Colorado potato beetles manipulate induced defenses in several Solanum hosts

Induced plant defenses occur in response to insect herbivory. Antagonism between phytohormones jasmonic acid (JA) and salicylic acid (SA) play an important role in regulating induced defenses. The antagonism appears to be phylogenetically widespread. In some cases, herbivores manipulate plant defenses for their own benefit. We recently demonstrated symbiotic bacteria from larvae of Colorado potato beetles (CPB; Leptinotarsa decemlineata) suppressed induced defenses in tomato. The suppression was mediated by negative crosstalk between JA and SA. However, little is known about the manipulation of induced defenses in wild and cultivated Solanum host plants of CPB. The aim of this study was to investigate whether antagonism between JA and SA occur to modify plant defenses and whether symbiotic bacteria from CPB larvae suppress plant defenses in several Solanum hosts. The Solanum host plants of CPB included tomato (S. lycopersicum), potato (S. tuberosum), eggplant (S. melongena), buffalobur (S. rostratum), horsenettle (S. carolinense). In all Solanum host plants, dual-application of JA and SA decreased JA-regulated plant defenses compared with JA application alone, suggesting antagonistic interactions between JA and SA are present. In addition, when plants were damaged by antibiotic-untreated larvae with the symbiotic bacteria, defensive enzymatic activity was lower than when damaged by antibiotic-treated larvae without the symbiotic bacteria. Thus, these data suggest that the symbiotic bacteria suppress plant defenses in Solanum host plants.