Downwind migration of the African army worm moth, Spodoptera exempta, studied by mark-and-capture and by radar

Abstract. 1. About 166,000 African armyworm moths, Spodoptera exempta (Walk.), were marked at an emergence site near Nairobi when they fed at night on trees baited with dyed molasses.
2. Six marked moths were captured in pheromone traps, including one at 90 km after flying for only one night, and another at 147 km.
3. Moth flight trajectories deduced from radar and from marking showed that migration was downwind.
4. During migration, moths become dispersed; hence the high densities that lead to outbreaks must be produced by concentration.
5. Some moths were ready to mate on the same night they completed their long-distance flight.     

Pheromone-mediated optomotor anemotaxis and altitude control exhibited by male oriental fruit moths in the field

Abstract. In the field over short grass, pheromone-stimulated oriental fruit moth males, Grapholita molesta (Busck), flying under high windspeeds tended to steer courses more into the wind and to increase their airspeeds compared with those flying in low windspeeds.Thus, optomotor anemotaxis enabled the males to steer relatively consistent upwind track angles and to maintain an upwind progress of between c. 50–100 cm/s despite variable wind velocities.Zigzagging flight tracks were observed at both 10 m and 3 m from the source, as were tracks with no apparent zigzags.Transitions from casting to upwind flight or vice-versa were observed.The durations of the intervals between reversals during both upwind zigzagging flight and casting were consistent with those observed in previous wind-tunnel experiments.The control of altitude was more precise during upwind zigzagging flight than during casting.In general, the side-to-side deviations in the tracks were greater than the up-and-down deviations, with both the side-to-side and vertical distances and their ratios being consistent with previous wind-tunnel studies of pheromone-mediated flight.One difference between the field and laboratory flight tracks was that males in the field exhibited much higher airspeeds than in the wind tunnel.Males occasionally were observed to progress downwind faster than the wind itself, and further analysis showed that they were steering a downwind course in pheromone-free air following exposure to pheromone, which is the first time this has been recorded in moths.We propose that such downwind flight may aid in the relocation of a pheromone plume that has been lost due to a wind-shift, by enabling the moth to catch up to the pheromone as it recedes straight downwind away from the source.     

Onset and spread of an African army worm upsurge

Abstract. 1. Onset and spread of the severe outbreaks of African armyworm, Spodoptera exempta (Walk.), over Ethiopa, Kenya, Tanzania and Burundi in late 1984 have been analysed in relation to trap and weather records.
2. Although first outbreaks in each country appeared progressively further south, winds on the best estimated dates of moth concentration and egg laying blew from directions precluding moth movements between them.
3. Such independently developing outbreaks are called 'primary' to distinguish them from any 'secondary' outbreaks that may develop from them.
4. Parent moths giving rise to all seven areas of primary outbreaks were derived from low-density populations that had persisted through the dry season, probably near the coast of East Africa.
5. Primary outbreaks developed on the south-eastern sides of individual rainstorms over the highlands, most likely because windborne moths were concentrated there by convergent winds.
6. Of the secondary outbreaks within Kenya, Tanzania and Burundi, most were derived from only one area of primary outbreaks in Kenya, which were therefore critical for effective control of spread; the paucity of other secondaries was presumably due to a lack of timely rainstorms or other concentrating mechanisms.     

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.     

Changes in distribution of an archaic moth, Micropterix calthella, in St Petersburg, Russia, between 1989 and 2005

Aim  This work aimed to assess changes in the number of suitable habitats and habitat occupancy by Micropterix calthella (L.) moths (Lepidoptera, Micropterigidae) in the city of St Petersburg between 1989 and 2005.
Location  The city of St Petersburg, Russia.
Methods  The study compares results of the survey conducted on 9–12 June 2005 with data collected in 1989 and is based on the assessment of the quality and occupancy of 103 habitats that were found potentially suitable for M. calthella in 1989. If habitats contained wet microsites with undisturbed litter and dense field layer vegetation with a high abundance of flowering Ranunculus sp., they were considered potentially suitable for M. calthella ; in these habitats, moths were searched for on flowers of Ranunculus – visually and/or by extensive sweep-netting.
Results  Both the number of habitats suitable for M. calthella and the number of habitats occupied by this species decreased since 1986 from 103 to 72 and from 58 to 34, respectively. The disappearance of habitats was primarily due to the building of residential blocks within the city (16 sites) and railway renovation (10 sites), while changes in habitat management, primarily in parks and recreation zones (five sites), were less important. The average distance from the city centre to the nearest population of M. calthella increased from 8.7 ± 1.5 to 12.9 ± 3.0 km (mean ± SE).
Main conclusion  The data for 2005 fit the prediction that M. calthella moths, which are unable to re-colonize potentially suitable habitats due to their low migratory ability, will disappear from the city. At the present rate of extinction, this process may take some 20–30 years to complete (or nearly complete).     

Oviposition preferences in relation to larval growth rates and survival in the pine beauty moth, Panolis flammea

Abstract. 1. Adult female pine beauty moths, Panolis flammea (D & S), when given a choice of whole plants or needle pairs of four provenances of Lodgepole pine, Pinus contorta (Douglas), laid most eggs on that provenance on which the larvae attained their greatest growth rates.
2. When presented with a greater number of Lodgepole pine provenances and Pinus sylvestris L, P.flammea oviposition preferences reflected the trade-off between growth rate and survival.
3. There is some evidence to suggest that the moths are responding to the monoterpene composition of the plants.
4. Adult moths showed no preference for Lodgepole pine needles of a range of ages (1–4 years), ovipositing uniformly on all age classes.     

Close-range behaviour of male pea moths, Cydia nigricana, responding to sex pheromone re-released via the substrate

The close-range orientation behaviour of male pea moths, Cydia nigricana (F.) (Lepidoptera: Tortricidae), to a substrate contaminated with synthetic sex pheromone was studied in the field. The substrate was a sheet of polypropylene grass on a 1 m diam arena, on the upwind edge of which a pheromone trap had been placed previously for 1 h. After removal of the trap, moths continued to be attracted to the arena and to the vacated trap position. Video-recorded tracks showed that the moths behaved anemotactically whilst on the arena. When the arena was revolved so that the vacated trap position was on the downwind edge, moths continued to fly upwind on the arena, even though they were flying away from the original trap position and down a concentration gradient.     

AUTUMN MIGRATION OVER PUERTO RICO AND THE WESTERN ATLANTIC: A RADAR STUDY

Migration over Puerto Rico was recorded by time-lapse filming of the display of a long-range surveillance radar on 108 days and 93 nights in the period 13 August-13 November in 1970 and 1971. Altitudes were recorded on nine days.
Passerine movements to the E-SSE from Puerto Rico and Hispaniola occurred on many nights. Their density was greatest between late September and mid-November, especially when the easterly Trade Winds abated. Shorebirds and passerines moving SE, S and SW on a broad front approached from over the ocean intermittently throughout the period, with largest numbers from mid-September to early November. Arrivals occurred at all hours of the day and night. Many were at altitudes of 3 to 6 km, including some believed to be passerines. Birds that flew high by day descended after sunset. Many continued southwards over or past Puerto Rico.
The tracks of birds arriving from over the ocean were correlated with wind direction, but were rarely downwind. The variance in tracks was slightly greater on cloudy than on clear nights, but there was no evidence of serious disorientation in any situation. There was a negative correlation between the density of arrival from the north and the easterly component of the wind. This, together with evidence that the eastern edge of most passerine flights was near Puerto Rico, suggests the existence of lateral wind drift. The relationships of estimated headings to wind and to tracks also suggested that the birds were drifted, contrary to the situation in spring.
The shorebirds and passerines arriving from the NW-NE were concluding overwater flights of 2000–3000 km from SE Canada and the eastern U.S.A., often along clockwise-curved routes. Some that continued to South America flew 4000 km or more non-stop.     

Wind as a factor influencing flower-visiting by Hadena bicruris (Noctuidae) and Deilephila elpenor (Sphingidae)

Abstract. 1. In a low-speed wind tunnel, male as well as female moths of Hadena bicruris responded to floral odours with positive anemotaxis. Hitherto, such orientation has only been demonstrated for male moths in response to pheromones.
2. H.bicruris had a maximum flight speed of 4.5–5.4ms^-1 and stopped its flower visiting at a wind speed of 2.5–2.8 m s^-1.
3. Deilephila elpenor had a similar maximum flight speed (4.5— 5.1 ms^-1), but it continued visiting flowers up to wind speeds of 3.0–5.0 ms^-1.
4. Apart from mechanical resistance during flight and flower visits, wind might have adverse effects on the energy budget and on evaporative water loss.     

SPRING MIGRATION OVER PUERTO RICO AND THE WESTERN ATLANTIC, A RADAR STUDY

Migration over Puerto Rico was recorded by time-lapse filming of the display of a long-range surveillance radar on 40 days and 37 nights in the period 2 March-29 May 1971. Moderate density movements occurred every night; low density movements occurred on most days. Many birds, primarily passerines, took off from Puerto Rico each evening at 20–45 minutes after sunset.
Almost all birds flew to the west, NW or north. Birds were seen approaching from the direction of the Windward Islands and Venezuela, over Puerto Rico, and departing towards the Bahamas and eastern coast of the U.S. Uni- and multivariate analyses showed that the number of birds departing W-N each evening was positively correlated with following winds.
There is less night-to-night variation in the amount of migration at Puerto Rico than in eastern North America. However, this is apparently the result of less variable weather in the tropics, not the result of any lesser degree of meteorological selectivity by the migrants.
The tracks of the birds were correlated with wind direction. Birds moved WNW-NW with NE side winds but NW-NNW with SE following winds. The tracks were rarely exactly downwind. The variance amongst the directions of individual birds at any given time was usually small and not correlated with cloud cover or magnetic disturbances. The estimated headings of the birds varied from day to day in a pattern suggesting adjustment of headings to compensate at least partially for lateral wind drift.
In autumn many birds approach Puerto Rico from the north or even east of north; in spring few birds moved in the opposite directions. This difference in routes takes advantage of prevailing wind patterns.     

Mating disruption in Agrotis segetum monitored by harmonic radar

The long-range, pheromone-mediated, flight behaviour of male moths under natural and mating disruption conditions was monitored by means of harmonic radar. Individual male turnip moths, Agrotis segetum (Denis & Schiffermüller) (Lepidoptera: Noctuidae), tagged with radar transponders, were released and tracked in plots with or without disruptive doses of sex pheromone. In addition, male attraction to pheromone-baited traps and mating of calling females in treated and untreated plots was investigated. High doses of a four-component pheromone blend reduced trap catch by 79% and mating of females by 62% when compared with control plots in pre-radar experiments. Surprisingly, this effect was not associated with any pronounced differences in flight behaviour of males between a treatment and a control plot as revealed by harmonic radar recordings. In total, 20 flight tracks from a control plot and 22 flight tracks from a treatment plot were analysed. Moths could be followed for up to 77 min, corresponding to a track length of 7350 m. Mean ground speed ranged from 0.7 m s^–1 to 5.4 m s^–1. There was a strong trend (P = 0.06) for a greater number of male orientations to traps from downwind in the control field compared to the treatment field. Many flight tracks were fragmented due to radar shadow. Advantages and constraints using harmonic radar to study the pheromone-mediated flight behaviour of nocturnal moths are discussed.     

Radar observations of the spring migration into northeastern China of the oriental armyworm moth, Mythimna separata, and other insects

Abstract. 1. The spring migration of the oriental armyworm moth, Mythimna separata (Walker), and other insects into northeastern China was observed by radar at a site in central Jilin province. Samples of the migrants were obtained in a net flown from a kite, and M.separata populations in the surrounding region were monitored with a trap network. 2. The radar regularly detected echoes which were of the type characteristic of large insects, and three out of four large insects in the aerial samples were noctuid moths, including one M.separata. Catches of armyworm moths in the regional trap network peaked during the period of radar observations. 3. Migration occurred at night. It commenced with a take-off flight at dusk and generally continued until dawn, with numbers often being highest around midnight. Most migration took place at altitudes below 500 m, with strong layer concentrations forming at 200–400 m during the middle part of some nights. 4. Migration was approximately downwind. The net movement was overwhelmingly to the northeast because southwesterly winds occurred most frequently and were relatively strong, and because migration was more intense and prolonged on these winds. Orientation tended to be to the left of the downwind direction, and was most often to the north or northeast. 5. Migration into northeastern China was accomplished in a series of night-time movements of 100–300 km rather than by a single non-stop flight. 6. The net movement of insects towards the northeast was sufficient to produce the observed regional infestation of M.separata moths. Oviposition by immigrant armyworm moths in vulnerable crops would have been at a level where economically significant damage would be expected from the resulting larval population. 7. Analogous springtime migrations of noctuids leading to temporary colonizations of habitats at higher latitudes occur in other continents. Such colonizations may be unproductive if, as appears possibly the case for northeastern China, prevailing winds later in the season are generally unfavourable for a return migration towards overwintering areas at lower latitudes.     

Host tree influences on the dispersal of first instar gypsy moths, Lymantria dispar (L.)

Abstract. 1. In laboratory tests, first instar gypsy moths attempted dispersal more frequency when exposed to less acceptable foliage.
2. First instars from small eggs attempted dispersal less frequently than larvae from large eggs when exposed to foliage from highly acceptable or marginally acceptable hosts. Dispersal rates of larvae from medium sized eggs were intermediate.
3. These results (1–2) confirm and expand upon the findings of Capinera & Barbosa (1976).
4. In the field, data on the relative densities of larvae on different host species support the conclusion that the frequency of dispersal attempts is inversely related to host acceptability.
5. The implications of these findings for the population dynamics of the gypsy moth are discussed.     

Effects of sex pheromone in electrostatic powder on mating behaviour by Lobesia botrana males

Abstract:  In laboratory trials, mating behaviour of males of Lobesia botrana Den. and Schiff. (Lep., Tortricidae) was investigated after treatment with an electrostatically chargeable powder, Entostat^TM. Male moths were powdered with either blank Entostat or Entostat containing sex pheromone. Significantly more Entostat adhered to L. botrana males when sex pheromone was added to the powder compared with blank Entostat. Powdering male moths with Entostat, with or without sex pheromone, caused a significant reduction in antennal response when antennae were placed 2 cm away in downwind direction, while there was little effect when antennae were placed 25–100 cm from the EAG in downwind direction. In a flight study, powdering males of L. botrana caused significant increase in time before flight initiation and reduction in proportion of males making contact with calling females compared with untreated males. In a mating experiment in Petri dishes (to minimize required search time to locate female), significantly fewer females mated successfully (based on dissection of bursa copulatrix) when males had been treated with pheromone-loaded powder. Overall, powdering males of L. botrana caused considerable suppression of mating behaviour on various levels, and these suppressing effects were increased after adding sex pheromone to Entostat.     

Magnetic compass sense in the large yellow underwing moth, Noctua pronuba L.

Many animals are now known to have a magnetic sense which they use when moving from one place to another. Among insects, this sense has only been studied in any detail in the honey bee. A role for a magnetic compass sense in cross-country migration has not so far been demonstrated for any insect. On clear nights the large yellow underwing moth, Noctua pronuba, has been shown to orientate by both the moon and the stars. However, radar studies have shown moths to be well-oriented on overcast nights as well as clear nights. We report here that when large yellow underwings are placed in an orientation cage on overcast nights and the Earth's normal magnetic field is reversed, there is a corresponding reversal in the orientation of the moth. We conclude that this species makes use of the Earth's magnetic field in maintaining compass orientation on overcast nights. We also show that the preferred compass orientation to the Earth's magnetic field is the same as the compass direction that results from orientation to the moon and stars.     

Track analysis of the Mexican species of Buprestidae (Coleoptera): testing the complex nature of the Mexican Transition Zone

Aim  We analysed the geographical distributions of species of Buprestidae (Coleoptera) in Mexico by means of a panbiogeographical analysis, in order to identify their main distributional patterns and test the complex nature of the Mexican Transition Zone, located between the Nearctic and Neotropical regions.
Location  Mexico.
Methods  The geographical distributions of 228 species belonging to 33 genera of Buprestidae were analysed. Localities of the buprestid species were represented on maps and their individual tracks were drawn. Based on a comparison of the individual tracks, generalized tracks were detected and mapped. Nodes were identified as the areas where generalized tracks converged.
Results  Thirteen generalized tracks were obtained: one was restricted to the Mexican Transition Zone and five to the Neotropical region (Antillean and Mesoamerican dominions), a further two occurred in both the Nearctic region (Continental Nearctic dominion) and the Mexican Transition Zone, and a further five in both the Neotropical region (Mesoamerican dominion) and the Mexican Transition Zone. Seven nodes were identified at the intersections of the generalized tracks – in the Mesoamerican dominion (Mexican Pacific Coast, Mexican Gulf and Chiapas biogeographical provinces) and the Mexican Transition Zone (Trans-Mexican Volcanic Belt, Balsas Basin and Sierra Madre Oriental biogeographical provinces).
Main conclusions  We conclude that the geographical distribution of Buprestidae is mainly Neotropical, corresponding to the Mesoamerican dominion and the Antillean dominion of the Neotropical region, and the Mexican Transition Zone. Most of the generalized tracks and nodes correspond to the Mexican Transition Zone, thus confirming its complex nature. We suggest that the nodes we have identified could be particularly important areas to choose for conservation prioritization.     

The relationship between outbreaks, rainfall and low density populations of the African armyworm, Spodoptera exempta, in Kenya

This study has demonstrated that low numbers of African armyworms (Spodoptera exempta) (Walker) (Lepidoptera: Noctuidae) can be found throughout the year in parts of the coastal and highland regions of Kenya where there is frequent rainfall. During the study period the numbers of moths caught in pheromone traps in these regions built up during the short and long rains, and decreased dramatically during the intervening dry seasons. There was a lag of one to two months between the peaks for rainfall and moth numbers. This contrasts with the situation at sites of the seasonal outbreaks of armyworm larvae, where a sudden preceding influx of moths coincides with the rainfall. A positive correlation was found, for the long rains seasons only, between the number of armyworm outbreaks throughout the country and the peak numbers of moths in coastal and highland regions.It is suggested therefore that the peak numbers of moths trapped in the eastern highlands and coastal regions during the rainy seasons arise principally from outbreaks in the extensive seasonal grasslands. These grassland areas diminish considerably during the prolonged dry periods between the two rainy seasons, and it is only the eastern highland and coastal regions that are likely to provide suitable habitats for breeding during the dry seasons. The significance of these populations for initiating the first outbreaks of the following season is discussed.     

Behavioral strategies underlying pheromone-modulated flight in moths: lessons from simulation studies

Several mechanisms have been proposed to underlie the characteristic `zigzag' tracks produced by moths flying up an odor plume. To test which, if any, of these are capable of reproducing the animals' behavior, we constructed behavioral-level simulations. The simulations are as tightly constrained as possible by the known biology, and incorporate realistic physical effects such as air turbulence, and delays due to sensory transduction and axonal condition, to mimic the dynamics of sensory information encountered by real moths. Formulated as schemas, the models all share a common set of sensory and motor systems, but differ in the interposed control systems. We analyzed the behavior of the models with the same methods we use for real moths. Even the simplest of the models was capable of successful orientation some of the time, and of producing flight tracks similar to those of moths. Individuals which succeeded in tracking the odor plume produced average behavior not significantly different from that of real moths. As a population, however, none of the models was as successful as the moths. The best of the models had a success rate in tracking the plume of about 30%, compared to the average of 70% seen in the insects. Accepted: 25 March 1998     

Nocturnal migration of dragonflies over the Bohai Sea in northern China

Abstract.  1. A sudden increase and subsequent sharp decrease of catches of dragonflies in a searchlight trap, with Pantala flavescens Fabricius (Odonata: Libellulidae) predominating, observed at Beihuang Island in the centre of the Bohai Gulf, in 2003 and 2004, indicated a seasonal migration of these insects over the sea during the night in China. The movements were associated with the onset of fog.
2. Simultaneous radar observations indicated that the nocturnally migrating dragonflies generally flew at altitudes of up to 1000 m above sea level, with high density concentrations at about 200–300 or 500 m; these concentrations were coincident with the temperature inversion.
3. During early summer, the dragonflies oriented in a downwind direction, so that the displacement direction varied between different altitudes. In contrast, during late summer, the dragonflies were able to compensate for wind drift, even headwind drift, so as to orient south-westward no matter how the wind changed, and thus the displacement direction was towards the south-west.
4. The duration of flight, estimated from the variation of area density derived from radar data and hourly catches in the searchlight trap through the night, was about 9–10 h. The displacement speed detected using radar was ≈5–11 m s⁻¹. Therefore, the dragonflies might migrate 150–400 km in a single flight.
5. The dragonflies were thought to originate in Jiangsu province and they migrated into north-east China to exploit the temporary environment of paddy fields in early summer. Their offspring probably migrated back south during late summer and autumn.