The Crucial Role of the Endosymbiont Pantoea sp. in Morphology and Mating of the Pistachio Green Stink Bug, Brachynema germari (Hemiptera: Pentatomidae)

The pistachio green stink bug, Brachynema germari Kolenati (Hemiptera: Pentatomidae), is one of the most important pests of pistachio nuts in many pistachio-growing regions in Iran(Mehrnejad 2001; Bigham & Hosseininaveh 2010). This insect harbors a gammaproteobacterial symbiont, related to the genus Pantoea, in the numerous crypts of its posterior midgut, which is vertically transmitted by infection of the egg masses and orally acquired by newborn nymphs. In the present study, the effects of the symbiont on host morphology, emergence rates, and mating frequency of B. germari were explored. For this purpose, two symbiont elimination strategies, high temperature and egg surface sterilization, were used and their effects were compared. We found external morphological changes (e.g. abnormalities in notum and wings) as well as significantly fewer emergence rates (in all stages, except for the first instar) in the surface-sterilized and heat-treated insects compared with the controls. Also, the second, third, and fourth regions of the midgut exhibited remarkable morphological changes in the aposymbiotic insects compared with the controls. Besides, less mating frequency was observed in the aposymbiotic population compared with the control. Together, these results provided a close relationship between the bacterial symbiont and B. germari and suggested the importance of the symbiont for the morphogenesis, development, and reproduction of the insect host.