatively little data are available regarding non-pathogenic viruses. Here we studied the virome of the parasitoid wasp Anagyrus vladimiri Triapitsyn (Hymenoptera: Encyrtidae), a biocontrol agent of mealybugs. By high-throughput sequencing of viral nucleic acids, we revealed three novel viruses, belonging to the families Reoviridae [provisionally termed AnvRV (Anagyrus vladimiri reovirus)], Iflaviridae (AnvIFV) and Dicistroviridae (AnvDV). Phylogenetic analysis further classified AnvRV in the genus Idnoreovirus, and AnvDV in the genus Triatovirus. The genome of AnvRV comprises 10 distinct genomic segments ranging in length from 1.5 to 4.2 kb, but only two out of the 10 ORFs have a known function. AnvIFV and AnvDV each have one polypeptide ORF, which is typical of iflaviruses but very un-common among dicistroviruses. Five conserved domains were found along both the ORFs of those two viruses. AnvRV was found to be fixed in an A. vladimiri population that was obtained from a mass rearing facility, whereas its prevalence in field-collected A. vladimiri was ~15 %. Similarly, the prevalence of AnvIFV and AnvDV was much higher in the mass rearing population than in the field population. The presence of AnvDV was positively correlated with the presence of Wolbachia in the same individuals. Transmission electron micrographs of females' ovaries revealed clusters and viroplasms of reovirus-like particles in follicle cells, suggesting that AnvRV is vertically transmitted from mother to offspring. AnvRV was not detected in the mealybugs, supporting the assumption that this virus is truly associated with the wasps. The possible effects of these viruses on A. vladimiri's biology, and on biocontrol agents in general, are discussed. Our findings identify RNA viruses as potentially involved in the multitrophic system of mealybugs, their parasitoids and other members of the holobiont.

Rickettsia association with two Macrolophus (Heteroptera: Miridae) species: A comparative study of phylogenies and within-host localization patterns.

Many arthropods host bacterial symbionts, some of which are known to influence host nutrition and diet breadth. Omnivorous bugs of the genus Macrolophus (Heteroptera: Miridae) are mainly predatory, but may also feed on plants. The species M. pygmaeus and M. melanotoma (=M. caliginosus) are key natural enemies of various economically important agricultural pests, and are known to harbor two Rickettsia species, R. bellii and R. limoniae. To test for possible involvement of symbiotic bacteria in the nutritional ecology of these biocontrol agents, the abundance, phylogeny, and distribution patterns of the two Rickettsia species in M. pygmaeus and M. melanotoma were studied. Both of the Rickettsia species were found in 100 and 84% of all tested individuals of M. pygmaeus and M. melanotoma, respectively. Phylogenetic analysis showed that a co-evolutionary process between Macrolophus species and their Rickettsia is infrequent. Localization of R. bellii and R. limoniae has been detected in both female and male of M. pygmaeus and M. melanotoma. FISH analysis of female gonads revealed the presence of both Rickettsia species in the germarium of both bug species. Each of the two Rickettsia species displayed a unique distribution pattern along the digestive system of the bugs, mostly occupying separate epithelial cells, unknown caeca-like organs, the Malpighian tubules and the salivary glands. This pattern differed between the two Macrolophus species: in M. pygmaeus, R. limoniae was distributed more broadly along the host digestive system and R. bellii was located primarily in the foregut and midgut. In contrast, in M. melanotoma, R. bellii was more broadly distributed along the digestive system than the clustered R. limoniae. Taken together, these results suggest that Rickettsia may have a role in the nutritional ecology of their plant-and prey-consuming hosts.

Wolbachia influence on the fitness of Anagyrus vladimiri (Hymenoptera: Encyrtidae), a bio-control agent of mealybugs.

BACKGROUND: Like numerous other animals, biocontrol agents (BCAs) of arthropod pests carry various microorganisms that may have diverse effects on the biology of their eukaryote hosts. We postulated that it is possible to improve the efficacy of BCAs by manipulating the composition of their associated microbiota. The parasitoid wasp Anagyrus vladimiri (Hymenoptera: Encyrtidae) from a mass-rearing facility was chosen for testing this hypothesis. RESULTS: High-throughput sequencing analysis indicated that fungal abundance in A. vladimiri was low and variable, whereas the bacterial community was dominated by the endosymbiont Wolbachia. Wolbachia was fixed in the mass-rearing population, whereas in field-collected A. vladimiri Wolbachia's prevalence was only approximately 20%. Identification of Wolbachia strains from the two populations by Multi Locus Sequence Typing, revealed two closely related but unique strains. A series of bioassays with the mass-rearing Wolbachia-fixed (W+ ) and a derived antibiotic-treated Wolbachia-free (W- ) lines revealed that: (i) Wolbachia does not induce reproductive manipulations; (ii) W- females have higher fecundity when reared individually, but not when reared with conspecifics; (iii) W+ females outcompete W- when they share hosts for oviposition; (iv) longevity and developmental time were similar in both lines. CONCLUSIONS: The findings suggest that W+ A. vladimiri have no clear fitness benefit under mass-rearing conditions and may be disadvantageous under lab-controlled conditions. In a broader view, the results suggest that augmentative biological control can benefit from manipulation of the microbiome of natural enemies.