Abstract
In many insects, mate finding relies on female-released sex pheromones, which have to be deciphered by the male olfactory system within an odorous background of plant volatiles present in the environment of a calling female. With respect to pheromone-mediated mate localization, plant odorants may be neutral, favorable, or disturbing. Here we examined the impact of plant odorants on detection and coding of the major sex pheromone component, (Z)-11-hexadecenal (Z11-16:Ald) in the noctuid moth Heliothis virescens. By in vivo imaging the activity in the male antennal lobe (AL), we monitored the interference at the level of olfactory sensory neurons (OSN) to illuminate mixture interactions. The results show that stimulating the male antenna with Z11-16:Ald and distinct plant-related odorants simultaneously suppressed pheromone-evoked activity in the region of the macroglomerular complex (MGC), where Z11-16:Ald-specific OSNs terminate. Based on our previous findings that antennal detection of Z11-16:Ald involves an interplay of the pheromone binding protein (PBP) HvirPBP2 and the pheromone receptor (PR) HR13, we asked if the plant odorants may interfere with any of the elements involved in pheromone detection. Using a competitive fluorescence binding assay, we found that the plant odorants neither bind to HvirPBP2 nor affect the binding of Z11-16:Ald to the protein. However, imaging experiments analyzing a cell line that expressed the receptor HR13 revealed that plant odorants significantly inhibited the Z11-16:Ald-evoked calcium responses. Together the results indicate that plant odorants can interfere with the signaling process of the major sex pheromone component at the receptor level. Consequently, it can be assumed that plant odorants in the environment may reduce the firing activity of pheromone-specific OSNs in H. virescens and thus affect mate localization.
Highlights
The ability of many insect species to use plant volatiles and pheromones to locate food, sexual partners, and appropriate egglaying places is crucial for survival and reproduction (Zwiebel and Takken, 2004; Vosshall, 2008; Carey and Carlson, 2011; Hansson and Stensmyr, 2011)
PLANT ODORANTS AFFECT PHEROMONE-INDUCED RESPONSES IN THE antennal lobe (AL) In order to analyze the interference between volatiles of host plants that are present in the environment of calling females and the major sex pheromone component Z11-16:Ald, we performed functional in vivo calcium imaging of the AL of male H. virescens
PLANT ODORANTS AFFECT THE PHEROMONE-INDUCED RESPONSE OF HR13-EXPRESSING CELLS To determine whether plant odorants may affect the pheromone receptors (PRs) for Z11-16:Ald on the antenna, we examined whether a HR13mediated pheromone response is altered in the presence of plant odorants
Summary
The ability of many insect species to use plant volatiles and pheromones to locate food, sexual partners, and appropriate egglaying places is crucial for survival and reproduction (Zwiebel and Takken, 2004; Vosshall, 2008; Carey and Carlson, 2011; Hansson and Stensmyr, 2011). Components of female sex pheromone blends are detected by specialized sensilla on the male antenna (Almaas and Mustaparta, 1991; Baker et al, 2004). Specific PBPs take distinct pheromone molecules from the air and transfer them through the lymph toward specific pheromone receptors (PRs) in the dendritic membrane of PhOSNs (Leal, 2003; Vogt, 2003; Grosse-Wilde et al, 2006, 2007; Forstner et al, 2009). Signals from general odorants, e.g., plant volatiles, are detected by general OSNs and transferred to sexually isomorphic ordinary glomeruli in the AL (Galizia et al, 2000; Hansson et al, 2003)
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