Molecular and neural mechanisms of sex pheromone reception and processing in the silkmoth Bombyx mori.

Takeshi Sakurai

doi:10.3389/fphys.2014.00125

Abstract

Male moths locate their mates using species-specific sex pheromones emitted by conspecific females. One striking feature of sex pheromone recognition in males is the high degree of specificity and sensitivity at all levels, from the primary sensory processes to behavior. The silkmoth Bombyx mori is an excellent model insect in which to decipher the underlying mechanisms of sex pheromone recognition due to its simple sex pheromone communication system, where a single pheromone component, bombykol, elicits the full sexual behavior of male moths. Various technical advancements that cover all levels of analysis from molecular to behavioral also allow the systematic analysis of pheromone recognition mechanisms. Sex pheromone signals are detected by pheromone receptors expressed in olfactory receptor neurons in the pheromone-sensitive sensilla trichodea on male antennae. The signals are transmitted to the first olfactory processing center, the antennal lobe (AL), and then are processed further in the higher centers (mushroom body and lateral protocerebrum) to elicit orientation behavior toward females. In recent years, significant progress has been made elucidating the molecular mechanisms underlying the detection of sex pheromones. In addition, extensive studies of the AL and higher centers have provided insights into the neural basis of pheromone processing in the silkmoth brain. This review describes these latest advances, and discusses what these advances have revealed about the mechanisms underlying the specific and sensitive recognition of sex pheromones in the silkmoth.

Highlights

Olfactory information plays pivotal roles in many aspects of an animal’s life including foraging, prey detection, finding hosts, and mating
The silkmoth Bombyx mori has the simplest possible sex pheromone system, in which a single pheromone compound releases programmed pheromone-source searching behavior, while most moth species utilize more complex system where blends of several pheromone components are required for behavioral responses in males
Though we refer to bombykal as a minor pheromone component in the present review according to the convention, biological activity of bombykal seems to be unusual for sex pheromone components in moths; bombykal is supposed not to contribute to attraction of male moths but to suppress initiation of the pheromonesource searching behavior triggered by bombykol (Kaissling et al, 1978; Daimon et al, 2012b)

Summary

INTRODUCTION

Olfactory information plays pivotal roles in many aspects of an animal’s life including foraging, prey detection, finding hosts, and mating. Further investigation may be necessary to define bombykal as a sex pheromone component of B. mori Regardless of such a unique effect of bombykal, a straightforward input-output relationship between bombykol and pheromone-source searching behavior allows researchers to correlate molecular and neural functions with behavioral responses. Calculations based on electrophysiological studies using radiolabeled bombykol have revealed that bombykol-sensitive ORNs are so sensitive that a single pheromone molecule can evoke an electrical signal (Kaissling, 1987) These receptor neurons show extremely high selectivity, and generally respond only to a single pheromone component (Kikuchi, 1975). We summarize and discuss the recent evidence of the underlying molecular mechanisms for the specificity and sensitivity of pheromone reception in B. mori

MOLECULAR COMPONENTS OF PHEROMONE RECEPTION

MUSHROOM BODY

Findings

EFFECTS OF SEROTONIN