Observations on the morphs of Macrosiphum avenae and Metopolophium dirhodum on cereals during the summer and autumn

From June to early August 1970, populations of Macrosiphum avenae and Metopolophium dirhodum on marked tillers of field barley were compared with the numbers of alatae trapped at crop height and at 12.2 m. There were always more M. dirhodum than M. avenae on the tillers. Only apterae were produced until mid-June when both alatae and apterae occurred; after mid-July only alate M. avenae were found. Until mid-June most of the flying alatae were caught at 12.2 m as they migrated from spring hosts to cereals. Thereafter, more alate M. avenae were trapped at 12.2 m than at crop level, whereas numbers of alate M. dirhodum were usually comparable at both heights. Although crop and flying populations occasionally showed temporal similarities, insufficient is known about their field distribution and the factors affecting their alate production and flight activity to interpret this relationship. In the autumn, two consecutive reproductive phases of M. dirhodum occurred on winter wheat grown in pots outdoors. Initially, apterous virginoparae and alatae, probably sexuparae, were produced, whereas only alate males appeared during the second phase. In contrast, M. avenae deposited mainly apterous virginoparae although some oviparae developed in October to lay scattered, probably infertile eggs on the tillers.     

Causes of regional and yearly variation in pea aphid numbers in eastern England

Regional variation in the number of pea aphids caught in the suction traps of the Rothamsted Insect Survey (RIS) was associated with the proportion of each region under pea crops. The degree of infestation of crops was similar in areas of high and low pea production as the mean annual abundance of aphids per hectare of crop remained constant. Yearly variation in abundance was loosely associated with temperature from January to July. Cold weather in January and February resulted in large numbers of aphids. Warm weather in February led to early colonization, and emigration from, pea crops as well as making early sowing of the crop more likely. A forecast of the time of first appearance of Acyrthosiphon pisum in the aerial plankton can be made, based on February temperature. Populations of A. pisum on peas appear to be regulated by alata production. High densities of aphids resulted in almost all the nymphs developing into alatae which, on reaching maturity, emigrated, causing populations on the crop to decline. This explains population crashes of the pea aphid observed at early growth stages of the crop, on vining and combining peas. Late sowing of peas, a probable effect of cold winters, results in higher aphid densities at flowering. The probable explanation for this is that late-sown crops are colonized at an earlier growth stage, so that the aphid population has a longer period of time in which to develop.     

THE ANALYSIS AND RECONSTRUCTION OF DIURNAL FLIGHT CURVES IN ALIENICOLAE OF APHIS FABAE SCOP.

Experiments, in which alate aphids were marked immediately after eclosion from the last nymphal instar and observed until they took flight, gave information which, together with the measured rate of moulting and a continuous record of temperature, has been used to construct theoretical daily curves for numbers flying from a bean crop. These curves have been matched against the observed curves for the same days.
The differences between curves so constructed for a period of 17 days and the observed curves for the same period are of the same order and kind as the differences between two measured curves in different sites at the same time.
The different types of daily flight curve can thus be accounted for in terms of the rate of production of alatae by moulting, the effect of temperature on the teneral ('drying out') period and the effect of low light intensity and temperature on take-off behaviour.     

Environmental effects on flying migrants revealed by radar

Migratory animals are affected by various factors during their journeys, and the study of animal movement by radars has been instrumental in revealing key influences of the environment on flying migrants. Radars enable the simultaneous tracking of many individuals of almost all sizes within the radar range during day and night, and under low visibility conditions. We review how atmospheric conditions, geographic features and human development affect the behavior of migrating insects and birds as recorded by radars. We focus on flight initiation and termination, as well as in‐flight behavior that includes changes in animal flight direction, speed and altitude. We have identified several similarities and differences in the behavioral responses of aerial migrants including an overlooked similarity in the use of thermal updrafts by very small (e.g. aphids) and very large (e.g. vultures) migrants. We propose that many aerial migrants modulate their migratory flights in relation to the interaction between atmospheric conditions and geographic features. For example, aerial migrants that encounter crosswind may terminate their flight or continue their migration and may also drift or compensate for lateral displacement depending on their position (over land, near the coast or over sea). We propose several promising directions for future research, including the development and application of algorithms for tracking insects, bats and large aggregations of animals using weather radars. Additionally, an important contribution will be the spatial expansion of aeroecological radar studies to Africa, most of Asia and South America where no such studies have been undertaken. Quantifying the role of migrants in ecosystems and specifically estimating the number of departing birds from stopover sites using low‐elevation radar scans is important for quantifying migrant–habitat relationships. This information, together with estimates of population demographics and migrant abundance, can help resolve the long‐term dynamics of migrant populations facing large‐scale environmental changes.     

The influence of weather on the flight altitude of nocturnal migrants in mid‐latitudes

By altering its flight altitude, a bird can change the atmospheric conditions it experiences during migration. Although many factors may influence a bird's choice of altitude, wind is generally accepted as being the most influential. However, the influence of wind is not clearly understood, particularly outside the trade‐wind zone, and other factors may play a role. We used operational weather radar to measure the flight altitudes of nocturnally migrating birds during spring and autumn in the Netherlands. We first assessed whether the nocturnal altitudinal distribution of proportional bird density could be explained by the vertical distribution of wind support using three different methods. We then used generalized additive models to assess which atmospheric variables, in addition to altitude, best explained variability in proportional bird density per altitudinal layer each night. Migrants generally remained at low altitudes, and flight altitude explained 52 and 73% of the observed variability in proportional bird density in spring and autumn, respectively. Overall, there were weak correlations between altitudinal distributions of wind support and proportional bird density. Improving tailwind support with height increased the probability of birds climbing to higher altitude, but when birds did fly higher than normal, they generally concentrated around the lowest altitude with acceptable wind conditions. The generalized additive model analysis also indicated an influence of temperature on flight altitudes, suggesting that birds avoided colder layers. These findings suggested that birds increased flight altitudes to seek out more supportive winds when wind conditions near the surface were prohibitive. Thus, birds did not select flight altitudes only to optimize wind support. Rather, they preferred to fly at low altitudes unless wind conditions there were unsupportive of migration. Overall, flight altitudes of birds in relation to environmental conditions appear to reflect a balance between different adaptive pressures.     

Bird movements at rotor heights measured continuously with vertical radar at a Dutch offshore wind farm

Assessing the impacts of avian collisions with wind turbines requires reliable estimates of avian flight intensities and altitudes, to enable accurate estimation of collision rates, avoidance rates and related effects on populations. At sea, obtaining such estimates visually is limited not only by weather conditions but, more importantly, because a high proportion of birds fly at night and at heights above the range of visual observation. We used vertical radar with automated bird‐tracking software to overcome these limitations and obtain data on the magnitude, timing and altitude of local bird movements and seasonal migration measured continuously at a Dutch offshore wind farm. An estimated 1.6 million radar echoes representing individual birds or flocks were recorded crossing the wind farm annually at altitudes between 25 and 115 m (the rotor‐swept zone). The majority of these fluxes consisted of gull species during the day and migrating passerines at night. We demonstrate daily, monthly and seasonal patterns in fluxes at rotor heights and the influence of wind direction on flight intensity. These data are among the first to show the magnitude and variation of low‐altitude flight activity across the North Sea, and are valuable for assessing the consequences of developments such as offshore wind farms for birds.     

BIRD MIGRATION OVER THE MALTESE ISLANDS

The present paper is based on data obtained during several years' observations and three recent surveys. Little has previously been published on migration through the Maltese Islands. The geographical, vegetational and climatic factors of the islands are discussed in so far as they affect the migrants. Visible migration is seen with anticyclonic weather and westerly winds. Birds are found grounded after night migration in cyclonic weather with southwesterly or easterly winds, much larger numbers and variety being seen with the latter. When there is a deterioration in the weather during the night, a large influx of birds is seen on the following morning, and in addition large flocks of migrating Turtle Doves are seen. Several trans-Saharan migrants may pass in smaller numbers during autumn than spring, but the difference may be more apparent than real because in early autumn the birds may depart after only a very short stay, and a few conspicuous species are absent or scarce. By contrast several species which winter north of the Sahara pass only or in much larger numbers during autumn, and these more than make up for those which are absent or rare. There is no evidence from bird ringing that in spring Malta regularly gets birds from Tunisia, at any rate from that part covered by the ringing stations (Cap Bon, Enfidaville, Gabes). The migrants which pass through Malta probably originate from an area in North Africa around Tripoli and some way westwards of it. During autumn the bulk of recoveries is from eastern European countries with a smaller percentage from northern and central Europe. Several species or groups of species are dealt with individually. In the discussion stress is laid on the very close relationship between migration and weather, especially the wind component. The comparatively small numbers of birds seen at Malta probably form part of a larger movement travelling on a broad front. It is argued that the large “falls” of migrants in bad weather result from drift acting on a mass passing mainly to one side or the other of the islands. Since much larger densities are seen with easterly than with westerly winds, it follows, if the hypothesis of drift be correct, that the numbers of birds travelling to the east of Malta are larger than those to the west of it. Moreover, since day migrants are seen with westerly winds and the bulk of night migrants with easterly ones, it is inferred that day migrants normally pass to the west, and the bulk of night migrants to the east, of the Maltese Islands. A parallel is drawn between the autumn migration and the performance of racing pigeons which are flown from the north and NE at this season.     

Resistance to the aphid Metopolophium festucae cerealium: effects of the host plant on flight and reproduction

The levels of resistance present in two cereal and four grass hosts of M. f. cerealium were assessed in terms of the percentage of alatae flying from the host and reproductive rates of alatae. Festuca rubra and F. arundinacea exhibited highest levels of resistance, inducing a greater proportion of the alatae to fly (94% and 84% respectively) after producing only a few nymphs. Although between 38% and 64% of alatae flew from L. multiflorum, oats, L. perenne and wheat these alatae deposited more nymphs on the hosts before flight than occurred on Festuca. The weight of alatae did not influence the flight response. The differences in the flight/reproductive response of M. festucae to various host plants are discussed in relation to possible host selection strategies of this species and to antixenotic/antibiotic host resistance experiments in general.     

Flight periodicity and infestation size of Sitona lineatus

Sitona lineatus displays two distinct flight periods; a post-teneral flight in the late summer and a post-diapausal flight in the spring. The late summer flight begins as soon as adults start to emerge from pupal cells during late July and continues until mid-October. Maximum aerial density is observed in late August. Less than 10% of newly emerged adults leave the crop by flight, the rest remain in the soil or move to overwintering sites by walking. Spring flight begins in late March if temperatures are above the 12.5°C flight threshold and reaches a peak in mid-April. Most migratory flight is downwind. Little trivial flight occurs and once individuals have located a crop, redistribution is by walking. Laboratory studies indicate that adults fly most often during the day, particularly at noon. The size of infestations appeared to be independent of the area of legumes grown in a locality with large differences occurring even between neighbouring fields. Examination of the yields of field experiments at Rothamsted demonstrate an unexpected trend for higher yields in later sown spring bean crops. This may be because late sowing avoids infestation by spring migrants.     

Effects of population density on alienicolae of Aphis fabae Scop.: V. Variations in size, relative wing length and numbers of antennal sensorla of field alatae

Size, relative wing length and numbers of antennal sensoria of alate Aphis fabae caught in a suction trap 12.2 m above ground and of migrants, flyers and non-flyers among alate A. fabae from field infestations on beans and beet are compared. The size of aphids in successive samples decreased throughout the period of colonization but, on average, beet aphids were bigger and broad bean aphids were smaller than field bean aphids. There were very few migrant alatae among the very large or the very small aphids from any of the crops, neither were aphids of these extreme sizes caught in the suction trap. Non-flyers and beet aphids generally had relatively shorter wings than migrants and bean aphids respectively. The numbers of antennal sensoria differed more between aphids from the three crops than between classes of alatae from the same crop, although trap aphids, presumed to be migrating from field beans had more sensoria than alatae taken from that crop. The mean dry mass of flyers was usually less than that of migrants of a similar size, although if the mass of nymphs deposited before flight is added, it is apparent that a flyer would be heavier than a migrant of the same size at maturity. This additional mass is thought to be due to increased development of the embryos in the ovarioles of flyers at this time and indicative of their greater adaptation for reproduction.     

Flight by night or day? Optimal daily timing of bird migration

Many migratory bird species fly mainly during the night (nocturnal migrants), others during daytime (diurnal migrants) and still others during both night and day. Need to forage during the day, atmospheric structure, predator avoidance and orientation conditions have been proposed as explanations for the widespread occurrence of nocturnal migration. However, the general principles that determine the basic nocturnal-diurnal variation in flight habits are poorly known. In the present study optimal timing of migratory flights, giving the minimum total duration of the migratory journey, is evaluated in a schematic way in relation to ecological conditions for energy gain in foraging and for energy costs in flight. There exists a strong and fundamental advantage of flying by night because foraging time is maximized and energy deposition can take place on days immediately after and prior to the nocturnal flights. The increase in migration speed by nocturnal compared with diurnal migration will be largest for birds with low flight costs and high energy deposition rates. Diurnal migration will be optimal if it is associated with efficient energy gain immediately after a migratory flight because suitable stopover/foraging places have been located during the flight or if energy losses during flight are substantially reduced by thermal soaring and/or by fly-and-forage migration. A strategy of combined diurnal and nocturnal migration may be optimal when birds migrate across regions with relatively poor conditions for energy deposition (not only severe but also soft barriers). Predictions about variable timing of migratory flights depending on changing foraging and environmental conditions along the migration route may be tested for individual birds by analysing satellite tracking results with respect to daily travel routines in different regions. Documenting and understanding the adaptive variability in daily travel schedules among migrating animals constitute a fascinating challenge for future research.     

Differences in Morphometry and Activity among Tabanid Fly Assemblages in an Andean Tropical Montane Cloud Forest: Indication of Altitudinal Migration?

Evidence suggests that variations along ecological gradients shape organism traits such as behavior or morphometry. We studied the effect of altitude on the flight activity of tropical tabanid fly assemblages of one species of Stypommisa Enderlein along a 1 km altitudinal gradient on the northwestern slopes of the Ecuadorian Andes. Our objectives were as follows: (1) to test the hypothesis that highland individuals present larger flight body structures; and (2) to compare the flight activity patterns of flies’ assemblages among altitudes and correlate it with weather factors. We sampled specimens in Malaise traps at 1180, 1680 and 2180 m of altitude from 0600 to 1830 h for 20 d at each site. Seven weather variables were measured every hour and flight activity was inferred from relative tabanid fly abundances/hour in traps. We measured morphometrical parameters that included tabanid fly body size, thorax volume, wing area and wing loading. Flight activity patterns revealed a bimodal distribution at 1680 m, and two asynchronous unimodal distributions, one at 1180 and one at 2180 m. GLM analyses revealed that temperature, mist and rainfall were the best predictors of fly activity differences among altitudes. Morphometrical analyses showed that body size and thorax volume increased with increasing altitude. Synchronous groups of flies at different altitudes (those between 1180–1680_(pm) m, and 1680_(am)–2180 m) were morphologically similar, suggesting that flies could be capable of migrating from highlands to lowlands at defined hours of the day depending on forest weather conditions.     

光照、温度和湿度对桔小实蝇飞翔活动的影响

于2004年6月在云南元江芒果园内通过性诱剂诱捕,对桔小实蝇Bactrocera dorsalis(Hendel)的飞翔活动日节律进行了全天24h的监测,并就光照、温度和相对湿度3个环境因子的影响进行了测试和综合分析。研究表明,桔小实蝇雄成虫仅在白天有光照的情况下进行飞翔活动,夜晚停止飞翔。在1d内有2个飞翔活动高峰期,分别发生在上午8∶00~9∶00和下午18∶00~20∶00,且前者进行飞翔活动的虫量相对后者要大。在下午2∶00左右进入白天飞翔活动的低谷。光刺激是桔小实蝇飞翔活动的基本条件,其趋光性因芒果园内树荫下的光照强度变化而异,在100~200lux之间对桔小实蝇飞翔活动明显有利,而当光照强度低于100lux或高于200lux,飞翔活动也相应减小。气温总体上位于桔小实蝇飞翔活动的适宜范围,而下午低于60%的相对湿度对其飞翔活动有一定的抑制作用。气温、湿度和光照对桔小实蝇飞翔活动的作用机理各不相同并且各因子之间也相互作用,最终对桔小实蝇的飞翔活动产生综合效应。     

Life history response of the mustard aphidLipaphis erysimi to phenological changes in its host

The mustard aphid,Lipaphis erysimi (Kaltenbach) is a serious pest of mustard in India and other tropical regions in the world. The population dynamics of this species is considerably influenced by immigrant alatae which migrate to the mustard crop from the off-season shelter. Aphids reproduce at a higher rate in the early vegetative stage of mustard plants when the developmental period is shortest and production of winged morphs is lowest. The population reaches an asymptote when the crop is 70 days old. The species regulates its developmental period, fecundity and intrinsic rate of increase in response to developmental changes of the mustard plant and maintains its dispersal throughout the duration of the mustard crop. In succeeding generations on a mustard plant new born nymphs took increasingly longer to develop into adults and over the same period these adults produced decreasingly fewer numbers of offspring. In the inflorescence and fruiting stages of mustard plants a higher proportion of the nymphs developed into alatae.     

Variation in the nocturnal flight behaviour of migratory birds along the northwest coast of the Mediterranean Sea

The Mediterranean Sea is one of the largest obstacles that has to be crossed by Palearctic birds migrating from Europe to Africa; it thus offers a good opportunity to study variations in migratory behaviour of birds facing a major ecological barrier. Using a passive infrared device, the flight directions of nocturnal migrants were determined and flight altitudes estimated at ten sites along the French and Spanish coast of the Mediterranean Sea in September and October 1995. The variation of migratory intensity, flight direction and altitude in the course of the night was examined. The highest density of migration was recorded within the first hour after sunset, followed by relatively high densities over the next several hours, and a progressive decrease in the last third of the night. In spite of broad variation in the course of the coastline relative to the basic directions of migration and specific reactions of the migrants to the local conditions, a decrease in seaward migration corresponding to an increase in landward migration from the first to the second half of the night was a general feature at nearly all sites. The results suggest a shift in the motivation of the birds depending on the time of arrival in a coastal area, leading to an adjustment in the flight behaviour of nocturnal migrants.     

An aerial netting study of insects migrating at high altitude over England

Day and night sampling of windborne arthropods at a height of 200 m above ground was undertaken at Cardington, Bedfordshire, UK, during July 1999, 2000 and 2002, using a net supported by a tethered balloon. The results from this study are compared with those from the classic aerial sampling programmes carried out by Hardy, Freeman and colleagues over the UK and North Sea in the 1930s. In the present study, aerial netting was undertaken at night as well as daytime, and so the diel periodicity of migration could be investigated, and comparisons made with the results from Lewis and Taylor's extensive survey of flight periodicity near ground level. In some taxa with day-time emigration, quite large populations could continue in high-altitude flight after dark, perhaps to a previously underrated extent, and this would greatly increase their potential migratory range. Any trend towards increases in night temperatures, associated with global warming, would facilitate movements of this type in the UK. Observations on the windborne migration of a variety of species, particularly those of economic significance or of radar-detectable size, are briefly discussed.     

The Effects of Chilling on the Fecundity and Life Span of Mass-reared Parasitoids (Hymenoptera: Braconidae) of the Mediterranean Fruit Fly, Ceratitis capitata (Wiedemann) (Diptera: Tephritidae)

Suppression of Mediterranean fruit fly (medfly), Ceratitis capitata (Wiedemann), populations may be achieved through the mass-rearing and augmentative aerial release of opiine braconid parasitoids. Typically, aerial release techniques require up to one hour of chilling of adult parasitoids at temperatures as low as 3.5°C prior to their dissemination. Such chilling potentially could affect the subsequent performance of the insects. Among three species of the genus Diachasmimorpha longicaudata (Ashmead), tryoni (Cameron), and krausii (Fullaway) there was little or no affect of chilling in the laboratory on female longevity, production of daughters, or offspring sex ratio. This is consistent with previous experiments that found chilling to have no discernable effect on the short-term mortality of D. tryoni or on its ability to take flight immediately after aerial release. While there was little effect of chilling on longevity and fecundity in a species from another opiine genus, Fopius arisanus (Sonan), exposure to low temperatures did result in a significantly more male-biased offspring sex ratio.     

The overwintering and abundance of cereal aphids

The longevity of Sitobion avenae varied inversely with temperature from 25 to over 100 days when reared outdoors on barley under lantern jars, being longest between December and April–May. This was due mainly to changes in the length of the pre- and post-reproductive periods rather than the length of the period of reproduction. Fecundity varied directly with temperature, from eight to sixty-seven nymphs per female. When reared on winter wheat and sheltered from wind, rain and snow, S. avenae survived best, Metopolophium dirhodum survived less well and Rhopalosiphum padi worst; when exposed in the open none of the three species survived. Close relationships were not demonstrable between the numbers of alate M. dirhodum, S. avenae and Rhopalosiphum spp. trapped in any year, between the abundance of these aphids and weather conditions between January and April, or between the numbers of these alatae and the size of crop infestations. This was probably because insufficient information was available about their biology, both inside and outside the crop.     

Effects of age and mated status on flight potential of Helicoverpa armigera (Lepidoptera: Noctuidae)

Abstract The effects of ageing and female mated status on the flight potential of Helicoverpa armigera (Hübner), collected as larvae from a pigeonpea crop in southern India, were investigated using a tethered-flight technique. In non-mated moths fed sugar solution, from the first night after adult eclosion, the durations of both total and longest continuous flight per night increased up to night 4 and remained at this level until at least night 6. Ovarian maturation was rapid with 77% of unmated moths having commenced oviposition by the third night. On the basis of field evidence it is likely that most females would be mated by the third or fourth night, provided plants with nectar or sugary exudates were locally available. In successfully-mated females a 15-fold decrease in total flight duration and a 28-fold decrease in longest continuous flight duration was observed in contrast to non-mated females of similar age. As host plants suitable for adult feeding and oviposition were locally available during the time of feral adult emergence, synchronous pre-reproductive migration was unlikely to occur in the population studied.     

Flight call rates of migrating thrushes: effects of wind conditions,humidity and time of day at an illuminated offshore platform

Many bird species call during migration, but call rates not necessarily reflect migration intensity. They rather seem to increase under deteriorating flight conditions. Often, nocturnal mass collisions at illuminated structures coincide with such conditions and are accompanied with high call rates of migrants. Thus, call rates could act as an indicator for situations with high collision risk for birds namely at offshore sites with hardly any alternatives for landing. In the face of increasing numbers of offshore wind farms knowledge about the environmental conditions in which maximum call rates occur, is needed for mitigation measures. In this first long‐term study at an offshore site in the southern North Sea we investigated the effect of weather on the frequency of flight calls of three thrush‐species at an illuminated platform. Flight calls were registered automatically during three autumn migration seasons. Besides generally higher call rates from 5 to 2 h before until 6 h after midnight, call rates increased with tailwinds, a change of the tailwind component during the first part of the night, offshore crosswinds and very high humidity. A monitoring programme is suggested that could help to reduce mass mortalities at illuminated structures.