OOS 30-10 - The influence of epiphytic pathogens on aphid feeding choice

Wednesday, August 9, 2017: 4:40 PM
Portland Blrm 258, Oregon Convention Center
Tory A. Hendry1, Kevin R. Besler1, Rachel L. Fay2 and Melanie R. Smee1, (1)Cornell University, (2)SUNY Potsdam

Herbivorous insects encounter diverse microbes while feeding on leaf surfaces. These microbes can influence insect health, feeding behavior and success, however the role of these interactions has not been explored in most systems. For example, some hemipteran insects such as aphids can become infected by a number of highly virulent plant-associated bacteria, including the common plant epiphyte Pseudomonas syringae. Virulence varies among P. syringae strains and some strains can be highly infective and kill the overwhelming majority aphids within days. Aphids do not appear able to recover from infection, raising the questions of how frequently aphids encounter highly virulent strains and how they respond to infection. Using oral infection and virulence assays, we screened a diversity of strains for variation in infectivity and virulence to pea aphids. We then investigated whether aphids are able to avoid highly virulent strains and if so which sensory modalities they may use to detect virulent bacteria. We performed two way choice assays and observed aphid feeding rates on leaves covered with bacterial strains compared to control leaves. Choice assays were also performed where aphids were unable to use vision or anntentation while settling onto leaves to feed.


We found that diverse P. syringae strains varied extensively in their virulence to aphids. Low virulence strains killed ~30% of aphids after four days while high virulence strains killed up to 90% of aphids. Aphids displayed significant avoidance of leaves painted with some highly virulent bacteria compared to controls. However, they did not avoid all bacteria on leaves, showing no significant avoidance of low virulence strains and some high virulence strains. Avoidance of virulent bacteria led to significantly decreased infection rates among aphids, with 13-30% of aphids becoming infected after exposure to only leaves with bacteria and only 0-3% becoming infected when given a choice between leaves with bacteria and control leaves. We found that aphids avoided virulent bacteria immediately after placement on a plant prior to feeding, thus evading infection. Surprisingly, avoidance disappeared when experiments were performed in the dark, suggesting that aphids use vision to avoid virulent epiphytic bacteria. These results suggest that visual detection of bacterial aggregates may be an important means for aphids to survive among virulent bacteria in the phyllosphere. Consequently, distributions of varied epiphytic bacteria may play a large role in aphid feeding decisions and dispersal patterns.