666 Invasive Stink Bugs and Related Species (Pentatomoidea)
is needed to understand the processes and their effects on adaptive evolution. Single nucleotide
polymorphisms observed within genes or pathways such as those involved in riboflavin biosyn-
thesis appear promising for understanding feeding success on soybean, but much work remains
to be done. Rapid genome evolution, however, was not observed over the 2-year span of the
Brown et al. (2014) study.Continuous accumulation of field data, in conjunction with genome sequencing analyses and capsule-
exchange experiments, would reveal which hypothesis is more plausible.
14.4 Facultative Symbionts in the Pentatomomorpha
In addition to the specific symbionts localized in symbiotic organs, facultative bacterial endosymbionts
have been reported from diverse species of the Pentatomomorpha. Facultative symbionts or secondary
symbionts in insects are generally not 100% prevalent but are partially infected among host populations;
they are not localized but, rather, spread to various host tissues and are not essential for the host’s devel-
opment and survival. The genus Wolbachia, famous as a sex-ratio distorter in many insects and other
arthropods (O’Neill et al. 1997, Werren et al. 2008), commonly is detected in the Pentatomomorpha. Of
the species that were investigated by Kikuchi and Fukatsu (2003), more than 30% were infected with
the bacteria. Actinobacteria species, some of which are known to produce a diverse array of antibiotics,
frequently have been detected from the midgut crypts of several pentatomid species including Thyanta
perditor ( F.), Edessa meditabunda F., Loxa deducta Wa l ker, Pellaea stictica (Dallas), Piezodorus guildi-
nii (Westwood), and Nezara viridula (Zucchi et al. 2012). Sodalis glossinidius first was described as a
facultative symbiont of tsetse flies, and then Sodalis-allied bacteria were detected from different insects
such as bird lice and spittle bugs (Fukatsu et al. 2007, Koga et al. 2013). A recent survey revealed that
the Sodalis symbionts are prevalent among the Pentatomoidea; in total, 13.6% of the investigated 108
species were infected with the symbiont (Hosokawa et al. 2015). Although the biological functions of
these facultative symbionts remain unclear, the prevalence of the symbionts implies their biological roles
in the host stink bugs. For example, facultative symbionts in aphids, such as Serratia symbiotica and
Hamiltonella defensa, confer the hosts with high-temperature tolerance, resistance against pathogens
and parasitoids, and body color alteration (Oliver et al. 2003; Tsuchida et al. 2004, 2010; Scarborough et
al. 2005). Future studies are required to reveal the biological importance of the facultative symbionts in
the Pentatomomorpha.
14.5 Concluding Remarks
Because of our continuous efforts over this last decade, the enormous diversity of microbial symbioses
in the Pentatomomorpha has been unveiled. This has highlighted the importance of stink bug symbiosis
not only in elucidating several long-standing evolutionary questions, such as the effect of the manner
of symbiont transmission (vertical or horizontal routes) on the evolutionary consequence of intimate
interactions and the effect of intra- and extracellular lifestyles on the genome evolution of the symbi-
otic bacteria but, also, secondarily improving strategies to control pest stink bugs. At the present time,
symbiotic associations of several key families remain to be investigated, such as those of the fami-
lies Dinidoridae, Tessaratomidae, and Phloeidae (Pentatomoidea). Further effort would provide us with
deeper and broader views on the evolutionary process of the microbial symbiosis in pentatomomorphan
insects, which should open a new window in the world of basic and applied science, ranging from evolu-
tionary ecology to agriculture biology.
In addition to the advanced accumulation of genomic information on symbiotic bacteria, host transcrip-
tome recently has been analyzed in several pentatomomorphan species such as Riptortus pedestris and
Dysdercus fasciatus (Futahashi et al. 2013, Bauer et al. 2014). Furthermore, in the near future, recent
advanced sequencing technologies will facilitate analysis of host genome as well as symbiont genome.
In fact, draft genomes of several heteropteran species, including Halyomorpha halys, have become open