Symbiosis in the Dryophthoridae weevils (coleoptera, curculionoidea): Morphological variability of symbiotic intracellular bacteria

Dryophthoridae weevils are phytophagous insects thriving on a broad host-plant spectrum. Some, such as Sitophilus spp. or Cosmopolites sordidus, are major agricultural pests of cereals and bananas, respectively. Previous studies have concluded that several Dryophthoridae species harbour intracellular bacteria (endosymbionts) in specialized organs named bacteriomes. In this work, we have demonstrated the presence of intracellular symbiosis in seven out of the eight Dryophthoridae species tested, and have assessed the morphological variability of these endosymbionts. Histological analyses of the endosymbionts in either the larval bacteriome or adult female ovaries reveal two fields of variability: physiologic (length variation during host development) and morphologic (both interspecific and intraspecific). These variations are expressed to different degrees in the species studied. Indeed, Sitophilus granarius displays much less pleiomorphism than S. zeamais. Such pleiomorphism may be a consequence of both genetic polymorphism and host/bacteria interaction.