The daily onset of flight in the crepuscular dung beetle Onitis alexis

The role of light intensity and temperature in determining the onset of flight in the crepuscular dung beetle Onitis alexis Klug (Coleoptera: Scarabaeidae) was examined. Flight under natural light was highly synchronized, with two-thirds of the beetles that flew flying over a period of 10–12 min. In six flights on different days, the mean time of onset varied by up to 13 min, but mean onset occurred at fixed light intensity. Absolute light intensity therefore appears to be a vital cue in determining flight onset. Mean onset remained at this intensity when dusk was advanced artificially by up to about 8 min. However, when dusk was brought further forward, mean flight occurred at lower intensities and onset of flight took place over a longer period. This is interpreted as an overlapping of the period of light intensities suitable for flight with the circadian rhythm that brings the beetles to the surface. No beetles flew when kept under constant bright light or in the dark during the dusk period. Under conditions of constant dusk, the beetles appeared uncoordinated and, although the median time of onset of flight was only 3 min later than in the control flight, onset of flight was spread out over a much longer period. At soil temperatures of 20–22 °C, over 90% of the beetles flew. This percentage decreased with decreasing temperature, and less than 10% flew at temperatures of 16–17 °C.

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L'incitation quotidienne au vol chez e bousier crépusculaire Onitis alexis Klug (Col. Scarabaeidae)

Résumé L'examen a porté sur le rôle de l'intensité lumineuse et de la température sur l'incitation au vol chez Onitis alexis. Le vol en lumière naturelle est fortement synchronisé, avec les deux tiers des adultes qui s'envolent en 10–12 min. Sur six vols pour différents jours, le moment moyen d'envol variait de 13 min, mais l'envol moyen avait lieu à une intensité lumineuse déterminée. La valeur absolue de l'intensité lumineuse paraît ainsi un signal crucial dans la détermination et l'incitation au vol. Le moment d'envol se maintient à cette intensité quand le crépuscule est artificiellement avancé jusqu'à 8 min environ. Cependant, quand le crépuscule est rendu encore plus précoce, l'envol moyen se produit à des intensités plus basses et est étalé. Ceci peut être interprété comme un chevauchement de la période des intensités lumineuses favorables à l'envol avec le rythme circadien qui conduit les bousiers à la surface. Aucun adulte ne vole quand il y a maintien de lumière constante ou d'obscurité à l'heure du crépuscule. En présence de crépuscule constant, les réponses sont hétérogènes, et, bien que le moment médian d'envol ne soit retardé que de 3 min, par rapport aux témoins, l'incitation à l'envol est étalée sur une période plus longue. Avec des températures au sol de 20–22 °C, plus de 90% des adultes s'envolent. Le pourcentage diminue avec la température, et moins de 10% s'envolent à 16–17 °C.

     

Daily flight activity of moths in the continuous daylight of the arctic summer

The daily onset of flight and the lime of activity of moths were studied at an arctic and a subarctic locality in midsummer under natural light conditions but with all other factors kept constant. The daily variation of light intensity is much smaller than at temperate latitudes, and the illumination is continuously at levels that normally inhibit the activity of moths. In spite of this, the investigated species showed a distinct daily periodicity with the activity occurring at about the same time of day as in the same or related species from lower latitudes. It is suggested that this is the result of a process of acclimatization to high light intensities.
A number of species show a diurnal activity pattern, and it is suggested that this is connected with their high temperature requirements. In the field, Anarta zetterstedti Staud. thermoregulates by settling frequently on dark rocks which can reach high temperatures when the sun is shining. This species can not fly unless its body temperature is above 30°C and it prefers an ambient temperature of about 36°C.     

Variability in odor-modulated flight by moths

Based on previous studies of odor-modulated flight where track parameter data was lumped and averaged, the speed and orientation of the moths' movement along their flight tracks have been said to be controlled to maintain certain “preferred” values. The results from our fine-scaled analysis of this behavior show that none of the track parameters typically measured are held constant. The moths' speed along the flight track is modulated substantially and predictably: fastest along the straight legs and slowest around the turns. In addition, about half of the individuals studied progressively reduced the peak speed along the straight legs as they approached the pheromone source. While most of the track legs between the turns were directed upwind, their orientations were widely distributed, indicating no preferred direction. Small fluctuations of orientation along some straight legs suggest corrective maneuvers to stabilize flight direction about an internal set point. The visual inputs hypothesized to control steering and speed, transverse and longitudinal image flow, changed continuously during upwind flight in pheromone, but no regular relationship between them was observed. We found that the orientation of the longitudinal body axis and the direction of thrust (course angle) were only rarely coincident during upwind flight to the odor source, suggesting that moths receive sensory input which differs quantitatively from that calculated by conventional methods. Our results strongly suggest that the long-accepted hypothetical mechanisms of control for this behavior do not operate in the manner in which they have been proposed. Accepted: 11 July 1997     

Lipid utilization during sustained flight of moths

Tethered moths were flown to exhaustion. In Spodoptera frugiperda flown for at least 16 hr and in Heliothis zea flown for at least 24 hr, the lipid content was considerably reduced. Triglycerides accounted for almost all of this reduction. In general, exhaustion was reached before the depletion of triglycerides. Exhausted moths with a triglyceride content of less than 2 mg also showed a greatly reduced diglyceride level.     

Analysis of zigzagging flight in moths: a correction

In 1978 we reported the results of an analysis of the zigzagging behaviour of male Plodia interpunctella flying up a plume of sex pheromone (Marsh et al. , 1978). Since then we have discovered that, owing to two technical faults, we used an incorrect time base in analysing the videotape records of the moths' tracks. The original tapes have now been re-analysed and a full revision paper is being prepared which shows that only one important conclusion must be changed. Meanwhile that incorrect conclusion has been cited at least twice (Schöne, 1980, p.236; Murlis & Jones, 1981) so we here summarize the correction to be made.     

Radar observations of moths migrating in a nocturnal low-level jet

Abstract. 1. Radar observations of insects migrating at night over central-western New South Wales have detected an instance of migration in a low-level wind jet.
2. From the characteristics of the radar echoes, and from the catches obtained in traps at ground level and at the altitude of migration, the migrants can be identified as noctuid and pyralid moths of a number of different species.
3. The migration, which was in a downwind direction, started at dusk and ended at about dawn. During the period immediately before first light, a large proportion of the migrants were concentrated into a 100m deep layer at an altitude of about 250m; this layer had not been present during the first half of the night.
4. The boundary layer wind profile at dawn exhibited a clear low-level jet structure, with a wind maximum between 100 and 300m, and strong shear in the wind direction below 300m. A strong surface temperature inversion, but not a wind-speed maximum, had been present the previous evening.
5. The formation of the layer concentration in the upper part of the jet may be accounted for in terms of previously described responses of nocturnally migrating insects to a surface temperature inversion. It is not therefore necessary to assume that the migrants were responding specifically to the presence of a wind-speed maximum.     

The use of hedgerows as flight paths by moths in intensive farmland landscapes

Linear boundary features such as hedgerows are important habitats for invertebrates in agricultural landscapes. Such features can provide shelter, larval food plants and nectar resources. UK butterflies are known to rely on such features, however their use by moths is understudied. With moth species suffering from significant declines, research into their ecology is important. This research aimed to determine whether UK moth species are using hedgerows as flight paths in intensive farmland. The directional movements of moths were recorded along hedgerows at 1, 5 and 10 m from the hedgerow face. The majority of moths recorded within the study were observed at 1 m from the hedgerow (68 %), and of these individuals, 69 % were moving parallel in relation to the hedge. At further distances, the proportion of parallel movements was reduced. These results suggest that hedgerows may be providing sheltered corridors for flying insects in farmland landscapes, as well as likely providing food plants and nectar resources, emphasising the importance of resource-based approaches to conservation for Lepidoptera.     

Behaviourally mediated crypsis in two nocturnal moths with contrasting appearance

The natural resting orientations of several species of nocturnal moth on tree trunks were recorded over a three-month period in eastern Ontario, Canada. Moths from certain genera exhibited resting orientation distributions that differed significantly from random, whereas others did not. In particular, Catocala spp. collectively tended to orient vertically, whereas subfamily Larentiinae representatives showed a variety of orientations that did not differ significantly from random. To understand why different moth species adopted different orientations, we presented human subjects with a computer-based detection task of finding and ‘attacking’ Catocala cerogama and Euphyia intermediata target images at different orientations when superimposed on images of sugar maple (Acer saccharum) trees. For both C. cerogama and E. intermediata, orientation had a significant effect on survivorship, although the effect was more pronounced in C. cerogama. When the tree background images were flipped horizontally the optimal orientation changed accordingly, indicating that the detection rates were dependent on the interaction between certain directional appearance features of the moth and its background. Collectively, our results suggest that the contrasting wing patterns of the moths are involved in background matching, and that the moths are able to improve their crypsis through appropriate behavioural orientation.     

Patterns of daily flight activity in onitine dung beetles (Scarabaeinae: Onitini)

Different species of African dung beetles emerge from the soil at characteristic times of the day to fly and colonize the freshly-deposited dung of mammalian herbivores. Onitine dung beetles in their natural habitat displayed one of five distinctive daily flight behaviours: dusk crepuscular (Onitis alexis Klug, O. caffer Boheman, O. fulgidus Klug, O. tortuosus Houston, O. vanderkelleni Lansberge, O. westermanni Lansberge); dusk/dawn crepuscular (O. pecuarius Lansberge and O. viridulus Boheman); dusk/dawn crepuscular and nocturnal (O. aygulus (Fabricius), O. mendax Gillet, O. uncinatus Klug); late afternoon-dusk and dawn-early morning [Heteronitis castelnaui (Harold)]; or diurnal flight activity [O. belial (Fabricius), O. ion (Olivier)]. These diagnostic daily flight behaviours span a light intensity range of over 6 orders of magnitude and have been retained in selected species introduced into Australia. Ambient light intensity appears to be the primary determinant of the daily flight period in onitine dung beetles. Because the dung of mobile herbivores is rapidly exploited by onitine species for feeding and breeding purposes, different flight behaviours result in a spatial and temporal partitioning of species in the local dung beetle community. The timing of flight may contribute to, or lead to avoidance of, competition between species which may ultimately affect colonization success. Many onitines show a strong preference for dung of specific herbivores, which may further reduce interspecific competition. All crepuscular-nocturnal species examined raised their thoracic temperatures endothermically to between 35°C and 40°C before the onset of flight. In O. aygulus the thoracic temperature excess was as large as 19.3°C. The thermal threshold below which the frequency of flight onsets drops off rapidly is about 12°C for O. aygulus and 17°C for O. alexis and O. pecuarius. Radiant loss of body heat during cool nights and dawns may explain why smaller species (<0.4 g body weight), in particular, are adapted behaviourally so that they fly only during the day or early dusk.     

Retinular fine structure in compound eyes of diurnal and nocturnal sphingid moths

Summary Retinular fine structure has been compared in the superposition compound eyes of three sphingid moths, one nocturnal, Cechenena, and two diurnal, Cephonodes and Macroglossum. Cechenena and Cephonodes have tiered retinas with three kinds of retinular cells: two distal, six regular and one basal. The distal retinular cells in Cechenena are special in having a complex partially intracellular rhabdomere not present in Cephonodes. Macroglossum lacks the distal retinular cell. In Cephonodes a unique rhabdom type, formed by the six regular retinular cells in the middle region of the retinula, is divided into three separate longitudinal plates arranged closely parallel to one another. Their constituent microvilli are consequently all nearly unidirectional. The ratio of rhabdom volume to retinular cell volume in the two diurnal sphingids is 10–27%; this is about the same as that (25%) of skipper butterflies, but significantly smaller than in the nocturnal Cechenena (60%). In the diurnal sphingids retinular cell membranes show elongate meandering profiles with septate junctions between adjacent retinular cells. From the comparative fine structure of their eyes the diurnal sphingids and the skippers would appear to be phylogenetically closely related.Supported in part by grants from Ministry of Education Japan (Special Project Research in Animal Behaviors)     

Convergent patterns of long-distance nocturnal migration in noctuid moths and passerine birds

Vast numbers of insects and passerines achieve long-distance migrations between summer and winter locations by undertaking high-altitude nocturnal flights. Insects such as noctuid moths fly relatively slowly in relation to the surrounding air, with airspeeds approximately one-third of that of passerines. Thus, it has been widely assumed that windborne insect migrants will have comparatively little control over their migration speed and direction compared with migrant birds. We used radar to carry out the first comparative analyses of the flight behaviour and migratory strategies of insects and birds under nearly equivalent natural conditions. Contrary to expectations, noctuid moths attained almost identical ground speeds and travel directions compared with passerines, despite their very different flight powers and sensory capacities. Moths achieved fast travel speeds in seasonally appropriate migration directions by exploiting favourably directed winds and selecting flight altitudes that coincided with the fastest air streams. By contrast, passerines were less selective of wind conditions, relying on self-powered flight in their seasonally preferred direction, often with little or no tailwind assistance. Our results demonstrate that noctuid moths and passerines show contrasting risk-prone and risk-averse migratory strategies in relation to wind. Comparative studies of the flight behaviours of distantly related taxa are critically important for understanding the evolution of animal migration strategies.     

Flight duration and flight muscle ultrastructure of unfed hawk moths

Flight muscle breakdown has been reported for many orders of insects, but the basis of this breakdown in insects with lifelong dependence on flight is less clear. Lepidopterans show such muscle changes across their lifespans, yet how this change affects the ability of these insects to complete their life cycles is not well documented. We investigated the changes in muscle function and ultrastructure of unfed aging adult hawk moths (Manduca sexta). Flight duration was examined in young, middle-aged, and advanced-aged unfed moths. After measurement of flight duration, the main flight muscle (dorsolongitudinal muscle) was collected and histologically prepared for transmission electron microscopy to compare several measurements of muscle ultrastructure among moths of different ages. Muscle function assays revealed significant positive correlations between muscle ultrastructure and flight distance that were greatest in middle-aged moths and least in young moths. In addition, changes in flight muscle ultrastructure were detected across treatment groups. The number of mitochondria in muscle cells peaked in middle-aged moths. Many wild M. sexta do not feed as adults; thus, understanding the changes in flight capacity and muscle ultrastructure in unfed moths provides a more complete understanding of the ecophysiology and resource allocation strategies of this species.     

Varying the length of dim nocturnal illumination differentially affects the pacemaker controlling the locomotor activity rhythm of Drosophila jambulina

Photic entrainment of animals in the field is basically attributed to their exposure to the dimly lit nights flanked by the dawn and dusk twilight transitions. This implicates the functional significance of the dimly lit nights as that of the twilight transitions. Recently, the authors have demonstrated that the dimly lit night at 0.0006 lux altered the attributes of the circadian rhythm of locomotor activity of Drosophila jambulina. The present study examined whether the durations of such dimly lit nights affect the entrainment and free-running rhythmicity of D. jambulina. Flies were subjected for 10 days to two types of 24-h lighting regimes in which the photophase (L) was at 10 lux for all flies but the scotophase, which varied in duration from 9 to 15 h, was either at 0 lux (D phase) for control flies or 0.0006 lux (the artificial starlight or S phase) for experimental flies. Thereafter, they were transferred to constant darkness (DD) to compare the after-effects of the dimly lit nights on the period (τ) of free-running rhythm in DD with that of the completely dark nights. Control flies were entrained by all LD cycles, but the experimental flies were entrained only by five LS cycles in which the duration of the S phases ranged from 10 to 14 h. The two LS cycles with very short (9 h) and long (15 h) S phases rendered the flies completely arrhythmic. Control flies started activity shortly before lights-on and continued well after lights-off. The experimental flies, however, commenced activity several hours prior to lights-on but ended activity abruptly at lights-off as the result of a negative masking effect of nocturnal illumination. Length of the midday rest was considerably shorter in the control than in the experimental flies in each lighting regime. The active phase in the control flies was predictably shortened; nonetheless, it was invariable in the experimental flies as the nights lengthened. Transfer from lighting regimes to DD initiated robust free-running rhythmicity in all flies including the arrhythmic ones subjected to LS cycles with 9 and 15 h of scotophases. The τ was profoundly affected by the nocturnal irradiance of the prior entraining lighting regime, as it was always shorter in the experimental than in the control flies. Thus, these results indisputably demonstrate the changes in fundamental properties of the circadian pacemaker of D. jambulina were solely attributed to the extremely dim nocturnal irradiance. This strain of D. jambulina is entrained essentially by the dimly lit natural nights, since it is never exposed to the prevailing photic cues such as the twilight transitions or bright photoperiod, owing to the dense vegetation of its habitat.     

The effect of temperature on the flight and mating of some moths in the genus Spilosoma

Patterns of flight activity have been recorded for caged male moths of Spilosoma lubricipeda and S. lutea under naturally changing light intensity. Male flight activity recorded in controlled-temperature cabinets ceased at about 2°. Mating success in S. lubricipeda declined with temperature, but moths mated at 2°. No results on mating were obtained for S. lutea because this species did not mate regularly in captivity.

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Zusammenfassung Das Flugaktivitätsmuster gekäfigter Falter von Spilosoma lubricipeda (L.) und S. lutea (Hufn.) wurde mit einem akustischen Verfahren ermittelt. Bei natürlichem Licht-Dunkel-Wechsel was S. lubricipeda am regelmäßigsten zwischen 23 und 02 Uhr Britischer Sommerzeit aktiv, während S. lutea zwei Gipfel-nach der Abend-und vor der Morgendämmerung—aufwies. In Käfigen mit einstellbarer Temperatur sank die Flugaktivität der Männchen unter etwa 2° auf null ab. Auch der Paarungserfolg nahm in kleinen Käfigen bei S. lubricipeda mit der Temperatur ab. Einige Falter paarten sich noch, wenn die Temperatur im Dunkeln 2° und im Licht 10° betrug, jedoch erhöhte sich dann die Anzahl der Nächte vor der Paarung stark. Die Paarungszeit wurde mit Hilfe von Sequenzphotographie ermittelt. Alle beobachteten Kopulationen geschahen im Dunkeln. Bei S. lutea konnten keine Ergebnisse über das Paarungsverhalten ermittelt werden, weil diese Art in Gefangenschaft nicht regelmäßig zur Paarung schreitet.

     

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.     

Pheromonotropic and pheromonostatic activity in moths

Pheromone biosynthesis in many species of moths requires a pheromonotropic neurosecretion, the pheromone biosynthesis activating neuropeptide (PBAN), from the brain-subesophageal ganglion-corpora cardiaca complex. Some investigators suggest that PBAN is released into the hemolymph and acts directly on sex pheromone glands (SPG) via a Ca⁺⁺/calmodulin-dependent adenylate cyclase. Others suggest, however, that PBAN acts via octopamine that is released by nerves from the terminal abdominal ganglion innervating the SPG. These findings suggest that there are controversies on the mode of action of PBAN and other pheromonotropic factors, sometimes even within the same species. Mating in many insects results in temporary or permanent suppression of pheromone production and/or receptivity. Such a suppression may result from physical blockage of the gonopore or deposition of pheromonostatic factor(s) by the male during copulation that result in suppressed pheromone production and/or receptivity in females either directly or by a primer effect. In several species of insects, including moths, a pheromonostatic factor is transferred in the seminal fluid of males. Similar to the controversies associated with the pheromonotropic activity of PBAN, sometimes even within the same species, there appear to be controversies in pheromonostasis in heliothines as well. This paper reviews these conflicting findings and presents some data on pheromonostatic and pheromonotropic activity in Heliothis virescens that support and conflict with current information, raising further questions. Answers to some of the questions are partly available; however, they remain to be answered unequivocally. © 1994 Wiley-Liss, Inc.     

A pulsed cloud of sex pheromone elicits upwind flight in male moths

ABSTRACT. Male oriental fruit moths do not fly upwind in a continuous uniform cloud of pheromone, but readily do so when the cloud is pulsed at 1 or 0.5/s or when a plume from a point source of pheromone is placed within the continuous cloud. It is suggested that males of moth species that require such fluctuating pheromone stimulation for upwind flight will normally receive it from a filamentous, point-source-produced plume. However, we hypothesize that upwind progress may cease close to the source due to excessively high emission rates or inappropriate blend ratios, when fluctuating sensory output becomes attenuated, despite higher actual molecular concentration fluctuations.     

Simultaneous monitoring of flight and oviposition of individual velvetbean caterpillar moths

ABSTRACT. A 'pivot' flight actograph was combined with a rolling oviposition surface to characterize the flight and oviposition behaviour of velvetbean caterpillar moths, Anticarsia gemmatalis Hubner. Tethered, caged control females laid significantly more eggs that those flown on the actograph. Mated females laid more eggs than unmated ones. However, mating did not affect longevity nor fight frequency and duration. Laboratory-reared and wild-type females also did not differ signficantly in longevity and flight. Both laboratory and wild mated females laid most of their eggs during the first 7 days whereas unmated ones delayed their oviposition. None of the female types produced a definite hourly, daily or lifetime pattern in flight frequency or duration. Of the 7672 recorded flights, about 3% were greater than 0.5 h. 'Long' flights (>0.5h) were made by some females before oviposition, as in colonization migration, but most interspersed flight with oviposition, as in extended search migration.     

Appetitive flight patterns of male Agrotis segetum moths over landscape scales

An analysis is presented of the first harmonic radar studies of pheromone-plume locating flights of male Agrotis segetum moths over distances of up to 500 m. Upon release most moths flew in a direction having a downwind component. The first significant changes in flight orientations occur in the immediate vicinity of a pheromone source. Moths that were initially flying downwind change course and start flying crosswind whilst those that initially flew crosswind change course and start flying upwind. It is shown that such behaviour is consistent with the adoption of an effective plume-location strategy, and conditions are identified when downwind flights would be more advantageous than crosswind ones. Additionally, some of the complex flight patterns that can arise at later times are shown to be compatible with the adoption of an optimal biased scale-free (Lévy-flight) searching strategy. It is found that disruptive doses of sex pheromone can have a marked influence upon male moth flight patterns.