The intrinsic diversity of Nezara viridula gut symbionts affects the host fitness decline promoted by primary symbiont elimination

Abstract

Pentatomid insects harbour an obligate gut symbiont, vertically transmitted via egg smearing by the females. The disruption of symbiont acquisition can be exploited for pest management, by spraying the egg surface with anti-symbiont agents, yet the insect response to symbiont deprivation remains a determining aspect of the success of this strategy. Here the effect of anti-symbiont egg masses treatment was assessed in an Italian population of the southern green stink bug Nezara viridula under field and laboratory conditions. In soybean fields, N. viridula was poorly affected by treatment, whereas in laboratory, nymphs deriving from treated egg masses underwent increased mortality and symbiont abundance decline. The primary symbiont dominated the microbiome of non-treated nymphs showing low mortality. Conversely, dysbiosis was recorded in treated samples as well as in control nymphs with high mortality. Nonetheless, dysbiosis induced by treatment was not in all cases associated with high mortality, and symbiont was missing in some non-treated samples as well. Five variants of a Pantoea symbiont were found, with higher variant diversity in untreated samples with low mortality. Altogether, our results provide information about the gut microbiota dynamics in the early nymphal instars of N. viridula and suggest a still incomplete dependence on the symbiont. However, egg masses anti-symbiont treatment increased mortality, therefore symbiont-targeted control may be used against N. viridula as a supplementary tool under high pest pressure.