Variation on a Theme: Vibrational Signaling in Caterpillars of the Rose Hook-Tip Moth, Oreto rosea

Abstract Vibrational communication in hook-tip moth caterpillars is thought to be widely used and highly variable across species, but this phenomenon has been experimentally examined in only two species to date. The purpose of this study is to characterize and describe the function of vibrational signaling in a species, Oreta rosea Walker 1855 (Lepidoptera: Drepanidae), that differs morphologically from previously studied species. Caterpillars of this species produce three distinct types of vibrational signals during territorial encounters with conspecifics — mandible drumming, mandible scraping and lateral tremulation. Signals were recorded using a laser-doppler vibrometer and characterized based on temporal and spectral components. Behavioural encounters between a leaf resident and a conspecific intruder were staged to test the hypothesis that signaling functions as a territorial display. Drumming and scraping signals both involve the use of the mandibles, being hit vertically on, or scraped laterally across, the leaf surface. Lateral tremulation involves quick, short, successive lateral movements of the anterior body region that vibrates the entire leaf. Encounters result in residents signaling, with the highest rates observed when intruders make contact with the resident. Residents signal significantly more than intruders and most conflicts are resolved within 10 minutes, with residents winning 91% of trials. The results support the hypothesis that vibrational signals function to advertise leaf occupancy. Signaling is compared between species, and evolutionary origins of vibrational communication in caterpillars are discussed

Lindeman and Yack Data set

Data set supporting figures and analyses on sound production mechanisms in the bark beetle, Dendroctonus valens

Data from: Bark beetles use a spring-loaded mechanism to produce variable song patterns

Many insects vary their song patterns to communicate different messages, but the underlying biomechanisms are often poorly understood. Here we report on the mechanics of sound production and variation in an elytro-tergal stridulator, male Dendroctonus valens bark beetles. Using ablation experiments coupled with high-speed video and audio recordings, we show that (1) chirps are produced using a stridulatory file on the left elytron (forewing) and a protrusion (plectrum) on the seventh abdominal segment, (2) chirps are produced by spring stridulation, a catch-and-release mechanism whereby the plectrum catches on a file tooth, and upon release, springs forward along the file, and (3) variability in chirp types is caused by introducing multiple catch and release events along the file to create regular interruptions. These results provide experimental evidence for the mechanics of elytrotergal stridulation, and provide insight into how an insect can incorporate variability into its acoustic repertoire using a spring-loaded mechanism

Hearing in the crepuscular owl butterfly (Caligo eurilochus, Nymphalidae)

Tympanal organs are widespread in Nymphalidae butterflies, with a great deal of variability in the morphology of these ears. How this variation reflects differences in hearing physiology is not currently understood. This study provides the first examination of the hearing organs of the crepuscular owl butterfly, Caligo eurilochus. We hypothesize that (1) its hearing may function to detect the high-frequency calls of bats, or (2) like its diurnal relatives it may function to detect avian predators, or (3) it may have lost auditory sensitivity as a result of the lack of selective pressures. To test these hypotheses we examined the tuning and sensitivity of the C. eurilochus Vogel’s organ using laser Doppler vibrometry and extracellular neurophysiology. We show that the C. eurilochus ear responds to sound and is most sensitive to frequencies between 1-4 kHz, as confirmed by both the vibration of the tympanal membrane and the physiological response of the associated nerve branches. In comparison to the hearing of its diurnally active relative, Morpho peleides, C. eurilochus has a narrower frequency range with higher auditory thresholds. We conclude that hearing in this butterfly is partially-regressed, and may reflect a trade-off between hearing and vision for survival in low light conditions

Egg laying cowpea beetle.

<p>A female <i>Callosobruchus maculatus</i> beetle inspects a seed prior to oviposition. Arrow points to a freshly laid egg on the seed surface.</p

Hearing in hooktip moths (Drepanidae: Lepidoptera)

This study presents anatomical and physiological evidence for a sense of hearing in hooktip moths (Drepanoidea). Two example species, Drepana arcuata and Watsonalla uncinula, were examined. The abdominal ears of drepanids are structurally unique compared to those of other Lepidoptera and other insects, by having an internal tympanal membrane, and auditory sensilla embedded within the membrane. The tympanum is formed by two thin tracheal walls that stretch across a teardrop-shaped opening between dorsal and ventral air chambers in the first abdominal segment. There are four sensory organs (scolopidia) embedded separately between the tympanal membrane layers: two larger lateral scolopidia within the tympanal area, and two smaller scolopidia at the medial margin of the tympanal frame. Sound is thought to reach the tympanal membrane through two external membranes that connect indirectly to the dorsal chamber. Summary The ear is tuned to ultrasonic frequencies between 30 and 65·kHz, with a best threshold of around 52·dB·SPL at 40·kHz, and no apparent difference between genders. Thus, drepanid hearing resembles that of other moths, indicating that the main function is bat detection. Two sensory cells are excited by sound stimuli. Those two cells differ in threshold by approximately 19·dB. The morphology of the ear suggests that the two larger scolopidia function as auditory sensilla; the two smaller scolopidia, located near the tympanal frame, were not excited by sound. We present a biophysical model to explain the possible functional organization of this unique tympanal ear

Dichotomous choice trials for <i>Callosobruchus maculatus</i> females (Indian and Brazilian strains) selecting seeds for oviposition.

<p>(A) Illustrations of the four seed conditions: Seed alone (Control), and three experimental conditions: Exp 1 seed has an egg laid by another female, Exp 2 has a living larva inside, with visual and chemical cues from the egg surface removed; Exp 3 is the same as for Exp 2 except the larva inside has been killed. (B, C) Results showing the proportion of trials where females chose the experimental condition over the control for the Indian and Brazilian strains respectively. The Indian strain avoids choosing a seed with a live larva even when external markers have been removed. Asterisks indicate significant departure from random expectation based on the adjusted <i>G</i> test (<i>P</i> < 0.05).</p

What does a butterfly hear? Physiological characterization of auditory afferents in Morpho peleides (Nymphalidae)

Many Nymphalidae butterflies possess ears, but little is known about their hearing. The tympanal membrane of butterflies typically comprises distinct inner and outer regions innervated by auditory nerve branches NII and NIII and their respective sensory organs. Using the Blue Morpho butterfly (Morpho peleides) as a model, we characterized threshold and suprathreshold responses of NII and NIII. Both are broadly tuned to 1–20 kHz with best frequencies at 1–3 kHz, but NIII is significantly more sensitive than NII. The compound action potentials (CAPs) of both branches increase their first peak amplitudes and areas in response to higher sound levels. NII and NIII differed in their suprathreshold CAP responses to sound frequencies, with stronger responses to 1–3 and 4–6 kHz, for NIII and NII respectively; results that are consistent with tympanal membrane mechanics. These results indicate that butterflies are capable of amplitude and frequency discrimination. Both auditory branches responded to playbacks of the flight and calls of predatory birds. We propose that the ears of butterflies, like those of many vertebrate prey such as some rabbits and lizards, function primarily in predator risk assessment

Data from: In that vein: inflated wing veins contribute to butterfly hearing

Insects have evolved a diversity of hearing organs specialized to detect sounds critical for survival. We report on a unique structure on butterfly wings that enhances hearing. The Satyrini are a diverse group of butterflies occurring throughout the world. One of their distinguishing features is a conspicuous swelling of their forewing vein, but the functional significance of this structure is unknown. Here we show that wing vein inflations function in hearing. Using the Common Wood-Nymph, Cercyonis pegala, as a model, we show that (1) these butterflies have ears on their forewings that are most sensitive to low frequency sounds (<5 kHz); (2) inflated wing veins are directly connected to the ears; (3) when vein inflations are ablated, sensitivity to low frequency sounds is impaired. We propose that inflated veins contribute to low frequency hearing by impedance matching

Latency to lay eggs on seeds in adult female cowpea beetles <i>Callosobruchus maculatus</i> during dichotomous choice trials.

<p>(A) A comparison of egg-laying latencies between Indian and Brazilian strain females showing that Indian females take longer to lay; the box plots indicate the median (solid line), mean (dashed line), and range of dispersion (lower and upper quartiles, and outliers) of the latency results. (B) Correlation between latency for egg laying and body mass of adult females from two strains (Indian as diamonds and Brazilian as circles).</p