Encounters of old foes on a new battle ground for an invasive tree, Albizia julibrissin Durazz (Fabaceae)

Studies of invasive species often demonstrate that exotic or invasive plants have reduced levels of predation when first introduced into novel geographic areas. In some systems, native predators may subsequently be introduced and the plant-predator association is re-established. In this study, we analyzed a recent reassociation between the introduced tree, Albizia julibrissin, and its native seed predator, Bruchidius terrenus, which has also been introduced, in the vicinity of Athens, GA, USA. We documented a rapid increase in the levels of bruchid beetle predation on seeds of A. julibrissin from 2001 to 2002 and substantial predation in the following 5 years. From a six-year survey, we found that relative susceptibility to beetle predation among individual trees remained consistent over time. Furthermore, we found that phenology had significant effects on beetle predation on fruits and seeds, with fruits developed from early flowers having higher levels of beetle attacks than ones developed from later flowers in the season. Finally, seeds and fruits attacked by beetles were more likely to be attacked by a Fusarium fungus, probably due to coinfestation of the two predators. Host-predator reassociation that causes substantial loss of fertility or shows a relationship with reproductive phenology may have population level demographic effects or evolutionary consequences and deserve further research attention.