Ultrastructural and molecular characterization of a bacterial symbiosis in the ecologically important scale insect family Coelostomidiidae.

Scale insects are important ecologically and as agricultural pests. The majority of scale insect taxa feed exclusively on plant phloem sap, which is carbon rich but deficient in essential amino acids. This suggests that, as seen in the related aphids and psyllids, scale insect nutrition might also depend upon bacterial symbionts, yet very little is known about scale insect-bacteria symbioses. We report here the first identification and molecular characterization of symbiotic bacteria associated with the New Zealand giant scale Coelostomidia wairoensis, using fluorescence in situ hybridization (FISH), transmission electron microscopy (TEM) and 16S rRNA gene-based analysis. Dissection and FISH confirmed the location of the bacteria in large, paired, multilobate organs in the abdominal region of the insect. TEM indicated that the dominant pleomorphic bacteria were confined to bacteriocytes in the sheath-enclosed bacteriome. Phylogenetic analysis revealed the presence of three distinct bacterial types, the bacteriome-associated B-symbiont (Bacteroidetes), an Erwinia-related symbiont (Gammaproteobacteria) and Wolbachia sp. (Alphaproteobacteria). This study extends the current knowledge of scale insect symbionts and is the first microbiological investigation of the ecologically important coelostomidiid scales.