Date Published: November 30, 2012
Publisher: Public Library of Science
Author(s): Man-Yeon Choi, Robert K. Vander Meer, Michel Renou. http://doi.org/10.1371/journal.pone.0050400
Our understanding of insect chemical communication including pheromone identification, synthesis, and their role in behavior has advanced tremendously over the last half-century. However, endocrine regulation of pheromone biosynthesis has progressed slowly due to the complexity of direct and/or indirect hormonal activation of the biosynthetic cascades resulting in insect pheromones. Over 20 years ago, a neurohormone, pheromone biosynthesis activating neuropeptide (PBAN) was identified that stimulated sex pheromone biosynthesis in a lepidopteran moth. Since then, the physiological role, target site, and signal transduction of PBAN has become well understood for sex pheromone biosynthesis in moths. Despite that PBAN-like peptides (∼200) have been identified from various insect Orders, their role in pheromone regulation had not expanded to the other insect groups except for Lepidoptera. Here, we report that trail pheromone biosynthesis in the Dufour’s gland (DG) of the fire ant, Solenopsis invicta, is regulated by PBAN. RNAi knock down of PBAN gene (in subesophageal ganglia) or PBAN receptor gene (in DG) expression inhibited trail pheromone biosynthesis. Reduced trail pheromone was documented analytically and through a behavioral bioassay. Extension of PBAN’s role in pheromone biosynthesis to a new target insect, mode of action, and behavioral function will renew research efforts on the involvement of PBAN in pheromone biosynthesis in Insecta.
Pheromones are a subset of semiochemicals produced by organisms for communication within members of the same species. Since the first pheromone was identified over 50 years ago , pheromone research has been expanded tremendously in animal and plant taxa, especially insects , . While pheromone identification and their elicited behaviors are well known for a wide variety of insects, the regulation of pheromone biosynthesis is poorly understood and is limited to some lepidopteran moths – For these moth species a neuropeptide hormone stimulates sex pheromone biosynthesis in female adults , . This neuropeptide was named pheromone biosynthesis activating neuropeptide (PBAN), it is synthesized in the subesophageal ganglion (SG) and released into the hemolymph to reach a target site, e.g., a pheromone gland –. PBAN/pyrokinin genes appear to be ubiquitous in insects and produce three or four peptides in addition to PBAN , . These peptides share a common functional epitope (FXPRL-NH2) or similar sequence at the C-termini , , which characterizes the PBAN/pyrokinin family of peptides , . The PBAN/pyrokinin peptide family has been found in a variety of insect Orders, and to date over 200 PBAN/pyrokinin family peptides have been reported from over 40 species (from GenBank, unpublished). In addition to regulation of sex pheromone biosynthesis in female moths, several other physiological functions for this family of peptides have been demonstrated, for example: (a) induction of melanization in moth larvae , ; (b) induction of diapause egg in moths , ; (c) stimulation of visceral muscle contraction in cockroaches ; (d) acceleration of puparium formation in the flesh fly ; and (e) termination of development of pupal diapause in heliothine moths . However, their involvement in the control of pheromone production has only been demonstrated for moth PBAN where it stimulates the biosynthesis of the sex pheromone , .
The DG is the source of the fire ant trail pheromone , which is released through the sting (Fig. 1A). The most abundant volatile trail pheromone component is Z,E-α-farnesene (Fig. S1A) . This component is responsible for the orientation of the ants along a pheromone trail. Our earlier studies on the trail pheromone  coupled with our recent characterization of the PBAN/pyrokinin family of peptides from fire ants , , , , provided the foundation for the discovery that Solenopsis invicta PBAN (SolinPBAN) regulates trail pheromone biosynthesis in the DG (Fig. 1B).
Taken together, our results demonstrate that the neuropeptide, SolinPBAN, stimulates trail pheromone biosynthesis in fire ants. The consequences of this discovery are: 1) after >20 years, the scope of PBAN’s activity is broadened to insect groups other than lepidopteran species; 2) the behavioral type of pheromone acted on is extended from only sex pheromones to include ant trail pheromones; 3) biosynthetic regulation is extended from fatty acid to the highly versatile isoprenoid pathway; and 4) molecular level manipulation of RNAi of PBAN and PBAN-R suggests the possibility of novel control methods for insect pests (47). We anticipate that the research model presented here will lead to yet broader elucidation of PBAN’s role in insect pheromone biosynthesis, as well as additional function(s).