Field and laboratory electroantennographic measurements of pheromone plume structure correlated with oriental fruit moth behaviour

Abstract. Peak-to-trough electroantennogram amplitudes (bursts), caused by the individual filaments of a plume of female pheromone, diminish as high-emission-rate sources are approached by male Grapholita molesta , and this reduction is correlated with in-flight arrestment (ceasing to advance upwind). These findings are consistent with the hypothesis that one cause of in-flight arrestment in response to high-concentration point sources is the attenuation of the peak-to- trough amplitudes close to the source. High burst frequency, high pheromone flux, or low levels of continuous neuronal activity all are less well correlated with arrestment. Rather, arrestment appears due to a reduction of chemosensory input to the CNS during flight up the plume, even though the actual molecular concentration continues to increase. In a laboratory wind tunnel, upwind flight initiation by more than 20% of males was elicited only by pheromone source concentrations evoking significant fluctuations in EAG amplitudes at downwind release points. The burst frequencies that evoked high levels of upwind flight initiation ranged from a mean of 0.4-2.2 bursts/s. Because a previous study revealed that flying male G. molesta change their course angle within 0.15 s of losing or contacting pheromone, these EAG burst frequencies indicate that during flight in a pheromone plume, many manoeuvres are probably made in response to contact with individual plume filaments. Thus, upwind flight tracks may be shaped by hundreds of steering reactions in response to encounters with individual pheromone filaments and pockets of clean air. Field-recorded EAGs reveal that burst amplitudes diminish from 3 to 30 m downwind of the source, whereas burst frequencies do not, averaging c. 1/s at 3, 10 and 30 m downwind.     

Guidance of flying male moths by wind-borne sex pheromone

ABSTRACT. On passing from clean air into a homogeneous cloud of sex pheromone in a wind tunnel flying male Adoxophyes orana (F.v.R.) (Lepidoptera: Tortricidae) turned more or less upwind and reduced the time and distance between their switchings of track from one side of the wind line to the other. These responses became adapted under the constant pheromone stimulation in the cloud, thereby arresting upwind progress; but the adapted moths would now 'lock-on' to an added pheromone plume and advance upwind along it. Moths also locked-on to the border of a pheromone cloud, not by turning back on losing the scent as previously supposed but by initiating the above programme of small-amplitude, crosswind movements (reversing anemomenotaxis). The onset and cessation of the pheromone stimulus produced anemotactic responses that differed quantitatively within a continuum, not two distinct kinds of response as previously supposed. The behavioural mechanism whereby uniform permeation of an area with synthetic sex pheromone can prevent males from finding females is reconsidered.     

Flight behaviour of Cadra cautella males in rapidly pulsed pheromone plumes

Abstract Airborne pheromone plumes in wind comprise filaments of odour interspersed with gaps of clean air. When flying moths intercept a filament, they have a tendency to surge upwind momentarily, and then fly crosswind until another filament is intercepted. Thus, the moment-to-moment contact with pheromone mediates the shape of a flight track along the plume. Within some range of favourable interception rates, flight tracks become straighter and are headed more due upwind. However, as the rate of interception increases, there comes a point at which the moth should not be able to discern discreet filaments but, rather, should perceive a 'fused signal'. At the extreme, homogeneous clouds of pheromone inhibit upwind progress by representative tortricids. In a wind tunnel, Cadra cautella (Walker) (Lepidoptera: Pyralidae) were presented with 10 ms pulses of pheromone at a repetition rate of 5, 10, 17 and 25/s and a continuous, internally turbulent plume. Pulse size and concentrations were verified with a miniature photoionization detector sampling surrogate odour, propylene, at 100 Hz. Male moths maintain upwind progress even at plumes of 25 filaments/s. Furthermore, moths exhibited greater velocities and headings more due upwind at 17 and 25 Hz than at the lower frequencies or with the continuous plume. It is hypothesized that either C. cautella possesses a versatile sensory system that allows the resolution of these rapidly pulsed pheromone plumes, or that this species does not require a 'flickering' signal to fly upwind.     

Helicoverpa zea males (Lepidoptera: Noctuidae) respond to the intermittent fine structure of their sex pheromone plume and an antagonist in a flight tunnel

Abstract. We investigated the behavioural response of male Helicoverpa zea (Boddie) to the fine-scale structure of an odour plume experimentally modified in a wind tunnel by using an air-pulsing device. Male H. zea flew upwind to pulsed filaments of a binary pheromone blend of (Z)-11-hexadecanal (Z11-16:Ald) and (Z)-9-hexadecanal (Z9-16:Ald) in the ratio of 20:1. Sustained upwind flight in experimentally altered intermittent plumes was dependent on concentration, as well as the frequency of generation of odour filaments. At a loading of 10μg of the major pheromone component, Zll-16:Ald, which gave an emission rate of approximately that released by a female H. zea , sustained upwind flight and source contact correlated positively with filament delivery rate, becoming significant at a minimum filament delivery rate of 2/s. Decreases in upwind progress and source location were recorded at a loading of 1 μg of Z11-16:Ald. At this suboptimal dosage, a high filament generation rate of 10/s was necessary for significant upwind progress and source contact. When an interspecific compound: (Z)-11-hexadecenyl acetate (Z11-16:OAc), was added to the attractive pheromone binary aldehyde blend of H. zea at a proportion of 10% of the major pheromone component, and pulsed from the same source, there was a significant reduction in sustained upwind progress and source location by males, indicating that Z11-16:OAc is antagonistic to the upwind progress of H. zea. However, Z11-16:OAc was less antagonistic when its filaments were isolated and alternated with pheromone filaments, indicating a strong effect of the synchronous arrival of odour filaments on the antenna needed for antagonism of upwind flight.     

Flight behaviour of males of two moths, Cadra cautella and Pectinophora gossypiella, in homogeneous clouds of pheromone

Abstract It is thought that orientation by male moths along pheromone plumes is guided by interception of filaments of pheromone along that plume and that clean air gaps are required for upwind progress. Given that several investigations have determined that cells sensitive to pheromone can resolve only low rates of encounter with pheromone filaments, generally up to 10 pulses/s, it would appear that individual filaments encountered at higher rates would not be resolved by the insects' sensory system and therefore the stimulus would be perceived as a non-flickering signal. Behaviourally, this has been thought to be expressed as the cessation of upwind progress. Previous studies with Cadra cautella (Walker) (Lepidoptera: Pyralidae) demonstrated that upwind flight by these males is not inhibited in rapidly pulsed plumes. Therefore, to determine whether a flickering signal is required for upwind progress by C. cautella , males were introduced to homogeneous clouds of pheromone in a wind tunnel and their behaviour recorded. For comparison, Pectinophora gossypiella (Saunders) (Lepidoptera: Gelechiidae), a species from a long-diverged lineage, was also used. Upwind progress by C. cautella is not impeded by the constant olfactory signal provided by a homogeneous cloud of pheromone, but this is not true for P. gossypiella . Furthermore, although C. cautella directs its flight upwind in a homogeneous cloud, its heading is not always due upwind. Potential mechanisms are discussed. It is suggested that C. cautella does not require a flickering signal to progress upwind.     

Use of bilateral information to determine the walking direction during orientation to a pheromone source in the silkmoth Bombyx mori

Odor source localization is an important animal behavior. Male moths locate mates by tracking sex pheromone emitted by conspecific females. During this type of behavior, males exhibit a combination of upwind surge and zigzagging flight. Similarly, the male walking moth Bombyx mori responds to transient pheromone exposure with a surge in movement, followed by sustained zigzagging walking. The initial surge direction is known to be influenced by the pheromone input pattern. Here, we identified the sensory input patterns that determine the initial walking direction of males. We first quantified the stimulus by measuring electroantennogram values, which were used as a reference for subsequent tests. We used a brief stimulus pulse to examine the relationship between sensory stimulus patterns and the turning direction of initial surge. We found that the difference in input timing and intensity between left and right antennae affected the walking direction, indicating that B. mori integrate bilateral pheromone information during orientation behavior. When we tested pheromone stimulation for longer periods, turning behavior was suppressed, which was induced by stimulus cessation. This study contributes toward understanding efficient strategies for odor-source localization that is utilized by walking insects.     

Fine-scale resolution of closely spaced pheromone and antagonist filaments by flying male Helicoverpa zea

The limits of a male moth's ability to resolve closely spaced odor filaments have been investigated. Male Helicoverpa zea normally respond to their conspecific sex pheromone blend by exhibiting an upwind flight, which culminates in source contact by at least 50% of the bioassayed individuals. When loaded onto the same filter paper source containing this hitherto attractive pheromone blend, or onto a separate filter paper and co-emitted from the same pipette source with pheromone, (Z)-11-hexadecenyl acetate severely reduced upwind flight and source contact by male H. zea. A similar level of upwind flight inhibition was recorded when the antagonist (Z)-11-hexadecenyl acetate was emitted from its own point source placed 1 mm upwind of the pheromone point source, both plumes being simultaneously emitted in a continuous mode to form a confluent strand. However, (Z)-11-hexadecenyl acetate was less effective in reducing upwind flight and source contact when it was isolated and pulsed from its own source, placed 1 mm either upwind, downwind or cross-wind of a pipette source from which pheromone was simultaneously being pulsed, such that both filaments were separated in time by 0.001–0. 003 s. These results suggest that male H. zea are able to distinguish between odor sources separated by as little as 1 mm in space and 0.001 s in time. Accepted: 31 March 1999     

Orientation to sex pheromone in the American cockroach: Analysis of chemo-orientation mechanisms

Male Periplaneta americana were photographed in a 2.4 m diameter arena containing a female sex pheromone source in the centre. Orientation pathways were digitized and analysed with regard to chemo-orientation mechanisms employed. Indirect components of chemo-orientation include arrestment near the pheromone source owing to an increase in turning rate and decrease in rate of locomotion, and zig-zag motor patterns that facilitate localization of the source. Most males were successful in locating the source if they moved to within 30 cm. Direct components of chemo-orientation include looping and relatively sharp correcting turns.No significant differences in orientation were observed between intact and unilaterally-antennectomized males, except that correcting turns close to the pheromone source were significantly less precise in males with one antenna. These results indicate that males with two antennae have an advantage over males with one antenna in being able to employ simultaneous information processing close to the pheromone source. Males with crossed antennae were unable to locate the pheromone source, suggesting that the fixed position of their antennae interfered with sensory information input.     

Impact of (Z)-7-dodecenol and turbulence on pheromone-mediated flight manoeuvres of male Trichoplusia ni

Abstract. Turbulence and chemical noise are two factors which may influence pheromone-mediated flight manoeuvres of a moth in natural habitats. In this study, the effects of turbulence and the behavioural antagonist (Z)-7-dodecenol on flight manoeuvres of male Trichoplusia ni (Hübner) were evaluated in a wind tunnel. Male moths increase airspeed and course angles when turbulence is increased. This leads to significant increases in the length of flight tracks, but significant reductions in the time taken to reach a pheromone source. In less disturbed pheromone plumes, distributions of course angles and track angles of male T.ni show a prominent peak centred about 0° relative to the upwind direction, indicating that moths can temporarily steer directly upwind toward a pheromone source.
When (Z)-7-dodecenol is released 10 cm upwind of a pheromone source to form an overlapping plume downwind, course angles, airspeeds and ground-speeds of male T.ni are reduced significantly compared with those in uncon-taminated pheromone plumes. This results in a longer flight time to reach a pheromone source. The decrease in flight speed would decrease the rate of contact with filaments, and thereby perhaps allow the moth to detect uncon-taminated pheromone filaments independently from filaments containing the behavioural antagonist.     

Control of hindlimb posture by wind-sensitive hairs and antennae during locust flight

Steering movements of tethered, flying locusts, Schistocerca gregaria, subjected to simulated yaw were examined under open-loop conditions. Lateral movements of hindlimbs or curling of the abdomen were monitored with a capacitive movement transducer and were interpreted as indicating the tendency of the animal to turn. Three responses to simulated yaw were noted: Yaw-correcting upwind turning tendencies (Figs. 1, 2, 3). Downwind turning tendencies (Figs. 2, 3, 4, 5), and transient adjustments of hindlimb position consistent with an upwind turning tendency occurred in animals that made either no sustained postural adjustments of hindlimbs, or that exhibited sustained downwind turning tendencies (Figs. 4, 5). Ablations of certain mechanoreceptors tested their roles in wind detection and wind angle determination. The expression of upwind turning tendencies, whether sustained or transient, depends on inputs from cephalic mechanosensory hairplates (Figs. 2, 3, 4, 5). With hairplates occluded, all locusts exhibited downwind turning tendencies. All downwind turning tendencies depend on inputs from the antennae (Figs. 2, 3). Antennae and hairplates operate in an apparent antagonism in the steering responses they produce, which may provide the control flexibility required for complex flight maneuvering.     

Investigations of Mechanisms of Pheromone Communication Disruption of Choristoneura rosaceana (Harris) in a Wind Tunnel

Although atmospheric treatment with synthetic pheromone is used commercially to control several lepidopteran pests, little is known about how mate-finding behavior is altered by this procedure. Mechanisms of disruption of the mate-finding behavior of Choristoneura rosaceana (Lepidoptera: Tortricidae) were examined in wind tunnel bioassays. Male moths were exposed to synthetic sex pheromone or pheromone components prior to or during upwind flight to a calling virgin female. The proportion of males successfully contacting a calling female was reduced only when the synthetic pheromone treatment was presented simultaneously. A synthetic source of the attractive four-component pheromone placed upwind of a calling female was more effective than a less attractive two-component blend in achieving disorientation. Habituation of the central nervous system does not appear to be a significant factor in disruption of mate-finding behavior of male C. rosaceana, as exposure to pheromone prior to the bioassay did not alter the proportion of males that achieved subsequent upwind flight. Disruption of mate-finding behavior of C. rosaceana in a wind tunnel is probably the result of a combination of mechanisms including adaptation of antennal receptors, camouflage of the female-produced plume, and false-trail following which contributed to the additive disruption effect observed with the most attractive four-component pheromone.     

Aim‐then‐shoot anemotaxis involved in the hopping approach of potato tuberworm moth Phthorimaea operculella toward a sex pheromone source

Male moths locate conspecific females by pheromone‐induced upwind flight maintained by detecting a visual flow, termed optomotor anemotaxis. Their behavioural pattern is characterized by an upwind surge in response to a pheromone stimulus and crosswind casting after odour loss, which is considered to be reset and restarted on receipt of another pheromone pulse. However, pheromone‐stimulated males of the potato tuberworm moth Phthorimaea operculella exhibit a series of short and straight intermittent flights, or hops, when moving upwind. It is unclear whether they navigate by employing the same behavioural pattern and wind detection mechanism as that used by flying moths. To analyze odour‐modulated anemotaxis in male potato tuberworm moths, a flat wind tunnel is constructed to give regular odour stimuli to an insect regardless of its location. Moths are subjected to pheromone pulses of different frequencies to test whether they show a behavioural pattern that is reset and restarted by a pheromone pulse. Moths on the ground are also subjected to crosswind shear to examine their detection of wind direction. Path analyses reveal that males surge upwind when they receive a pheromone pulse and exhibit casting by successive hops when they lose odour. This behavioural pattern appears to be similar to that of flying moths. When the direction of the airflow is switched orthogonally, males adjust their course angle accordingly when they are on the ground. It is suggested that, instead of optomotor anemotaxis, this ‘aim‐then‐shoot’ system aids the detection of wind direction, possibly by mechanosensory means.     

Odour-mediated upwind flight of Culex quinquefasciatus mosquitoes elicited by a synthetic attractant

Abstract A wind tunnel and video equipment are used to study the long-range and close-range responses of gravid females of Culex quinquefasciatus Say to a synthetic pheromone, eryrthro -6-acetoxy-5-hexadecanolide. In response to water and acetoxyhexadecanolide, together or independently, in the presence of wind, females follow meandering flight paths upwind. Females have a higher rate of turning and a lower flight-speed when landing at a site containing pheromone than at a comparable site without pheromone. Females stay longer at oviposition sites containing the attractant than at sites with no attractant.     

Cowpea weevil flights to a point source of female sex pheromone: analyses of flight tracks at three wind speeds

Abstract.  Two-day-old male cowpea weevils, Callosobruchus maculatus, fly upwind to a point source of female sex pheromone at three wind speeds. All beetles initiating flight along the pheromone plume make contact with the pheromone source. Analysis of digitized flight tracks indicates that C. maculatus males respond similarly to moths tested at several wind speeds. Beetles' mean net upwind speeds and speeds along their track are similar ( P  > 0.05) across wind speeds, whereas airspeeds increase ( P <  0.01) with increasing wind speed. Beetles adjust their course angles to fly more directly upwind in higher wind speeds, whereas track angles are almost identical at each wind speed. The zigzag flight paths are generally narrow compared with most moth flight tracks and interturn distances are similar ( P  > 0.05) at the wind speeds employed. The frequency of these counterturns across the wind line is almost constant regardless of wind speed, and there is little variation between individuals. The upwind flight tracks are more directly upwind than those typically seen for male moths flying upwind toward sex pheromone sources. Male moths typically produce a bimodal distribution of track angles to the left and right of the windline, whereas C. maculatus males' track angles are centred about 0°. Preliminary examination of two other beetle species indicates that they fly upwind in a similar fashion.     

Pulsed pheromone stimuli affect the temporal response of antennal receptor neurones of the adult cabbage looper moth

Abstract. Male cabbage looper moths, Trichoplusia ni (Hiibner) (Lepidoptera: Noctuidae), fly upwind in response to pheromone blends produced and released by calling conspecific females. Specialized sensilla on the male antenna contain sensitive, highly specific olfactory receptor neurones which respond to constant olfactory signals, with a phasic-tonic pattern of action potential discharge. Olfactory stimuli in nature are not uniform. They are thought to consist of pulses of odours whose distribution is shaped by wind and local environmental features. We begin to evaluate this natural situation by stimulating pheromone-sensitive sensilla with short (200 ms) paired pulses of the major component of the female's pheromone blend, (Z)-7-dodecen-l-ol acetate (Z-7,12:AC). Different stimulus protocols in which the pulses were separated from each other by varying intervals were evaluated. The interval between pulses had a large effect on the phasic component of the response. Intervals between pulses as short as 30 ms reduced the response to a second pulse by > 50%. When the intervals between pulses were longer than 3 s, significant differences were not seen between the responses to the first and second pulse. Implications for male orientation in natural, female-produced, pheromone plumes are discussed.     

Influence of plume structure and pheromone concentration on upwind flight of Cadra cautella males

Abstract. The effects of pheromone plume structure and its concentration on the pheromone-mediated flight of male Cadra cautella (Lepidoptera: Phycitinae) were investigated in a laminar-flow wind tunnel. When two C. caurella males flew simultaneously along a ribbon plume of mixed smoke and pheromone, their inflight behaviour was dependent on the instantaneous structure of the plume they encountered. When a male intercepted an intact ribbon filament, he sustained a crosswind course, whereas when he intercepted a turbulent filament (created by an upwind male fragmenting the ribbon plume), he adopted a flight course more due upwind. These results indicate that C. cautella males altered their in-flight manoeuvres in response to instantaneous changes in the fine structure of the pheromone plume. We also demonstrated that differences in the fine structure of the plume had more influence on the flight pattern of C. cautella males than a 1000-fold range in pheromone dose. The size of the plume was increased by adding wind deflectors upwind of the pheromone source, independent of source dosage, males following ribbon plumes flew slow zigzag tracks, whereas males following large, turbulent plumes flew directly to the source in fast, straight tracks with less counterturning.     

Interneurons sensitive to female pheromone in the deutocerebrum of the male silkworm moth, Bombyx mori

ABSTRACT. In response to minute quantities of female sex pheromone, the male silkworm moth, Bombyx mori L., walks upwind to locate the odour source. The axons of antennal receptors specific for the two known components of the pheromone terminate in the deutocerebrum. In this study, single interneurons were recorded extracellularly in the deutocerebrum of the male silkworm moth. Responses were characterized as the antennae were presented with puffs of clean air, or air containing either or both components of the female pheromone, bombykol and bombykal. An apparatus is described which added bombykol or bombykal to a constant air stream flowing over the antenna. Most units (87%) showed qualitatively different responses to bombykol and bombykal. A majority of the pheromone-sensitive units (65%) also showed mechanosensory responses to air puffs. Two units were recorded which were slightly inhibited by either bombykol or bombykal alone, but were excited by a mixture of the two.     

MaleHeliothis virescens maintain upwind flight in response to experimentally pulsed filaments of their sex pheromone (Lepidoptera: Noctuidae)

Aspects of the intermittent fine structure of an odor plume were mimicked and experimentally modified in the wind tunnel using an air-pulsing device. Filaments of a behaviorally active blend of six sex-pheromone components created by the device in a temporally regular fashion elicited sustained upwind flight and source location in male Heliothis virescens.Males did not exhibit sustained upwind flight in significant numbers until a frequency of 4 filaments/s was delivered, at a loading of 1 g of the major component, Z11-16: Ald, with the other components loaded at their appropriate ratios. A loading of 10 g Z11-16: Ald was found to be optimal at this filament delivery rate. Electroantennogram recordings to different filament delivery rates of the complete blend indicated that a stationary male antenna can respond to the pulse rates used in this study. Importantly, when a main component necessary for upwind flight, Z9-14:Ald, was isolated into its own filaments and pulsed alternately against filaments of the five other components (including the other component essential for upwind flight, Z11-16: Ald), upwind flight to the source was significantly reduced (9%) compared to upwind flight and source location in response to filaments composed of the entire blend (30%), indicating that the complete pheromone blend must arrive on the antenna simultaneously for optimal evocation of sustained upwind progress. Neurophysiological evidence from other studies suggests that higher-order interneurons whose phasic response is enhanced when the entire blend is presented simultaneously may be of importance in explaining this behavioral difference stemming from synchronous vsasynchronous arrival of the components.     

Flight tunnel response of codling moth Cydia pomonella to blends of codlemone,codlemone antagonists and pear ester

Upwind orientation flights of codling moth males Cydia pomonella L. to a single source of sex pheromone (E,E)‐8,10‐dodecadienol (codlemone) are significantly reduced when blending it with pheromone antagonists, either with codlemone acetate, (E,E)‐8,10‐dodecadienyl acetate, or with the codlemone isomer (E,Z)‐8,10‐dodecadienol. However, once activated by a pheromone stimulus, males no longer distinguish between a pheromone source and these antagonistic blend sources. This shows that the pheromone stimulus required for the initiation of an upwind flight response differs from the stimulus for maintaining upwind flight and landing at the source. In contrast to pheromone antagonists, males discriminate between pheromone alone and a blend source of pheromone and the plant volatile pear ester, ethyl (2E,4Z)‐2,4‐decadienoate. This indicates a difference in the detection and neural integration of pheromone and plant volatile stimuli.