In my laboratory we are broadly interested in how insects use their sensory systems to detect and process information from their natural environments to promote adaptive behaviours. We employ a variety of methodologies in acoustics, comparative neuroanatomy, electrophysiology, and animal behaviour to form an integrated view of an animal’s sensory experience. The central focus of my research program is on sound and vibration communication in insects.
Butterfly Hearing
Butterflies comprise 3 of 46 superfamilies (Hedyloidea, Papilionoidea, and Hesperoidea) in the order Lepidoptera. Most butterflies are diurnally active, and much research has focused on how they use vision and chemical senses for communication and orientation.
What about a sense of hearing? Do butterflies have ears? Although hearing is well studied in moths, who use their ears to detect the ultrasonic calls of bats, hearing in butterflies is poorly understood.
We are discovering that many butterflies have well developed ears on their wings. Our current research focuses on the evolution, structure, function, and physiology of hearing in this interesting group of insects.
Hearing in Diurnal Butterflies
Many Nymphalidae butterflies have ears and we have confirmed hearing in several species using neuroanatomical and neurophysiological methods. Ears are mostly sensitive to sound frequencies between 500 Hz and 6 kHz, overlapping the hearing range of humans. The function of hearing in diurnal butterflies is not understood, and we are testing two hypotheses : conspecific communication and predator detection.
The 'blue cracker' butterfly, Hamadryas feronia is believed to communicate acoustically with conspecifics, since this species produces loud clacking sounds during conspecific interactions (see Yack et al., 2000- pdf download).
Most species however, do not generate sounds, and we hypothesize that they are listening to the flight sounds, or possibly the foraging calls of predatory birds. The well known Morpho species for example possess ears (see Lane et al., Lucas et al.) that respond to the sounds made by birds during flight (Yack lab, unpublished).
Hearing in Nocturnal Butterflies
The hedylids are nocturnally active butterflies that live in the neotropics, and are special because they are believed to represent the ‘living ancestors’ of diurnal butterflies. We have described an ultrasound-sensitive ear on the ventral surface of the forewings (Yack & Fullard, Nature, 2000, pdf download; Yack et al. JCP 2007, pdf download). We are currently studying the neuroanatomy, physiology, and taxonomic distribution of these interesting ‘wing ears’.
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Bark Beetle Acoustics
Bark beetles (Scolytinae) impose significant threats to forests throughout the world, and management strategists rely heavily upon knowledge of pest species' life history attributes and sensory ecology to develop effective control programs.
Most bark beetle species produce acoustic signals, and these signals have been implicated to function in defense, courtship, aggression, and species recognition. Sound reception has also been suggested to play a role in the beetle’s ability to locate tree hosts. Despite the ubiquity of acoustic signaling in bark beetles, there is surprisingly little information about the characteristics and function of these signals in different species, or how these signals are received and transmitted through either the air or wood.
Using several different species, including the mountain pine beetle (Dendroctonus ponderosae), the dutch elm beetle (Scolytus multistriatus), the pine engraver (Ips pini), and the red turpentine beetle (D. valens) we are studying the function and physical characteristics of the signals of acoustic communication in adults and larvae, as well as the neural mechanisms that mediate acoustic behaviour.
Caterpillar Acoustics
Caterpillars (larval Lepidoptera) are important constituents of most terrestrial ecosystems, providing food to a large host of predators and parasitoids. They also include some of the most serious pests of crops and forests. Key to their success is an ability to communicate with their environment to facilitate foraging, defense, aggregation, shelter building, and competition for resources.
Surprisingly little is known about the mechanisms that caterpillars use to communicate, but there is increasing evidence that larval Lepidoptera exploit both airborne sounds and solid-borne vibrations to detect and broadcast signals in their environment.
In the Yack lab we are interested in studying novel forms of acoustic communication in caterpillars, and studying the function, evolution and neural control of acoustic behaviour.
We are currently focusing on three forms of acoustic communication in larval Lepidoptera.
Vibratory Communication
One model organism for studying vibratory communication is the North American masked birch caterpillar, Drepana arcuata. Late instars live solitarily on birch leaves, build silk leaf shelters, and use vibration signals to resolve territorial disputes over these shelters.
Continuing research on this species and its relatives in the family Drepanidae focuses on identifying vibration receptor organs, examining neural mechanisms and sensory cues affecting decision making and motivation, and learning about the evolutionary origins of ritualized acoustic communication.
The early instars live in communal groups and appear to use vibrations to communicate with others in their nest. These caterpillars are only 1-2 mm long and produce 4 different types of vibrations while moving about the nest and during interactions with nest mates.
We are currently investigating these signals and testing hypotheses relating to their function as contact or recruitment signals, or mechanisms for spacing.
In addition to D. arcuata, we have identified vibratory communication signals in more than a dozen other species. Vibrations are used to detect predators as well as conspecifics.
Airborne defensive sounds
Caterpillars are consumed by many predators, and consequently have evolved a wide range of anti-predator defenses.
Most studies on caterpillar defense involve communication with predators in the visual realm. Less is understood about how caterpillars exploit other sensory modalities of predators, such as hearing.
During the past few years we have identified several novel forms of sound production in caterpillars belonging to the superfamily Bombycoidea, which includes the large silk and hawkmoth caterpillars.
Sounds are produced using a wide range of mechanisms, including clicking and stridulating mandibles, whistling, and ‘burping’. Sounds appear to function in acoustic aposematism and deimatic displays.
Current studies focus on understanding the function and evolutionary origins of these interesting sounds, as well as identifying and characterizing novel sounds produced by other species. At present, little is known about the role of airborne sound production in caterpillars.
Near-field hearing
Many species of caterpillars have been observed to respond to sound, but there has been limited formal study of this phenomenon.
One model organism is the late instar caterpillar of Monarch butterflies (Danaus plexipuss). Caterpillars respond to low frequency sounds by freezing, contracting their heads, and vigorously flicking their thorax in a vertical direction. Sensory receptors have been identified as filiform trichoid sensilla located the thorax and abdomen.
Ongoing studies on hearing in caterpillars involve identifying novel receptors and sound-mediated behaviours in different species, performing neural recordings of the sensory cells, identifying projection patterns to the central nervous system, and studying the functional significance of near field hearing.