<b>Reunification of an invasive plant with its specialist herbivore selects for rapid adaptive changes in defensive volatiles</b>

Reassociation of invasive plant species with specialist herbivores can select for the restoration of original defense syndromes, however, we know little about how volatile components of plant defenses respond to such reunions. We studied populations of invasive Ambrosia artemisiifolia with varying reassociation histories with the specialist Ophraella communa and found that longer reassociations correlated with higher abundances and diversities of generalist herbivores in common garden experiments. Plants with longer reassociation histories were less attractive to O. communa, and this correlated with reduced emissions of limonene, in turn correlating with increased defense against O. communa. In contrast, longer reassociated plants were more attractive to the generalist Spodoptera littoralis and the reduced limonene emission correlated with weaker defense against Spodoptera. Our results imply that a specialist may drive the rapid evolution of volatile-related defenses, enhancing plant resistance to this specialist but at the cost of weaker defense against a generalist.