Flight-phase and visual-field related optomotor yaw responses in gregarious desert locusts during tethered flight

Tethered flying desert locusts, Schistocerca gregaria, generate yaw-torque in response to rotation of a radial grating located beneath them. By screening parts of the pattern, rotation of the unscreened grating turned out to induce a compensatory steering (by pattern motion within transversally oriented 90° wide sectors) as well as an upwind/downwind turning response (by pattern motion within the anterior ventral 90° wide sector). The strength and polarity of responses upon the unscreened grating results from a linear superposition of these two response components. The results are discussed with regard to a functional specialization of eye regions.In a typical experiment, 3 consecutive flight-phases, assumed to mirror start, long-range flight, and landing of a free-flying locust, were distinguished. They may result from a time dependent variation of the polarity and relative strength of upwind/downwind turning and compensatory steering responses. Starting and landing phases were under strong optomotor control and were dominated by the high-gain compensatory steering. In contrast, the phase of long-range flight was under weak optomotor control resulting from a low gain in both of the two response components. The biological significance of this variable strength of optomotor control on free flight orientation of swarming locusts is discussed.     

Stabilizing responses to sideslip disturbances in Drosophila melanogaster are modulated by the density of moving elements on the ground

Stabilizing responses to sideslip disturbances are a critical part of the flight control system in flies. While strongly mediated by mechanoreception, much of the final response results from the wide-field motion detection system associated with vision. In order to be effective, these responses must match the disturbance they are aimed to correct. To do this, flies must estimate the velocity of the disturbance, although it is not known how they accomplish this task when presented with natural images or dot fields. The recent finding, that motion parallax in dot fields can modulate stabilizing responses only if perceived below the fly, raises the question of whether other image statistics are also processed differently between eye regions. One such parameter is the density of elements moving in translational optic flow. Depending on the habitat, there might be strong differences in the density of elements providing information about self-motion above and below the fly, which in turn could act as selective pressures tuning the visual system to process this parameter on a regional basis. By presenting laterally moving dot fields of different densities we found that, in Drosophila melanogaster, the amplitude of the stabilizing response is significantly affected by the number of elements in the field of view. Flies countersteer strongly within a relatively low and narrow range of element densities. But this effect is exclusive to the ventral region of the eye, and dorsal stimuli elicit an unaltered and stereotypical response regardless of the density of elements in the flow. This highlights local specialization of the eye and suggests the lower region may play a more critical role in translational flight stabilization.     

Adjustment of flight speed of gregarious desert locusts (Orthoptera: Acrididae) flying side by side

In tethered flying locusts, optomotor thrust responses induced by translatory pattern motion within the lateral visual fields were studied under closed-loop conditions. By modulating thrust in a compensatory manner, locusts counteracted a bias motion superposed on the thrust-related motion. This way, pattern speed was kept at 0° s^–1, indicating the set point of the respective optomotor control circuit. Though the quality of bias compensation varied greatly, it was largely independent from pattern characteristics. It might indicate that the gain of behavior not only is controlled by an automatic mechanism but also is affected by spontaneous modulations. Compensation of bias motion was critically dependent on the relation between self- and bias-generated motion: Locusts did not take control over pattern motion if self- and bias-generated motion differed greatly. Instead, locusts adopted a constant, supposingly preferred, thrust value. Therefore, flight speed is assumed to be controlled by two systems: the optomotor and a preferred thrust system. In free flight, an equalization of the flight speed of locusts within a swarm might result from similar behavior. In combination with a presumed coordination of the locusts' course direction, this may explain the continued cohesion of swarms in the field.     

Modulation of whitefly take-off and flight orientation by wind speed and visual cues

The effect of different wind speeds on take-off and flight orientation of the sweetpotato whitefly, Bemisia tabaci Gennadius (Homoptera: Aleyrodidae), was studied in the presence of a green visual stimulus which reflected 550 ± 10 nm light, or a white stimulus of the same intensity. When the white light was present, take-off was negatively correlated with wind speed. Analysis of the flight tracks of whiteflies in 0, 15 and 30 cm/s wind with the white light present showed that flight was not directed toward the stimulus in zero wind, and that insects were carried downwind as the wind increased. Net displacement downwind was significantly slower than the wind speed, indicating that B. tabaci can control its rate of displacement relative to its surroundings, and is not always passively transported by the wind. In the presence of the green visual stimulus, take-off and flight behaviour of B. tabaci was markedly different to that observed in the presence of the white light. Taking off was more likely and whiteflies made upwind orientated flights, landing on the illuminated section of the screen when it reflected green light. At all wind speeds tested, the mean ground speeds of B. tabaci were approximately 20 cm/s whether the insects were flying upwind or downwind. This uniformity of ground speed regardless of the changing effects of wind-induced drift in different directions strongly suggests that whiteflies actively control their ground speed using visual flow fields in a manner similar to all other flying insects examined thus far.     

Response of Eretmocerus eremicus to skylight and plant cues in a vertical flight chamber

In the southwestern United States, Eretmocerus eremicus (Hymenoptera: Aphelinidae) is a native parasitoid of the Bemisia complex (Homoptera: Aleyrodidae). However, little information currently exists on its potential as a biological control agent of whiteflies or on the factors that influence its tendencies to disperse. In this study, we examined the flight behavior of male and female E. eremicus in response to skylight (here simulated by a mercury-vapor lamp) and plant cues (a 550-nm filtered light) in a vertical flight chamber. Approximately 90% of the parasitoids took off in response to the skylight cue. Both sexes were capable of sustained flights in excess of 60 min; however, males had higher rates of climb than females (3.31±0.17 and 2.63±0.19 cm s^–1, respectively). When a plant cue was presented during the parasitoid's phototactic flight, four relatively distinct responses were observed. Fifty-one percent of the individuals responded to the plant cue throughout their flight by flying toward or by landing on the cue. The majority of these parasitoids were females. Approximately 12% of the wasps exhibited an intermittent, positive response to the plant cue. Twenty percent exhibited a `migratory' response. These parasitoids, which were predominantly males, failed to respond to the plant cue until they had flown for a considerable period. Finally, 17% failed to respond to the target during their flight. Approximately 37% of the individuals that showed a positive response to the plant cue actually landed on it and the majority of these were female. The differential response to the plant cue by male and female parasitoids could be, in part, because females are driven to locate hosts in which to oviposit, and males are driven to find mates.     

Motion parallax and figural properties of depth control flight speed in an insect

Male gypsy moths (Lymantria dispar L.) are able to control their forward flight speed solely by means of optical cues derived from the lateral parts of their visual field. Thereby, relative motion of the objects is required, which under free flight conditions would derive from the self-induced motion of the stationary objects within a surrounding structured in depth. Besides this motion parallax, however, the control system for forward flight speed demands figural properties of the objects such as differences in their angular extension or contrast. In a natural surround, the images of objects closer to the moth have higher angular velocity and, in addition, are usually larger and have higher contrast than those of objects farther away. The experiments have shown that this natural pairing of angular velocity and figural properties is essential to induce a thrust response which appears suitable to counteract involuntary changes in forward flight speed, as e.g. caused by changes in wind speed under free flight conditions. Inverse pairing of the visual stimuli caused the moths to either enlarge the error signal according to positive feedback within the control circuit, or to increase thrust to a maximum as always found in experiments without motion parallax or in the absence of differences in figural properties. The open-loop experiments furthermore established that the set point of angular velocity of the closer objects lies within the range of 4.5–9°/s, and that pattern speed modulation has to cover this range in order to induce a compensatory thrust modulation. The response is largely independent of the magnitude of relative motion as long as it is present; the response amplitude, however, strongly depends on the amplitude of pattern speed modulation.The results are discussed with regard to other visual cues used for the control of forward flight speed in insects, the algorithm underlying the figure-ground discrimination in flies, and the perception of depth in man as known from psychophysical experiments.     

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.     

Pesticide-induced mortality of natural enemies of the onion maggot,Delia antiqua [Dip.: Anthomyiidae]

Pesticide-induced differential mortality betweenDelia antiqua(MEIGEN)and several other organisms associated with its natural control [D. platura(MEIGEN),Coenosia tigrina (F.),Entomophtora muscae (COHN), andAphaereta pallipes (SAY)] were evaluated under simulated field conditions. Direct and residual differential mortalities were described for 3 herbicides (Chloro-IPC, nitrofen, and CDAA), 3 fungicides (maneb, chlorothalonil, and copper sulfate), and 1 insecticide (malathion). The recommended field application rates of these chemicals produced high positive differential mortality levels betweenD. antiqua and some of the natural mortality agents. Chloro-IPC, a preplant and midseason herbicide, induced 100% mortality ofA. pallipes over the 3-day residual test period. Modifications in behavioral orientation and death patterns ofD. antiqua adults infected withE. muscae were also noted in malathion-treated flies such that subsequent conidial dispersal was highly restricted. Michigan Agricultural Experimental Station Journal Article Number 10133.     

The optomotor yaw response of the desert locust, Schistocerca gregaria

Abstract The optomotor yaw response of the desert locust, Schistocerca gregaria (Forsk.), was investigated under open- and closed-loop conditions. When flying tethered in the centre of a vertically striped hollow sphere, the polarity of response of the locust was always the same as the stimulus. The response, therefore, appears suitable to stabilize body posture against passive rotations around the yaw-axis in free flight. Responses were induced by contrast frequencies up to 150 Hz with a maximum of amplitude at about 20 Hz. The characteristic curve, measured between 0.3 and 160 Hz, is widened up towards higher frequencies as compared with those of bees and flies.
Variability was the most striking feature in the locust's yaw response. The amplitude of modulation not only varied greatly between individuals but also changed with the same visual stimulus in the course of an experiment. We therefore suppose that the locust's turning behaviour is subject to gain control mechanisms and that spontaneous gain modulations are responsible for the observed variability in the stimulus-response conversion.     

Genetic and phenotypic variation for flight ability in the cactophilicDrosophila species,D. aldrichi andD. buzzatii

The flight ability ofDrosophila aldrichi (Patterson & Crow) andD. buzzatii (Patterson & Wheeler) using tethered flights, was measured with respect to age-related changes, genetic variation and adult body size variation induced by rearing at different larval densities.Drosophila buzzatii flew for much longer thanD. aldrichi, especially females, but age-related changes in flight duration were significant only forD. aldrichi. Effects of body size on flight ability were significant inD. buzzatii, but not inD. aldrichi. InD. buzzatii, there was a significant genotype-environment interaction (larval density × line) for flight duration, with short and average flight duration isofemale lines showing longer flights, but a long flight duration line shorter flights as body size decreased (i.e., as larval density increased). Heritability estimates for flight duration were similar in the two species, but flight duration showed no significant genetic correlations with developmental time, body size or wing dimensions (except for one wing dimension inD. buzzatii). Although not significantly different between the species, heritabilities for life-history traits (adult size and developmental time) showed contrasting patterns — with higher heritability for body size (body weight and thorax length) inD. buzzatii, and higher for developmental time inD. aldrichi. In agreement with limited previous field evidence,D. buzzatii is better adapted for colonization than isD. aldrichi.     

Ethylene Is Responsible for a Disturbed Development of Plant Reproductive System under Conditions of Space Flight

The development of reproductive organs was studied on three dwarf cultivars of wheat Triticum aestivum and the fast-cycling Brassica rapa plants, grown under earth control conditions, during the space flight in the Mir orbital station, and in a earth experiment that simulated growth conditions during the space flight, including an elevated content of ethylene in the air (1 mg/m³ on average). We found that the embryological characteristics of the plants were not affected by space flight conditions. The elevated ethylene content in air resulted in some changes in the morphometric characteristics of inflorescences and a greater frequency of sterility similar under conditions of space flight and control earth experiment. We conclude that the abnormalities and modifications in the development of reproductive organs, induced by space flight conditions, were caused by a secondary factor, an elevated ethylene content in the cabin air, rather than by microgravity.     

Variability in the area,energy and time costs of wintering waders responding to disturbance

Birds’ responses to human disturbance are interesting due to their similarities to anti‐predator behaviour, and understanding this behaviour has practical applications for conservation management by informing measures such as buffer zones to protect priority species. To understand better the costs of disturbance and whether it will impact on population size, studies should quantify time‐related responses as well as the more commonly reported flight initiation distance (FID). Using waders wintering on an estuarine area, we experimentally disturbed foraging birds on the Wash Embayment, UK, by walking towards them and recording their responses (FID, alert time, time spent in flight, time taken to resume feeding, and total feeding time lost). We present data for 10 species of conservation concern: Curlew Numenius arquata, Oystercatcher Haematopus ostralegus, Bar‐tailed Godwit Limosa lapponica, Grey Plover Pluvialis squatarola, Redshank Tringa totanus, Knot Calidris canutus, Turnstone Arenaria interpres, Ringed Plover Charadrius hiaticula, Sanderling Calidris alba and Dunlin Calidris alpina. Larger species responded more strongly, response magnitude was greater under milder environmental conditions, and responses varied over both small and large spatial scales. The energetic costs of individual responses, however, were low relative to daily requirements and disturbance events were unlikely to be frequent enough to seriously limit foraging time. We suggest, therefore, that wintering wader populations on the Wash are not currently significantly negatively impacted by human disturbance during the intertidal foraging period. This is also likely to be the case at other estuarine sites with comparable access levels, visitor patterns, invertebrate food availability and environmental conditions.     

Parasitism and dispersal potential of Sirex noctilio: implications for biological control

1 Sirex noctilio F. (Hymenoptera: Siricidae) is a wood‐boring wasp that attacks many pine species, including commercial trees planted throughout the world. Management of its populations is largely based on biological control using the nematode Beddingia siricidicola. Adult females are sterilized by the nematode, but are free to move and attack new trees, promoting nematode dispersal. Although generally successful, wasp management through nematode introductions has sometimes been inadequate. 2 We evaluated the effect of parasitism by B. siricidicola on flight performance of woodwasps under laboratory conditions. Using flight mills, we recorded a total of 46 flight trials over 23 h, obtained from infected and control (uninfected) females. 3 Although all wasps lost weight during flight, parasitized females were significantly smaller and suffered larger weight losses than uninfected females. In addition, total flight distance and velocity were lower in parasitized females. 4 Because nematode infection transmission relies on healthy wasps attacking trees previously visited by nematode‐bearing females, differential dispersal capacity could limit biological control success.     

Locomotor Behavior of Flightless Harmonia axyridis Pallas (Col., Coccinellidae)

To improve the efficiency of the lady beetle H. axyridis as a biological control agent against aphids, a flightless population was obtained by feeding adults with a mutagen and selecting their progeny for nonflying but otherwise morphologically normal individuals. These flightless adults attempted to fly but immediately fell. They softened their fall by opening their elytrae and wings. The inability to fly could result from change in their flying behavior compared to control adults. The flight duration was very much shorter, and the wing beat frequency and, more particularly, the amplitude of the wing beats were clearly lower. More time was spent in the other components of the flight behavior such as wing rotation, wing immobility, and wing folding. The sequence of these patterns differed slightly, due mainly to change in their frequency. The locomotor behavior was not modified by the mutation, which affected only the wing muscles. Searching behavior of mutant adults differed from that of control adults only in that they took longer to encounter and ingest aphids. Nevertheless, the larval growth and reproductive rate remained unchanged. The behavioral and biological features of these flightless adults indicate that it should be possible to use them in biological control programs.     

Three‐dimensional flight tracking shows how a visual target alters tsetse fly responses to human breath in a wind tunnel

Tsetse flies Glossina spp. (Diptera; Glossinidae) are blood‐feeding vectors of disease that are attracted to vertebrate hosts by odours and visual cues. Studies on how tsetse flies approach visual devices are of fundamental interest because they can help in the development of more efficient control tools. The responses of a forest tsetse fly species Glossina brevipalpis (Newstead) to human breath are tested in a wind tunnel in the presence or absence of a blue sphere as a visual target. The flight responses are video recorded with two motion‐sensitive cameras and characterized in three dimensions. Although flies make meandering upwind flights predominantly in the horizontal plane in the plume of breath alone, upwind flights are highly directed at the visual target presented in the plume of breath. Flies responding to the visual target fly from take‐off within stricter flight limits at lower ground speeds and with a significantly lower variance in flight trajectories in the horizontal plane. Once at the target, flies fly in loops principally in the horizontal plane within 40 cm of the blue sphere before descending in spirals beneath it. Successful field traps designed for G. brevipalpis take into account the strong horizontal component in local search behaviour by this species at objects. The results suggest that trapping devices should also take into account the propensity of G. brevipalpis to descend to the lower parts of visual targets.     

Behavior of Carpophilus hemipterus in a vertical flight chamber: transition from phototactic to vegetative orientation

The freeflight behavior of Carpophilus hemipterus (L.) (Coleoptera: Nitidulidae) was investigated in a vertical flight chamber to measure takeoff propensity relative to beetle age and to determine the effect of food odors on phototactic orientation. A high-pressure sodium lamp presented from above induced a phototactic flight response, especially in beetles 3–7 days old. The majority of phototactic flights lasted less than 15 min for both males (73%) and females (85%), but ranged up to 100 min. A bimodal periodicity in flight propensity was recorded during the photophase with a small peak in activity occurring 14–10 h prior to scotophase and a large 4 h peak occurring from 3 h prior to scotophase to 1 h after when the onset of scotophase would normally have occurred. Beetles maintained with water as adults usually displayed higher levels of flight activity than did beetles maintained with artificial diet.After a period of vertical flight, photokinetic and phototactic response 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 measure and an increase in horizontal displacement.When food odor (apple cider vinegar) was introduced the rate of climb dropped rapidly and beetles usually landed regardless of how long they had been in flight. When the food odor was removed, takeoff occurred and the beetle returned to its previous rate of climb. When food odor was repeatedly introduced during the same flight, there was no apparent cumulative effect, and each time it was removed, the beetle re-initiated phototactic flight. Unlike true migratory flight in which response to vegetative cues is temporarily inhibited until the insect has engaged in a period of phototactic flight, C. hemipterus flight could be better characterized as extended foraging in which phototactic flight is readily interrupted by encounters with food odor.

---

Résumé Le comportement de vol libre de C. hemipterus L. a été examiné dans une chambre à vent verticale pour déterminer la tendance au vol après l'émergence et observer l'influence de l'odeur d'aliments sur le vol phototactique. Une lampe à haute pression de sodium induit une réponse de col phototactique, qui débute le 3^e jour et reste puissante jusqu'au 8^e jour. La majorité des vols phototactiques duraient moins de 15 pour les mâles (73%) et les femelles (85%), mais pouvait se prolonger jusqu'à 100. Les femelles nourries sur régime artificiel présentaient la plus forte proportion de vol dépassant 35. Cependant, les adultes maintenus exclusivement en présence d'eau ont présenté un niveau d'activité de vol encore supérieur. Une tendance au vol à périodicité quotidienne bimodale a été notée avec un petit pic d'activité à 14–10 heures avant la scotophase et un grand pic durant 4 heures, de 3 heures avant la scotophase à une heure après le début de la scotophase.Après une période de vols verticaux, les réactions photocinétiques et phototactiques ont diminué, et l'instabilité des vols augmenté comme en a témoigné la diminution du taux total d'ascensions et l'accroissement de la variabilité de ce paramètre et des déplacements horizontaux. L'introduction d'odeurs d'aliments pendant le vol phototactique provoque une diminution immédiate du taux d'ascension et conduit généralement à un atterrissage indépendamment du temps antérieur de vol. Quand l'odeur était supprimée le décollage avait lieu et l'insecte retrouvait sont taux antérieur d'ascension. Quand la même odeur d'aliment a été réintroduite à répétition pendant le même vol, il n'y a pas eu d'effets cumulatifs apparents. Par opposition avec d'autres insectes présentant un véritable comportement migrateur pour lesquels la désinhibition des réactions végétatives ne se produit qu'après une longue période de locomotion continue, le vol de C. hemipterus est mieux caractérisé comme un comportement de prospection pour lequel les aliments inhibent immédiatement la dispersion.

     

Flight Speed of Tethered Reticulitermes flavipes (Kollar) (Isoptera: Rhinotermitidae) Alates

Alates of the Eastern subterranean termite, Reticulitermes flavipes (Kollar) were collected over two flight seasons (2002 and 2004) and flown on flight mills. Data were collected to test if alate mass, colony origin, or gender influenced flight speed. Flight speed ranged from 3.14 to 69.12 cm s⁻¹ and the maximum distance flown by an alate was 458.3 m. Alate mass (P = 0.9406), gender (P = 0.3976), colony origin (P = 0.1244), and the interaction of gender and colony (P = 0.7093) did not significantly influence flight speed. Additionally, an electronic counting device was used to provide instantaneous flight speeds and allowed flight speed to be modeled during acceleration, cruising, and deceleration periods of flight. Mean (±SEM) flight speeds in 2004 were 20.64 (±2.21) cm s⁻¹ (n = 13) for males and 17.76 cm s⁻¹ (n = 1) for the single female flown, falling within the range of the 2002 values.     

The activity of pleurodorsal muscles during flight and at rest in the moth Manduca sexta (L.)

In the moth Manduca sexta, the paired mesothoracic flight steering muscle II PD2m takes part in the generation of the flight rhythm and is spontaneously active in the non-flying animal. This spontaneous activity is modulated by optomotor stimuli and directionally selective. The directional response characteristics are analyzed. Another spontaneously active steering muscle pair, the III PD2c, is situated in the metathorax. The activities of this pair and of a third muscle pair, the III PD3 are also influenced by visual stimulation.The responses of all 6 muscles to optomotor stimuli which simulate the flight situations yaw, roll, thrust and lift are analyzed. Each situation elicits a unique pattern of activation/deactivation within this set of muscles. The activity pattern in non-flying animals allows the prediction of flight steering mechanisms such as changes of wing area in flight turns and provides a useful basis for the analysis of visuo-motor pathways.     

How locusts separate pattern flow into its rotatory and translatory components (Orthoptera: Acrididae)

The ability of desert locusts,Schistocerca gregaria, to separate pattern flow within the lateral visual fields into its rotatory and translatory components was studied in tethered flight under open-loop conditions. The optomotor turning behavior results from the sum of compensatory steering and upwind/downwind turning induced by the rotatory and translatory component of pattern flow, respectively. Thereby, the analysis of the visual stimulus is supposedly achieved by linear binocular interaction, i.e., by summation and subtraction of the optomotor effectiveness of the pattern flow on either side. Our results indicate that, in addition, locusts take into account the relative contribution of the rotatory and the translatory stimulus component to the sum total of pattern flow. This yields a factor which modifies the gain of the control loop of either of the response components to give a nonlinear response. It results in a weakening of the behavior upon stimuli composed of rotatory and translatory components. We discuss our results as an adaptation by which an animal avoids inappropriate behavior upon ambiguous stimulus situations.