Consequences of bacterial inoculation on herbivore development, behaviors, and tri-trophic interactions

Non-pathogenic, soil microbes can influence plant growth and induce changes associated with phytohormones that may influence plant-insect interactions. Much of this work has focused on mycorrhizal fungi or certain rhizobacteria. Plant growth promotion mediated by these soil microbes may deter ovipositional behaviors, directly or indirectly influence performance of above ground herbivores, or attract natural enemies, but only a few studies have explored these interactions. The objectives of these experiments were to screen blends with commercial potential that could deter oviposition in no-choice greenhouse assays, negatively impact larval development on treated clippings under growth chamber conditions, and recruit natural enemies in pan traps with a final emphasis on FAW larval parasitism in field settings. FAWs deposited most of their eggs (55%) on the grass in the control plants and less than 29% on the PGPR treated grass, suggesting that microbes can mediate interactions between females and ovipositional hosts; although we do not suspect this will alter local populations. Inoculation of bermudagrass with some PGPR blends resulted in fresh larval weights, pupal weights, and adult eclosion that did not negatively impact S. furgiperda development; however, the use 3 of blends did impact larval weights and 2 blends impacted pupal weight and eclosion. PGPR strains have shown to increase attraction of natural enemies under laboratory settings, but the importance of that finding was not found in the present studies and has yet to be confirmed. These experiments are one of the first to examine parasitoid recruitment to plants treated with PGPR under field conditions and the first attempt to use microbial inoculants to manipulate natural enemies in turfgrass.  Induced resistance in plants derived from microbe inoculation to plant pathogens is well documented in the literature, but whether these interactions are specific to plant pathogens or extends to herbivores, like insects, remains inconclusive.