Hidden life-history traits of an ambrosia beetle

Ambrosia beetles (Coleoptera: Curculionidae: Scolytinae) are fungal farmers that have an obligate nutritional relationship with ambrosia fungi. Fungus-farming is a trait that leads to division of labor and favors sociality (i.e., cooperative fungiculture). However, the social organization of ambrosia beetles has been overlooked probably due to their cryptic lifestyle within tunnel systems inside their hosts. Using a novel rearing technique, we gained insights into the life cycle, gallery construction, social system, and mating behavior of Xyleborus bispinatus. This ambrosia beetle has been associated with the transmission of the fungal pathogen Raffaelea lauricola, the causative agent of laurel wilt disease. Our study revealed a breeding system characterized by overlapping generations, delayed dispersal of adult females, cooperative brood care, fungus gardening, division of labor, female-biased sex ratio, and cannibalism, all taking place in a gallery system much more complex than previously assumed. Most interesting, the enigmatic male behavior was finally observed and described. Although males displayed behaviors such as allogrooming and fungus cropping, they seemed to be more concerned in their reproductive tasks by continuously scanning the galleries searching for potential partners. Males attempted to mate with mature and teneral females; however, successful copulation mainly occurred with the latter. Additionally, longer mating events resulted in more offspring produced per female. This study documents several social behaviors of X. bispinatus and describes for the first time the mating behavior of an ambrosia beetle.