Abstract
Aphidoidea, endosymbiotic bacteria, bacteriocytes, transovarial transmission of endosymbiotic bacteria The ultrastructure, distribution and transovarial transmission of endosymbiotic bacteria in representatives of six aphid families: Eriosomatidae (Pemphigus spyrothecae, Prociphilus fraxini), Anoeciidae [Anoecia (Anoecia) corni], Drepanosiphidae [Mindarus abietinus, Sipha (Rungsia) maydis, Clethrobius comes, Myzocallis (Lineomyzocallis) walshii], Thelaxidae (Thelaxes dryophila), Aphididae (Delphiniobium junackianum, Aphis viburni, Cavariella theobaldi, Macrosiphoniella tanacetaria) and Lachnidae (Schizolachnus pineti, Eulachnus rileyi) were studied at the ultrastructural level. The ovaries of aphids are accompanied by large organs termed bacteriomes that consist of giant cells termed bacteriocytes. The bacteriocyte cytoplasm is tightly packed with endosymbiotic bacteria. Ultrastructural observations have shown that the bacteria Buchnera aphidicola (primary symbiont of aphids) present in various species are characterized by significant differences in both size and organization of their cytoplasm. In the aphids, Prociphilus fraxini, Sipha (Rungsia) maydis, Thelaxes dryophila, Aphis viburni, Cavariella theobaldi, Macrosiphoniella tanacetaria, Eulachnus rileyi and Schizolachnus pineti, in addition to Buchnera aphidicola, secondary endosymbionts are also present. The bacteriocytes containing secondary endosymbionts are less numerous than those with Buchnera. In Eulachnus rileyi (Lachnidae), in addition to primary and secondary endosymbionts, there is a third type of microorganism. In all species examined both the primary and secondary endosymbionts are transovarially transmitted from mother to offspring.
Highlights
Many insects live in symbiotic associations with prokaryotic or eukaryotic microorganisms
Numerous extensive studies have revealed that endosymbiotic microorganisms may occur in the body of a host insect extracellularly or intracellularly
It is suggested that secondary endosymbionts may compensate for the loss of the primary endosymbiont of aphids, the bacterium Buchnera and are able to supplement insufficient provisioning of amino acids usually provided by Buchnera (Koga et al, 2003; Burke et al, 2009)
Summary
Many insects live in symbiotic associations with prokaryotic (i.e. bacteria) or eukaryotic (i.e. yeasts) microorganisms. Numerous extensive studies have revealed that endosymbiotic microorganisms may occur in the body of a host insect extracellularly (e.g. in the gut lumen) or intracellularly (in specialized cells of mesodermal origin termed bacteriocytes or mycetocytes) (see Buchner, 1965; Douglas, 1989, 1998; Moran & Baumann, 2000; Ishikawa, 2003; Baumann, 2005; Kikuchi, 2009 for further details). Bacteriocytes contain bacteria, whereas mycetocytes harbour yeasts Both bacteriocytes and mycetocytes are large, polyploid cells that as a rule are integrated into large organs termed bacteriomes or mycetomes, respectively. In contrast to primary endosymbionts, secondary ones may occur within bacteriocytes and in other cells (e.g. fat body cells) or even free in the haemolymph (Moran & Telang, 1998; Fukatsu et al, 2000; Oliver et al, 2006, 2010). The secondary endosymbionts may be transmitted either vertically or horizontally (Buchner, 1965)
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