Symposium on Agroacoustics: How Do Acoustic Inputs to the Central Nervous System of the Bollworm Moth Control its Behavior?

Abstract

The nervous system of the bollworm moth, Heliothis zea (Boddie), a noctuid moth that is a major pest of cotton, corn, and tomatoes, is served by two pairs of acoustic sense cells. The moths use the acoustic receptors to detect the ultrasonic cries of predatory bats that feed on these moths. Bats use pulsed high frequency sounds to echolocate and capture moths for food. The moths have developed an avoidance behavioral reaction that protects them from predatory bat capture when they detect the echolocating cries of the bats. A pair of acoustic receptors are located in each tympanic organ located on the lateral wall of the metathorax on each side of the moth. A1 receptor, the most sensitive unit, can detect 20 kilohertz frequencies at sound pressure levels of 35 dB (0 dB re 20 @m Pa). The A2 receptor is about 20 dB less sensitive and is also tuned to be most sensitive to 20 kHz sounds. Pulse rates of 10/sec and pulse durations of 10 msec were most effective for eliciting evasive reactions in the bollworm moth. In field and laboratory behavior tests, we have determined that the moths can detect 85 dB pulses of ultrasound (20 kHz) at a distance of 50-80 feet from the moth and after detection the moths make evasive reactions. My recent research has focused on identification of the neural circuits from the acoustic receptors to and through the central nervous system (meso- metathoracic ganglia and prothoracic ganglion and brain) to the motor nerves responsible for executing the evasive reactions. The structure of the various parts of the circuits responsible for the behavioral reactions have been identified using histochemical techniques (cobalt chloride and lucifer yellow) that mark only the axons carrying the acoustic information (action potentials) and the motor nerve commands from these nerves to the muscles responsible for directed flight. Electrophysiological techniques were used to monitor the information flow in the acoustic axons that feed the moth coded information on the high frequency sounds in its environment. If the information is from the A1 receptor, it is processed in the brain to produce behavior commands that are transmitted by the motor nerves to generate a behavioral reactions that produce turn reactions. The information from the A2 receptor is transmitted to neurons in the mesothoracic ganglion directly and produce rapid unpredictable evasive reactions (spirals, dives, and cessation of flight) and do not require "brain" processing. The anatomical circuits, behavioral reaction times, and electrophysiological monitoring of neural activities confirm these findings. These and other studies have demonstrated that the behavior of the moth is influenced or controlled by sensory inputs that can have positive and negative effects on the moth behavior. When the flying moth is attracted to an ultraviolet light and a sound source at the light source generates a pulses of high frequency sound, the moth will make an evasive reaction to the sound stimuli in preference to the continued attraction to the visual stimuli. In other instances, another nocturnal moth species that is attracted to a sex pheromone (an olfactory attractant) can be terminated (behavior turned off) if the trap containing the pheromone is constructed of specific colors that cause an avoidance reaction to the visual stimuli that are dominant over the attractive odor. These model acoustic studies are establishing the boundaries and conditions that must be met in the neural circuits of the central nervous system of the moth for specific sensory stimuli to be functionally effective. Normal or usual behaviors can be turned on and off when the proper sensory stimuli are presented according to specific "criterion" conditions. To obtain maximum benefits from the use of non-insecticidal technologies to control insects, a full understanding of the levels of neural processing of sensory stimuli is needed, as is an understanding of the spheres and levels of dominance that specific sensory stimuli exert in the control of the behavior of the insect pest.