Gut bacteria of Spodoptera frugiperda establish endophytic association and affect the interactions of their host herbivore with maize plants

Insects and plants established long-lasting associations with microbes, whose role on insect–plant associations remains largely unknown. We hypothesized that both plant endophytes and insect symbionts benefit their hosts during insect–plant interactions. In the present study, we used the maize-Spodoptera frugiperda (JE Smith, 1797) (Lepidoptera: Noctuidae) system and five bacterial symbionts: a maize endophyte (Rhizobium larrymoorei IILzm-Idp03), two residents (Enterococcus spodopteracolus IIL-Sfm05 and E. entomosocium IILSfc-sus01) and one transient (Bacillus sp. IIL-Sfb05) gut bacteria of S. frugiperda. The ant-associated actinobacterium Streptomyces novaecaesareae IIL-ASP45 was also tested for not sharing any interactions with the maize-herbivore system studied. Bacteria associated with maize and/or S. frugiperda promoted plant growth depending on the inoculation strategy used. The tested bacteria colonized roots and leaves of plants regardless of their original host. Mortality and/or S. frugiperda larval efficiency of food utilization was affected in plants inoculated with IILSfc-sus01, IILSfb05, IILzm-Idp03 and IILASP45, but not with IILSfm05. The expression of selected maize-defensive genes and the volatile organic compounds (VOCs) profile was altered in all inoculated plants. Changes in VOCs did not affect adult S. frugiperda female preference for oviposition, but significantly affected the number of eggs laid/plant.