Frankliniella occidentalis facilitate Salmonella enterica survival in the phyllosphere

Recent studies have revealed interactions between phytophagous insects, enteric human pathogens, such as Salmonella enterica, and plants. Most notably, S. enterica fails to grow on healthy plants, yet feeding behaviors unique to some phytophagous insects are hypothesized to directly or indirectly facilitate bacterial persistence. We investigated whether tomato leaves with macroscopic feeding damage, caused by adult Western flower thrips (Frankliniella occidentalis), support higher S. enterica populations. To explore this hypothesis, we assessed S. enterica populations in response to varying insect densities, plant age, insect sex, and artificial damage. In a series of experiments, groups of F. occidentalis were initially confined to tomato plants, which were later inoculated with S. enterica. Following an infestation period, leaves visibly damaged by adult F. occidentalis supported significantly higher S. enterica populations as well as electrolyte leakage (a proxy for cellular damage) than leaves lacking visible feeding damage. As a reference control, direct leaf damage analogous to thrips feeding was also evaluated using directed, hydraulic pressure. The gender of the insect did not uniquely influence S. enterica population dynamics. This study indicates two new relevant findings. Cellular damage induced by F. occidentalis feeding is only one of the possible biological mechanisms creating an enhanced environment for S. enterica, and artificial damage to mesophyll did not influence S. enterica populations like F. occidentalis infestation.