Occurence of endosymbiosis in Dryophtoridae weevils: cytological insights into bacterial symbiotic structures
Résumé
To gain a better understanding of the occurrence of intracellular symbiosis in the
Dryophthoridae family, nine species worldwide were analyzed in relation to the
presence/absence and the structure of bacteriomes, the specialized organs
harbouring the symbiotic bacteria. Staining protocols have indicated the presence of
bacteriomes in seven species: Sitophilus rugicollis, Diocalandra [rumenti,
Sphenophorus siriatopunctata, Sipalinus gigas, Trigonotarsus rugosus, Dynam is
borassi and Rhynchophorus palmarum. Strong evidence also suggests the presence of
intracellular bacteria within Siiophilus uateriae. However, Siiophilus linearis has
been shown to be completely devoid of intracellular endosymbionts. In all symbiotic
species, the larval bacteriome does not exhibit any diversity with regard to the form
and the location, always in the anterior part of larvae. It is delimited by a thin
membrane, it contains an important tracheal network and it is attached to the
intestine at many sites. At least two cell types have been observed within the
bacteriome: bacteriocytes, the polyploid cells harbouring bacteria and, between
them, small flat cells forming the interstitial tissue. Taken together, these results
argue in favor of a common origin of the symbiotic structures in the Dryophthoridae
family.