Vertical Transmission of a Pentatomid Caeca-Associated Symbiont
2006
Prado, S.S. | Rubinoff, D. | Almeida, R.P.P.
We present molecular data for an endosymbiont of the insect family Pentatomidae, located in the gastric caeca of Nezara viridula (L.) (Hemiptera: Pentatomidae) stink bugs. Restriction fragment length polymorphism and polymerase chain reaction analysis suggest that this bacterium is consistently present in caeca of N. viridula from a variety of geographic locations. The bacterium is present in different midgut sections in nymphs versus adults. The bacterium also was detected on eggshells after nymphs had hatched but not in ovarioles, suggesting oral rather than transovarial transmission. Surface sterilization of egg masses generated aposymbiotic insects. Aposymbiotic individuals reached the adult stage, females laid viable eggs, and the offspring remained aposymbiotic in the following generation. No clear fitness decrease was observed in aposymbiotic individuals over two generations. Phylogenetic analysis of a partial 16S rRNA data set with 21 Gammaproteobacteria suggested the inadequacy of neighbor-joining and maximum parsimony models to account for homoplasy apparent in a molecular data set, including a range of insect endosymbionts. Maximum likelihood-based analysis suggests that the N. viridula endosymbiont is closely related to a caeca-associated symbiont found in another stink bug family (Plataspidae). The high AT content of the symbiont's 16S rRNA in relation to other insect endosymbionts, its location in the midgut of the host insect, oral transmission, and survival of aposymbiotic individuals suggest this symbiosis may be recently established.
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