Diversity of proteobacterial endosymbionts in hemlock woolly adelgid (Adelges tsugae) (Hemiptera: Adelgidae) from its native and introduced range

Abstract

Knowledge of intraspecific variation in symbioses may aid in understanding the ecology of widespread insects in different parts of their range. We investigated bacterial symbionts of Adelges tsugae, a pest of hemlocks in eastern North America introduced from Asia. Amplification, cloning, and sequencing of bacterial 16S rDNA, in situ hybridizations, and electron microscopy revealed that A. tsugae harbours up to five bacterial phylotypes, according to population. Three Gammaproteobacteria species are maternally transmitted. The first, designated 'Ca. Pseudomonas adelgestsugas' resides in the haemocoel, and was detected in all populations except Taiwan. The second phylotype, 'Ca. Serratia symbiotica', resides in bacteriocytes of populations on Tsuga sieboldii in Japan and in E. North America. The third phylotype, designated 'Ca. Annandia adelgestsuga', clustered within a lineage of several insect endosymbionts that included Buchnera aphidicola. It was detected in bacteriocytes in all populations, and in salivary glands of first instars. Two Betaproteobacteria phylotypes were detected in some Japanese T. sieboldii and eastern North America populations, and were observed only in salivary glands with no evidence of maternal transmission. Our results support the ideas that symbiont gain and loss has been volatile in adelgids, and that symbionts may help to trace the source of invasive species.

The Pine Bark Adelgid, Pineus strobi, Contains Two Novel Bacteriocyte-Associated Gammaproteobacterial Symbionts

“…They represented a sister clade of "Candidatus Purcelliella pentastirinorum," but their relationship was not well established (BI ϭ 88%, ML ϭ 55%). While phylogenetic analysis of "Candidatus Annandia adelgestsuga" by von Dohlen et al (19) suggested B. aphidicola as the closest relative, its position was, similarly to our results, only weakly supported. In agreement with the 16S rRNA data, 23S rRNA-based phylogenies of phylotypes 1 and 2 suggested an affiliation with Providencia sp.…”

“…Sequence type 1 showed the highest similarity to various Providencia rettgeri strains (95.5 to 95.7%), isolated from corals (35) or pathogenic to silkworms (36), among others. Phylotype 2 was most similar to "Candidatus Annandia adelgestsuga" (94.9%), a bacteriocyte-associated symbiont of the hemlock woolly adelgid Adelges tsugae (19). The two sequence types showed only low sequence similarity (89.2 to 90.7% for type 1 and 83.4 to 84.9% for type 2) to bacteriocyte-associated gammaproteobacterial symbionts of other adelgids, including A.…”

“…Given its similarity to "Candidatus Annandia adelgestsuga" (19), the polymorphic symbiont likely represents a novel species in the candidate genus Annandia within the Gammaproteobacteria. We thus propose two novel tentative names according to the recommendations of Murray and Stackebrandt (45).…”

“…Adelgids (Insecta: Hemiptera: Adelgidae), comprising the two major clades Adelges and Pineus, live exclusively on various conifers, where they feed on parenchyma cell sap or phloem (16). To date, bacteriocyte-associated symbionts of only a few Adelges species have been investigated on the molecular level (17)(18)(19). In contrast to their aphid sister group, these insects harbor surprisingly diverse symbionts belonging to the Gammaproteobacteria and the Betaproteobacteria.…”

“…In contrast to their aphid sister group, these insects harbor surprisingly diverse symbionts belonging to the Gammaproteobacteria and the Betaproteobacteria. While aphids generally contain a single obligate symbiont that coevolved with its host (1), adelgids seem to have a more complex evolutionary history involving multiple symbiont acquisition and replacement events (17)(18)(19).…”