Olfactory-mediated Behaviors Research Articles

Physical Processes and Real-Time Chemical Measurement of the Insect Olfactory Environment

Odor-mediated insect navigation in airborne chemical plumes is vital to many ecological interactions, including mate finding, flower nectaring, and host locating (where disease transmission or herbivory may begin). After emission, volatile chemicals become rapidly mixed and diluted through physical processes that create a dynamic olfactory environment. This review examines those physical processes and some of the analytical technologies available to characterize those behavior-inducing chemical signals at temporal scales equivalent to the olfactory processing in insects. In particular, we focus on two areas of research that together may further our understanding of olfactory signal dynamics and its processing and perception by insects. First, measurement of physical atmospheric processes in the field can provide insight into the spatiotemporal dynamics of the odor signal available to insects. Field measurements in turn permit aspects of the physical environment to be simulated in the laboratory, thereby allowing careful investigation into the links between odor signal dynamics and insect behavior. Second, emerging analytical technologies with high recording frequencies and field-friendly inlet systems may offer new opportunities to characterize natural odors at spatiotemporal scales relevant to insect perception and behavior. Characterization of the chemical signal environment allows the determination of when and where olfactory-mediated behaviors may control ecological interactions. Finally, we argue that coupling of these two research areas will foster increased understanding of the physicochemical environment and enable researchers to determine how olfactory environments shape insect behaviors and sensory systems.

Chronic exposure to low concentrations of waterborne cadmium during embryonic and larval development results in the long‐term hindrance of antipredator behavior in zebrafish

Cadmium has been recognized for some time as a potent environmental pollutant with the capability of disrupting olfactory-mediated behaviors. Failing to respond to chemical cues in the environment could adversely affect foraging, reproduction and predator avoidance. Recognizing this impaired perception as a serious ecological problem has been undermined by the fact that the damage is often reversible; short depuration periods of 5 d may allow for the re-establishment of responses to chemical cues. In this experiment, early life stage zebrafish were continuously exposed for 50 d at 0, 0.2, 2.0, and 20 microg Cd/L. The subjects were depurated for 14 d and then subjected to behavioral testing where antipredator responses to chemical alarm cues were observed. Our data show that continuous exposure during rearing to a concentration as low as 20 microg Cd/L is sufficient at eliminating antipredator behavior in zebrafish (Danio rerio) even after the source of the cadmium had been removed for 14 d. Furthermore, subjects raised under a 10-fold lower concentration also showed alteration in their behavioral responses, taking significantly longer to respond to the predation threat. Exposure to low levels of cadmium throughout development may alter neurogenesis, subsequently resulting in long-term impairment of chemical cue perception.

The Effects of the Herbicide Metolachlor on Agonistic Behavior in the Crayfish, Orconectes rusticus

Previous research suggests that agricultural herbicides interfere with olfactory-mediated behavior, such as responses to alarm signals and the ability to locate food, in aquatic organisms. In crayfish, aggressive interactions are also mediated by chemical signals. These social signals are important in establishing dominance, which in turn has an impact on an individual's ability to find and use mates, food, and habitat space. In this study, we investigated the impact of exposure to sublethal levels of the herbicide metolachlor on the ability of crayfish to respond to olfactory signals used in agonistic behaviors. Crayfish were exposed to three different environmentally relevant concentrations (60 ppb, 70 ppb, and 80 ppb) of metolachlor for 96 hours. Each exposed crayfish was then placed in a fight arena and was allowed to interact with a naïve, untreated crayfish for 15 minutes. We analyzed several characteristics of fighting behavior, including initial aggressiveness, time to fight, intensity levels, duration, number of encounters, and the winner and loser of each fight. Crayfish exposed to 80 ppb metolachlor were less likely to initiate and win encounters against naïve conspecifics than any other treatment group. Analysis of fight dynamics shows that metolachlor does not alter the temporal fighting dynamics within crayfish aggression. We conclude that high sublethal concentrations of metolachlor may be interfering with the ability of crayfish to receive or respond to social signals and thus affect certain agonistic behaviors.

The Kisspeptin Receptor GPR54 Is Required for Sexual Differentiation of the Brain and Behavior

GPR54 is a G-protein-coupled receptor, which binds kisspeptins and is widely expressed throughout the brain. Kisspeptin-GPR54 signaling has been implicated in the regulation of pubertal and adulthood gonadotropin-releasing hormone (GnRH) secretion, and mutations or deletions of GPR54 cause hypogonadotropic hypogonadism in humans and mice. Other reproductive roles for kisspeptin-GPR54 signaling, including the regulation of developmental GnRH secretion or sexual behavior in adults, have not yet been explored. Using adult wild-type (WT) and GPR54 knock-out (KO) mice, we first tested whether kisspeptin-GPR54 signaling is necessary for male and female sexual behaviors. We found that hormone-replaced gonadectomized GPR54 KO males and females displayed appropriate gender-specific adult sexual behaviors. Next, we examined whether GPR54 signaling is required for proper display of olfactory-mediated partner preference behavior. Testosterone-treated WT males preferred stimulus females rather than males, whereas similarly treated WT females and GPR54 KO males showed no preference for either sex. Because olfactory preference is sexually dimorphic and organized during development by androgens, we assessed whether GPR54 signaling is essential for sexual differentiation of other sexually dimorphic traits. Interestingly, adult testosterone-treated GPR54 KO males displayed "female-like" numbers of tyrosine hydroxylase-immunoreactive and Kiss1 mRNA-containing neurons in the anteroventral periventricular nucleus and likewise possessed fewer motoneurons in the spino-bulbocavernosus nucleus than did WT males. Our findings indicate that kisspeptin-GPR54 signaling is not required for male or female copulatory behavior, provided there is appropriate adulthood hormone replacement. However, GPR54 is necessary for proper male-like development of several sexually dimorphic traits, likely by regulating GnRH-mediated androgen secretion during "critical windows" in perinatal development.

Relating olfactory neurotoxicity to altered olfactory-mediated behaviors in rainbow trout exposed to three currently-used pesticides

Odor-evoked neurophysiological responses can form the basis for behavioral responses. Here we first characterized olfactory-mediated behavioral and neurophysiological responses of juvenile rainbow trout to the amino acid l-histidine, then looked at whether there were similar responses to the carbamate antisapstain IPBC and the herbicides atrazine and Roundup ®, and lastly explored how exposures to these pesticides modified the l-histidine responses. Trout were behaviorally attracted to 10 −7 M l-histidine (as assayed in a counter-current olfactometer), but this preference behavior switched to indifference with higher histidine concentrations. Neurophysiologically, the summed electrical responses of peripheral olfactory neurons, as measured using electro-olfactogram (EOG), was 0.843 ± 0.252 mV to 10 −7 M l-histidine. Of the pesticides, only Roundup ® evoked EOGs, indicating the amino acid-based pesticide may have acted as an odorant, and generated a behavioral response: it was avoided at active ingredient [AI; glyphosate isopropyl amine] concentrations ≥ 10 mg/l. With 30 min pesticide exposures, 10 −7 M l-histidine preference behavior was eliminated following exposure to 1 μg/l IPBC and atrazine, and 100 μg/l AI Roundup ®. Similarly, 10 −7 M l-histidine-evoked EOGs were significantly reduced by exposure to 1 μg/l IPBC, 10 μg/l atrazine, and 100 μg/l AI Roundup ®. When combined together, the results demonstrate that typical preference behavior can be abolished when neurophysiological responses are reduced by >60% of control. This asymmetry in response thresholds suggests that behavioral responses may be more sensitive toxicological endpoints than neurophysiological responses.

Maternal and littermate deprivation disrupts maternal behavior and social‐learning of food preference in adulthood: Tactile stimulation, nest odor, and social rearing prevent these effects

Maternal and littermate (social) separation, through artificial rearing (AR), disrupts the development of subsequent maternal behavior and social learning in rats. The addition of maternal-licking-like stimulation during AR, partially reverses some of these effects. However, little is know about the role of social stimuli from littermates and nest odors during the preweaning period, in the development of the adult maternal behavior and social learning. The purpose of this study was to examine the effects of peer- and peer-and-odor rearing on the development of maternal behavior and social learning in rats. Female pups were reared with mothers (mother reared-MR) or without mothers (AR) from postnatal day (PND) 3. AR rats received three different treatments: (1) AR-CONTROL group received minimal tactile stimulation, (2) AR-ODOR females received exposure to maternal nest material inside the AR-isolation-cup environment, (3) AR-SOCIAL group was reared in the cup with maternal nest material and a conspecific of the same-age and same-sex and received additional tactile stimulation. MR females were reared by their mothers in the nest and with conspecifics. In adulthood, rats were tested for maternal behavior towards their own pups and in a social learning task. Results confirm our previous report that AR impairs performance of maternal behavior and the development of a social food preference. Furthermore, social cues from a littermate, in combination with tactile stimulation and the nest odor, reversed the negative effects of complete isolation (AR-CONTROL) on some of the above behaviors. Exposure to the odor alone also had effects on some of these olfactory-mediated behaviors. These studies indicate that social stimulation from littermates during the preweaning period, in combination with odor from the nest and tactile stimulation, contributes to the development of affiliative behaviors.

Adrenergic Enhancement of Inhibitory Transmission in the Accessory Olfactory Bulb

Noradrenergic modulation of dendrodendritic synapses between the mitral and granule cells in the accessory olfactory bulb (AOB) is postulated to play a key role in the formation of memory in olfactory-mediated behaviors. Current models propose that noradrenaline (NA) increases excitation of mitral/tufted cells (M/TCs) by decreasing the release of GABA from granule cells. However, surprisingly little is known about the actions of NA at the cellular level in the AOB. Here, in recordings from AOB slices, we show that NA decreases the firing frequency of M/TCs in response to stimulation. This effect is attributable to an increase in the GABA inhibitory input to M/TCs. Application of NA (10 microM) produced an approximately 20-fold increase in the frequency of GABA-induced miniature IPSCs (mIPSCs) without changing their amplitude. A pharmacological analysis indicated that the increase in mIPSCs frequency results from activation of alpha1 adrenergic receptors. In addition to increasing the mIPSC frequency, NA also potentiated GABA inhibitory currents induced by direct stimulation of granule cells. Together, our results suggest that NA increases the release of GABA from granule cells by acting on presynaptic receptors. Thus, the role of the noradrenergic activity in the AOB may be opposite than suggested previously: we find that the overall effect of NA in the AOB is inhibition of M/TCs.

Leptin regulates olfactory-mediated behavior in ob/ ob mice

We have investigated olfactory-mediated pre-ingestive behavior in leptin ( ob/ ob) and leptin receptor ( db/ db) mutant mice compared to age- and gender-matched wild-type (wt) mice. Olfactory-mediated behavior was tested using a buried food paradigm 5 times/day at 2-h intervals for 6 days. Mean food-finding times of ob/ ob and db/ db mice were approximately 10 times shorter than those of wt mice. To test the effect of leptin replacement in ob/ ob mice, leptin (1 or 5 μg/g body weight in sterile saline) or carrier was injected i.p. once daily prior to testing. Mean food finding times in ob/ ob mice injected with carrier or with 1 μg/g leptin were similar and were 2–3 times faster than in wt mice. Mean food finding times in ob/ ob mice injected with 5 μg/g leptin tripled compared to carrier-injected ob/ ob mice and were of the same order of magnitude as those of wt mice, suggesting functional leptin replacement. A 3-factor repeated measures ANOVA demonstrated significant differences between the 6 cohorts ( P = 0.0001), food finding times ( P ≤ 0.0001), and cohort by day interaction ( P ≤ 0.0001). Post hoc tests suggested that the ob/ ob + 5 μg/g leptin cohort performed more like the wt cohort in the food-finding test than like the ob/ ob or ob/ ob + carrier cohort. Potential local sites of leptin production and action were identified with immunohistochemistry and in situ hybridization in epithelial and gland cells of the olfactory and nasal mucosae. Our results strongly suggest that leptin acting through leptin receptors modulates olfactory-mediated pre-ingestive behavior.

Atypical Membrane Topology and Heteromeric Function of Drosophila Odorant Receptors In Vivo

Drosophila olfactory sensory neurons (OSNs) each express two odorant receptors (ORs): a divergent member of the OR family and the highly conserved, broadly expressed receptor OR83b. OR83b is essential for olfaction in vivo and enhances OR function in vitro, but the molecular mechanism by which it acts is unknown. Here we demonstrate that OR83b heterodimerizes with conventional ORs early in the endomembrane system in OSNs, couples these complexes to the conserved ciliary trafficking pathway, and is essential to maintain the OR/OR83b complex within the sensory cilia, where odor signal transduction occurs. The OR/OR83b complex is necessary and sufficient to promote functional reconstitution of odor-evoked signaling in sensory neurons that normally respond only to carbon dioxide. Unexpectedly, unlike all known vertebrate and nematode chemosensory receptors, we find that Drosophila ORs and OR83b adopt a novel membrane topology with their N-termini and the most conserved loops in the cytoplasm. These loops mediate direct association of ORs with OR83b. Our results reveal that OR83b is a universal and integral part of the functional OR in Drosophila. This atypical heteromeric and topological design appears to be an insect-specific solution for odor recognition, making the OR/OR83b complex an attractive target for the development of highly selective insect repellents to disrupt olfactory-mediated host-seeking behaviors of insect disease vectors.

The Molecular Basis of Odor Coding in the Drosophila Larva

We have analyzed the molecular basis of odor coding in the Drosophila larva. A subset of Or genes is found to be expressed in larval olfactory receptor neurons (ORNs). Using an in vivo expression system and electrophysiology, we demonstrate that these genes encode functional odor receptors and determine their response spectra with 27 odors. The receptors vary in their breadth of tuning, exhibit both excitation and inhibition, and show different onset and termination kinetics. An individual receptor appears to transmit signals via a single ORN to a single glomerulus in the larval antennal lobe. We provide a spatial map of odor information in the larval brain and find that ORNs with related functional specificity map to related spatial positions. The results show how one family of receptors underlies odor coding in two markedly different olfactory systems; they also provide a molecular mechanism to explain longstanding observations of larval odor discrimination.

Impacts of carbamate pesticides on olfactory neurophysiology and cholinesterase activity in coho salmon ( Oncorhynchus kisutch)

Many freshwater aquatic environments in the Pacific Northwest of North America contain neurotoxic pesticides, an issue of concern given the use of many of these habitats by Pacific salmon ( Oncorhynchus sp.). Pesticides such as carbamates are known to affect fundamental physiological systems (such as the enzyme acetylcholinesterase (AChE)), and have been shown to affect salmonid olfactory-mediated behaviors. A neurophysiological measure of olfactory function, the electro-olfactogram (EOG), was used in this study to examine the impacts of acute localized exposure to three carbamates (the insecticide carbofuran, the antisapstain IPBC, and the fungicide mancozeb) on olfactory function in the coho salmon ( Oncorhynchus kisutch). We also examine the potential for these pesticides to alter AChE levels in the primary olfactory system and brain with brief exposures (30 min to only the olfactory rosette (OR)). In results, we find that the EOG in coho salmon is highly sensitive to brief localized exposures of two of these three carbamate pesticides. The effective nominal concentration required to cause a 50% reduction in EOG amplitude (EC 50) for carbofuran was 10.4 μg/l and for IPBC was 1.28 μg/l. For mancozeb, the EC 50 was higher at 2.05 mg/l. All three carbamates also affected AChE activity levels in the OR and brain (BR): carbofuran exposure at 200 μg/l significantly inhibited AChE activity in the OR, and both IPBC and mancozeb significantly increased AChE activity in BR at multiple concentrations with acute localized exposure. These carbamate effects highlight the sensitivity of salmon olfactory neurophysiology to pesticides acting not only potentially via AChE-inhibition, but also by other currently unknown modes of action.

Odor-evoked field potentials as indicators of sublethal neurotoxicity in juvenile coho salmon (Oncorhynchus kisutch) exposed to copper, chlorpyrifos, or esfenvalerate

The sublethal effects of three different pesticides (a metal, organophosphate, and pyrethroid) on juvenile coho salmon (Oncorhynchus kisutch) were evaluated using paired electrophysiological recordings from the olfactory epithelium and the olfactory bulb. Animals were exposed to copper (5–20 µg·L–1), chlorpyrifos (0.625–2.5 µg·L–1), or esfenvalerate (0.05–0.20 µg·L–1) for 7 days. Sublethal neurotoxicity was examined by recording odor-evoked field potentials from the sensory epithelium and olfactory forebrain using two natural odorants (taurocholic acid or L-serine). Copper and chlorpyrifos decreased the amplitudes of the epithelial and bulbar responses to both odorants in a concentration-dependent manner. Benchmark concentrations for a 20% loss of sensory function were 4.4 µg·L–1 for copper and 0.72 µg·L–1 for chlorpyrifos. Esfenvalerate did not affect the amplitude of odor-evoked field potentials. However, in the olfactory bulbs of coho exposed to 0.2 µg esfenvalerate·L–1, L-serine evoked distinct and irregular bursts of postsynaptic activity in the olfactory bulb, possibly indicating sublethal excitotoxicity to central networks. Collectively, these data indicate that periodic, non-point source contamination of salmon habitats with current-use pesticides could interfere with olfactory function and, by extension, olfactory-mediated behaviors that are important for the survival and migration of salmonids.

Sublethal effects of copper on coho salmon: impacts on nonoverlapping receptor pathways in the peripheral olfactory nervous system.

The sublethal effects of copper on the sensory physiology of juvenile coho salmon (Oncorhynchus kisutch) were evaluated. In vivo field potential recordings from the olfactory epithelium (electro-olfactograms) were used to measure the impacts of copper on the responses of olfactory receptor neurons to natural odorants (L-serine and taurocholic acid) and an odorant mixture (L-arginine, L-aspartic acid, L-leucine, and L-serine) over a range of stimulus concentrations. Increases in copper impaired the neurophysiological response to all odorants within 10 min of exposure. The inhibitory effects of copper (1.0-20.0 micrograms/L) were dose-dependent and they were not influenced by water hardness. Toxicity thresholds for the different receptor pathways were determined by using the benchmark dose method and found to be similar (a 2.3-3.0 micrograms/L increase in total dissolved copper over background). Collectively, examination of these data indicates that copper is broadly toxic to the salmon olfactory nervous system. Consequently, short-term influxes of copper to surface waters may interfere with olfactory-mediated behaviors that are critical for the survival and migratory success of wild salmonids.

Fenvalerate treatment affects development of olfactory glomeruli in Manduca sexta.

Low doses of fenvalerate, a widely used type-II pyrethroid insecticide, have been shown previously to produce abnormal olfactory centers in the brain and abnormal olfactory-mediated behavior in beetles (Wegerhoff et al. [1998] Neuroreport 9:3241-3245). Here, we use the experimental advantages of the moth Manduca sexta to explore the cellular changes that lead to these abnormalities. Our results indicate that treatment with fenvalerate may affect multiple aspects of the development of the primary olfactory centers, the antennal lobes, in Manduca, including ingrowth of olfactory receptor axons, axon fasciculation, and targeting within the antennal lobe, and intercellular signaling between the receptor axons and the glial cells that ordinarily surround and stabilize the developing olfactory glomeruli.

Diazinon disrupts antipredator and homing behaviors in chinook salmon (Oncorhynchus tshawytscha)

Neurotoxic pesticides are known to contaminate surface waters that provide habitat for salmonids, including some listed for protection under the U.S. Endangered Species Act. Despite their widespread use, the impacts of these pesticides on the neurological health of wild salmon are not well understood. Of particular concern are the organophosphate and carbamate insecticides that block synaptic transmission by inhibiting neuronal acetylcholinesterase. Here we assess the effects of diazinon, an organophosphate insecticide, on alarm pheromone induced antipredator responses and homing behavior in chinook salmon (Oncorhynchus tshawytscha). Nominal exposure concentrations (0.1, 1.0, and 10.0 µg·L-1) were chosen to emulate diazinon pulses in the natural environment. In the antipredator study, diazinon had no effect on swimming behavior or visually guided food capture. However, the pesticide significantly inhibited olfactory-mediated alarm responses at concentrations as low as 1.0 µg·L-1. Similarly, homing behavior was impaired at 10.0 µg·L-1. Our results suggest that olfactory-mediated behaviors are sensitive to anticholinesterase neurotoxicity in salmonids and that short-term, sublethal exposures to these insecticides may cause significant behavioral deficits. Such deficits may have negative consequences for survival and reproductive success in these fish.

Diazinon disrupts antipredator and homing behaviors in chinook salmon (<i>Oncorhynchus tshawytscha</i>)

Neurotoxic pesticides are known to contaminate surface waters that provide habitat for salmonids, including some listed for protection under the U.S. Endangered Species Act. Despite their widespread use, the impacts of these pesticides on the neurological health of wild salmon are not well understood. Of particular concern are the organophosphate and carbamate insecticides that block synaptic transmission by inhibiting neuronal acetylcholinesterase. Here we assess the effects of diazinon, an organophosphate insecticide, on alarm pheromone in - duced antipredator responses and homing behavior in chinook salmon (Oncorhynchus tshawytscha ). Nominal exposure concentrations (0.1, 1.0, and 10.0 mg·L -1 ) were chosen to emulate diazinon pulses in the natural environment. In the antipredator study, diazinon had no effect on swimming behavior or visually guided food capture. However, the pesti- cide significantly inhibited olfactory-mediated alarm responses at concentrations as low as 1.0 mg·L -1 . Similarly, homing behavior was impaired at 10.0 mg·L -1 . Our results suggest that olfactory-mediated behaviors are sensitive to

REGULATORY EFFECTS OF ENVIRONMENTAL CHEMICAL SIGNALS ON SEARCH BEHAVIOR AND FORAGING SUCCESS

To appreciate the mechanisms governing olfactory-mediated behavior, pro- cesses of chemical signal production and transmission in fluid media (air or water) must be understood. With new tools becoming available in analytical chemistry and fluid dy- namics, investigators can now quantitatively address the processes governing chemical signals in field habitats. This study identifies the role of amino acids as signal molecules regulating search behavior and foraging success by estuarine mud snails (Ilyanassa ob- soleta). For the first time, methods are described for measuring chemical signal production, release, and transport in field habitats, over temporal and spatial scales consistent with olfactory information processing. Rates of advection and turbulent mixing were determined, and shear velocities and roughness Reynolds numbers were estimated to characterize bottom boundary layer flows. Nearly instantaneous chemical measurements were made using a computerized microprobe system and conservative tracer to establish the environmental distributions of signal molecules at rates similar to those sampled by olfactory receptor neurons. In addition, we determined the dissolved free amino acid (DFAA) compositions (up to 18 amino acids), concentrations, and effluent release rates for live intact and injured fiddler crabs (Uca pugilator) and hard clams (Mercenaria mercenaria), which are common prey from mud snail habitats. The field site populated by mud snails was found to be more conducive at broadcasting stronger chemical signals over longer distances than most other estuarine and ocean habitats. Live fiddler crabs released amino acids at very low fluxes (0.1 nmol-min-'-g (wet tissue aiass)-V), while live intact clams took up amino acids from seawater. Once injured, hard clams and fiddler crabs released DFAAs at 88 and 6804 nmol-min-1-g-1, respectively. Mud snails were significantly attracted to injured clams and crabs, but not to intact prey, as compared with controls. Synthetic mixtures of amino acids, simulating fluids leaking from injured prey, were also highly attractive. When we tested for effects of amino acid composition, concentration, mean volume flow rate (of chemical input), and flux, in separate experiments, only flux directly correlated with the number of mud snails attracted. The attraction of mud snails is thus more tightly coupled to the physical transport of chemical stimuli than to the molecular properties of specific amino acids.

Behavioral responses to atrazine and diuron in goldfish.

Experiments were performed in goldfish to determine the effects of a short-term exposure (24 h) to atrazine or diuron (0.5, 5, 50 microgram/L) on some behavior endpoints related to swimming and social activities. Observations were also made to assess the influence of such exposure on the behavioral responses of fish to the flow of a crude skin extract solution from conspecifics, active in social chemocommunication and producing alarm behaviors. Additive tests were run to check the behavioral responses of previously unexposed goldfish to the flow of a solution of atrazine- or diuron-contaminated water, at three concentrations (0.1, 1, 10 mg/L). Significant burst swimming reactions appeared in response to a 24-h exposure to atrazine, at the lowest concentration tested (0.5 microgram/L). A 24-h exposure to 5 microgram/L atrazine or diuron was found to induce various significant behavioral alterations in fish. At this concentration, both herbicides decreased grouping behavior and atrazine also increased surfacing activity. Herbicide-exposed fish showed a decreased grouping behavior during the flow of the skin extract solution. Sheltering was also decreased during the flow of the biological solution in fish exposed to atrazine. Moreover, fish exposed to diuron clearly displayed attraction responses to the flow of the skin solution. Previously unexposed fish showed a significant increase in burst swimming reactions in response to the flow of a solution of atrazine- or diuron-contaminated water, at all concentrations tested (0.1, 1, 10 mg/L). Furthermore, the diuron-contaminated flow was found to be significantly attractive at the highest concentration. These results indicate that a short-term exposure to a relatively low concentration (5 microgram/L) of atrazine or diuron can affect various behaviors of fish not only directly but also indirectly by altering the chemical perception of natural substances of eco-ethological importance. In consideration of the basic role of olfaction in fish behavior, these results also emphasize the need for further developments on the possible effects of aquatic toxicants on olfactory-mediated behaviors.

Mating-Induced Changes in Olfactory-Mediated Behavior of Laboratory-Reared Normal, Sterile, and Wild Female Mediterranean Fruit Flies (Diptera: Tephritidae) Mated to Conspecific Males

Laboratory-reared normal, sterile, and wild female Mediterranean fruit flies, Ceratitis capitata (Wiedemann), were mated with laboratory-reared normal, sterile, and wild male flies to assess the ability of males to alter olfactory-mediated behavioral responses of females to male-produced pheromone or host fruit odor. Virgin females of all 3 types showed a preferential attraction and arrestment on yellow spheres emitting male-produced pheromone in a laboratory flight tunnel. Laboratory-reared normal and wild females mated to laboratory reared normal, sterile, or wild males switched their behavior showing strong preferential attraction to, arrestment on, and egg-laying in (for laboratory-reared females) yellow spheres emitting host fruit odor (guava) over male-produced pheromone. Sterile females did not show a significant switch in behavior except when mated to sterile males. The olfactory-mediated behavioral switch was most evident in the laboratory-reared normal female × laboratory-reared normal male mating. These findings suggest that irradiation of males inducing gamete sterility does not affect the factor(s) from the male accessory gland associated with altering female olfactory behavior. The ability of sterile males to alter adequately olfactory-mediated behavior of wild females is discussed in the context of the sterile insect technique for control of Mediterranean fruit flies in the field.

Restoration of olfactory mediated behavior after olfactory bulb deafferentation

Transection of olfactory nerve fibers leads to deafferentation of olfactory bulbs and a loss of olfactory mediated behavior. Nerve transection studies have shown that during recovery, olfactory nerve fibers can reestablish connections with the olfactory bulbs. Two groups of experimental animals were studied to determine if olfactory mediated behavior returns after recovery. One group ( n = 18) received bilateral olfactory nerve transection (BTX), while the second group ( n = 4) received a sham surgical procedure. Performance on odor detection and discrimination tasks was measured during recovery periods ranging from 1–120 days. Return of olfactory mediated behavior was first observed 19 days after nerve transection. Performance levels improved with recovery time and by day 40 animals returned to criterion level (≥ 90% correct response). Sham animals maintained a criterion level of performance throughout the recovery period. Horseradish peroxidase (HRP) was used to trace reconnection of olfactory nerve fibers. The absence of HRP label in the bulbs of animals examined one day after BTX, verified the completeness of the nerve transection procedure. After 10 days of recovery, a few HRP labeled axons were observed and the amount of HRP in the bulb increased with recovery time. The results of this study demonstrate that olfactory receptor axons can reestablish functional connections with the deafferented olfactory bulb and these connections are sufficient to restore olfactory mediated behavior.