The analysis of flight paths of male Egyptian cotton leafworm moths, Spodoptera littoralis, to a sex pheromone source in the field

ABSTRACT. The flight of male Spodoptera littoralis (Boisd.) (Noctuidae) towards a pheromone source was recorded during the early part of the night using a cine camera and an image intensifier. The cine films were analysed frame by frame to produce flight tracks from which it was possible to calculate the mean advance rate of moths towards the pheromone source and their projected ground speed, for a series of positions downwind of the source. As wind speed was measured the moth's air speed was also estimated. The moths compensated for changes in wind speed by varying their air speed, hence maintaining a ground speed independent of wind speed. The ground speed itself was found to decrease as moths flew closer to the pheromone source.     

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.     

Pheromone-mediated upwind flight of male gypsy moths, Lymantria dispar, in a forest

Abstract Lymantria dispar L. males flying upwind in a pheromone plume in a forest were video-recorded at 2.5, 10 and 20 m from the source of pheromone. Males flew slower and steered more across the wind as they approached the source. In concert, their ground speed decreased and track angles increased. In contrast to these changes, their drift angles were fairly constant and the transverse component of image flow, above and/or below the moths eyes, showed almost no change. The inter-turn duration (time between sequential turns), a temporal aspect of the male flight manoeuvres, showed a consistent but relatively small increase as the distance from the source increased. The flight tracks narrowed as the males approached close (2.5 m) to the source. Because of unpredicted correlations between physical variables (i.e. temperature, wind velocity) and the distance from the source, we used principal components analysis to generate a set of completely independent variables. Greater than 90% of the variability in the data could be explained by four principal factors which corresponded well with known relationships in the flight manoeuvres. All four of these factors showed a significant regression against distance to the source. Although uncontrolled factors such as temperature and wind velocity may have contributed to changes in flight behaviour, recent data indicate that, in addition to concentration, certain temporal and spatial characteristics (i.e. burst period, burst return period) of plumes in wind vary systematically with distance from the source. We propose that L.dispar males might adjust their flight manoeuvres in response to these changes.     

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.     

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.     

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     

Effects of intermittent and continuous pheromone stimulation on the flight behaviour of the oriental fruit moth, Grapholita molesta

ABSTRACT. When male oriental fruit moths, Grapholita molesta (Busck) (Tortricidae), casting in clean air entered an airstream permeated with pheromone their flight tracks changed immediately on initial contact with pheromone, but after a few seconds returned to casting as if in clean air. The degree of change in the flight track was directly related to the concentration of pheromone. Although little net uptunnel movement occurred in response to the continuous stimulation provided by a uniformly permeated airstream, when an intermittent stimulus provided by a point-source plume was superimposed onto the permeated airstream moths were able to 'lock on' and zigzag uptunnel in the plume. The percentage of moths doing so corresponded to the difference between the peak concentration within the plume and the background concentration of pheromone permeating the airstream. Moths also locked onto, and flew upwind along the pheromone-clean-air boundary formed along a pheromone-permeated side corridor. Because a similar response was observed along a horizontal edge between a pheromone-permeated floor corridor and clean air, we conclude that the intermittent stimulation at the edge perpetuated the narrow zigzagging response to pheromone.     

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.     

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.     

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.     

Attraction range of a sex pheromone trap for the damson‐hop aphid Phorodon humuli (Hemiptera: Aphididae)

The attraction range of olfactory response by winged female gynoparae (autumn migrants that give birth to oviparae, the sexual females) and male damson–hop aphids Phorodon humuli (Schrank) is investigated in field experiments over 2 years by analyzing the spatial patterns of catches in concentric circles of yellow‐painted traps (60 in total) around a central trap releasing the species' sex pheromone, (1RS,7S,7aS)‐nepetalactol. Males are more likely than females to be found in the central trap, with 65.6% of the 1824 males caught there compared with 11.2% of 1346 females. Both morphs are more numerous in traps axial with the mean wind direction and centred on the pheromone‐release trap than at other angles. Males are approximately five‐fold more numerous in traps downwind than at similar distances upwind of the pheromone, showing that its presence stimulates landing. For males, the estimated active space of the lure extends 6 m downwind. Catches of females are equally numerous up and downwind of the pheromone lure because females orienting on the axis of the pheromone source continue to respond to visual cues in their flight path if they overshoot the olfactory one. For females, the active space of a pheromone lure is less than 2 m downwind. It is unimportant for either morph whether the pheromone‐release trap is yellow or transparent. In these experiments, both morphs orient with, track and probably arrive in the pheromone source trap from at least 26 m, the distance to the nearest aphid‐infested hops.     

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.     

Real-time measurement of pheromone release from individual female moths and synthetic dispensers in a wind tunnel by recording of single receptor-neurone responses

Measurements of single neurone activity in the peripheral pheromone receptors of male Agrotis segetum (Denis & Schiffermüller) (Lepidoptera: Noctuidae) were performed in a wind tunnel using a portable electrophysiological recording unit. Filter paper and rubber septa loaded with synthetic sex pheromone, as well as individual conspecific female glands, were used as pheromone sources. Recordings, up to 3 h long, were analysed for temporal variation in spiking activity. The recordings were performed 2 m downwind of the source, where the pheromone plume had a width of approximately 12 cm, as could be measured with the single cell preparations. The system allowed reliable measurements of relative pheromone concentration with a 20-s time resolution. The release rate from rubber septa loaded with pheromone was more or less constant over time, whereas the release rate from filter paper loaded with pheromone decreased to one tenth of the initial value within 6 min from the application of the pheromone. The release of pheromone from female pheromone glands was pulsed with an interval of 2–10 min between bursts. This pulsing was not caused by retraction of the gland, as the glands were forcibly extruded during the entire experiment, but should reflect variation in transport of pheromone to the gland surface and subsequent release. The demonstrated stability of the preparations using tungsten electrodes, the reliable monitoring of female-produced pheromone plumes at several metres distance, and the time resolution obtained are important steps towards field monitoring of natural pheromone plumes, as well as pheromone concentration and distribution in applications for mating disruption.     

Flying Faster: Flight Height Affects Orthokinetic Responses During Moth Flight to Sex Pheromone

Male Oriental Fruit Moths (Grapholita molesta) flew faster toward a pheromone source as they flew higher above striped and dotted floor patterns. The moths significantly (P?<?0.05) increased their ground speed over floor patterns of transverse stripes or pseudo randomly placed dots. The moths’ track angles (flight path angle off the windline) decreased significantly (P?<?0.05) when they flew 40 cm above the floor patterns vs. flight at 10 cm up, and they tended to steer more upwind flight (smaller course angles) at the upper, 40 cm, height compared to 10 cm up. Turn frequencies and reversal distances across the wind line were also affected by dot density. However, the interaction of small changes in flight speed, course angle, turn widths and turn frequencies are difficult to assess; I have subsumed all their affects into a simple measure of “total distance” flown by the moths by summing the length of all flight vectors analyzed for the other metrics, but no differences were found. By far, the largest change in flight was the positive orthokinetic response to increased flight height above both striped and dotted floor patterns (Fig. 2; P?<?0.05), and nearly all other changes appear to be entirely due to faster moth flight with little or no changes in steering or turning patterns.     

Free flight capacity determination in a sustained flight tunnel: effects of age and sexual state on the flight duration of Prostephanus truncatus

Abstract. . Adult Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae) steering anemotactically upwind to a pheromone source in a wind tunnel, respond normally to, and alter their ground speed according to the direction and speed of, the movement of ground patterns beneath them. By manipulating this optomotor reaction component of their behaviour, studies were conducted on their flight duration. The results show a great deal of individual variation in flight duration, and the general data on single flights were skewed towards short flights. Pre-reproductive and inter-reproductive male and female beetles flew significantly longer than older beetles that had passed their peak of reproduction. There was no significant difference in the flight duration of male and female beetles at any age. The overall results suggest mat younger P. truncatus are capable of long-distance flights, and support the proposition that flight could be important in the spread of the beetle.     

Effect of the fine-scale structure of pheromone plumes: pulse frequency modulates activation and upwind flight of almond moth males

Abstract. The effects of plume intermittency and volume on behavioural and flight responses to pheromone of male Cadra cautella (Walker) (Lepidoptera: Phycitinae) were investigated in a pulling wind tunnel. The fine-scale structure of turbulent pheromone plumes was mimicked and manipulated using a pulser device that generated continuous ribbon plumes or intermittent plumes with defined pulse frequency and volume. As pulse frequency increased from 0.6 to 5 Hz and injected volume increased from 0.5 to 5 mls^-1, males flew progressively higher air and ground speeds, turned less frequently, and steered smaller course angles, resulting in straighter flight tracks. The faster the frequency of pulses and the greater the volume of the plume, the higher the proportion of males responding, the shorter their latencies, and the less time spent in the behaviour. Flight tracks of male C.cautella to point sources of pheromone depend on the frequency of filaments encountered.     

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.     

Flight speed of male spruce bud worm moths in a wind tunnel at different wind speeds and at different distances from a pheromone source

ABSTRACT. Flying male spruce budworm ( Choristoneura fumiferana [Clem.]) moths responding to virgin females and to synthetic pheromone in a wind tunnel maintained a constant rate of upwind progress when held by moving optomotor cues at a constant distance from the pheromone source. When allowed to progress upwind to the source, however, they slowed their upwind speed progressively as they approached it. They also adjusted their flight speed to maintain similar rates of upwind progress at different wind speeds.     

Metabolic response to alarm pheromone in honey bees

Exposure to alarm pheromone elicits increases in oxidative metabolism in Apis mellifera. The following quantitative results are reported: (1) The alarm response, measured by short-term elevated oxygen consumption in each bee, increases with increasing numbers of bees in the test groups. The rate of increase in response per bee shows a group effect which is greatest in small groups (1–100 bees) and remains constant in larger groups (up to 6,700 bees). (2) The pheromone concentration affects the reaction elicited. The greater the dose, the larger is the reaction up to a concentration of 2.4 μg/ml. Greater doses elicit no greater response. (3) Response to the pheromone by winter bees is maximum at 20°C and decreases at air temperatures above or below this value. (4) This metabolic reaction may provide a tool for quantitating temperament of honey bees.     

Flight behaviour of Bemisia tabaci in a vertical flight chamber: effect of time of day, sex, age and host quality

Abstract. The free-flight behaviour of Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae), the sweet potato whitefly, was investigated in a vertical flight chamber. A mercury-vapour lamp presented from above induced a phototactic flight response. Although flight propensity was comparable from 06.00 to 19.00 hours, flight duration was maximum between 06.00 and 10.00 hours. Males flew longer than females and their mean flight duration remained constant throughout the day. Females flew longer from 06.00 to 13.00 hours than from 13.00 to 19.00 hours. Both sexes were capable of sustaining flight for more than 2h, although less than 5% of those tested did so.
Flight activity also was influenced by age and by host quality. The propensity to take off, proportion exhibiting phototactic orientation and flight duration varied with the age of the whitefly. Host quality influenced the timing of flight behaviour. Whiteflies reared on senescing plants exhibited greater take-off rates and initiated longer phototactic flights up to 4 days following adult eclosion when compared to individuals reared on vegetative plants. Thereafter, individuals reared on vegetative plants exhibited greater response levels. Whiteflies reared on vegetative plants weighed more and survived longer than did individuals reared on senescing plants.
Whiteflies that responded to the overhead light initially exhibited a strong photokinetic and phototactic response. Over the course of the flight, these responses declined and flight instability increased, as indicated by an overall decrease in the mean rate of climb, accompanied by an increase in the variability of this parameter and an increase in horizontal displacement. Although males and females displayed similar flight characteristics, females exhibited a greater rate of climb than did males, and for both sexes, individuals that flew longer than 25 min had a greater rate of climb than did individuals that flew for less than 25 min.