Vibrational behavior of psyllids (Hemiptera: Psylloidea): functional morphology and mechanisms

Abstract

Vibrational behavior of psyllids was first documented more than six decades ago. Over the years, workers have postulated as to what the exact signal-producing mechanisms of psyllids might be but the exact mechanism has remained elusive. The aim of this study is to determine the specific signal-producing structures and mechanisms of the psyllids. Here we examine six hypotheses of signal-producing mechanisms from both previous and current studies that include: wing vibration, wing-wing friction, wing-thorax friction, wing-leg friction, leg-abdomen friction, and axillary sclerite-thorax friction. Through selective removal of possible signal producing structures and observing wing-beat frequency with a high-speed video recorder, six hypotheses were tested. Extensive experiments were implemented on the species Macrohomotoma gladiata Kuwayama, while other species belonging to different families, i.e., Trioza sozanica (Boselli), Mesohomotoma camphorae Kuwayama, Cacopsylla oluanpiensis (Yang), and Cacopsylla tobirae (Miyatake) were also examined to determine the potential prevalence of each signal-producing mechanism within the Psylloidea. Further, scanning electron microscopy (SEM) was used to examine possible rubbing structures. The result of high speed photography showed that wing-beating frequency did not match the dominant frequency of vibrational signals, resulting in the rejection of wing vibration hypothesis. As for the selective removal experiments, the axillary sclerite-thorax friction hypothesis is accepted and wing-thorax friction hypothesis is supported partially, while others are rejected. The SEM showed that the secondary axillary sclerite of forewing bears many protuberances that would be suitable for stridulation. In conclusion, the signal-producing mechanism of psyllids involves two sets of morphological structures. The first is stridulation between the axillary cord and anal area of the forewing. The second is stridulation between the axillary sclerite of the forewing and the mesothorax.