Plant Odors Research Articles

Morphology and physiology of olfactory neurons in the lateral protocerebrum of the silkmoth Bombyx mori

Insect olfaction is a suitable model to investigate sensory processing in the brain. Olfactory information is first processed in the antennal lobe and is then conveyed to two second-order centres—the mushroom body calyx and the lateral protocerebrum. Projection neurons processing sex pheromones and plant odours supply the delta area of the inferior lateral protocerebrum (∆ILPC) and lateral horn (LH), respectively. Here, we investigated the neurons arising from these regions in the brain of the silkmoth, Bombyx mori, using mass staining and intracellular recording with a sharp glass microelectrode. The output neurons from the ∆ILPC projected to the superior medial protocerebrum, whereas those from the LH projected to the superior lateral protocerebrum. The dendritic innervations of output neurons from the ∆ILPC formed a subdivision in the ∆ILPC. We discuss pathways for odour processing in higher order centres.

Transgenerational inheritance of learned preferences for novel host plant odors in Bicyclus anynana butterflies.

Many phytophagous insects have strong preferences for their host plants, which they recognize via odors, making it unclear how novel host preferences develop in the course of insect diversification. Insects may learn to prefer new host plants via exposure to their odors and pass this learned preference to their offspring. We tested this hypothesis by examining larval odor preferences before and after feeding them with leaves coated with control and novel odors and by examining odor preferences again in their offspring. Larvae of the parental generation developed a preference for two of these odors over their development. These odor preferences were also transmitted to the next generation. Offspring of butterflies fed on these new odors chose these odors more often than offspring of butterflies fed on control leaves. In addition, offspring of butterflies fed on banana odors had a significant naïve preference for the banana odors in contrast to the naïve preference for control leaves shown by individuals of the parental generation. Thus, butterflies can learn to prefer novel host plant odors via exposure to them during larval development and transmit these learned preferences to their offspring. This ability potentially facilitates shifts in host plant use over the course of insect diversification.

Plant odors trigger clearing behavior in foraging trails- do they represent olfactory obstacles?

Foraging trails of leaf-cutting ants may be exposed to plant material that interferes with foragers’ flux either by physically blocking it or due to secondary metabolites which affect insect behavior. We hypothesized that plant secondary metabolites such as plant volatiles may interfere with pheromone communication, triggering clearing behavior. We impregnated small pieces of paper with different plant odors from native and exotic species and placed them in the middle of foraging trails of the leaf-cutting ant Acromyrmex lobicornis. As a control, we used papers impregnated with trail odor. The paper used as substrate for the odors did not constitute a physical obstacle based on its small surface area. Papers treated with trail odor did not interfere with ant flux and were not removed from the trail. However, when papers were treated with plant odors, they were removed from the trail in most of the cases and ant flux was reduced significantly by 15–28%. We found that ants tapped the tip of their gaster against the ground around the treated papers only when they were impregnated with foreign odors. The number of gaster tappings as well as the time between the placement of the paper and its removal increased with plant odor concentration. However, the decision to remove the paper was not correlated with the number of gaster tappings. Interestingly, clearer ants were smaller than forager ants, suggesting there is morphological differentiation in clearing behavior of the trail. Results from the current study also suggest that odors trigger clearing behavior on foraging trails and affect trail marking behavior. Our results provide information about the potential for plant compounds to constitute obstacles, even when they do not physically obstruct the trail. We conclude that odors may trigger clearing behavior by interfering with pheromone communication.

Ecological aesthetic assessment of a rebuilt wetland restored from farmland and management implications for National Wetland Parks.

While wetlands are usually used as a natural approach to remove biodegradable pollutants in surface water, their purification efficiencies coupled with their aesthetic features are of less concern. The water quality, plant landscape, acoustic environment and odour indicators were investigated in the surface water inlet and outlet of the Fujin National Wetland Park (FNWP), restored from farmlands in Northeast China. Major concentrations of pollutants in the inlet and the outlet subjected to surface flow wetland treatment were monitored, and the removal efficiencies were calculated based on 54 water samples (6 sites×3 seasons×3 replicates). The results showed that the total nitrogen (TN) and organic carbon in surface water decreased significantly after the wetland treatment, while the total phosphorus (TP) did not decrease significantly. The removal efficiencies for TN and BOD5 changed seasonally and reached 69.08% and 60.44%, respectively. An ecological aesthetic index (EAI) was developed based on the trophic state index coupled with plant landscape, acoustic and odour indicators, and the calculated EAI showed that the outlet delivered a more aesthetically harmonious appearance than the inlet in spring and autumn, but not in summer. Based on the current aquatic macrophyte species and documented purification efficiencies in FNWP, we recommend an improved ecological aesthetic management approach that utilizes and arranges diverse native plants from the surrounding wetlands (e.g. Scirpus validus) in addition to local Nelumbo nucifera, Nymphaea tetragona and Myriophyllum spicatum, and conserves the indicative and endangered species (Aldrovanda vesiculosa), from the visual appeal of the waterscape.

Evolution of temporal dynamic of volatile organic compounds (VOCs) and odors of hemp stem during field retting.

New non-destructive approach to evaluate the retting process was investigated. Increase of retting duration led to a decrease of VOCs emitted by plants and change of color and plant odor. The variation of VOCs and odor could be used as indicators for the degree of retting. In the hemp industry, retting is an upstream bioprocessing applied to the plants to facilitate the decortication of fibres from the central woody part of the stem. This treatment is currently carried out in an empirical way on the ground which leads to variability in the hemp stems quality, and thus to the hemp fibres quality. Therefore, controlling retting treatment is a crucial step for high-performance hemp fibre. In this study, a new approach is used to assess the retting degree by following the evolution of VOCs emitted by plants during different retting durations. Either harvest time or retting induces a change in VOCs released by plants. During plant maturity, volatile compounds emitted decreased with a factor of about 2, in relation to VOCs released at the end of flowering. Regardless of the harvest period, the majority of VOCs and odor concentrations, monitored by olfactometric analysis, decrease gradually until some of them disappear at the end of retting. Likewise, the green plant odor disappears during retting with an increase of dry plants odor and an appearance of fermented odor at the end of retting. Following the evolution of VOCs emitted by plants during retting could be a tool for farmers to improve the retting management.

EAG Responses of Adult Lobesia botrana Males and Females Collected from Vitis vinifera and Daphne Gnidium to Larval Host-Plant Volatiles and Sex Pheromone.

We analysed electroantennogram (EAG) responses of male and female adults of the European grapevine moth Lobesia botrana (Denis et Schiffermüller) (Lepidoptera: Tortricidae) collected as larvae from grapevine (Vitis vinifera L.) and flax-leaved daphne (Daphne gnidium L.). The host-plant odorants tested were either V. vinifera-specific [1-octen-3-ol, (E)-β-farnesene, (E)-4,8-dimethyl-1,3,7-nonatriene], D. gnidium-specific (2-ethyl-hexan-1-ol, benzothiazole, linalool-oxide, ethyl benzanoate), or were shared by both host-plants (linalool, methyl salicylate). Sex pheromone compounds were also tested. The male response to the major pheromone component (E7,Z9-12:Ac) was higher than to any other stimuli, whereas the response to the minor pheromone components (E7,Z9-12:OH and Z9-12:Ac) was not different from the response to the plant odorants. The female response to pheromone was lower or not different from that to plant odorants. Methyl salicylate elicited a higher response in females and (E)-β-farnesene elicited a higher response than several other plant odorants in both sexes. Non-significant interactions between host-plant odorant and sex indicated an absence of sex specialization for host-plant volatile detection. The lack of a significant interaction between plant volatiles and larval host-plants suggested that there was no specialization for plant-volatile detection between V. vinifera and D. gnidium individuals.

Antennal ionotropic receptors IR64a1 and IR64a2 of the parasitoid wasp Microplitis mediator (Hymenoptera: Braconidate) collaboratively perceive habitat and host cues

Ionotropic receptors (IRs), as a member of the conserved chemoreceptor families in the peripheral nervous system, play a critical role in the chemoreception of Drosophila. However, little is known about IRs in Hymenoptera insects. Here, we comprehensively characterized the gene structure, topological map and chemosensory roles of antennal IRs (MmedIRs) in the hymenopteran parasitoid wasp Microplitis mediator. We found that the IRs were conserved across various insect species. In the in situ hybridization assays, most IRs showed female antennae biased features, and there was no co-expression of the IRs and the olfactory receptor co-receptor (ORco). Moreover, three IR co-expressed complexes, IR75u-IR8a, IR64a1-IR8a and IR64a2-IR8a, were detected. Two genes with high similarity, IR64a1 and IR64a2, were located in distinct neurons but projected to the same sensillum. In two-electrode voltage-clamp recordings, IR64a1 was widely tuned to the chemicals from habitat cues released from host plants over long distances, whereas IR64a2 responded to a narrow range host cues and plant odors with low-volatility. Notably, IR64a2 was able to perceive Z9-14: Ald, a vital sex pheromone component that is released from Helicoverpa armigera, which is the preferred host of M. mediator. Furthermore, most ligands of IR64a1 and IR64a2 can trigger electrophysiological responses in female wasps. We propose that IR64a1 and IR64a2 collaboratively perceive habitat and host cues to assist parasitoids in efficiently seeking hosts.

Plant volatiles are a salient cue for foraging mammals: elephants target preferred plants despite background plant odour

To forage nonrandomly, animals must discriminate among food items. Foods differ in look, smell and taste, providing cues for foragers with appropriate senses. Irrespective of the sensory modality, however, foragers can only use cues effectively if they can detect sensory signals above background noise. Recent evidence shows that foraging mammalian herbivores can detect plant odours, but their capacity to select preferred plants in a noisy olfactory background is unknown. Using choice trials, we tested whether the African elephant, Loxodonta africana, uses plant odour as a salient cue despite increasingly complex and challenging background odours. We first established their preference for familiar plant species. We then tested their capacity to discriminate and select preferred plants based on odour alone. We found that elephants successfully chose preferred species even when presented with complex background odours from nonpreferred plants mimicking multispecies vegetation patches. Elephants also succeeded despite our attempt to mask distinguishing odours with large amounts of a synthetic green leaf volatile. GC–MS analysis confirmed that volatile organic compound profiles differed between plant species. In demonstrating that elephants exploit plant odours even when the signal from preferred plants is embedded in sensory noise of background odours, we provide crucial behavioural evidence that olfaction provides an efficient mechanism for selective, nonrandom foraging. Whether mammalian herbivores recognize novel odours, for example from newly invading plant species, or when air pollution degrades odours of familiar plants, needs investigating. Accounting for the capacity of mammalian herbivores to use plant odour cues will improve models of both their foraging behaviour and the ecosystem impacts of their foraging.

Searching behavior of the parasitoid Tamarixia triozae mediated by the host plant and experience

In the tritrophic system Solanaceae–Bactericera cockerelli Sulc (Hemiptera: Triozidae)—Tamarixia triozae Burks (Hymenoptera: Eulophidae), we studied naive and experienced T. triozae female attraction induced by the host plant (natal and alternate) and herbivory infestation. Naive females are not attracted to healthy nor to infested plants (no choice). Early experience produces attraction to combined odors of plant and host, and the host plant induces preference when experience occurs on the natal host plants, but not when it occurs on alternate host plants. The results indicate that plants mediate female parasitoid response and that T. triozae needs to learn to find its hosts in order to optimize its host-searching behavior. This need to learn and the preference triggered by learning on the natal host plant suggest that it would be convenient to give T. triozae experience to improve its initial efficiency when it is used on an alternate cultivated host plant.

Odors from phylogenetically-distant plants to Brassicaceae repel an herbivorous Brassica specialist

Specialist insect herbivores are constrained by highly specific odor recognition systems to accept suitable host plants. Given that odor recognition leads specialist insects to accept a limited range of plants, we hypothesized that phylogenetically distant plants produce odors that are physicochemically different from host odors and would be less attractive or even repellent to a specialist herbivore. We tested this hypothesis by examining behavioral and ovipositional responses of swede midge (Contarinia nasturtii, Diptera: Cecidomyiidae), a specialist of brassicas, to broccoli sprayed with non-host essential oils. Specifically, we asked: (1) How do essential oils from different plant species influence host-seeking and oviposition behaviors of swede midge? (2) Do odors from non-host plants that are not phylogenetically related or physicochemically similar to host plants affect host-seeking or ovipositional behavior of swede midge? In oviposition assays, we found that non-host odors varied in their ability to modify female midge behavior and that phylogenetic relatedness was negatively correlated with larval density. In y-tube assays, we found that female midges most frequently avoided non-host odors that were more similar to brassica odors. Females were less likely to oviposit on or choose any treated host plants, but particularly avoided garlic, spearmint, thyme, eucalyptus lemon, and cinnamon bark treatments. Overall, we found that plant phylogenetic relatedness and odor similarity are related to repellency. Therefore, altering the diversity of plant odors by explicitly accounting for plant phylogenetic distance and odor similarity, relative to host plants, may be an important, underexploited tactic for sustainably managing challenging pests.

Health Benefits of Furanocoumarins ‘Psoralidin’ An Active Phytochemical of Psoralea corylifolia: The Present, Past and Future Scenario

Background:Phytoconstituents of fruits, vegetables, spice and herbs are important for human health. Phytoconstituents play an important role in the growth, development, defensive mechanism, colors, odour and flavors of plants. Psoralea corylifolia Linn (P. corylifolia) commonly known as ‘Bakuchi’ belongs to Leguminosae family widely distributed in China and Southeastern Asian countries.Methods:Various electronic databases such as PubMed, Science Direct, Scopus and Google were searched to collect the data of the present review. Further, all the collected information was categorized into different section as per the aim of the paper. Moreover, analyzed data were also presented in the graphical abstract.Results:Seventy-two research and review papers have been collected and were included in the present review. Nineteen papers contained general information’s of P. corylifolia, Psoralens and psoralidin whereas thirty paper data were presented in the pharmacological activities sections and remaining in the Analytical tools and discussion section. From these databases, we can say that P. corylifolia possesses antibacterial, anti-inflammatory, antifungal, antioxidant, antiflarial, estrogenic, antitumour, and immunomodulatory activities. Psoralens are mainly used in the treatment of psoriasis, vitiligo and dermatitis. Topical or oral psoralens followed by UVA radiation exposure are one of the best treatments of leucoderma. Psoralidin exhibits antioxidant, anti-apoptotic, anti-inflammatory and antitumor activities.Conclusion:This review summarizes an overview of P. corylifolia, psoralen and its derivative psoralidin with respects to their pharmacological activities, medicinal uses, biological activities and bioanalytical aspects. These data will be helpful in the translation of information from traditional to the modern medicine of psoralidin.

An Egg Parasitoid Efficiently Exploits Cues From a Coevolved Host But Not Those From a Novel Host.

Egg parasitoids have evolved adaptations to exploit host-associated cues, especially oviposition-induced plant volatiles and odors of gravid females, when foraging for hosts. The entire host selection process is critical for successful parasitism and relevant in defining host specificity of parasitoids. We hypothesized that naïve egg parasitoid females reared on their coevolved host are able to exploit cues related to the coevolved host but not those from a novel host. We used the egg parasitoid Trissolcus japonicus, its coevolved host Halyomorpha halys, and the non-coevolved host Podisus maculiventris to evaluate this hypothesis. H. halys, a polyphagous pest native from Eastern Asia, has invaded North America and Europe, resulting in serious damage to crops. T. japonicus is the most effective egg parasitoid of H. halys in its native area and thus considered a major candidate for biological control. This parasitoid was detected in North America and Europe as a result of accidental introductions. Laboratory host range of T. japonicus includes P. maculiventris, an American predatory stink bug used as a biological control agent of several pests. Using T. japonicus reared on its natural host H. halys, we tested in a Y-tube olfactometer the responses of naïve parasitoid females to volatiles from tomato plants with a deposited egg mass and feeding punctures of either H. halys or P. maculiventris. Additionally, using two different olfactometer set-ups, we tested T. japonicus responses to volatiles emitted by eggs and mature males and females of H. halys or P. maculiventris. Tomato plants subjected to oviposition and feeding by H. halys were preferred by the wasp compared to clean plants, suggesting a possible activation of an indirect defense mechanism. Furthermore, T. japonicus females were attracted by cues from gravid females and mature males of H. halys but not from eggs. By contrast, naïve parasitoid females never responded to cues associated with P. maculiventris, although this non-target host is suitable for complete parasitoid development. Such lack of responses might reduce the probability of T. japonicus locating and parasitizing P. maculiventris under field conditions. Our experimental approach properly simulates the parasitoid host-location process and could be combined with the required host specificity tests for risk assessment in biological control programs.

Effects of Host Plants Reared under Elevated CO2 Concentrations on the Foraging Behavior of Different Stages of Corn Leaf Aphids Rhopalosiphum maidis.

Climate change is a major environmental concern and is directly related to the increasing concentrations of greenhouse gases. The increase in concentrations of atmospheric carbon dioxide (CO2), not only affects plant growth and development, but also affects the emission of plant organic volatile compounds (VOCs). Changes in the plant odor profile may affect the plant-insect interactions, especially the behavior of herbivorous insects. In this study, we compared the foraging behavior of corn leaf aphid (Rhopalosiphum maidis) on barley (Hordeum vulgare L.) seedlings grown under contrasted CO2 concentrations. During the dual choice bioassays, the winged and wingless aphids were more attracted by the VOCs of barley seedlings cultivated under ambient CO2 concentrations (aCO2; 450 ppm) than barley seedlings cultivated under elevated CO2 concentrations (eCO2; 800 ppm), nymphs were not attracted by the VOCs of eCO2 barley seedlings. Then, volatile compositions from 14-d-old aCO2 and eCO2 barley seedlings were investigated by GC-MS. While 16 VOCs were identified from aCO2 barley seedlings, only 9 VOCs were found from eCO2 barley seedlings. At last, we discussed the potential role of these chemicals observed during choice bioassays. Our findings lay foundation for functional response of corn leaf aphid under climate change through host plant modifications.

Heart rate and heart rate variability in infants during olfactory stimulation

Background: Various plant odours have been shown to decrease heart rate and increase parasympathetic nervous activity. However, ‘innate’ autonomic responses without the influences of experience, assumptions and prejudices of odours remains unclear.Aim: To clarify changes in heart rate and heart rate variability in infants while presenting different components of plant odours.Subjects and methods: The study participants included 17 infants aged 1–3.5 months. Each infant was exposed to the odours of α-pinene, D-limonene and air (as a control) for 2 minutes after a 2-minute resting period without any odours. The intervals of heartbeat (R-R intervals) were recorded during this process.Results: Heart rate significantly decreased in response to the odour of limonene. Frequency analysis of heart rate variability revealed that the power value at 0.2 Hz was significantly higher during the odour presentation of limonene compared to the baseline and that at 0.1 Hz and 0.4 Hz was significantly lower during α-pinene presentation.Conclusion: Autonomic responses to specific natural odours may be partly shaped innately, while underlying physiological mechanisms may be different between infants and adults.

Key Amino Residues Determining Binding Activities of the Odorant Binding Protein AlucOBP22 to Two Host Plant Terpenoids of Apolygus lucorum.

Odorant binding proteins (OBPs) are considered to be highly expressed at antennae sensillum lymph and play crucial roles in detection of insect host plant volatiles. The polyphagous mirid bug Apolygus lucorum is one of a series of insect pests on many important agricultural crops that heavily rely on sophisticated olfaction to locate host plants. Previously, putative OBP genes and their tissue-related expression patterns in this pest species have been clarified. In this study, we characterized the ligand spectrum and the molecular binding mechanism of the antennae-biased AlucOBP22 to host plant volatiles of A. lucorum. Frist, the recombinant AlucOBP22 protein was constructed and purified, and its binding affinities to selected host plant volatiles were assessed. Two terpenoids, β-ionone and β-caryophyllene, could highly bind to AlucOBP22. Next, three-dimensional model prediction indicated that AlucOBP22 employed six α-helices to form a typical pocket for ligand accommodation. Molecular docking analysis suggested that both β-ionone and β-caryophyllene were located at the AlucOBP22 pocket with some hydrophobic amino acid residues close to the two chemicals, suggesting that hydrophobic interactions might be crucial for ligand-specific binding. Finally, site-directed mutagenesis combined with fluorescence binding assays revealed that mutants of five hydrophobic residues Leu5, Ile40, Met41, Val44, and Met45 displayed significantly decreased or completely abolished binding affinities to the two ligands. Our findings showed the specific binding characteristic of AlucOBP22 and suggested that hydrophobic residues and their hydrophobic interactions were involved in AlucOBP22 binding to terpenoids, which provided new insights into the molecular interaction mechanisms of hemipteran insect OBPs to host plant odors.

Olfactory discrimination between chemical cues from coastal vegetation in two palaemonid shrimps,Palaemon vulgarisSay, 1818 andP. affinisH. Milne Edwards, 1837 (Decapoda: Caridea: Palaemonidae)

Many decapod crustaceans have highly developed chemosensory systems, with naturally occurring waterborne chemicals used to inform movement and other behavioural processes. I show that two species of intertidal palaemonid shrimps from geographically disparate locations, the North American grass shrimp Palaemon vulgaris (Say, 1818) and the New Zealand tide pool shrimp P. affinis H. Milne Edwards, 1837, possess the ability to discriminate between chemical cues produced by intertidal plants. Both species displayed a variable, but broadly comparable, response to plant odours, showing an attraction to aquatic, emergent species irrespective of taxonomy, and either showing no response or an avoidance to non-aquatic coastal species. While the chemical basis for an attraction or avoidance to these plant species is unclear, the ability to differentiate between plant species could have important implications for the behaviour of these shrimps, assisting them to locate and orient towards structurally complex habitats when visual acuity is limited.

Genome-Wide Identification and Characterization of Olfactory Receptor Genes in Chinese Perch, Siniperca chuatsi.

Olfaction, which is mediated by olfactory receptor (OR) genes, is essential in the daily life of fish, especially in foraging. However, Chinese perch (Siniperca chuatsi) is believed to prey with reliance on vision and lateral sensation, but not on olfaction. Therefore, understanding the evolutionary dynamics of the Chinese perch OR repertoire could provide insights into genetic evidence for adapting to a decreasing reliance on olfaction. Here, we reported a whole-genome analysis of the Chinese perch OR repertoire. Our analysis identified a total of 152 OR genes, including 123 functional genes and 29 pseudogenes, and showed their genomic organization. A phylogenetic tree was constructed, and the phylogenetic relationships of teleosts ORs was illustrated. The dN/dS (global ratios of non-synonymous to synonymous) analysis demonstrated that OR groups all appeared to be under purifying selection. Among the five Percomorpha fishes, Chinese perch only had 22 subfamilies, suggesting a decrease in OR diversities. The species-specific loss of subfamily 56 and 66 in Chinese perch, of which the genes belonged to subfamily 66, were orthologs of OR51E2, which recognized the plant odorant β-ionone, indicating that extremely piscivorous fish which might lose those receptors responded to plant-related odors. Finally, the expression profiles of OR genes in the olfactory epithelium at different developmental stages were investigated using RNA-seq data. From the aforementioned results, the evolution of the OR repertoire may be shaped by the adaption of vision-dependent specializations for foraging in Chinese perch. The first systematic study of OR genes in Chinese perch could provide valuable genomic resources for the further investigation of olfactory function in teleosts.

Plant Approach-Avoidance Response in Locusts Driven by Plant Volatile Sensing at Different Ranges.

Several hypotheses have been proposed to explain how herbivorous insects approach plants by sensing plant volatiles. Insect antennae and maxillary palps are believed to have crucial roles in the detection of host plant volatiles. However, few studies have assessed the roles of these olfactory organs in food selection in terms of the effects of individual volatile compounds from plants at various distances. Therefore, we assessed the palp-opening response (POR), biting response, and selection behavior of locust (Locusta migratoria) nymphs in response to volatile compounds from host and non-host plants at various distances. Thirty odorants were identified as the active volatiles to locust by the POR tests. At a distance of 3m, locusts were attracted to a few common volatiles (1% v/v) of both host and non-host plants, while few components of volatiles acted as repellants at this distance. At a distance of 1m, locusts responded more readily to volatile compounds. At a distance of 1cm, locusts mainly used their palps to detect volatiles. However, some components that acted as attractants at long distances had no effect on the biting response at a short distance. Together, the results suggest that plant volatiles generally attract locust nymphs at long distances, but the effects are influenced by distance and concentration. Moreover, there are substantial functional differences in the use of antennae and palps for detecting volatiles at various distances. Overall, the mechanism of food selection by locusts via olfaction can be divided into several continuous ranges according to the sensitivities of the two chemosensory organs and the characteristics of the plant odorants.

Glomerular Organization of the Antennal Lobes of the Diamondback Moth, Plutella xylostella L.

The antennal lobe of the moth brain is the primary olfactory center processing information concerning pheromones and plant odors. Plutella xylostella is a major worldwide pest of cruciferous vegetables and its behavior is highly dependent on their olfactory system. However, detailed knowledge of the anatomy and function of the P. xylostella olfactory system remains limited. In the present study, we present the 3-Dimentional (3-D) map of the antennal lobe of P. xylostella, based on confocal microscopic analysis of glomerular segmentation and Neurobiotin backfills of Olfactory Receptor Neurons (ORNs). We identified 74–76 ordinary glomeruli and a macroglomerular complex (MGC) situated at the entrance of the antennal nerve in males. The MGC contained three glomeruli. The volumes of glomeruli in males ranged from 305.83 ± 129.53 to 25440.00 ± 1377.67 μm3. In females, 74–77 glomeruli were found, with the largest glomerulus ELG being situated at the entrance of the antennal nerve. The volumes of glomeruli in females ranged from 802.17 ± 95.68 to 8142.17 ± 509.46 μm3. Sexual dimorphism was observed in anomalous supernumerary, anomalous missing, shape, size, and array of several of the identified glomeruli in both sexes. All glomeruli, except one in the antennal lobe (AL), received projections of antennal ORNs. The glomeruli PV1 in both sexes received input from the labial palp nerve and was assumed as the labial pit organ glomerulus (LPOG). These results provide a foundation for better understanding of coding mechanisms of odors in this important pest insect.

Do age and mating status affect olfactory response of the parasitoid, Microplitis croceipes (Hymenoptera: Braconidae) to host-related plant odors?

Background: Parasitic wasps (parasitoids) use volatile organic compounds released by herbivore-infested plants to locate their hosts. Response of parasitoids to plant odors may be plastic and dependent on their physiological state. Using Microplitis croceipes (Hymenoptera: Braconidae), a relatively specialized larval endoparasitoid of Heliothis virescens (Lepidoptera: Noctuidae), we asked whether age and mating status of parasitoids affect their olfactory response to host-related odors. Methods: Four odor stimuli of varying complexity were selected based on previous reports of parasitoid response to cotton volatiles: cis-3-hexenol (a green leaf volatile), α-pinene (a constitutive monoterpene), a 50/50 v/v binary mixture ( cis-3-hexenol + α-pinene), and H. virescens-infested cotton odors. Female M. croceipes used in Y-tube olfactometer bioassays were either mated or unmated, and grouped 1-3, 4-6, and 7-9 d-old. Female parasitoids used in electroantennogram (EAG) recording were mated and grouped 1-3, 4-6, 7-9 and 10-12 d-old. Results: In Y-tube olfactometer bioassays, neither age nor mating status played a major role in the attraction of parasitoids to test odor stimuli, with two exceptions: 4-6 d-old mated parasitoids showed attraction to the binary mixture, and 1-3 d-old mated parasitoids showed attraction to H. virescens-infested cotton. Age did not affect EAG response of parasitoids to test stimuli. Conclusions: The present results suggest that age and mating status do not play a major role in modulating olfactory responses of M. croceipes to host-related plant odors. Instead, plasticity of olfactory response may be limited in M. croceipes due to strong innate sensitivity to host-related odor cues.