Listening in the bog: I. Acoustic interactions and spacing between males of Sphagniana sphagnorum

A New Genus of Andean Katydid with Unusual Pronotal Structure for Enhancing Resonances

Katydids employ acoustic signals to communicate with others of their species and have evolved to generate sounds by coupling the anatomical structures of their forewings. However, some species have evolved to implement an additional resonance mechanism that enhances the transmission and sound pressure of the acoustic signals produced by the primary resonators. Secondary resonators, such as burrow cavities or horn-shaped structures, are found in the surrounding environment but could also occur as anatomical modifications of their bodies. Chamber-like structures have been described in species of katydids with modified pronota or wings. It has been shown that these modified structures directly affect the transmission and filtering of acoustic signals and can function as a Helmholtz resonator that encapsulates the primary sound source. By morphological and acoustic analysis, we describe a new genus of Conocephalinae and investigate the physical properties of their sound production structures for three new species from the Andes of Colombia and Ecuador. Males of the new genus, here described as Tectucantus n. gen., have a characteristic inflated pronotum enclosing the reduced first pair of wings and extending rearward over the first abdominal segments. We test the hypothesis that the pronotal cavity volume correlates with the carrier frequency of specific calls. The cavity of the pronotal chamber acts as a Helmholtz resonator in all three Tectucantus species and, potentially, in other distantly related species, which use similar secondary body resonators.

Documenting nocturnal activity of dragon-headed katydids (Lesina blanchardi) under artificial light

Across the genera of katydids from the family Tettigoniidae, both diurnal and nocturnal species have been identified. The Saint Louis Zoo Bayer Insectarium filmed dragon-headed katydids (Lesina blanchardi) overnight using red light-emitting diodes (LEDs) to examine the activity of this presumed nocturnal species to provide quantitative information about these insects that are otherwise immobile when keepers are present. Evidence from the literature suggests that LED bulbs emitting long-wavelength red and infrared lights are less likely to cause changes to the subjects' behavioral budgets and movements through the habitat. Three katydids were filmed for 5 nights, and time-interval scan sampling was used to record their positions and whether they were active every 15 min for two 2-h periods starting at midnight and noon. A modified Shannon's diversity index determined that katydids were recorded in more areas when under only red LEDs at night as compared to artificial daytime working lights. Similarly, repeated measures analysis of variance indicated that insects were significantly more active under nighttime red LEDs when compared to daytime working lights. While we cannot be sure if behaviors recorded under red LEDs are the same as those that would be performed under total darkness in situ, the use of red LED illumination ex situ to facilitate overnight filming did not suppress nocturnal movement or activity for our subjects.

Listening in the bog: II. Neural correlates for acoustic interactions and spacing between Sphagniana sphagnorum males

Males of the katydid Sphagniana sphagnorum maintain inter-male distances from one another using agonistic song interactions with a frequency-modulated song that consists of alternating audio and ultrasonic parts. We studied the neuronal representation of this song in auditory receptors and interneurons of receivers, using playbacks of songs that mimicked the absolute and relative sound pressure levels of the two song modes varying with distance. The tuning and sensitivity of both receptors and interneurons strongly determine their responses to the two song modes at different distances. Low-frequency interneurons respond preferentially to the audio mode of the song at larger distances. High-frequency (HF) interneurons respond preferentially to the HF component of the song at close range. ‘Switch interneurons’ are sensitive to both spectral song components, but exhibit a typical activity switch towards the high-frequency mode at distances nearer than 3–6 m. The activity of the latter two groups of interneurons correlates with the distance in the field at which males begin to interact acoustically with their neighbours. Important information about the rate of changes in the song mode is represented by the afferent activity despite the influence of the masking song produced by a sympatric katydid species.