Hawkmoth Pheromone Transduction Involves G-Protein-Dependent Phospholipase Cβ Signaling

Area of Science:

• Insect olfaction
• Neuroethology
• Sensory transduction

Background:

• Nocturnal moths rely on acute olfactory senses for mate detection, requiring highly sensitive and temporally resolved pheromone detection.
• The mechanisms underlying insect pheromone detection are debated, with hypotheses including ionotropic and G-protein-coupled receptor signaling pathways.
• Understanding these mechanisms is crucial for explaining insect sensory adaptations to ecological niches.

Purpose of the Study:

• To investigate the role of G-protein-coupled transduction in pheromone detection by male *Manduca sexta* hawkmoths.
• To determine how different temporal components of the olfactory response are modulated by signaling pathways and circadian timing.
• To resolve discrepancies in the literature regarding insect olfactory transduction mechanisms.

Main Methods:

• In vivo electrophysiological recordings from pheromone-sensitive sensilla of male *Manduca sexta*.
• Pharmacological disruption of G-protein-coupled transduction pathways and phospholipase C activity.
• Application of bacterial toxins to selectively disrupt specific G-alpha subunits (Gαo, Gαs, Gαq, Gα12/13).
• Analysis of distinct temporal response components (phasic, tonic, late) during rest and activity phases.

Main Results:

• Disruption of G-protein-coupled transduction and phospholipase C specifically impaired the phasic pheromone response component during the hawkmoth's activity phase.
• Targeted disruption of Gαo and sustained activation of Gαs affected the phasic response, while Gαq and Gα12/13 were ineffective.
• Expression of phospholipase Cβ4 exhibited circadian rhythmicity, indicating clock-modulated metabotropic signaling.

Conclusions:

• Circadian clock-modulated G-protein-coupled transduction cascades are essential for maximizing pheromone detection sensitivity and temporal resolution during the hawkmoth's activity period.
• The findings support a model where distinct olfactory response components are mediated by specific signaling pathways, resolving previous conflicting data.
• This study highlights the importance of circadian timing in insect chemosensation for efficient mate finding.