Olfactory Hairs Research Articles

Subtle morphological changes in the visual and antennal sensory system of bees and wasps across an urbanisation gradient

Increased temperature and fragmentation of green spaces in urban areas could drive variations in functional traits of insects. Such morphological shifts may occur for sensory systems, which were previously reported to be prone to change with habitat characteristics in non-urban contexts. Here, we measured traits related to the visual and antennal sensory systems in the bees Halictus scabiosae and Osmia cornuta and the wasp Polistes dominula along an urbanisation gradient within Milan (Italy). We hypothesised that fragmentation could filter for better visual properties, and that higher temperature could filter for fewer thermoreceptors and more olfactory hairs. While controlling for body size, results show subtle but appreciable responses to urbanisation in one or more traits in all species, though not always supporting our hypotheses. O. cornuta shows marginally higher ommatidia density and smaller ommatidia diameter (associated with better visual resolution) in more fragmented sites, as well as marginally fewer thermoreceptors in hotter sites, in agreement with our two predictions. On the other hand, H. scabiosae has marginally smaller antennae and P. dominula has smaller eyes at warmer locations, and the wasp also has smaller antennae and 9th flagellomeres in more fragmented areas. Perhaps higher temperatures accelerate development of sensory system at higher speed than the rest of body in these two species. Our results represent the first evidence of urbanisation effects on the visual and antennal sensory systems of bees and wasps and underline how such effects may involve a much broader bouquet of traits then previously observed.

Cloning and functional analysis of the molting gene CYP302A1 of Daphnia sinensis

BackgroundMolting is an important physiological process in the growth and development of arthropoda, which is mainly regulated by juvenile hormone and ecdysone. CYP302A1 is a key enzyme which plays a critical role in the synthesis of ecdysone in insects, but it has not been identified in cladocera.ResultsThe CYP302Al gene of Daphnia sinensis was cloned and its function was analyzed in this paper. The CYP302Al gene of D. sinensis was 5926 bp in full-length, with an open reading frame (ORF) of 1596 bp that encoded 531 amino acids (aa), a molecular weight of 60.82 kDa and an isoelectric point of 9.29. The amino acid sequence analysis revealed that there were five characteristic conserved regions of cytochrome P450 family (namely helix-C, helix-K, helix-I, PERF and heme-binding). In dsRNA mediated experiment, the expression level of CYP302A1 gene decreased significantly (knock-down of 56.22%) in the 5% Escherichia coli concentration treatment. In addition, the expression levels of EcR and USP and HR3 genes in the downstream were also significantly decreased, whereas that of FTZ-f1 gene increased significantly. In the 5% E. coli treatment, the molting time at maturity of D. sinensis prolonged, and the development of embryos in the incubation capsule appeared abnormal or disintegrated. The whole-mount in situ hybridization showed that the CYP302A1 gene of D. sinensis had six expression sites before RNA interference (RNAi), which located in the first antennal ganglion, ovary, cecae, olfactory hair, thoracic limb and tail spine. However, the expression signal of the CYP302A1 gene of D. sinensis disappeared in the first antennal ganglion and obviously attenuated in the ovary after RNAi.ConclusionThe CYP302A1 gene played an important role in the ecdysone synthesis pathway of D. sinensis, and the knock-down of the gene affected the molting and reproduction of D. sinensis.

Sensory plasticity in a socially plastic bee.

The social Hymenoptera have contributed much to our understanding of the evolution of sensory systems. Attention has focussed chiefly on how sociality and sensory systems have evolved together. In the Hymenoptera, the antennal sensilla are important for optimizing the perception of olfactory social information. Social species have denser antennal sensilla than solitary species, which is thought to enhance social cohesion through nestmate recognition. In the current study, we test whether sensilla numbers vary between populations of the socially plastic sweat bee Halictus rubicundus from regions that vary in climate and the degree to which sociality is expressed. We found population differences in both olfactory and hygro/thermoreceptive sensilla numbers. We also found evidence that olfactory sensilla density is developmentally plastic: when we transplanted bees from Scotland to the south‐east of England, their offspring (which developed in the south) had more olfactory hairs than the transplanted individuals themselves (which developed in Scotland). The transplanted bees displayed a mix of social (a queen plus workers) and solitary nesting, but neither individual nor nest phenotype was related to sensilla density. We suggest that this general, rather than caste‐specific sensory plasticity provides a flexible means to optimize sensory perception according to the most pressing demands of the environment. Sensory plasticity may support social plasticity in H. rubicundus but does not appear to be causally related to it.

Endogenous fatty acids in olfactory hairs influence pheromone binding protein structure and function in Lymantria dispar

The gypsy moth utilizes a pheromone, (7R,8S)-2-methyl-7,8-epoxyoctadecane, for mate location. The pheromone is detected by sensory hairs (sensilla) on the antennae of adult males. Sensilla contain the dendrites of olfactory neurons bathed in lymph, which contains pheromone binding proteins (PBPs). We have extracted and identified free fatty acids from lymph of sensory hairs, and we demonstrate that these function as endogenous ligands for gypsy moth PBP1 and PBP2. Homology modeling of both PBPs, and docking of fatty acids reveal multiple binding sites: one internal, the others external. Pheromone binding assays suggest that these fatty acids increase PBP-pheromone binding affinity. We show that fatty acid binding causes an increase in α-helix content in the N-terminal domain, but not in the C-terminal peptide of both proteins. The C-terminal peptide was shown to form a α-helix in a hydrophobic, homogeneous environment, but not in the presence of fatty acid micelles. Through partition assays we show that the fatty acids prevent adsorption of the pheromone on hydrophobic surfaces and facilitate pheromone partition into an aqueous phase. We propose that lymph is an emulsion of fatty acids and PBP that influence each other and thereby control the partition equilibria of hydrophobic odorants.

Chronic stress aggravates inflammation of nasal mucosa in allergic rhinitis-induced mice model

To investigate the effect of chronic stress on inflammation of nasal mucosa using an unpredictable chronic mild stress (UCMS) model to mimic chronic stress-like disorders. We divided BALB/c mice into four groups: control (n = 5), UCMS-exposed (n = 5), AR-induced (n = 5) and UCMS-exposed/AR-induced groups (n = 5). We measured cortisol as a marker of chronic stress and cytokines such as IFN-γ and IL-4, IL-5 representing Th1 and Th2 response, respectively, and we also examined the nasal mucous membrane histologically. UCMS exposure was confirmed by an increase in the levels of cortisol. Although there was no significant difference in Th1 cytokine (IFN-γ) levels within the groups, Th2 cytokine (IL-5) levels were significantly increased in stressed groups (UCMS-exposed and UCMS-exposed/AR-induced groups) compared to non-stressed groups (control and AR-induced groups). The histological examination of the nasal mucous membrane after antigen challenge in stressed group revealed severe dilation of blood vessels and injured olfactory hairs on the olfactory mucous membrane and severe swelling in the respiratory epithelium, compared to non-stressed group. These results suggest that chronic stress can aggravate inflammation of nasal mucosa in AR-induced mice model by shifting to the Th2 response by up-regulation of Th2 cytokines expression.

Olfaction in insects

Summary Odorants provide insects with crucial information about their environment and trigger various insect behaviors. A remarkably sensitive and selective sense of smell allows the animals to detect extremely low amounts of relevant odorants and thereby recognize, e.g., food, conspecifics, and predators. In recent years, significant progress has been made to­wards understanding the molecular elements and cellular mechanisms of odorant detection in the antenna and the principles under­lying the primary processing of olfactory signals in the brain. These findings show that olfactory hairs on the antenna are specifically equipped with chemosensory detector units. They contain several binding proteins, which transfer odorants to specific receptors resid­ing in the dendritic membrane of olfacto­ry sensory neurons (OSN). Binding of odor­ant to the receptor initiates ionotropic and/or metabotropic mechanisms, translating the chemical signal into potential changes, which alter the spontaneous action potential frequency in the axon of the sensory neurons. The odor-dependent action potentials propagate from the antennae along the axon to the brain leading to an input signal with­in the antennal lobe. In the antennal lobe, the first relay station for olfactory information, the input signals are extensively processed by a complex network of local interneurons be­fore being relayed by projection neurons to higher brain centers, where olfactory perception takes place.

A Drosophila Protein Family Implicated in Pheromone Perception Is Related to Tay-Sachs GM2-Activator Protein

Low volatility, lipid-like cuticular hydrocarbon pheromones produced by Drosophila melanogaster females play an essential role in triggering and modulating mating behavior, but the chemosensory mechanisms involved remain poorly understood. Recently, we showed that the CheB42a protein, which is expressed in only 10 pheromone-sensing taste hairs on the front legs of males, modulates progression to late stages of male courtship behavior in response to female-specific cuticular hydrocarbons. Here we report that expression of all 12 genes in the CheB gene family is predominantly or exclusively gustatory-specific, and occurs in many different, often non-overlapping patterns. Only the Gr family of gustatory receptor genes displays a comparable variety of gustatory-specific expression patterns. Unlike Grs, however, expression of all but one CheB gene is sexually dimorphic. Like CheB42a, other CheBs may therefore function specifically in gustatory perception of pheromones. We also show that CheBs belong to the ML superfamily of lipid-binding proteins, and are most similar to human GM2-activator protein (GM2-AP). In particular, GM2-AP residues involved in ligand binding are conserved in CheBs but not in other ML proteins. Finally, CheB42a is specifically secreted into the inner lumen of pheromone-sensing taste hairs, where pheromones interact with membrane-bound receptors. We propose that CheB proteins interact directly with lipid-like Drosophila pheromones and modulate their detection by the gustatory signal transduction machinery. Furthermore, as loss of GM2-AP in Tay-Sachs disease prevents degradation of GM2 gangliosides and results in neurodegeneration, the function of CheBs in pheromone response may involve biochemical mechanisms critical for lipid metabolism in human neurons.

Responses of the olfactory receptor neurons of the corn stalk borer Sesamia nonagrioides to components of the pheromone blend and their inhibition by a trifluoromethyl ketone analogue of the main component.

Two types of olfactory hairs and three types of olfactory receptor neurons (ORN) have been characterized on the antennae of male Sesamia nonagrioides Lef for the first time. Type A sensilla housed a cell which fired large spikes in response to (Z)-11-hexadecenyl acetate (Z11-16:Ac), the major component of the sex pheromone, and a second cell firing smaller spikes in response to (Z)-11-hexadecenal (Z11-16:Ald), a minor component of the pheromone blend. Type B sensilla housed one cell firing large spikes to Z11-16:Ac and a cell firing smaller spikes to another minor component of the pheromone blend, (Z)-11-hexadecenyl alcohol (Z11-16:OH). No cell responding to dodecyl acetate, another minor component of the natural extract, was found. Fluorinated ketones were tested as inhibitors of the cell responses to pheromone compounds. The fluorinated derivatives tested, (Z)-11-hexadecenyl trifluoromethyl ketone (Z11-16:TFMK), n-hexadecyl trifluoromethyl ketone (16:TFMK), (Z,E)-9,11-tetradecadienyl trifluoromethyl ketone (Z9,E11-14:TFMK), 3-octylthio-1,1,1-trifluoropropan-2-one (OTFP), (Z)-11-tetradecenyl trifluoromethyl ketone (Z11-11:TFMK) and 1,1-difluoro-(Z)-11-hexadecenyl methyl ketone (Z11-16:DFMK), had no or only weak excitatory effects. However, the neuron responses to the pheromone compounds were significantly decreased in the presence of a constant stimulation with Z11-16:TFMK and the effect was reversible. The latencies of the responses to the acetate and aldehyde cells were significantly increased. The effects were not specific, since Z11-16:TFMK also inhibited the responses of the ORNs of Spodoptera littoralis Boisd. Correspondingly, Z9,E11-14:TFMK, an analogue of the main component of the pheromone of this latter insect, inhibited responses of S nonagrioides ORNs. Implications of these results on the utilization of Z11-16:TFMK as a communication disruptant are discussed.

Inactivation of olfactory sensilla of a single morphological type differentially affects the response of Drosophila to odors.

The olfactory organs on the head of Drosophila, antennae and maxillary palps, contain several hundred olfactory hairs, each with one or more olfactory receptor neurons. Olfactory hairs belong to one of three main morphological types, trichoid, basiconic, and coeloconic sensilla, and show characteristic spatial distribution patterns on the surface of the antenna and maxillary palps. Here we show that targeting expression of the cell-death gene reaper to basiconic sensilla (BS) causes the specific inactivation of most olfactory sensilla of this type with no detectable effect on other types of olfactory sensilla or the structure of the antennal lobe. Our data suggest that BS are required for a normal sensitivity to many odorants with a variety of chemical structures, through a wide range of concentrations. Interestingly, however, in contrast to other odorants tested, the behavioral response of ablated flies to intermediate concentrations of propionic and butyric acids is normal, suggesting the involvement of sensilla unaffected by ectopic reaper expression, probably coeloconic sensilla that respond strongly to these two organic acids. As inactivation of BS causes an underestimation of the concentration of both acids detectable at both the highest and lowest odorants concentrations, our results suggest that concentration coding for these two odorants relies on the integration of signals from different subsets of sensilla, most likely of different morphological types.

Olfaction in the Gypsy Moth, Lymantria dispar: EFFECT OF pH, IONIC STRENGTH, AND REDUCTANTS ON PHEROMONE TRANSPORT BY PHEROMONE-BINDING PROTEINS

The pheromone-binding proteins (PBPs) are 16-kDa abundant proteins in specialized olfactory hairs in insects. The mechanism by which the PBPs remove the pheromone from the inner surface of sensory hairs and deliver it to the sensory cell remains unclear. Existing qualitative models postulate that pheromone is released near the dendrite by a decrease in pH or by a reduced form of the PBP. This study focuses on the two PBPs from the gypsy moth and the enantiomers of the pheromone cis-2-methyl-7,8-epoxyoctadecane. The pH dependence of pheromone binding has revealed three ionizations that are important. The type of ligand influences two of these ionizations. We propose that the (-)-enantiomer of the pheromone interacts with one of the ionizable residues on the protein while the (+)-enantiomer does not. Simultaneous variation of pH and KCl concentration in the physiological range or reduction of disulfide bridges does not change the affinity of PBP for pheromone. We propose a revised model of pheromone transport from the inner surface of the sensory hair to the sensory neuron.

Olfactory perireceptor and receptor events in moths: a kinetic model.

A mathematical model of perireceptor and receptor events has been developed for olfactory sensilla on the antennae of the moth Antheraea polyphemus. The model includes the adsorptive uptake of pheromone molecules by the olfactory hair, their transport on and within the hair by diffusion, the formation of a complex of pheromone and the extracellular pheromone-binding protein (PBP), the interaction of the complex pheromone-PBP with the hypothetical receptor molecule on the plasma membrane of the olfactory cell, the deactivation of the pheromone and, finally, its enzymatic degradation. In the model the PBP with its reduced form (with one or two intramolecular disulfide bonds) first acts as a carrier of the odorant. Later, while the pheromone is bound, it changes to an oxidized form (three disulfide bonds) with a scavenger function (carrier-to-scavenger model). This process of pheromone deactivation rather than the enzymatic pheromone degradation is responsible for the fall of the receptor potential after stimulus offset. The model is based on morphometrical, radiometrical, electrophysiological and biochemical data reported by several authors. The study supports the idea that peripheral events rather than intracellular signalling processes govern the kinetics of the receptor potential in the unadapted receptor cell.

Expression patterns of two putative odorant-binding proteins in the olfactory organs of Drosophila melanogaster have different implications for their functions.

The aqueous medium bathing the dendrites of olfactory neurons contains high concentrations of odorant-binding proteins (OBPs) whose role is still unclear. OBPs may facilitate interactions between odorants and their membrane-bound receptors, perhaps by increasing the water solubility of hydrophobic molecules. Alternatively, OBPs may be involved in the inactivation of odorants and other volatile molecules, preventing desensitization and/or protecting olfactory neurons from toxic chemicals. We report here novel features of the localization of two putative OBPs, PBPRP2 and PBPRP5, that have important and different implications for their role in olfaction. Unlike several other putative OBPs of Drosophila melanogaster that are only found in adult olfactory organs, PBPRP5 is also expressed in the larval olfactory organs, suggesting that it plays a common role in olfaction at both stages. In the adult, PBPRP5 expression is restricted to the sensillum lymph that bathes the olfactory dendrites of a subset of olfactory hairs, the basiconic sensilla. Since individual basiconic sensilla differ in olfactory specificity, PBPRP5 may be able to bind to and mediate olfactory responses to a wide range of odorants. In contrast, PBPRP2 is present in the space immediately below the antennal cuticle and in the outer cavity of approximately 30% of the double-walled coeloconic sensilla on the antennal surface. In neither case is PBPRP2 in contact with the dendritic membranes of olfactory neurons, making a carrier function unlikely for this protein. Instead, PBPRP2 may act as a sink, binding to odorants and other volatile chemicals and limiting their interactions with olfactory neurons.

A quantitative model of odor deactivation based on the redox shift of the pheromone-binding protein im moth antennae.

Recent in vitro experiments with homogenates of isolated olfactory hairs of Antheraea polyphemus suggest that the pheromone-binding protein (PBP) is involved not only in pheromone solubilization and transport but also in pheromone deactivation. PBP occurs in a reduced form with one or two disulfide bridges (PBP(red)) and in the oxidized form with three bridges (PBP(ox)). From kinetic experiments it was concluded that the pheromone is first bound to PBP(red). This complex activates the receptor molecules and then turns into the oxidized form which--according to our working hypothesis--is unable to activate further receptor molecules. Apparently, the pheromone bound to the PBP (both forms) is protected from enzymatic degradation into nonexcitatory metabolites. A quantitative kinetic model of pheromone deactivation was developed (in collaboration with J. Thorson, Oxford) in which the receptor molecules are considered to act as enzymes catalyzing the redox shift of the binding protein.

Atomic-force microscopy on the olfactory dendrites of the silkmoths antheraea polyphemus and A. pernyi

Olfactory transduction is thought to occur in the outer dendritic membrane of insect olfactory receptor neurons. Electrophysiological studies have indicated that the outer dendritic membrane has non-specific cation channels and inositol-triphosphate-dependent Ca2+ channels. The presence of such channels is further supported by the observation that pheromone-stimulated dendrites take up cobalt. However, to date, there is no structural evidence for these channels. Therefore, in order to search for putative ion channels, we have imaged the membrane of the olfactory dendrites in the scanning electron microscope (SEM) and the atomic-force microscope (AFM), after extruding the dendrites out of the olfactory hairs and fixing them on plastic coverslips. With the aid of the SEM, we could see the beaded structure of the dendrite but no fine structural details, as the membrane was sputtered with gold. With the use of the contact mode of the AFM, we could see "pores" that were deeper than 3 nm and with a diameter of about 15 nm. The density of the "pores" was approximately 20/ microm2 or 10 000 pores per thick dendrite. We believe these to be putative ion channels based on indirect evidence. <KWDG LANGUAGE="EN">

Effects of temperature on silkmoth olfactory responses to pheromone can be simulated by modulation of resting cell membrane resistances

Electrophysiological parameters were measured at different temperatures in resting and pheromone-stimulated olfactory sensilla trichodea of male Antheraea polyphemus (Saturniidae). A method for selective cooling of either the olfactory hair or the antennal branch was developed. The resting preparation resistance increased with lower temperatures, the transepithelial potential decreased. These effects were also observed when the antennal branch was cooled, but were absent during cooling the hair, suggesting a major influence of auxiliary cells on the transepithelial potential and resistance. Together with the preparation resistance, the responses to pheromone stimuli increased with lower temperatures. Computer simulation of the current flow in the sensillum showed that the temperature dependence of responses to pheromone can be explained by modulation of resting resistances of cell membranes alone, without effects of temperature on stimulus transduction. The weak temperature dependence of transepithelial potential might be due to temperature dependence of the electrogenic pump producing the transepithelial potential. Selective cooling of the olfactory hair had no effect on the shape of nerve impulses, cooling of the antennal branch caused changes similar to that obtained by cooling the entire sensillum. This supports the idea that the nerve impulses are generated in the soma of the receptor cell.

Small‐scale fluid dynamics of olfactory antennae

A critical step in the process of olfaction is the arrival at the surface of a chemosensory structure of chemical signals from the environment. Many organisms use appendages bearing arrays of microscopic hairs to pick up chemical signals from the surrounding water or air. In this study a general model of fluid flow between neighboring hairs in an array is used to explore the effects of hair size, spacing, and speed on flow near olfactory hairs. If an array of hairs is moved more rapidly: 1) the volume flow rate through it rises, causing higher molecule encounter rates even though a smaller proportion of the odorants passing through the array have time to diffuse to hair surfaces, and 2) velocity gradients along hair surfaces become steeper, causing greater sensitivity to changes in odorant concentration. The more closely‐spaced the hairs, the less sensitive they are to these effects of changing speed.

Redox‐Shift of the Pheromone‐Binding Protein in the Silkmoth Antheraea Polyphemus

In pheromone-sensitive hairs of the male silkmoth Antheraea polyphemus, two electrophoretically distinct pheromone-binding proteins (PBPs) are present. They indicate no amino acid sequence diversity according to peptide mapping, but differ in their redox state, as shown by free-sulfhydryl-group-specific cleavage at cysteine residues with 2-nitro-5-thiocyanobenzoic acid. In kinetic studies, the pheromone was initially bound mainly by the reduced PBP but later by the oxidized PBP, where all six cysteine residues form disulfide bonds. This redox shift was observed only in the homogenate of isolated olfactory hairs, where proteins of the sensillum lymph and receptive dendrites are present. In control experiments with purified binding proteins, the proportion of pheromone bound to the oxidized PBP did not increase with increasing incubation time, suggesting that disulfide formation does not occur spontaneously but is mediated by the sensory hairs, possibly by interaction with the receptor cell membrane. These data suggest that arriving hydrophobic pheromone molecules are first bound by the reduced PBP and transported through the aqueous sensillum lymph towards the receptor molecules of the dendritic membrane. The oxidized complex might not be able to activate further receptors and, thus, effectively deactivate the pheromone molecules within the sensillum lymph.

Chemistry of sex attraction.

The chemical communication system used to attract mates involves not only the overt chemical signals but also indirectly a great deal of chemistry in the emitter and receiver. As an example, in emitting female moths, this includes enzymes (and cofactors, mRNA, genes) of the pheromone biosynthetic pathways, hormones (and genes) involved in controlling pheromone production, receptors and second messengers for the hormones, and host plant cues that control release of the hormone. In receiving male moths, this includes the chemistry of pheromone transportation in antennal olfactory hairs (binding proteins and sensillar esterases) and the chemistry of signal transduction, which includes specific dendritic pheromone receptors and a rapid inositol triphosphate second messenger signal. A fluctuating plume structure is an integral part of the signal since the antennal receptors need intermittent stimulation to sustain upwind flight. Input from the hundreds of thousands of sensory cells is processed and integrated with other modalities in the central nervous system, but many unknown factors modulate the information before it is fed to motor neurons for behavioral responses. An unknown brain control center for pheromone perception is discussed relative to data from behavioral-threshold studies showing modulation by biogenic amines, such as octopamine and serotonin, from genetic studies on pheromone discrimination, and from behavioral and electrophysiological studies with behavioral antagonists.

Aedes aegypti: Sensilla trichodea and stimulus-conducting structures

Much of the morphology of the olfactory sensilla on the antennae of the mosquito Aedes aegypti (L.) has been described, however little is known about the fate of odour molecules once they have been adsorbed onto the surfaces of sensilla. A stimulus-conducting system of pores, pore kettles, and pore tubules has been described for the sensilla trichodea (olfactory hairs) of several insects but not mosquitoes. Scanning electron microscopy was used to identify the s. trichodea of Ae. aegypti and to attempt visualization of their pore openings. Chemical fixation, cryopreparation, freeze drying, and negative staining, with high resolution transmission electron microscopy (TEM), were used to locate putative stimulus-conducting structures associated with the pores. TEM sections using Dalton's fixative or freeze drying showed pores and pore tubules, whereas pore tubules were poorly preserved in cryoprepared sections. The putative stimulus-conducting structures were clearly demonstrated by negative staining of whole sensilla which was quick and easy. The current hypothesis of olfactory stimulus conduction is extended to include Ae. aegypti.

Sex pheromone reception in Mamestra brassicae L. (Lepidoptera): Responses of olfactory receptor neurones to minor components of the pheromone blend

Three receptor cell types tuned to pheromone compounds were characterized in the antennae of male Mamestra brassicae L. These receptor cells are housed in two types of olfactory hairs differing in length and position on the flagellar segments. Two cell types are housed in each lateral hair, a male specific sub-type of trichoid sensilla. The first one (A cell) is narrowly tuned to Z11-16:Ac, the main component of the pheromone blend. Its companion cell (B cell) is equally tuned to Z9-14:Ac and Z11-16:OH, two compounds known to decrease the flight response of males to pheromone sources. Shorter olfactory hairs, medioventrally located on the flagellar segments, responded to Z9-14:Ac and to a minor component of the pheromone blend, Z11-16:Ald. According to positive cross-adaptation and to the similitude of action potential shape, responses to both compounds were attributed to the same cell type. No receptor cell specifically tuned to Z9-16:Ac, a minor pheromone component, was found on the antennae. However, high concentrations of Z9-16:Ac increased the firing of B cells. These results are discussed in relation to sensory encoding in M. brassicae.