Determining whether mate-searching males use directional information in female signals in the treehopper, Umbonia crassicornis

Background/Question/Methods: Many insect species use substrate vibrations as a primary form of communication.  Localization of a vibration source, which is necessary for many social interactions, can be difficult for small insects.  The mechanisms and behavioral strategies used during localization are poorly understood, especially for species that transmit their vibrational signals through living plants. Males of the treehopper Umbonia crassicornis (Hemiptera: Membracidae) use vibrations to locate a potential mate on a host plant. After the male produces a vibrational signal that is detected by the female she replies with a vibrational signal of her own. This duet is usually repeated until the searching male reaches the stationary female.  The goal of this study was to determine if the vibration generated by the female provides directional information to the searching male.  To characterize male search behavior and localization accuracy during natural duets, I placed a receptive female at a randomly determined position on a potted host plant 1-1.5 m tall. I then placed a male at a location with a 50-cm path length to the female (N=27 unique pairs). I determined from video recordings each location where the male stopped to signal, as well as the male’s direction of travel after receiving the female’s vibrational reply.  

Results/Conclusions: Males gain directional information from female vibrational signals: males correctly oriented to the female after approximately 70% of female replies, significantly better than the proportion expected by chance.  Males stopped to signal at an average of 35 locations, and took an average of 12 minutes to locate the responding female. This is the first quantitative characterization of male searching behavior during natural vibrational interactions in a plant-dwelling insect. Future research will investigate the cues used by males to determine the direction of the female, and the factors that limit localization accuracy.