Abstract
Sex pheromone communication of moths helps to understand the mechanisms underlying reproductive isolation and speciation. Helicoverpa armigera and Helicoverpa assulta use (Z)-11-hexadecenal (Z11-16:Ald) and (Z)-9-hexadecenal (Z9-16:Ald) as pheromone components in reversed ratios, 97:3 and 5:95, respectively. H. armigera also produces trace amount of (Z)-9-tetradecenal (Z9-14:Ald) in the sex pheromone gland, but H. assulta does not. Wind tunnel studies revealed that the addition of small amounts (0.3%) of Z9-14:Ald to the main pheromone blend of H. armigera increased the males' attraction, but at higher doses (1%, 10%) the same compound acted as an inhibitor. In H. assulta, Z9-14:Ald reduced male attraction when presented as 1% to the pheromone blend, but was ineffective at lower concentrations (0.3%). Three types (A–C) of sensilla trichodea in antennae were identified by single sensillum recording, responding to Z11-16:Ald, Z9-14:Ald, and both Z9-16:Ald and Z9-14:Ald, respectively. Calcium imaging in the antennal lobes (ALs) revealed that the input information of the three chemicals was transmitted to three units of the macroglomerular complex (MGC) in ALs in both species: a large glomerulus for the major pheromone components, a small one for the minor pheromone components, and a third one for the behavioral antagonists. The type A and C neurons tuned to Z11-16:Ald and Z9-16:Ald had a reversed target in the MGC between the two species. In H. armigera, low doses (1, 10 μg) of Z9-14:Ald dominantly activated the glomerulus which processes the minor pheromone component, while a higher dose (100 μg) also evoked an equal activity in the antagonistic glomerulus. In H. assulta, instead, Z9-14:Ald always strongly activated the antagonistic glomerulus. These results suggest that Z9-14:Ald plays different roles in the sexual communication of two Helicoverpa species through activation of functionally different olfactory pathways.
Highlights
To mate successfully, male moths have to correctly identify sex pheromones released by conspecific females
Behavioral Response of Males to Different Synthetic Blends In the wind tunnel, males of H. armigera were highly attracted to the binary pheromone blend (Z11-16:Ald and Z9-16:Ald) at the gland ratio (97:3) and showed robust mate-seeking behavior (Figure 1A)
olfactory sensory neurons (OSNs) and Related Glomeruli Mediating Attraction and Aversion Sex pheromones are first detected by OSNs on the antennae and the signals are sent to the macroglomerular complex (MGC) of the antennal lobes (ALs) via a labeled-line system, as exemplified in many moth species (Christensen and Hildebrand, 1987; Vickers and Christensen, 2003; Berg et al, 2005; Lee et al, 2006a,b)
Summary
Male moths have to correctly identify sex pheromones released by conspecific females. Sex pheromone components are first detected by olfactory sensory neurons (OSNs) in the sensilla trichodea on antennae of male moths (Hansson et al, 1987; Kaissling et al, 1989; Cossé et al, 1998; Baker et al, 2004). Male Heliothine moths possess a special and large macroglomerular complex (MGC), which usually consists of three or four glomeruli and is dedicated to processing the intra- and interspecific pheromone information, as demonstrated by electrophysiological recording combined with staining of AL neurons (Hansson et al, 1991; Vickers et al, 1998; Berg et al, 2005). For several Heliothine species, two essential sex pheromone components of respective pheromone blends are represented in two separate MGC glomeruli, and at least one other glomerulus of the MGC is used to process known behavioral antagonists (Hansson et al, 1995; Vickers et al, 1998; Vickers and Christensen, 2003; Lee et al, 2006a,b; Zhao and Berg, 2010)
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