Flight of Heliothis virescens males in the field in response to sex pheromone

Abstract. The behaviour of Heliothis virescens males flying upwind in the field in a sex pheromone plume was videorecorded and analysed. Males flew faster and straighter, with less counterturning, and heading more directly into the wind when they were 9-11m away from the odour source than when they were 1–3 m away. Regardless of their distance from the source or the windspeed, they maintained an average groundspeed of c. 200 cm s^_1, except when they arrived within 1 m of the source, when their groundspeed slowed significantly. Two or more males flying in the plume at the same instant often exhibited either extremely straight and directly upwind tracks or else zigzagging tracks with significant counterturning (as did males flying through the field of view of the cameras at slighdy different times). The males' position, either in the centre of the plume's axis or along one side, might explain these differences in track straightness, which previous studies with H.virescens have shown to be caused by higher frequencies of contact with plume filaments. When a significant shift in wind direction occurred, males tended to make an initial movement in the direction of the shift, perhaps due to latencies of response in both the olfactory and visual systems associated with flying into clean air. The males' behaviour in the field overall was similar to that observed in the wind tunnel, except that their airspeeds and groundspeeds were significantly higher than those observed in the laboratory. The fact that they flew faster in the field can be explained both by the significandy higher windspeeds that males need to compensate for in the field to attain a preferred velocity of image motion, as well as by a higher height of flight over the ground in die field causing a slower apparent motion of images at a given groundspeed compared with the laboratory.     

Manoeuvres used by flying male oriental fruit moths to relocate a sex pheromone plume in an experimentally shifted wind-field

ABSTRACT. In a wind-field experimentally shifted in direction by 35d?, flying male Grapholita molesta (Busck) zigzagging upwind either maintained contact with a pheromone plume and followed it across during the shift or lost it and commenced casting at c. 90d? across the shifting windline to locate it eventually in its new position. Males accomplished both of these results by integrating the previously described systems of optomotor anemotaxis and self-steered counterturning, but with faster reaction-times to pheromone on and off than heretofore calculated for this species. We found no evidence that males following the plume across used chemotaxis as proposed for another species, Rather, the sawtoothed-shaped tracks were a result of the anemotactic and counterturning systems responding rapidly and reiteratively to each loss and gain of pheromone along the plume in the shifting wind. The response to an increase or decrease in pheromone concentration by males was to change their course angle to more upwind or more crosswind, respectively, on the very first reversal (within c. 0.15 s) after the concentration changed. Because males adjusted their airspeeds more slowly to changes in concentration, the groundspeeds along the more upwind-orientated legs were lower than those along cross-wind legs, contributing to the sawtoothed shape of tracks of plume-followers. The self-steered counterturning programme also reacted quickly to concentration changes, the reversal intervals tending to be shorter following each contact with pheromone than after each excursion into cleaner wind. Following casting after losing the plume, males relocating the pheromone plume exhibited an upwind ‘surge’ of narrow zigzagging flight because on the first leg in the plume they steered a course more directly upwind than on the previous leg and increased the frequency of counterturning to its highest value while maintaining the relatively high airspeed acquired while casting.     

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.     

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.     

Effects of pheromone plume structure and visual stimuli on the pheromone-modulated upwind flight of male gypsy moths (Lymantria dispar) in a Forest (Lepidoptera: Lymantriidae)

The pheromone-modulated upwind flight ofLymantria dispar males responding to different pheromone plume structures and visual stimuli designed to mimic trees was video recorded in a forest. Males flying upwind along pheromone plumes of similar structure generated tracks that were similar in appearance and quantitatively similar in almost all parameters measured, regardless of the experimentally manipulated visual stimuli associated with the pheromone source. Net velocities, ground speeds, and airspeeds of males flying in point-source plumes were slower than those of males flying in the wider, more diffuse plumes issuing from a cylindrical baffle. The mean track angle of males flying in plumes issuing from a point source was greater (oriented more across the wind) than that of males flying in plumes issuing from a transparent cylindrical baffle. Males flying in point-source plumes also turned more frequently and had narrower tracks overall than males responding to plumes from a cylindrical baffle. These data suggest thatL. dispar males orienting to pheromone sources (i.e., calling females) associated with visible vertical cylinders (i.e., trees) use predominantly olfactory cues to locate the source and that the structure of the pheromone plume markedly affects the flight orientation and the resultant track.     

Evidence of active or passive downwind dispersal in mark–release–recapture of moths

Modelling moth dispersal in relation to wind direction and strength could greatly enhance the role of pheromone traps in biosecurity and pest management applications. Anemotaxis theory, which describes moth behaviour in the presence of a pheromone plume and is used as a framework for such models. Currently, however, that theory includes only three components: upwind, zigzagging, and sideways casting behaviour. We test anemotaxis theory by analysing the data from a series of mark–release–recapture experiments where the wind direction was known and the insects were trapped using an irregular grid of pheromone traps. The trapping results provide evidence of a downwind component to the flight patterns of the released insects. This active or passive downwind dispersal is likely to be an appetitive behaviour, occurring prior to the elicitation of pheromone‐oriented flight patterns (pheromone anemotaxis). Given the potential for significant displacement during downwind dispersal, this component will have impact on final trap captures and should be considered when constructing moth dispersal models.     

Odor-modulated upwind flight of the sphinx moth,Manduca sexta L.

1. Male and female Manduca sexta flew upwind in response to the odor of female sex-pheromone gland extract or fresh tobacco leaf respectively, and generated very similar zigzagging tracks along the odor plume. 2. After loss of odor during flight, males and females alike: (1) first flew slower and steered their flight more across the wind, then (2) stopped moving upwind, and finally (3) regressed downwind. 3. Males flying upwind in a pheromone plume in wind of different velocities maintained their ground speed near a relatively constant 'preferred' value by increasing their air speed as the velocity of the wind increased, and also maintained the average angle of their resultant flight tracks with respect to the wind at a preferred value by steering a course more precisely due upwind. 4. The inter-turn duration and turn rate, two measures of the temporal aspects of the flight track, were maintained, on average, with remarkable consistency across all wind velocities and in both sexes. The inter-turn durations also decreased significantly as moths approached the odor source, suggesting modulation of the temporal pattern of turning by some feature of the odor plume. This temporal regularity of turning appears to be one of the most stereotyped features of odor-modulated flight in M. sexta.     

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.     

Manoeuvres of female Brachymeria intermedia flying towards host-related odours in a wind tunnel

Abstract. Mature female Brachymeria intermedia (Hymenoptera: Chalcididae) were conditioned to fly towards vanilla odour in a wind tunnel. We analysed the tracks of wasps flying along turbulent plumes of either host odour (pupae of the gypsy moth, Lymantria dispar) or vanilla odour, along either a ribbon plume or a turbulent plume of vanilla odour, and before and after plume removal. Wasps flew in similar shallow zigzagging tracks along the turbulent plume of host and vanilla odours. When the plume was removed while wasps were flying upwind along a turbulent plume of vanilla odour, wasps either maintained an upwind course or drifted sideways, alternating upwind and downwind courses before turning around and flying downwind. No wasp casted upon loss of the plume.     

Influence of pheromone concentration and ambient temperature on flight of the gypsy moth, Lymantria dispar (L), in a sustained-flight wind tunnel

Abstract. The effects of pheromone concentration and ambient temperature on male gypsy moth, Lymantria dispar (L.) (Lepidoptera), flight responses to pheromone were investigated in a wind tunnel. As the pheromone dose increased from 10 ng to 1000 ng, males flew at progressively slower airspeeds and ground speeds, and reduced their wingbeat frequencies. Furthermore, the moths steered significantly smaller course angles as the pheromone concentration increased, indicating that they were adopting a more upwind heading. The overall width of the flight tracks also decreased when males flew in more concentrated pheromone plumes. Estimation of plume dimensions using a male wing-fanning assay showed that as pheromone dosage increased, the resultant active spaces became wider, indicating that an inverse relationship existed between the dimensions of the time-averaged plume and the width of track reversals and that most turns were initiated within the plume. When males were flown at cool (20°C) and warm (26°C) ambient temperatures but to equivalent pheromone emission rates, they exhibited higher airspeeds and ground speeds at the higher temperature but steered larger course angles. Track widths, and length of track legs were, however, similar at the two temperatures. The mean turning frequency was nearly the same (c. 4 turns/s) across all the concentrations and temperatures tested even though the moths' thoracic temperature differed by 5°C when the ambient temperature was varied.     

Optomotor anemotaxis polarizes self-steered zigzagging in flying moths

ABSTRACT. Experiments with oriental fruit moth males, Grapholita molesta (Buck), provide evidence that a pheromone plume in zero wind elicits an endogenous, self-steered programme of counterturning (zigzagging) flight, and that wind experienced in flight establishes the polarity of the counterturns; they become aligned so that displacement occurs toward the source, even after the wind is stopped. In zero wind, males located a pheromone source more frequently when they had experienced a wind after having already taken flight before the wind was stopped (46%) compared with those that took flight later and therefore only experienced wind while they were in contact with the ground (14%). Furthermore, males placed in a stationary pheromone plume in zero wind located the source, eventually, on 21% of occasions. The flight tracks of these males, as well as those having experienced a wind only while on the ground, often exhibited repetitive counterturns (zigzags) of c. 180–200. However, the counterturns meandered around the flight tunnel, the inter-reversal track angles having no consistent direction. Sometimes the males displaced down-tunnel in the stationary plume, sometimes up, eventually locating the source and performing a courtship display. The inter-reversal track angles of males counterturning in wind, on the other hand, displayed a consistent orientation of c. 60 to either side of the wind line, resulting in consistent upwind displacement toward the source. With no pheromone present, with or without wind, counterturns were not observed.     

An analysis of anemotactic zigzagging flight in male moths stimulated by pheromone

ABSTRACT. The zigzagging behaviour of male Plodia interpunctella flying up a plume of sex pheromone was investigated in a horizontal wind tunnel by detailed analysis of the moths' ground tracks, groundspeeds, orientations and airspeeds. The moths ‘homed in’ on the source of the pheromone plume by progressively reducing airspeed and turning more into wind, thereby reducing groundspeed and the distance between track reversals and so narrowing down their zigzags (Fig. 16). Track angles and times between reversals were unaffected. Removing the wind-borne pheromone plume while a moth was flying along it confirmed that zigzagging can be an anemotactic response to losing the scent rather than a chemotactic response to the plume. For the first 1–2 s after the moth entered pheromone-free air the zigzagging was indistinguishable from that shown when the plume remained; thereafter it widened progressively until the moths were flying to and fro at c. 90° to the wind. The after-effect of odour stimulation persisted for many zigs and zags and many seconds (Figs. 4 and 5). Moths flying along pheromone plumes compensated efficiently for differences of wind speed, showing similar distributions of track angles to wind, and of ground-speeds, in winds of 0.1, 0.2 and 0.3 ms^-1 (Figs. 12 and 13). Groundspeed varied with track angle to wind and this relationship was also similar in the three wind speeds (Fig. 14). This constancy of track angles and groundspeeds was due to the moths both increasing their airspeeds and turning more into wind at the higher wind speeds (Fig. 17). Thus the direction of the apparent movement of the ground pattern beneath the moths varied with wind speed. It is inferred that the moths, although unable to sense the wind directly, are able to compensate for changes in wind speed by integrating the wind-dependent optomotor input with information about their own airspeed, or with information about their own turning movements. Maintaining some ‘preferred’ relationship between these inputs by adjustments of orientation and airspeed, would then serve to maintain a given combination of track angle and groundspeed independently of wind speed. The preferred relationship is repeatedly re-set by the changing olfactory input from the pheromone plume, which also controls the switching between left and right of the upwind direction.     

Detection of short pure-tone stimuli in the noctuid ear: what are temporal integration and integration time all about?

The interception of a pheromone filament induces flying moths to surge briefly nearly straight upwind; in the absence of pheromone moths cease upwind progress and zigzag crosswind. We tested males of the almond moth, Cadra cautella (Lepidoptera, Pyralidae), in a low-turbulence wind tunnel in wind velocities of 20, 40 and 80 cm s⁻¹. A mechanical pulse generator was set to produce plumes either with same pheromone pulse frequency (pulse generation frequency of 2.9 Hz, interpulse distances from 7 cm to 28 cm) or plumes with same interpulse distance across the three wind velocities (interpulse distance of 14 ± 2 cm, pulse generation frequency of 1.7–5.0 Hz). In plumes of similar pulse frequency, the faster the speed of the wind the slower the ground speed of flight. However, in plumes of similar interpulse distance, ground speed remained relatively constant independent of the wind speed. A `realized' frequency of pulse interception for males flying along the various combinations of pulse frequencies and wind velocities was calculated using the males' average airspeed and the spatial distribution of pheromone pulses in the plume. Realized frequency of pulse interception ranged from 1.3- to 3.0-fold higher than the frequency of pulse generation. The flight tracks of males reflected the regime of realized pulse interception. These results suggest that upwind flight orientation of male C. cautella to pheromone in different wind velocities is determined by the flux of filament encounter. Accepted: 3 September 1997     

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.     

Effects of moth size on velocity and steering during upwind flight toward a sex pheromone source byLymantria dispar (Lepidoptera: Lymantriidae)

Free-flying male gypsy moths (Lymantria dispar)head upwind in response to sex pheromone. Males typically fly in a zigzag path, with mean ground speeds modulated by pheromone concentration and ambient temperature, but not by wind speed. We studied the effect of male size on ground speeds and additional flight track parameters. Mean net ground speed along the wind line was fastest among large males and was slower in medium and small males. Similarly, mean airspeeds and ground speeds along the flight tracks increased from small to large males. Males from all three size classes steered similar mean course angles. Small males, however, had larger mean track angles than larger males, and mean drift angles were also larger for small males. Turning rates (frequency of turns across the wind line) and interturn distances (net crosswind displacement between turn apices) were not significantly different among the three size classes; however, large males had a trend toward a reduced mean turning rate and increased mean interturn distance. The steering of similar course angles by males from all three size classes and the higher airspeeds among larger males (the two variables males can actively control during free flight) suggest that changes in other flight parameters are a result primarily of increased ground speed among large males.     

An analysis of anemotactic flight in female moths stimulated by host odour and comparison with the males' response to sex pheromone

ABSTRACT. The flight pattern of mated female navel orangeworm moths, Amyelois transitella (Walker), responding to odour from potential larval hosts is zigzagging upwind flight. However, at times these moths are capable of flying nearly directly upwind towards the odour source (track angles near 0). This response indicates that these females are capable of very accurate anemotactic control of their heading or course angle, since small angular errors in this measure would translate into larger deviations from direct upwind flight. Males of this species exhibit flight patterns similar to those of females, including track angles clustered about 0 when flying upwind to a source of the female-produced pheromone, but under these experimental conditions they flew with a higher average airspeed than the females. When females lose contact with an odour plume they initiate a well-defined programme of cross-wind counterturning or casting, which may normally increase their chances of retrieving contact with that plume when the wind direction shifts. The resultant track angles of females increase significantly by 0.8 s after plume loss, indicating that the female has initiated changes in both her course angle and airspeed. By 1 s after plume loss the females' track angles are no longer unimodally distributed about 0, but are bimodally distributed about -90 and +90. Males responded more rapidly to the loss of a pheromone plume, demonstrating a significant change in track angle 0.4 s after plume loss. Overall, female and male A.transitella exhibited remarkably similar anemotactic flight manoeuvres during upwind flight to odour sources as well as after plume loss.     

Directional control by male gypsy moths of upwind flight along a pheromone plume in three wind speeds

By attaching a reflective strip to the thorax, we documented with video recordings in a wind tunnel the spatial orientation of male gypsy moths, Lymantria dispar, as they flew along a plume of sex pheromone. In wind speeds of 61, 122, and 183 cm s⁻¹, moths flew very similar tracks along a pheromone plume. Moths aimed their thrust closer to upwind in increasing wind speeds using a roll maneuver. As a result, the orientation of their visual flow field, represented by the slip angle (the angular distance between the direction of flight and the longitudinal body axis), remained relatively constant. We propose that directional control during self-steered zigzagging is achieved by rolling, thereby maintaining a set slip angle. Following a roll at the apex of a turn that aligns the moth with its preferred slip angle, a moth banks toward a cross wind leg. By banking moths may maintain a stable image flow at oblique angles to their longitudinal body axis. Accepted: 16 July 1998     

Factors influencing the landing of maleEpiphyas postvittana (Walker) exhibiting pheromone-mediated flight (Lepidoptera: Tortricidae)

The effects of changes in various visual and olfactory properties of a white card surface on the landing position of male Epiphyas postvittanaexhibiting pheromone-mediated flight were studied in a wind tunnel. Males landed predominantly at the most downwind position of a surface in line with the pheromone source, regardless of the strength of the source. The position on the surface that males landed was strongly influenced by visual factors. The landing position of males appeared to be influenced by visual cues along all three axes of the surface. Decreases in either the dimension horizontally perpendicular to the wind direction or the vertical dimension resulted in greater numbers of males landing farther upwind on the surface than the downwind edge. Visual changes in the axis along the wind direction also affected the position at which males landed. For example, when presented with two white card surfaces with a 4- cm gap between them, males tended to land on the downwind edge of the upwind surface (on which the source was located). When the gap was bridged with clear Mylar, the landing pattern was significantly different, with the greater proportion of males landing on the downwind surface. However, when Mylar was placed on the plexiglass floor of the tunnel (in addition to bridging the gap), the landing pattern on the surface was not significantly different from that on the two surfaces without the Mylar bridge. It is suggested that during the prelanding and landing phases of pheromone-mediated flight, male moths orient to visual features of the surface containing the pheromone source rather than to visual features of the source (conspecific female moth) itself.     

Behaviour of flying oriental fruit moth males during approach to sex pheromone sources

Abstract. The pheromone-modulated upwind flight tracks of Grapholita molesta (Busck) males were video recorded as they approached a point-source of pheromone in a wind tunnel. The field of view of the video recording was divided longitudinally into 33 cm sections and the flight behaviour of the males in these sections was measured and compared as they approached from 233 cm to 50 cm downwind of the pheromone source. As the males approached the source, their mean ground speeds decreased. The mean values of their track angles increased with respect to due upwind (0), indicating movement more across the wind. These changes resulted mainly from the males decreasing their air speeds as they progressed up the plume toward the source. They did not change the average direction of their steering (course angle). Thus, the increase in track angles resulted from the males allowing themselves to drift more in the wind as they approached the odour source. The males also increased their average rate of counterturning as they approached the source. The net result of all these behavioural changes was a track that slowed and grew narrower, giving the impression that the males were 'homing-in' on the pheromone source as they approached. Causes of these systematic changes in behaviour are considered with respect to the known systematic changes in pheromone plume structure as the distance to the source decreases.