Submitted to: PLoS One
Publication Type: Peer reviewed journal
Publication Acceptance Date: 10/9/2012
Publication Date: 11/14/2012
Citation: Davis, T.S., Horton, D.R., Munyaneza, J.E., Landolt, P.J. 2012. Experimental infection of plants with an herbivore-associated bacterial endosymbiont influences herbivore host selection behavior. PLoS One. 7(11):e49330. doi:10.1371/journal.pone.0049330. Interpretive Summary: The potato psyllid is a damaging agricultural pest that infects plants with a pathogen known as ‘Zebra Chip Disease’. Although psyllid populations and Zebra Chip Disease are of tremendous concern to agriculturalists, there remains little know about how infection with the pathogen affects psyllid behavior. Researchers at the USDA-ARS laboratory in Wapato, Washington are seeking to determine whether the pathogen plays a significant role in psyllid attraction and population dynamics. They discovered that infected potato plants were attractive to psyllids, but after psyllids fed on infected potato plants they migrated to uninfected potato plants. They also found that infected potato plants emitted distinct volatile chemicals that could be responsible for psyllid attraction, and that infected plants did not appear to have negative consequences for psyllid reproduction. Their findings have important implications for the epidemiology of Zebra Chip Disease, and contribute new knowledge to factors that may responsible for the spread of significant agricultural pathogens.
Technical Abstract: Although bacterial endosymbioses are common among phloeophagous herbivores, little is known regarding the effects of symbionts on herbivore host selection and population dynamics. We tested the hypothesis that plant selection and reproductive performance by a phloem-feeding herbivore (potato psyllid, Bactericera cockerelli) is mediated by infection of plants with a bacterial endosymbiont. We controlled for the effects of herbivory and endosymbiont infection by exposing potato plants (Solanum tuberosum) to psyllids infected with “Candidatus Liberibacter solanacearum” or to uninfected psyllids. We used these treatments as a basis to experimentally test plant volatile emissions, herbivore settling and oviposition preferences, and herbivore population growth. Three important findings emerged: (1) plant volatile profiles differed with respect to both herbivory and herbivory plus endosymbiont infection when compared to undamaged control plants; (2) herbivores initially settled on plants exposed to endosymbiont-infected psyllids but later defected and oviposited primarily on plants exposed only to uninfected psyllids; and (3) plant infection status had little effect on herbivore reproduction, though plant flowering was associated with a 39% reduction in herbivore density on average. Our experiments support the hypothesis that plant infection with endosymbionts alters plant volatile profiles, and infected plants initially recruited herbivores but later repelled them. Also, our findings suggest that the endosymbiont may not place negative selection pressure on its host herbivore in this system, but plant flowering phenology appears correlated with psyllid population performance.