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.     

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.     

Habitat cues synergize to elicit chemically mediated landing behavior in a specialist phytophagous insect,the grape berry moth

Many phytophagous insects locate their host plant using mixtures of volatile compounds produced by the plant. A key behavior in the host location process that has been the focus of decades of behavioral research is optomotor anemotaxis. Another key step in host location is landing on (or near) the odor source. In previous work, rubber septa emitting a synthetic blend of volatiles extracted from young shoots of grape plants, Vitus spp. (Vitaceae), elicited equivalent levels of oriented upwind flight by female grape berry moths (GBM), Paralobesia viteana (Clemens) (Lepidoptera: Tortricidae), as did actual (control) grape shoots. However, in contrast to the shoots, females did not land on the odor source. In this study, we used flight tunnel assays to investigate the landing response of GBM females with respect to chemical and visual stimuli, as well as differences in relative humidity. When stimuli were presented individually, only the synthetic blend of host plant volatiles elicited equivalent levels of oriented upwind flight compared to the plants. Interestingly, wet cotton strips elicited low but consistent levels of upwind flight. In paired assays, only the synthetic blend paired with wet cotton strips elicited landing, although at significantly lower levels than that elicited by grape shoots. To achieve landing rates equivalent to live grape shoots, grape berry moth females required all three stimuli we tested: host odor cues, moisture, and visual cues simulating a grape shoot. These results suggest the cues have a synergistic effect, and that landing behavior requires complex sensory processing using multiple sensory inputs. Furthermore, these results suggest that moisture plays an important role in the host plant location process.     

Orientation of flying male Anobium punctatum (Coleoptera: Anobiidae) to sex pheromone: separating effects of visual stimuli and physical barriers to wind

Abstract. Flying male woodworm, Anobium punctatum , are able to locate a source of female pheromone offered as a point source but land more quickly if the same odour source is presented on a model 'tree' (cylinder). We tested the response to a two-dimensional black 'tree' marked as a silhouette on the upwind screen of the wind tunnel, with or without a hidden upwind barrier to the wind. The beetles responded equally to pheromone presented on a visual silhouette with wind barrier and to the hidden upwind wind-barrier alone, suggesting that the wind-barrier itself has a significant effect on insect orientation and landing: visual stimuli do not add to the landing response if the barrier is present. However, without the barrier upwind, landing was faster when the visual stimulus was present than without. This is the third forest-living species to be shown to respond in this way, which suggests this phenomenon may be more widespread. The possibility that this phenomenon is present in other, non-forest, phytophagous insects, their predators and parasitoids is discussed.     

Nocturnal orientation in the black carpenter antCamponotus pennsylvanicus (DeGeer) (Hymenoptera: Formicidae)

Summary The black carpenter antCamponotus pennsylvanicus (DeGeer), a predominantly nocturnal Formicine ant, responds to a hierarchy of visual and tactile cues when orienting along odor trails at night. Under illumination from moonlight or artificial light, workers rely upon these beacons to mediate phototactic orientation. In the absence of moonlight or artificial lights, ants were able to orient visually to terrestrial landmarks. In the absence of all landmarks, save for overhanging tree branches, ants could negotiate shortcuts or make directional changes in response to visual landmarks presented within the tree canopy on a moonless night. When experimental manipulations placed the ants in total darkness, they could no longer negotiate shortcuts and would resort to thigmotactic orientation along structural guidelines to reach a food source. The hierachical organization of these diverse cues in a foraging strategy is discussed, as well as their adaptive significance toC. pennsyhanicus.     

Effect of a vertical object on the sex pheromone-mediated flight and landing behaviors of the male lightbrown apple moth,Epiphyas postvittana (walker) (Lepidoptera: Tortricidae)

A small (2.5-cm-wide) vertical (10-cm-high) white object influenced the sex pheromone-mediated flight and landing behaviors of maleEpiphyas postvittana. When the vertical object was positioned on a horizontal surface to the side (3–5 cm) and upwind of a pheromone source (in the middle of the surface), the distribution of landing positions of males on the surface was different from that when the object was not present; males tended to land in positions skewed toward the side of the source that the object was on. The closer the object was positioned to the source, the greater the number of males that landed on the object (rather than on the horizontal surface). This difference in landing positions (when the object was present) corresponded with changes in the flight tracks; the tracks of males flying to the surface with an object were skewed toward the object and had higher amplitude intertrack reversal distances than the tracks of males flying to a surface without a vertical object. Positioning of a vertical object progressively upwind of the source resulted, apparently, in decreased effects on the landing (and presumably flight) behavior of males. The effect of the vertical object on the flight and landing behaviors of males corresponded largely with changes in pheromone plume structure (visualized with smoke) induced by the extra turbulence in the airflow over the source. Thus it appears that the vertical object influences the behavior of maleE. postvittana largely through the olfactory sensory modality. However, when a clear, Mylar object, in place of the white object, was placed on the surface, more males landed on the Mylar object (than did on the white object), suggesting that the vertical object may also influence the behavior of males through the visual modality.     

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     

Visual and olfactory cues for mate orientation behaviour in male white-spotted longicorn beetle, Anoplophora malasiaca

Olfactory and visual cues were shown to mediate short‐distance orientation in Anoplophora malasiaca (Thomson) (Coleoptera: Cerambycidae). In a laboratory test, more than 80% (n = 42) of males walked straight upward when presented with an untreated surface with a 75° slope. When a freshly killed female was fixed at a short distance (10 cm ahead and 5 cm to left/right) from the starting point, 50% of males (n = 30) were oriented toward the female before direct contact. Similar behavioural responses were observed when female extract was directly applied to the slope or to a glass rod model fixed on the slope. When black, white, and transparent coloured rods with the extract were presented, the orientation response was significantly greater for black than to white and transparent rods, to which only a negligible response was observed.     

The importance of location and visual cues during foraging in the German wasp (Vespula germanica F.) (Hymenoptera: Vespidae)

Abstract

The way in which foraging wasps use cues for prey location and choice appears to depend on both the context and on the type of prey. Vespula germanica is an opportunistic, generalist prey forager, and individual wasp foragers often return to hunt at sites of previous hunting success. In this paper, we studied which cues are used by this wasp when relocating a food source. Particularly we analysed the response to a displaced visual cue versus a foraging location at which either honey or cat food had been previously presented. We conclude that location is used over a displaced visual cue for directing wasp hovering, although the landing response is directed differently according to bait type. When wasps are exploiting cat food, location also elicits landing, but if they are exploiting honey, a displaced visual cue elicits landing more frequently than location.     

Odor tracking flight of male Manduca sexta moths along plumes of different cross-sectional area

Males of the hawkmoth, Manduca sexta, track wind-borne plumes of female sex pheromone by flying upwind, while continuously turning from side-to-side and changing altitude. Their characteristic “zigzagging” trajectory has long been thought to result from the interaction of two mechanisms, an odor-modulated orientation to wind and a built-in central nervous system turning program. An interesting and as of yet unanswered question about this tracking behavior is how the cross-section of an odor plume or its clean-air “edges” affects moths’ odor tracking behavior. This study attempts to address this question by video recording and analyzing the behavior of freely flying M. sexta males tracking plumes from pheromone sources of different lengths and orientations with equal odor concentration per unit area. Our results showed that moths generated significantly wider tracks in wide plumes from the longest horizontally-oriented sources as compared to narrower point-source plumes, but had relatively unaltered tracks when orienting to plumes from the same length sources oriented vertically. This suggests that in addition to wind and the presence of pheromones, the area of the plume’s cross section or its edges may also play an important role in the plume tracking mechanisms of M. sexta.     

Close encounters: contributions of carbon dioxide and human skin odour to finding and landing on a host in Aedes aegypti

In a wind‐tunnel study, the upwind flight and source location of female Aedes aegypti to plumes of carbon dioxide (CO₂) gas and odour from human feet is tested. Both odour sources are presented singly and in combination. Flight upwind along the plumes is evident for both CO₂ and odour from human feet when the odours are presented alone. Similarly, both odour sources are located by more than 70% of mosquitoes in less than 3 min. When both CO₂ and odour from human feet are presented simultaneously in two different choice tests (with plumes superimposed or with plumes separated), there is no evidence that females orientate along the plume of CO₂ and only a few mosquitoes locate its source. Rather, the foot odour plume is navigated and the source of foot odour is located by over 80% of female Ae. aegypti. When a female is presented a plume of CO₂ within a broad plume of human foot odour of relatively low concentration, the source of CO₂ is not located; instead, flight is upwind in the diffuse plume of foot odour. Although upwind flight by Ae. aegypti at long range is presumably induced by CO₂ and the threshold of response to skin odours is lowered, our findings suggest that, once females have arrived near a prospective human host, upwind orientation and landing are largely governed by the suite of human odours, whereas orientation is no longer influenced by CO₂.     

Visual and olfactory cue interaction in resource-location by the blowfly, Lucilia sericata

Abstract. The interactions between olfactory and visual cues in the landing responses of the blowfly Lucilia sericata (Meigen) (Diptera: Calliphoridae) were examined in a laboratory wind tunnel. The odour of liver and sodium sulphide solution released at 1 L/min, resulted in a greater number of landings, closer to, but downwind of, the central odour release point, than when odour was absent. Three-day-old protein-deprived females landed in greater numbers than protein-fed female flies of the same age; no difference existed between 6-day-old protein-fed or protein-deprived females. Six-day-old, protein-fed flies landed closer to the odour source than did 3-day-old, protein-fed flies. In the presence of odour, flies landed closer to the central release point when it was accompanied by a visual cue. No such effect of the visual cue was evident in the absence of odour. When a plain white sticky-surface (25 × 25 cm) was paired with an identical white surface plus odour, approximately equal numbers of flies landed when the surfaces were placed together; increasingly higher numbers of flies landed on the surface with the odour cue when the distance between the surfaces was increased. When a white surface with a visual cue was presented with the plain white surface plus odour, more flies landed on the white surface with the visual cue than on the plain white surface with odour when they were close together. However, as these two surfaces were moved apart, flies landed increasingly more on the surface with the odour than the surface with the visual cue. The results show that while odour cues may enhance the induction of landing by female L. sericata , visual cues are important when selecting a final landing site.     

Sex differences in olfaction‐mediated visual acuity in blowflies and its consequences for gender‐specific trapping

The behaviour of 650 female Calliphora vicina Robineau‐Desvoidy (Diptera: Calliphoridae) was examined in a wind tunnel using odour, in combination with six artificial visual stimuli, ranging from a simple black square to a three‐dimensional model of a dead mouse. The carcasses of laboratory mice were used to provide a natural odour and visual source, and a blend consisting of dimethyl trisulphide, mercaptoethanol, and o‐cresol was used to provide a synthetic lure. Significant differences were found in attraction to these odour sources: 90% of the flies oriented upwind to the natural source and 62% to the synthetic lure. No significant differences were found in upwind orientation towards different visual stimuli, but flies showed significantly more landings if the visual cues provided a vertical contrast against the background. A horizontal contrast gave no difference in landing rate compared to treatments without visual cues. In a field study, the blowfly genera Pollenia, Calliphora, and Lucilia were caught. The overall blowfly catch was significantly higher when an odour lure was present (Pollenia: 3×, Calliphora: 15×, Lucilia: >79×). A significant three‐way interaction between visual cue, genus, and gender was found. The saprophagous Lucilia and Calliphora showed a gender‐specific response to visual stimuli, whereas the parasitic Pollenia did not. A 2:1 female:male sex ratio was found for Calliphora spp. and a 12:1 sex ratio for Lucilia spp. The data suggest that landing responses of male and female saprophagous blowflies, and consequently trap catches, result from olfaction, but also from gender‐specific visual responses when under the influence of odour.     

Orientation in the Ant Paraponera clavata

Visual and nonpheromone olfactory orientation processes of the giant tropical ant Paraponera clavata were investigated in homing foragers which had been previously trained to visit a food source. Experienced foragers can select directions visually, with pheromone trails (Breed et al., 1987), or with environmental odors. High-contrast canopy cues, but not low-contrast lateral landmarks, serve as strong visual orientation cues.     

Oriented flight responses of female Mediterranean fruit flies to calling males, odor of calling males, and a synthetic pheromone blend

Male Mediterranean fruit flies,Ceratitis capitata (Wiedemann), produce volatile chemicals thought to be attractive sex pheromones. We demonstrated for the first time that male odor elicits upwind flight and zigzagging upwind flight patterns in mature unmated females. Such flight patterns indicate the mechanisms involved in female location of the pheromone source and arrival at that source. Similar female oriented upwind flight responses occurred with a three component blend comprised of ethyl-(E)-octenoate, geranyl acetate, andE,E-alpha farnesene. These findings clarify the role of male sex pheromone in mate-location strategies in this species and provide new bioassay criteria for evaluating attraction responses to male pheromone and synthetic blends.     

Visual cues collimate the trajectories of almond moth Cadra cautella males flying in wind and still air within a wind‐formed plume of pheromone

Male Cadra cautella (Walker) moths are videotaped in three dimensions in a 3‐m long wind tunnel as they fly within a 65‐cm wide plume of pheromone. Moths are presented two floor patterns, either ‘aligned’, a 25‐cm wide ‘trail’ of solid red circles along the tunnel's midline, or ‘offset’, in which the trail veers 25 cm to the left at the tunnel's midpoint. These visual patterns are presented either in a continuous airflow or airflow that is stopped before moths reach the tunnel's halfway point. Moths fly relatively straight paths over the aligned pattern in still air after the wind is stopped. With the offset pattern in wind and when the wind is stopped, moths swerve towards the offset pattern before again progressing along the plume. Prominent visual cues appear to ‘collimate’ (i.e. align with a directional cue) the moth's course as long as the moth remains in contact with pheromone. In wind, these moths appear to favour trajectories that enhance visual feedback, even if the path taken is not directly upwind. During wind lulls, this manoeuvre may enable moths to continue progress towards calling females along a visually set course. The centring of trajectory over prominent visual cues suggests that these moths favour a route that enhances visual feedback.     

Starvation period and age affect the response of female Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) to odor and visual cues

The effects of starvation or age on the walking or flying response of female Frankliniella occidentalis to visual and/or odor cues in two types of olfactometer were examined in the laboratory. The response of walking thrips starved for 0, 1, 4, or 24h to an odor cue (1microl of 10% p-anisaldehyde) was examined in a Y-tube olfactometer. The take-off and landing response of thrips (unknown age) starved for 0, 1, 4, 24, 48 or 72h, or of thrips of different ages (2-3 days or 10-13 days post-adult emergence) starved for 24h, to a visual cue (98 cm(2) yellow sticky trap) and/or an odor cue (0.5 or 1.0 ml p-anisaldehyde) was examined in a wind tunnel. More thrips walked up the odor-laden arm in the Y-tube when starved for at least 4h (76%) than satiated thrips (58.7%) or those starved for 1h (62.7%, P<0.05). In the wind tunnel experiments the percentage of thrips to fly or land on the sticky trap increased between satiated thrips (7.3% to fly, 3.3% on trap) and those starved for 4h (81.2% to fly, 29% on trap) and decreased between thrips starved for 48 (74.5% to fly, 23% on trap) and 72 h (56.5% to fly, 15.5% on trap, P<0.05). Fewer younger thrips (38.8%) landed on a sticky trap containing a yellow visual cue of, those that flew, than older thrips (70.4%, P<0.05), although a similar percentage of thrips flew regardless of age or type of cue present in the wind tunnel (average 44%, P>0.05).     

Spatial Orientation in Blattella germanica L. Larvae

The aim of these experiments was to investigate the type of cues used in homing processes by young Blattella germanica L. larvae. Several types of stimuli were tested: path integration with kinesthetic cues and visual orientation with landmark cues. Tests measured the escape direction of larvae from the food box after disturbance. Either type of cue alone, path integration or visual landmarks, was sufficient to allow larvae to orient towards their shelters, but they oriented more precisély when both types of cue were used. When several landmark cues (proximal and distal) were present, their relative angular position seemed important in the orientation process. Macroscopic shapes in the environment appeared to be used as a global image, memorized to reach the shelter.     

Orientation responses of the grasshopper, Melanoplus sanguinipes, to visual, olfactory and wind stimuli and their combinations

Prereproductive adults of the grasshopper, Melanoplus sanguinipes (F.) (Orthoptera, Acrididae), demonstrated orientation and movement towards both visual and olfactory stimulus sources in a still-air chamber. Visual stimuli (wheat and lima bean foliage, vertical black or yellow-green stripes, and a yellow-green broad leaf pattern) were approached more frequently than the control white background surface. Olfactory stimuli (chopped wheat foliage and a four-component, synthetic, grass odor blend of volatiles) elicited an even greater positive response than the visual stimuli. Changing the proportions of the four volatiles in the blend significantly reduced positive orientation responses to the stimulus source. Visual cues of wheat foliage and olfactory cues of either chopped wheat odor or the grass odor blend gave greater responses when combined than when presented separately.In flowing air or wind, nearly all insects demonstrated a rapid positive response to odors of chopped wheat and the grass odor blend, significantly greater than the response to the same stimuli in still air. However, positive responses to visual cues were not significantly greater in wind than in still air. When combined with the olfactory stimuli in flowing air, visual cues did not increase the incidence of response. Grasshoppers responding to grass odors in wind moved more rapidly and directly toward the source, and stopped less often and for shorter durations than insects responding to odor in still air or to visual cues.We conclude from these studies that M. sanguinipes adults show orientation behavior to both visual and olfactory stimuli from food plant sources, although leaf odors elicit a stronger positive response particularly when carried by wind.     

On the function of sex pheromone components in Periplaneta americana: improved odour source localization with periplanone-A

ABSTRACT. The female American cockroach, Periplaneta americana L., produces two sex pheromone components: periplanone-A (PA) and periplanone-B (PB). PB induces male locomotion and upwind orientation. PA, when presented alone, has the same effect but with a higher threshold concentration. When added to PB in the natural ratio, however, PA reduces rather than increases locomotory activity. To examine whether PA affects male orientation in the natural blend, a pheromone source was suspended above the centre of a circular arena. Efforts were made to exclude air movements so that pheromone concentration declined centrifugally. Males walking in a PB gradient spent more time near the source than in the peripheral areas when low doses were presented. At emission rates approximately equivalent to those of a female, however, they were not able to locate the pheromone source as precisely as at lower rates. In contrast, males walking in a PA gradient spent more time in the centre of the arena when the pheromone dosage was increased. When PA was added to natural levels of PB, males walked more slowly and stopped more frequently near the source than with PB alone. Thus PA improves chemo-orientation of males when presented in a natural ratio with PB. A reduction of linear velocity near the pheromone source (an orthokinetic effect) is involved in this process.