Date Published: September 11, 2019
Publisher: Public Library of Science
Author(s): Yi-Chang Liao, Zong-Ze Wu, Man-Miao Yang, Sean Michael Prager.
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: wingbeat, 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 measuring wing beat frequency with high speed videos, 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 microscope (SEM) was used to examine possible rubbing structures. The result of high speed video recordings showed that wingbeat frequency did not match the dominant frequency of vibrational signals, resulting in the rejection of wingbeat 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 the forewing bears many protuberances that would be suitable for stridulation. In conclusion, the signal producing mechanism of psyllids may involve two sets of morphological structures. The first is stridulation between the axillary sclerite of the forewing and the mesothorax. The second is stridulation between the axillary cord and anal area of the forewing.
Vibrational communication is prevalent among the insects with more than 18 orders having been recorded to communicate via substrate-borne signals . Vibrational signals of insects usually play an important role in mating behavior [2–4]. Other functions of vibrational signals also include defense  and food searching [6–8]. In Hemiptera, the mechanisms of vibrational signal producing vary greatly, for example, members of Heteroptera (bugs) can emit vibrational signals by stridulation, tymbal buckling, or abdomen vibration, while many species of Auchenorrhyncha (cicadas, planthoppers, leafhoppers, treehoppers) utilize a tymbal organ to produce vibrational signals . Additionally, whiteflies (Sternorrhyncha, Aleyrodoidea) produce vibrational signals through abdominal oscillation  and aphids (Aphidoidea) emit vibrational signals by rubbing the abdomen and hind legs against substrates . As well, psyllids (Psylloidea) are comparatively active singers during their mating behavior but until now their mechanisms of signal production have been poorly understood [12–16].
As a result of the wing-cut experiments, we were able to elucidate the crucial relationship between signal production and wings. We ensured that psyllids are not able to emit signals without forewing and it is now clear that the hindwing is certainly not evolved in signal production. The psyllids with only forewings left were able to produce signals, and the signal amplitude of those individuals was not significantly different compared with control treatment (Fig 3; Table 1). According to this evidence, we confirm the importance of the forewing in contributing to the signal producing mechanism of psyllids.