Evidence of horizontal transmission of primary and secondary endosymbionts between maize and rice weevils (Sitophilus zeamais and Sitophilus oryzae) and the parasitoid Theocolax elegans

Grain weevils are hosts of two cellular endosymbionts: Wolbachia and “Sitophilus Primary Endosymbiont” (SPE). Wolbachia is a facultative endosymbiont, while SPE is an obligatory endosymbiont. Both Wolbachia and SPE are transmitted vertically, that is, from mother to offspring. There are circumstances in which transmission occurs among conspecific organisms or organisms of distinct species (horizontal transmission), and both vertical and horizontal transmissions play significant roles in shaping the host's ecology and evolution. We found molecular evidence for the horizontal transfer of Wolbachia between the maize weevil (Sitophilus zeamais Motschulsky) and the rice weevil (Sitophilus oryzae (L.)) and evidence of horizontal transfer of Wolbachia and SPE between the maize weevil and the parasitoid Theocolax elegans Westwood (Hymenoptera: Pteromalidae). Using 16S rRNA fragments of both symbionts, we verified the co-existence of two Wolbachia strains in maize weevil individuals from a Mexican population, one of which is typically from this species, while the other is from rice weevils. This finding provides evidence of the horizontal transmission of the endosymbiont between maize and rice weevil and supports the contention of similarity and relatedness between these weevil species. We also observed 100% similarity of 16S rRNA fragments between Wolbachia and SPE sequenced from the weevil parasitoid T. elegans and the maize weevil. This evidence suggests the horizontal transmission of both endosymbionts from the maize weevil to its parasitoid T. elegans. In addition to the importance of these findings for the ecology and evolution of weevils, the potential use of endosymbionts in innovative tactics of arthropod pest management in stored products also deserves attention and remains virtually unexplored.