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Downwind migration of the African armyworm moth Spodoptera exempta studied by mark-and-capture and radar

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Downwind migration of the African armyworm moth Spodoptera exempta studied by mark-and-capture and radar

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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.

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... African countries located further south (Zambia, Malawi) showed more similarities to each other compared with countries further north (Kenya, Rwanda, Ghana and Sudan) (e.g., fewer individuals were assigned to cluster 3 in the north compared to the south). This pattern of genetic separation coincides with the known migratory routes of the congeneric African armyworm (Spodoptera exempta) in eastern Africa, which follow the movement of the dominant winds each season, typically moving moths towards the north-west from Kenya and northern Tanzania, and a more south-westerly movement across southern Africa from Malawi 33,34 . This is also aligned with the movement of the inter-tropical convergence zone (ITCZ), with the wind direction (and hence seasonal migration) being broadly south-easterly north of the equator and north-easterly south of the equator 34 . ...
... This pattern of genetic separation coincides with the known migratory routes of the congeneric African armyworm (Spodoptera exempta) in eastern Africa, which follow the movement of the dominant winds each season, typically moving moths towards the north-west from Kenya and northern Tanzania, and a more south-westerly movement across southern Africa from Malawi 33,34 . This is also aligned with the movement of the inter-tropical convergence zone (ITCZ), with the wind direction (and hence seasonal migration) being broadly south-easterly north of the equator and north-easterly south of the equator 34 . Based on the high levels of mixing between FAW populations alongside this evidence of some genetic structuring between northern and southern populations, it is hypothesised that FAW may also follow the movement of the dominant winds if they are migratory in Africa as, like many other insects, they rely on wind to support high-altitude long-distance flights 2,5,35,36 . ...
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Understanding the population structure and movements of the invasive fall armyworm (FAW, Spodoptera frugiperda ) is important as it can help mitigate crop damage, and highlight areas at risk of outbreaks or evolving insecticide resistance. Determining population structure in invasive FAW has been a challenge due to genetic mutations affecting the markers traditionally used for strain and haplotype identification; mitochondrial cytochrome oxidase I (COIB) and the Z-chromosome-linked Triosephosphate isomerase (Tpi). Here, we compare the results from COIB and Tpi markers with highly variable repeat regions (microsatellites) to improve our understanding of FAW population structure in Africa. There was very limited genetic diversity using the COIB marker, whereas using the TpiI4 marker there was greater diversity that showed very little evidence of genetic structuring between FAW populations across Africa. There was greater genetic diversity identified using microsatellites, and this revealed a largely panmictic population of FAW alongside some evidence of genetic structuring between countries. It is hypothesised here that FAW are using long-distance flight and prevailing winds to frequently move throughout Africa leading to population mixing. These approaches combined provide important evidence that genetic mixing between invasive FAW populations may be more common than previously reported.
... In this study, we collected the first-reported date of FAW appearance for each monitoring site in the Yangtze River Valley by systematic field investigations. As highly active flights of moths occur during dominant periods of emergence [37,38], and air temperature is one of the most important climatic factors in FAW's development, we then determined the eclosion peak days as the emigration dates of the first and second generations of the newly-invaded FAW populations by analyzing the historical daily mean temperatures. Subsequently, large-scale synoptic patterns in corresponding periods of both the last five years from 2014 to 2018 and 2019 were studied to illustrate and interpret the rapid aerial spread of FAW. ...
... Previous studies illustrated a strong correlation between the numbers emerging each night and the peak volume density measured by radar during the following evening [37,38]; thus, the accuracy of calculation of the FAW dispersal can be improved by identifying the peak emergence days of FAW investigated in maize fields, which are determined by the development of FAW responding to the surrounding temperature [40]. The most commonly studied factor of the relationship between life-history stage and environment is the effect of air temperature [30]. ...
Article
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The fall armyworm (FAW), native to the Americas, has rapidly invaded the whole of Southern China since January 2019. In addition, it can survive and breed in the key maize- and rice- growing area of the Yangtze River Valley. Furthermore, this pest is also likely to continue infiltrating other cropping regions in China, where food security is facing a severe threat. To understand the potential infestation area of newly-invaded FAW from the Yangtze River Valley, we simulated and predicted the possible flight pathways and range of the populations using a numerical trajectory modelling method combining meteorological data and self-powered flight behavior parameters of FAW. Our results indicate that the emigration of the first and second generations of newly-invaded FAW initiating from the Yangtze River Valley started on 20 May 2019 and ended on 30 July 2019. The spread of migratory FAW benefitted from transport on the southerly summer monsoon so that FAW emigrants from the Yangtze River Valley can reach northern China. The maize-cropping areas of Northeastern China, the Korean Peninsula and Japan are at a high risk. This study provides a basis for early warning and a broad picture of FAW migration from the Yangtze River Valley.
... The polyphagous larvae can occur in large high-density aggregations, and rapidly consume crops and grasses in localised areas. After emergence, armyworm moths fly downwind and can be concentrated by convergent winds associated with rainstorms (Pedgley et al., 1982; Riley et al., 1983; Rose et al., 1985). Trajectory analysis, based on daily wind-fields, has been used to estimate downwind migration of African Armyworm (Tucker et al., 1982; Tucker, 1994). ...
... The polyphagous larvae can occur in large high-density aggregations, and rapidly consume crops and grasses in localised areas. After emergence, armyworm moths fly downwind and can be concentrated by convergent winds associated with rainstorms ( Pedgley et al., 1982;Riley et al., 1983;Rose et al., 1985). Trajectory analysis, based on daily wind-fields, has been used to estimate downwind migration of African Armyworm ( Tucker et al., 1982;Tucker, 1994). ...
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Moths of the African Armyworm, Spodoptera exempta, displace downwind and are con- centrated by convergent wind flows associated with rainstorms. The moths land and breed, sometimes resulting in outbreaks of larvae at high densities which cause considerable dam- age to crops and grassland. Moths emigrating from an outbreak site can initiate further outbreaks in other locations and a model was developed to forecast their fate. The model simulates population change from one week to the next and movement over a grid of one degree-square units. The model predicts the direction, distance and dispersion of moths based on prevailing winds. Rainfall is central to S. exempta biology and is estimated from rain-gauges or Meteosat cold-cloud data. Rainfall determines emigration from the source outbreak, and aggregation, fecundity, mortality and food quality at the potential desti- nations of the displaced moths. To forecast one armyworm generation (c. 5 weeks) ahead, historical frequencies of rainfall patterns are used. Repeated sampling of this rainfall fre- quency distribution in an ensemble forecast allows a spatial probability footprint of out- break risk to be calculated. The forecast comprises a prediction of the probabilities of low, medium and high outbreak risk in each degree square of the grid.
... Many studies have used dusts, dyes, and paints applied to insects (herbivores in the majority of cases) internally and externally, on mass-reared laboratory populations and field-collected samples, and some experiments have been devised for insects to self-mark (Gentry and Blythe, 1978; see reviews by Reynolds et al., 1997; Hagler and Jackson, 2001). However, there have been few studies in which dyes and dusts have been applied directly to natural populations in the field (Rose et al., 1985; Bell, 1988) and only one (Prasifka et al., 1999) where the purpose was to mark beneficial insects. The aim of this project was to develop a method of marking field populations of beneficial insects in order to monitor their dispersal from refuges into crops. ...
Article
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Dyes and dusts have been used to mark insects internally and externally for decades, the majority of examples coming from laboratory-reared pest species used in mark-release-recapture studies. Using dyes or dusts to mark populations of pests and beneficial insects simultaneously in the field has received less attention. We evaluated a water-soluble fluorescent dye and a resin-based fluorescent pigment sprayed on crops to mark beneficial and pest insects, and monitored the dispersal of marked insects. Our results show that resin-based dyes provide an effective mark on several species of insects among several orders. The resin-based dye is also relatively inexpensive, non-toxic, UV-stable and water resistant, unlike a water-soluble dye. Using the resin-based dye in a broccoli production system, we were able to monitor simultaneously the movement of field populations of the parasitoids, Diadegma semiclausum (Hellén) (Hymenoptera: Ichneumonidae), and Apanteles ippeus (Nixon) (Hymenoptera: Braconidae) and the adult stage of the host, diamondback moth, Plutella xylostella (L.) (Lepidoptera: Plutellidae). Resin-based dye applied on a crop is an effective way to mark and monitor the dispersal of populations of beneficial and pest insects in relation to agricultural practices, integrated pest management and conservation biological control.
... Some movement patterns appear to maximize the discovery of short-lived, dispersed and unpredictable habitats. For example, during the dry season, the African armyworm moth, Spodoptera exempta, is carried downwind, the direction toward the Inter-Tropical Convergence Zone, where convergent winds are likely to produce rain and to concentrate moth density [18]. Similarly, the movement of Spodoptera frugiperda in Central America may be a strategy to locate areas of recent rain and therefore to elevate the prospect of finding a host [19]. ...
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Moth migration has been assumed to involve hitching a ride in favorable winds. A new study has shown that silver Y moths migrate only on nights when winds would displace them southward, implying that they detect their direction of movement while airborne, likely by a magnetic sense.
... We have used this system to monitor Spodoptera exempta and Helico6erpa armigera moths flying below radar cover (i.e. under about 20-30 m) ( Farmery, 1982;Riley et al., 1983Riley et al., , 1992Rose et al., 1985). The Farmery device (like many night-time video and infrared illuminator combinations) is ineffective in twilight and daytime when the luminance of the sky greatly lowers its sensitivity to insect targets. ...
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This paper provides an overview of the recent literature on electronic, remote-sensing and computer-based techniques for observing and monitoring insect movement in the field and in the laboratory. Topics (such as entomological radar) which are covered in detail elsewhere in this Special Issue are deliberately omitted. Techniques which have been used, or which have potential for use, in monitoring insects in the field, include optical and opto-electronic devices, videography, thermal imaging, radio frequency identification (RFID), radio-telemetry, X-ray radiography and computed tomography, sodar and sonar. The discussion includes optical sensors and insect trapping, instrumented beehives, acoustic detection of insects in grain, fruit and soil, and various laboratory methods for studying insect movement, such as actographs, treadmills, automatic flight mills, and the video recording and analysis of movement in wind tunnels and in indoor arenas. Airborne and satellite imaging of insect habitats is mentioned, but only in the context of the use of these techniques to deduce changes in population distribution in some migratory species. Finally, some of the main constraints to progress in the sensing of insect movement, and areas where rapid advances seem possible, are discussed.
... For each cluster of three bars, bars with the same letter are not significantly different (P > 0.05) as determined by overlap of 95% confidence intervals. disperse as adults over immense distances (Hendricks et al., 1973; Rose et al., 1985; Showers et al., 1989; Westbrook et al., 1995). The majority of respondents gave this risk element a medium/high rating (Figure 3A), but there was little agreement about the sufficiency of data to reach a conclusion (Figure 3B). ...
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Eggs and larvae of Copitarsia spp. (Lepidoptera: Noctuidae) are frequently intercepted on fresh commodities arriving in the United States from Mexico, Central America, and South America. Copitarsia spp. are not known to occur in the US and, thus, are considered actionable pests by the US Department of Agriculture, Animal and Plant Health Inspection Service (USDA, APHIS). Whenever the genus is detected in imported goods, shipments must be disinfested, destroyed, or returned to the country of origin. Inspections and interdictions might be unnecessary if Copitarsia spp. were unlikely to establish in the US or if consequences of Copitarsia establishment were trivial. Consequently, we prepared a qualitative pest risk assessment to characterize the degree of risk posed by the genus to US agricultural and natural ecosystems. Published literature was consulted to describe the biology and ecology of the genus. Trade statistics and interception records were summarized to identify pathways of introduction. With this information, experts assigned risk ratings to each of eleven elements identified by USDA, APHIS that pertained to the likelihood or consequence of exotic-pest establishment. The likelihood of Copitarsia spp. becoming established in the US was considered high, but confidence in this assessment was low. Similarly, consequences of Copitarsia establishment were rated high, but confidence in this assessment was moderate. Overall, the assessment revealed that Copitarsia pose a high degree of risk to the US and phytosanitary measures to exclude the pest seem warranted. However, additional research is needed to address critical data gaps and refine assessments of risk for individual species within the genus.
... One of the most devastating migratory crop pests in sub-Saharan Africa is the larval stage of the African armyworm moth, Spodoptera exempta (Lepidoptera: Noctuidae), a major pest of staple cereals, such as maize, wheat, sorghum, millet and rice, as well as pasture grasses (Rose et al. 2000). S. exempta moths are highly migratory, being capable of flying > 100 km per night over several nights (Rose et al. 1985). The seasonal pattern of outbreaks follows the movement of the intertropical convergence zone and the seasonal rains, such that early season outbreaks in central Tanzania from October onwards act as source populations for subsequent outbreaks that occur downwind at one generation intervals (approximately monthly) at increasingly northerly latitudes in Tanzania and into neighbouring Kenya and beyond (Rose et al. 2000). ...
Article
Wolbachia are common vertically transmitted endosymbiotic bacteria found in < 70% of insect species. They have generated considerable recent interest due to the capacity of some strains to protect their insect hosts against viruses and the potential for this to reduce vector competence of a range of human diseases, including dengue. In contrast, here we provide data from field populations of a major crop pest, African armyworm (Spodoptera exempta), which show that the prevalence and intensity of infection with a nucleopolydrovirus (SpexNPV) is positively associated with infection with three strains of Wolbachia. We also use laboratory bioassays to demonstrate that infection with one of these strains, a male-killer, increases host mortality due to SpexNPV by 6-14 times. These findings suggest that rather than protecting their lepidopteran host from viral infection, Wolbachia instead make them more susceptible. This finding potentially has implications for the biological control of other insect crop pests.
... In the exper¬ iments reported here 73% mating efficiency was achieved by the third night when moths were given ad libitum sucrose solution, and Kou & Chow (1987) found that 30% and 70% of sugarfed female H.armigera called (and by impli¬ cation were reproductively mature), by nights 2 and 3 respectively. Much of our current understanding of the physiology and behaviour of migration in the Noctuidae is based on extensive research on the gregarious form of the African army worm, Spodoptera exempta, where there is good field evidence for pre-reproductive migration with mass departure from the breeding site (Rose & Dewhurst, 1979; Riley el al., 1983; Rose et al., 1985; Page, 1988) consistent with the classical oogenesis-flight syndrome model of Johnson (1969). On the basis of this field evidence, Parker & Gatehouse (1985), using a flight bal¬ ance apparatus, defined long ( migratory') fliers as those S. exempta moths with a total flight duration of 3=120 min made up of individual flights of 3=30 min. ...
Article
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.
... Such assays have proved useful in assessing flight behaviour of insects ranging from flies and true bugs to butterflies, moths, and beetles [33]. In some noctuids [13,[34][35][36][37][38][39] including H. armigera, migratory flight typically occurs early in adult life in the pre-reproductive period [40]. A better understanding of migratory flight would enable tracking population movements, estimating proportion of gene flow across migrating pathways, periods of emigration and immigration and designing better management strategies. ...
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Despite its deleterious impact on farming and agriculture, the physiology and energetics of insect migration is poorly understood due to our inability to track their individual movements in the field. Many insects, e.g. monarch butterflies, Danaus plexippus (L.), are facultative migrants. Hence, it is important to establish whether specific insect populations in particular areas migrate. The polyphagous insect, Helicoverpa armigera (Hübner), is especially interesting in this regard due to its impact on a variety of crops. Here, we used a laboratory-based flight mill assay to show that Helicoverpa armigera populations clearly demonstrate facultative migration in South India. Based on various flight parameters, we categorized male and female moths as long, medium or short distance fliers. A significant proportion of moths exhibited long-distance flight behavior covering more than 10 km in a single night, averaging about 8 flight hours constituting 61% flight time in the test period. The maximum and average flight speeds of these long fliers were greater than in the other categories. Flight activity across sexes also varied; male moths exhibited better performance than female moths. Wing morphometric parameters including forewing length, wing loading, and wing aspect ratio were key in influencing long-distance flight. Whereas forewing length positively correlated with flight distance and duration, wing loading was negatively correlated.
... Strategic control is particularly appealing for migratory pest species, because it can help to limit the geographical spread of the pest, so allowing resources for its control to be better focused. African armyworm moths are highly migratory, being able to migrate 100 km or more per night over several nights (Rose et al., 1985). Their movements are largely governed by the seasonal progression of the inter-tropical convergence zone (ITCZ). ...
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Summary A new strategy to control African armyworm in Tanzania, which combines forecasting of armyworm outbreaks with the utilisation of the natural disease of the armyworm, Spodoptera exempta nucleopolyhedrovirus (SpexNPV) has been developed and piloted in Tanzania. Community based armyworm forecasting (CBAF) has shown that village forecasters achieved a high level of forecasting accuracy, with 75% of all positive forecasts having corresponding outbreaks. Results from both ground and aerial applications have shown that SpexNPV is effective in controlling African armyworm if sprayed early in the outbreaks and thus could be used to replace chemical insecticides for armyworm control. Field trials indicate that SpexNPV could be produced by harvesting infected larvae from previously sprayed outbreaks. Thus, when combined with improved forecasting, SpexNPV could provide a new affordable and safe technique for the control of armyworm in Tanzania, and a new mechanism for the strategic control to this important migratory pest.
... African armyworm moths are highly migratory, being able to migrate 100 km or more per night over several nights (Rose et al., 1985). Their movements are largely governed by the seasonal progression of the inter-tropical convergence zone (ITCZ). ...
Article
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A new strategy to control African armyworm in Tanzania is reviewed, with the utilization of the natural disease of the armyworm, Spodoptera exempta nucleopolyhedrovirus (SpexNPV) for control of armyworm outbreaks in Tanzania serving as case- study. Also the opportunity of linking novel control methods with Community Based Armyworm Forecasting (CBAF) is reviewed. Results from both ground and aerial application have shown that, SpexNPV is effective in controlling African armyworm if sprayed early in the outbreaks, with the mortality rate reaching 80% in 4days and >90% overall and could replace chemical insecticides in Tanzania. Further studies from the villages implementing CBAF, revealed that village forecasters achieved high level of forecasting accuracy; 75% of all positive forecasts had corresponding outbreaks, while only 25% had no outbreaks. Out of all the negative forecasts, 91% had no outbreaks while only 9% had outbreaks. This study has demonstrated that, not only SpexNPV has a potential of controlling armyworm outbreaks in Tanzania, but it also provide a mechanism for strategic control to this important migratory pest.
... Most outbreaks occur on the eastern half of sub-Saharan Africa, as far north as Sudan and as far south as South Africa [29]. The adult moths are highly migratory, often flying hundreds of kilometres over consecutive nights [30], with moth movements largely determined by the seasonal progression of the inter-tropical convergence zone (ITCZ). Therefore, it is believed that early-season armyworm outbreaks in central Tanzania essentially act as “source” populations for moths that will subsequently migrate to northern Tanzania and further northwards towards the horn of Africa [29]. ...
Article
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Background Numerous recent studies have shown that resident symbiotic microorganisms of insects play a fundamental role in host ecology and evolution. The lepidopteran pest, African armyworm (Spodoptera exempta), is a highly migratory and destructive species found throughout sub-Saharan Africa, that can experience eruptive outbreaks within the space of a single generation, making predicting population dynamics and pest control forecasting extremely difficult. Three strains of Wolbachia have recently been identified infecting this species in populations sampled from Tanzania. In this study, we examined the interaction between Wolbachia pipiensis infections and the co-inherited marker, mtDNA, within populations of armyworm, as a means to investigate the population biology and evolutionary history of Wolbachia and its host. Results A Wolbachia-infected isofemale line was established in the laboratory. Phenotypic studies confirmed the strain wExe1 as a male-killer. Partial sequencing of the mitochondrial COI gene from 164 individual field-collected armyworm of known infection status revealed 17 different haplotypes. There was a strong association between Wolbachia infection status and mtDNA haplotype, with a single dominant haplotype, haplo1 (90.2% prevalence), harbouring the endosymbiont. All three Wolbachia strains were associated with this haplotype. This indicates that Wolbachia may be driving a selective sweep on armyworm haplotype diversity. Despite very strong biological and molecular evidence that the samples represent a single species (including from nuclear 28S gene markers), the 17 haplotypes did not fall into a monophyletic clade within the Spodoptera genus; with six haplotypes (2 each from 3 geographically separate populations) differing by >11% in their nucleotide sequence to the other eleven. Conclusions This study suggests that three strains of Wolbachia may be driving a selective sweep on armyworm haplotype diversity, and that based on COI sequence data, S. exempta is not a monophyletic group within the Spodoptera genus. This has clear implications for the use of mtDNA as neutral genetic markers in insects, and also demonstrates the impact of Wolbachia infections on host evolutionary genetics.
... There are only a few reports of dyes being used in mark without capture studies. Rose et al. (1985) sprayed trees in Kenya with a molasses solution containing 0.5%; neutral red dye, to mark teneral moths of the African Armyworm, Spodoptera exempta (Walker): this exploited the tendency of the moths to congregate in trees before und ertaking migra- tory flights. The dye accumulated in the gut and fat body, and marked moths were caught in pheromone traps up to 147 km from the emergence site. ...
... flight-capable) form (e.g. Riley et al. 1983;Rose et al. 1985). Area densities of largish insects are, however, dwarfed by those of small species such as the rice brown planthopper (Table 7.1). ...
Chapter
Migratory flight close to the Earth’s surface (within the so-called flight boundary layer) occurs in some insects, but the vast majority of migrants ascend above this layer and harness the power of the wind for transport. The resulting displacements range from dispersive movements over a few tens of metres to seasonal migrations covering thousands of kilometres. In this chapter, we summarize knowledge of the use of the aerosphere by insects, focusing particularly on longer migrations, in relation to: the height and duration of flight, direction and speed of movement, seasonal and diel patterns, and responses to atmospheric conditions and phenomena. The seasonal mass movements have major ecological consequences in the invaded areas, and these are discussed briefly. We also highlight recent comparisons of insect movement strategies with those of flying vertebrates and mention interactions between these groups in the atmosphere. We conclude with some suggestions for the future development of these topics.
... Using information regarding current and expected atmospheric conditions when deciding to depart or land may increase survival and the chance to land in a suitable area while decreasing the animal's metabolic cost of transport. Wind speed and direction have pronounced effects on migratory departure and landing in insects and birds, and consequently these may affect the intensity of migration aloft (Rose et al. 1985, Dokter et al. 2011, Chapman et al. 2015a, chapter 11 in Drake and Reynolds 2012, Hu et al. 2016, Nilsson et al. 2019. ...
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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. Several similarities and differences in the behavioral responses of different aerial migrants include 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 during flight 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 in 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 that face large-scale environmental changes.
... In certain other migratory noctuids, migration should enhance discovery of ephemeral resources not tied to a seasonally predictable cardinal direction. The African armyworm moth, Spodoptera exempta, like the desert locust, is transported downwind towards the inter-tropical convergence zone [16]. The migration of Spodoptera frugiperda in Central America, presumably downwind, also may be a strategy to locate areas of recent rain and therefore hosts [17]. ...
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A recent study has found that, as migrating silver Y moths pass high overhead above central England in the spring, their headings were generally aimed towards north---a reversal of direction relative to that of autumn migrants. The silver Y must detect its direction of movement, likely by a magnetic sense which must reverse with the season.
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The performance of tethered flies on a laboratory flight mill was used to assess the flight capacity of Hypoderma tarandi (L.) and Cephenemyia trompe (Modeer). Maximum total flying times for H. tarandi females were 31.5 h, but most flies flew < 20 h (mean 8.5 h (SD 7.2 h)). The longest continuous flight was 12 h. For both species, mating greatly altered the flight behaviour of females. Unmated laboratory-reared females were reluctant to fly, and flew less continuously than mated wild-caught flies. Hypoderma tarandi males typically flew for short periods of a few minutes with long rests between flights. Cephenemyia trompe females seldom exceeded 10 h of total flying time (mean 4.9 h (SD 3.2 h), maximum 10.8 h), but were capable of many hours of sustained flight. Field-trapped C. trompe males normally flew < 8 h (mean 2.8 h (SD 2.1 h), maximum 7.1 h). In free flight the speed of C. trompe males was ≈8 m/s. Maximum flight distances during the lifetime of a fly were estimated to be 600–900 km for female H. tarandi, 220–330 km for female C. trompe, and 200–400 km for males of both species. Hypoderma tarandi could maximally reduce its mass to about 40% of initial mass, and the mass loss rate during flight was 3.5-fold that of basal metabolism (i.e., without flying) at 22 °C. The adaptive significance of the extraordinary capacity for sustained flight of female oestrids is related to the migratory behaviour of their vertebrate host, Rangifer tarandus (L.).
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The existence of a trade-off between flight and reproduction in the migratory noctuid, Spodoptera exempta (Wlk.), was examined in experiments in which female moths were flown on flight balances and then provided with distilled water or sucrose solution. For individuals flight-tested from the night of eclosion (night 0) through night 1 and fed only distilled water, there was a linear, negative relationship between weight-related fecundity and flight duration. When flight was recorded through night 2, a curvilinear relationship was obtained suggesting that highly active moths suffer a smaller decrease in fecundity than predicted from its rate of decline with increasing flight duration in less persistent fliers. The hypothesis that this reflects an energetically expensive, initial phase of each flight, followed by a less costly, cruising phase is examined. Fecundity was independent of flight duration in females provided with sucrose after flight but was related to moth weight, as it was in all unflown moths. Effects of flight and feeding on longevity and mating frequency are also reported. There is a clear trade-off between flight and fecundity in S.exempta which is only evident in moths denied access to a source of carbohydrate after flight. The results indicate the importance of nectar sources in the field in allowing restoration of lipid reserves depleted during migratory flight. An important implication of this conclusion is that lipid is the resource limiting to fecundity in this species and not protein as is generally supposed for leaf-feeding insects. This might be expected in highly active species as lipid is the resource for which the energetically expensive functions of flight and reproduction must compete.
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Field and laboratory evidence now suggests that the African armyworm, Spodoptera exempta, is specifically adapted for survival at low population densities, providing a new basis for understanding the significance of its phase polyphenism and migratory strategy. This conclusion allows deductions to be made as to the expected extent of displacement of flying moths from low and, when they occur as a result of impeded or inadequate dispersal of parent moths, high density populations. The proposed migratory strategy which depends on the genetic determination of flight potential also provides a framework for interpreting observed patterns of armyworm outbreaks through the season and in relation to rainfall. Traits associated with a low-density, “armyworm” strategy are shared by other Noctuids which may have similar life histories.
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Abstract EFSA was asked for a partial risk assessment of Spodoptera frugiperda for the territory of the EU focussing on the main pathways for entry, factors affecting establishment, risk reduction options and pest management. As a polyphagous pest, five commodity pathways were examined in detail. Aggregating across these and other pathways, we estimate that tens of thousands to over a million individual larvae could enter the EU annually on host commodities. Instigating risk reduction options on sweetcorn, a principal host, reduces entry on that pathway 100‐fold. However, sweetcorn imports are a small proportion of all S. frugiperda host imports, several of which are already regulated and further regulation is estimated to reduce the median number entering over all pathways by approximately 10%. Low temperatures limit the area for establishment but small areas of Spain, Italy and Greece can provide climatic conditions suitable for establishment. If infested imported commodities are distributed across the EU in proportion to consumer population, a few hundreds to a few thousands of individuals would reach NUTS 2 regions within which suitable conditions for establishment exist. Although S. frugiperda is a known migrant, entry directly into the EU from extant populations in sub‐Saharan Africa is judged not feasible. However, if S. frugiperda were to establish in North Africa, in the range of thousands to over two million adults could seasonally migrate into the southern EU. Entry into suitable NUTS2 areas via migration will be greater than via commercial trade but is contingent on the establishment of S. frugiperda in North Africa. The likelihood of entry of the pest via natural dispersal could only be mitigated via control of the pest in Africa. If S. frugiperda were to arrive and become a pest of maize in the EU, Integrated Pest Management (IPM) or broad spectrum insecticides currently used against existing pests could be applied.
Article
A multidisciplinary study was undertaken on the bionomics of the African armyworm in eastern Africa as a basis for the development of control strategies for this important pest of cereal crops and pastures. Relevant findings from studies on seasonal distribution, migration, field infestations and population cycles are reviewed in relation to understanding the causes for the onset and spread of armyworm outbreaks. It is concluded that the onset of the first outbreaks of an armyworm epidemic is caused by oviposition at high density by moths concentrated by wind convergence at storm outflows. The sources of these moths seem to be low-density populations which survive from one season to the next at sites receiving unseasonable rainfall. Some areas in Tanzania and Kenya are particularly prone to early outbreaks which are potentially critical for the initiation of a subsequent spread of outbreaks downwind throughout eastern Africa. These areas have low and erratic rainfall, and are near the first rising land inland from the coast. Below average rainfall prior to the development of outbreaks increases the probability of their occurrence. Their subsequent spread is enhanced by storms downwind which concentrate moths in flight and by sunshine during caterpillar development. Persistent wet weather reduces the spread of outbreaks. This study demonstrates the importance and value of developing and implementing a long-term monitoring system over a large region, in this case in Africa, not only for the generation of data used by the forecasters for the prediction and location of possible outbreaks, but also for obtaining a clearer understanding of the epidemiology of a highly mobile pest.
Article
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Long-distance migration has evolved in many organisms moving through different media and using various modes of locomotion and transport. Migration continues to evolve or become suppressed as shown by ongoing dynamic and rapid changes of migration patterns. This great evolutionary flexibility may seem surprising for such a complex attribute as migration. Even if migration in most cases has evolved basically as a strategy to maximise fitness in a seasonal environment, its occurrence and extent depend on a multitude of factors. We give a brief overview of different factors (e.g. physical, geographical, historical, ecological) likely to facilitate and/or constrain the evolution of long-distance migration and discuss how they are likely to affect migration. The basic driving forces for migration are ecological and biogeographic factors like seasonality, spatiotemporal distributions of resources, habitats, predation and competition. The benefit of increased resource availability will be balanced by costs associated with the migratory process in terms of time (incl. losses of prior occupancy advantages), energy and mortality (incl. increased exposure to parasites). Furthermore, migration requires genetic instructions (allowing substantial room for learning in some of the traits) about timing, duration and distance of migration as well as about behavioural and physiological adaptations (fuelling, organ flexibility, locomotion, use of environmental transport etc) and control of orientation and navigation. To what degree these costs and requirements put constraints on migration often depends on body size according to different scaling relationships. From this exposé it is clear that research on migration warrants a multitude of techniques and approaches for a complete as possible understanding of a very complex evolutionary syndrome. In addition, we also present examples of migratory distances in a variety of taxons. In recent years new techniques, especially satellite radio telemetry, provide new information of unprecedented accuracy about journeys of individual animals, allowing re-evaluation of migration, locomotion and navigation theories.
Article
There is considerable debate concerning the fate of populations of noctuid moths, founded during the summer, by migrants moving considerable distances northward of areas where permanent populations persist. This paper compares the female calling behavior of moth species that maintain permanent populations in Canada with those that are known immigrants. Residents initiate calling soon after emergence, regardless of climatic conditions, while the mean age of calling for immigrant species is variable, even under favorable conditions. Furthermore the onset of calling by immigrants is strongly influenced by prevailing temperature and photoperiodic conditions during adult life. These differences may only be of importance for the northward spring dispersal, but as fall conditions induce a delay in the onset of calling of known immigrants it is proposed that this could potentially permit a southerly, upper air migration to suitable overwintering sites.
Article
Background: Numerous recent studies have shown that resident symbiotic microorganisms of insects play a fundamental role in host ecology and evolution. The lepidopteran pest, African armyworm (Spodoptera exempta), is a highly migratory and destructive species found throughout sub-Saharan Africa, that can experience eruptive outbreaks within the space of a single generation, making predicting population dynamics and pest control forecasting extremely difficult. Three strains of Wolbachia have recently been identified infecting this species in populations sampled from Tanzania. In this study, we examined the interaction between Wolbachia pipiensis infections and the co-inherited marker, mtDNA, within populations of armyworm, as a means to investigate the population biology and evolutionary history of Wolbachia and its host. Results: A Wolbachia-infected isofemale line was established in the laboratory. Phenotypic studies confirmed the strain wExe1 as a male-killer. Partial sequencing of the mitochondrial COI gene from 164 individual field-collected armyworm of known infection status revealed 17 different haplotypes. There was a strong association between Wolbachia infection status and mtDNA haplotype, with a single dominant haplotype, haplo1 (90.2% prevalence), harbouring the endosymbiont. All three Wolbachia strains were associated with this haplotype. This indicates that Wolbachia may be driving a selective sweep on armyworm haplotype diversity. Despite very strong biological and molecular evidence that the samples represent a single species (including from nuclear 28S gene markers), the 17 haplotypes did not fall into a monophyletic clade within the Spodoptera genus; with six haplotypes (2 each from 3 geographically separate populations) differing by >11% in their nucleotide sequence to the other eleven. Conclusions: This study suggests that three strains of Wolbachia may be driving a selective sweep on armyworm haplotype diversity, and that based on COI sequence data, S. exempta is not a monophyletic group within the Spodoptera genus. This has clear implications for the use of mtDNA as neutral genetic markers in insects, and also demonstrates the impact of Wolbachia infections on host evolutionary genetics.
Article
Selection for the capacity for prolonged tethered flight in Spodoptera exempta resulted in heavier moths, with significantly larger abdominal glyceride glycerol contents in females of two flight-selected strains (87% and 49% higher than in the comparable non-selected strain) and in males of one of them (80% higher). All flight-selected strains contained individuals of both sexes with very high abdominal glyceride levels. There was no significant relationship between abdominal total glyceride glycerol after flight and flight duration for non-selected moths, but an inverse linear relationship was evident in both sexes from a flight-selected strain. Oxygen consumption during tethered flights by flight-selected moths ranged from 28.2 to 56.6 ml O2g-1h-1. Using these and previous data, notional energy budgets were calculated to account for flight, reproduction and resting metabolism for non-selected and flight-selected S. exempta flown on the flight balances and provided thereafter with distilled water. The results confirm the trade-off between flight and reproduction reported by Gunn et al. (1989). A similar approach using data for two non-selected strains from the field in Kenya indicated genetic variation in migratory potential, reflected both in pre-reproductive period and resources available for flight. We conclude that elevated glyceride levels are a component of the migratory syndrome in S. exempta and that this is the major factor underlying the curvilinear relationship between flight duration and fecundity obtained by Gunn et al. (1989).
Book
Many of the world's most serious insect pests are highly mobile. Knowledge of their movements is an essential requirement for outbreak prediction and effective pest management. This book describes how direct observations of insects in flight, using special-purpose 'entomological' radars, have contributed greatly to current understanding of insect migration and foraging. Take-off, height selection, orientation, and responses to the often complex atmospheric environment receive particular attention, while the outcomes of these behaviours, in he form of seasonal patterns of population movement, are also considered. Coverage extends to radar-based research on foraging strategies, dispersal, bee learning and the movements of beneficial insects. The essentials of radar theory are introduced and there are sections on entomological radar design, alternative remote-sensing technologies and insect echo on weather radars. This comprehensive work is an essential reference for crop-protection entomologists, aeroecologists, biologists studying animal movement, radar ornithologists and meteorologists, and biometeorologists. It will also be of great interest to the wider radar community. Please note that reprints are not available. Try an inter-library loan, or consider purchasing a copy.
Article
Newly-emerged Spodoptera exempta (Walker) (Lepidoptera: Noctuidae) moths contain high levels of lipid held largely in the abdominal fat body, the quantity depending on the larval feeding conditions. There is a positive relationship between weight-related lipid content and moth weight, which is consistent for female but not for male moths, suggesting that larval feeding conditions producing large individuals allow the accumulation of quantitatively disproportionate lipid reserves. Male and female moths have comparable levels of abdominal protein. Changes in the water content in starved moths or ones provided with distilled water or sucrose solution show that while starved individuals die rapidly from desiccation, water-fed moths regulate their water contents between narrow limits which are higher for females than for males. Sucrose-fed moths maintain higher, more variable water contents probably due to the phagostimulatory effect of the sugar. Reproducing and unmated moths are able to supplement their lipid and, to a lesser extent, their protein reserves following carbohydrate uptake. During both larval and early adult stages, the capacity to accumulate lipid reserves in excess of those apparently required for reproduction, suggests that these reserves also provide the main fuel for the prolonged flights of which migratory individuals are known to be capable.
Article
The African armyworm is a migrant moth which, in its larval form, can cause severe plagues which destroy cereal crops, sugarcane and pastures in many parts of Africa. This paper reviews the relevant aspects of a multidisciplinary study into the dispersal behaviour and re-concentration of moths, migratory flight, source areas, population upsurges and the seasonal movement of moths. It introduces the new concepts of primary and critical outbreaks.
Article
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.
Article
Pseudaletia unipuncta (Haw.) (Lepidoptera: Noctuidae) virgin females, maintained at either 10 or 25d̀C under LD 12:12 or 16:8 h, started calling at different ages. For a given photoperiod, calling was initiated 11 days later at 10d̀C than at 25d̀C, while for a given temperature, calling at LD 12:12 h was 3–4 days later than at LD 16:8 h. At 10d̀C 50.8% of females did not call within 35 days at LD 12:12 h compared with 30.8% at LD 16:8 h. Calling started earlier in the scotophase at 10d̀C than at 25d̀C and at LD 16:8 h than at LD 12:12 h. Under all treatments calling generally advanced on successive nights. The time elapsed between the mean onset time of calling and the mid-scotophase was relatively constant under both photoperiod conditions at 25d̀C, but at 10d̀C was more variable. The mean time spent calling increased significantly with calling age but did not differ significantly between the four experimental conditions tested. Older (15 days) females transferred from 10d̀C, LD 16:8 h to 25d̀C at either LD 163 or 12:12 h, required less time to initiate calling than younger (5 days) ones. Those transferred from 10d̀C, LD 12:12 h took the same time, regardless of their age at the time of the transfer. Females experiencing either a decrease or increase in daylength as well as a temperature increase, required respectively more or less time to initiate calling, compared with individuals that only experienced an increase in temperature. If temperature was the only parameter changed females that initiated calling soon after the transfer immediately adjusted their calling periodicity to prevailing conditions. When both temperature and photoperiod were altered, it took several days before calling periodicity adjusted to the new regime. The ecological implications of temperature and photoperiodic conditions on the possible autumn migration of P. unipuncta are discussed.
Article
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.
Article
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A range of techniques was used to quantify the nocturnal flight behaviour of Helicoverpa armigera (Hübner) in pigeon pea (Cajanus cajan) crops near Hyderabad, in central India. These included visual observations in the field, the use of field cages and a vehicle-mounted net, optical and video imaging in the infra-red, and radar. Moth emergence from the soil was observed to start at dusk and recruitment continued steadily throughout the first half of the night. Little activity was observed in moths on the night of emergence, except for weak flying or crawling to daytime refuges. Flight activity of one-day old moths started about 20 min after sunset, peaked 15 min later and within about an hour of sunset had declined to a low level which persisted for the rest of the night. Flight of reproductively mature moths was most frequent about 1 h after sunset and at this time mainly comprised females searching for oviposition sites and nectar sources. By about 2 h after sunset, flight had decreased markedly, but there was a slight increase in activity in the second half of the night caused by males undertaking mate-finding flights. Under the conditions studied, the majority of H. armigera dispersed below 10 m, and there were no mass ascents to higher altitudes like those observed at outbreak sites of the African armyworm, Spodoptera exempta (Walker) (Lepidoptera: Noctuidae). The contrasting migratory strategies of H. armigera and S. exempta are briefly discussed.
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Article
A method of field application of strontium chloride (SrCl2) and the assessment of local dispersal of marked Helicoverpa armigera moths in a mark-capture experiment in southern India are described. A 1.7 ha field of pigeonpea sustaining a population of approximately 400,000 larvae was treated with a single application of SrCl2 plus surfactant at 10 kg/ha, using a motorised high volume sprayer. An estimated 50,400 moths emerging over a 20 day period were unequivocally marked with Sr at a marking efficiency of 55%. Catches of moths in an array of 14 battery operated light traps and 29 pheromone traps, up to 3.5 km distant were analysed by atomic absorption spectrophotometry. Low recaptures of marked moths (7%) in the treated field suggested the rapid exodus of emergent moths, even while the crop remained attractive, and their dilution or replacement by immigrants. The distribution of marked moths in lights and pheromone traps is consistent with a predominantly downwind dispersal close to the ground during the early part of the night and more random movement later on.
Article
A research programme in New Brunswick coordinating the use of radar, specially-instrumented aircraft, and observations from platforms extending above the forest canopy has established the massive scale and regularity of evening take-off flights by spruce budworm moths, Choristoneura fumiferana , and of subsequent nocturnal dispersal at levels high above the ground. A night-viewing telescope showed moths taking off from the tree crowns up until 2330 h, 2.5 h after sunset, while radar dot echoes of uniform strength and size began to appear each night at about the same time. Direct identification of radar echoes was provided by simultaneous catches of budworm moths taken in insect-collecting nets on Cessna 185 aircraft. Moths collected during emigration, displacement, and immigration contained a high proportion of egg-carrying females.Radar recorded the rates of climb and the altitudes reached by the flying moths and provided extensive data on their numbers, density, orientation, direction, speed, and duration of displacement. Airborne moths became concentrated in zones of wind convergence, and line-echoes from moths at wind-shift fronts were detected on radar at distances of 30 km. The time of passage of wind-shift fronts over a surface site was detectable by pilot-balloon observations and by sensing equipment on a 24-m meteorological tower. Wind-fields over New Brunswick, as found from a DC-3, showed a marked contrast between the high degree of wind uniformity on many evenings and convergent winds on other evenings. Attention is focussed on the potential effects of meso-scale sea breeze fronts, of which one example is presented, and of storm cells on moth concentration and dispersal.Through the use of radar, spruce-budworm moth dispersal has been viewed for the first time in its entirety and the integrated research programme has provided new data for better evaluation of the significance of moth dispersal in the initiation and spread of infestations.
Article
In a study of long-range dispersal of the boll weevil, Anthonomus grandis Boheman, in Mississippi in 1974, 162,028 marked adults were released in the center of a trap grid. Eighty-six were captured in traps located on concentric circles at 5-mi intervals for a distance of 50 miles. Two boll weevils were captured at a distance of 45 miles. This is the longest recored for marked boll weevils; it equals the distance recorded for an unmarked boll weevil in Mexico.
Article
In 1969 the early summer injury of the oriental armyworm, Mythimna separata WALKER, was negligible in Tohoku district, with the exception of a localized infestation on a pasture land, while the next generation insects caused severe damage to rice plants and a few other graminaceous crops extensively over the district in the late summer. It seems difficult to explain this extraordinary increase of the armyworm populations merely by the mutiplication of endemic populations. Examination of synoptic weather maps and wind records from the district during the critical oviposition period of the armyworm indicated that the moth immigration borne on a westerly wind was possible when an atomospheric depression rapidly moved from Kirin province of North China to northern Japan across the Japan Sea in late July. The supposition that the moth immigration occurred on this occasion was supported by baittrap catches of the adults in two localities. Distribution of the outbreak areas suggested that some of the immigrant moth-swarms invaded the eastern provinces across the lower parts of the central mountain-range. © 1976, JAPANESE SOCIETY OF APPLIED ENTOMOLOGY AND ZOOLOGY. All rights reserved.
Article
Air speed, ground speed, and track of the bean leafroller, Urbanus proteus (L.), the cloudless sulphur, Phoebis sennae eubule (L.), and the buckeye, Precis coenia (Hübner), were determined by timing individuals flying between 2 parallel lines. Stepwise discriminant analysis revealed no significant differences among leafrollers, sulphurs, and buckeyes in regard to average air speed (22.0, 18.5, and 19.0 km/h, respectively) and track (147°, 147°, and 150°). Most of the butterflies observed were flying in the same direction, referred to as the migratory direction, approximately 150° SSE. No significant differences were found among tracks of leafrollers flying in early afternoon, late afternoon, or in opposing crosswinds. Thus migrating leafrollers apparently compensate both for sun movement and perhaps wind direction in maintaining a relatively constant track.
Article
1. Details are given of the numbers of Laphygma exigua Hubner in the British Isles each year from 1856-1966. The arrival of a large, well-documented, immigration of this moth in May 1962 is considered in relation to the meteorological situation, and a back-track is produced of the surface winds that probably carried the moths from North Africa to the British Isles. 2. Similar back-tracks are also shown for the years 1947-66 and each is associated with the appearance of L. exigua in the British Isles. Two probable sources of the moth, the Iberian Peninsula and North Africa (with the Canary Islands and Madeira), are indicated; which is operative depends on the time of the year. 3. For this moth to arrive in the British Isles from the Iberian Peninsula or beyond, requires a warm south-westerly airstream associated with an Atlantic depression west of Ireland; for it to arrive from the mainland of North Africa the requirements are a similar south-westerly wind in association with an anticyclone off the coast of North Africa moving into the Iberian Peninsula. 4. The arrival of this moth in Holland is also discussed.
Article
Emigration of moths of the Noctuid Spodoptera exempta (Wlk.) from their developmental sites occurred within a few hours of emergence, and captive moths have lived in semi-outdoor conditions for several weeks. Flight has been recorded at all times of night in the Kenya highlands, and has shown a very marked association, seasonally, nightly and even hourly, with rain; it has been observed at temperatures down to 13°C, and inferred at temperatures several degrees lower, so that over the greater part of eastern Africa flight activity is very unlikely to be restricted by low temperatures. The breeding season of S. exempta differs markedly and consistently in different parts of eastern Africa; outbreaks of larvae recorded over the past forty years in Kenya, Tanzania and Uganda have been confined to November-July (very largely to December-May), alternating with those recorded over the past twenty years in Ethiopia, which have been confined to March-December (very largely April to August). The progressive establishment of a network of fifty light-traps in these countries since late 1962 has repeatedly recorded the arrival of invading moths before the first infestations of larvae, and has also provided evidence of a strikingly complete seasonal evacuation of much of the region; all traps in Kenya and most of those in Tanzania have revealed a period of several months in every year without a single moth of S. exempta. Seasonal successions of moth catches and outbreaks of larvae have provided repeated evidence of a progressive northward movement of populations of S. exempta , developing in March in Tanzania and Kenya, and extending across Ethiopia, in some years as far as northern Eritrea by June. The extent of these inferred displacements is consistent with the evidence so far available on behaviour and other factors affecting range of flight, which has been examined in as much detail as the limited data permit. Evidence of a return migration southwards to Kenya and Tanzania is relatively scanty. There are some indications of a north to south sequence of moth catches and outbreaks; the heaviest infestations in Kenya and Tanzania during the four-year period of detailed study were preceded by the largest catches so far recorded at the relevant time of year in Ethiopia; and in several years the first moths arriving in Kenya and Tanzania, in November-December, have appeared with the onset of the north-east monsoon, representing the southward movement of the intertropical convergence zone. Conversely, appearances of moths towards the northern limits of their inferred seasonal migration, in Ethiopia and around the Gulf of Aden in June, have shown an analogous association with the establishment of the south-west monsoon, i.e. , with the northward movement of the intertropical convergence zone. Brief reference is made to evidence of seasonal migration in other parts of Africa; possibly in some years the eastern African populations may be supplemented by migrants from the south. Two recorded moth ‘ swarms ’ have been associated with weather systems characterised by particularly vigorous wind-convergence. It is suggested that wind-convergence may have contributed to the density of the ‘ swarms ’ and of the subsequent infestations of larvae. The overall effect of the seasonal changes in distribution which have been demonstrated is to bring the population into areas experiencing seasonal rains. Such a pattern of seasonal migration is likely to be of particular survival value for grass-eating insects, and such concentration of the insects as may be attributable to the associated wind-convergence may be significant in relation to the status of such insects as pests of cereal crops. Records in the literature of long-range geographical displacements of some other Lepidoptera have been found to be associated in a similar manner with analogous systems of wind and weather in other parts of the world.
Article
A service for forecasting infestations of the larvae of Spodoptera exempta in Kenya, Tanzania and Uganda has been in operation since 1969; it uses nightly moth catches from a network of light traps, together with reports of larvae and meteorological information, to provide weekly forecast probabilities of larvae damaging cereal crops and grazing, in order that control measures may be organized in time. The principles on which the forecasting service is based, operational aspects, and the performance of the service to date, are summarized and illustrated by the formulation and subsequent verification of actual forecasts for representative periods of January and April for 7 years, as examples of the regular assessments undertaken to improve the accuracy of the forecasting service.
Article
Mass emergences of moths from conspicuous gregarious-phase caterpillars in high densities are important sources of migrant moths, which are borne downwind to cause a progression of armyworm outbreaks northwards from Tanzania to Ethiopia, and southwards from Rhodesia to South Africa. This progression might possibly be checked by destroying outbreak caterpillars. The sources of moths which cause the first outbreaks before the progression starts are not known, and the possibility is examined that these come from scattered populations of solitary-phase caterpillars hidden at the bases of green grasses, where they are sometimes found at considerable density. Recent analyses of weather patterns on the estimated dates of arrival of the moths responsible for fourteen groups of outbreaks in Rhodesia suggest that outbreaks could often be caused by convergent windflow concentrating low-density moth populations from sources between Rhodesia and the Mozambique coast, and that these sources may persist for several months. A model is presented which attempts to relate the phase forms found in the field with the life system of the armyworm.
Article
This paper surveys the known historical records of foreign butterflies and moths in New Zealand appearing in the literature between 1855 and 1967. Then detailed observations made bet~veen 1968 and 1976 are discussed, uith particular reference to the fact that many of these mizrant species have been able to breed in New Zealand for varying periods of time. Finall! the flights across the 1 asman Sea are discussed, mith reference to both the prex ailing. 11 eather patterns at the time and to the significance of these migrant insects in the colonisation of New Zealand. RECORDS FROM THE LITER ITURE
Article
The movement of sterile adult tobacco budworms, Heliothis virescens (F.), and corn earworms, Heliothis zea (Boddie), from St. Croix to the islands of Vieques and St. Thomas was detected by operating traps baited with females on the other islands and by inspecting host plants for the presence of marked eggs. On Vieques, 18 of 260 tobacco budworms and 2 of 5 corn earworms captured were marked insects that had been released on St. Croix. On St. Thomas, 5 of 223 tobacco budworms captured were marked insects that had been released on St. Croix. On Vieques, 4 marked tobacco budworm eggs were found. The islands are therefore not completely isolated from each other from the standpoint of insect movement.
Article
Laboratory-reared adult tobacco budworms, Heliothis virescens (F.), marked with dyes (fed in the larval diet) and sterilized by 60Co irradiation were released at separate points in northeastern Mexico and southern Trexas and recovered in sex-lure traps set at known distances at cardinal compass directions. In Mexico, male moths dispersed 10 miles (16.1 km) north in 24 h, and a distance-dilution effect was indicated. In southern Texas, moths dispersed as much as 70 miles (112.6 km) from the release point within an estimated period of 4-5 days. The locations of major areas of cultivated host plants in southern Texas were reflected by the high densities of native moths caught in the baited survey traps, but the numbers of marked, released moths caught at the various locations did not correspond to the numbers of native tobacco bud worms caught.
Article
From estimates of the most likely egg–laying dates of 53 outbreaks of Spodoptera exempta (Wlk.) in East Africa, and from estimates of the likelihood of rainstorms (20 mm or more a day) at the outbreak sites around those dates, it is shown that concentrated laying by moths leading to outbreaks early in the season (January to March) in 1974–75 was associated with rainstorms at the time of oviposition. However, there was no such association in April and May. The mechanism of association is unknown; moths may be concentrated whilst airborne, or they may reach and stay in limited areas wetted by rain, where new grass growth might be expected.
Article
Fresh evidence is described which supports the theory that moths of the Noctuid Spodoptera exempta (Wlk.) (the adult stage of the African armyworm) are migratory. The evidence comes from four main sources: a study of fluctuations in numbers of moths caught in a network of light-traps operated in East Africa; the fertilisation rates in samples of females as shown by dissection; the sex ratios in samples of moths caught in light-traps; and a study of the behaviour of moths in the field during the period immediately following emergence. In certain of these features S. exempta is compared and contrasted with the related S. triturata (Wlk.), in which the evidence points against extensive migration. It is concluded that migration occurs in S. exempta , probably on an extensive scale, and that it therefore has an important bearing on the occurrence and distribution of outbreaks of the larvae.
Article
An entomological radar was used to observe insect flight activity at a coastal locality in north-western Tasmania during the spring of 1973. Insects were regularly observed to take off at dusk, and local movements from nearby islands were detected on several occasions. Large-scale southward movements of insects across Bass Strait were also observed and were found to be associated with the warm anticyclonic airflows which occur ahead of a cold front. Light-trap catches indicated that the insects were noctuid moths, with Persectania ewingii (Westw.), Heliothis punctiger Wllgr. and Agrotis munda Wlk. dominant. The movements appear to have originated mainly in Victoria and south-eastern South Australia, but it is tentatively suggested that the ultimate source of the moths was in the region stretching westwards from north-western Victoria and south-western New South Wales towards the shores of the Spencer Gulf, South Australia.
Article
Techniques used in the radar detection and identification of individual flying insects are outlined, and laboratory and field measurements of the radar cross section of the desert locust, Schistocerca gregaria (Forsk.), are presented. The cross section was strongly aspect-dependent, and had an average value of approximately 1 cm2 at a radar wavelength of 3·2 cm. An example is given of the periodic fluctuation in radar cross section (the radar ‘signature’) produced by locusts in free flight, and the spectral contents of the signatures obtained from 35 laboratory-bred free-flying locusts are described. The fundamental components of the signatures, presumed to be at the wing beat frequency, were closely grouped about 23 Hz. It is suggested that the feasibility of using radar signatures as a means of insect identification will largely depend on the degree to which the species of interest are characterised by specific wing beat frequencies. Estimates of locust flying speed and heading deduced from photographs of locust and balloon radar tracks produced a mean value of 5·3 m s-1. Undetected small-scale flight manoeuvres may introduce negative errors in the estimation of flying speed. It is concluded that radar will provide unique observational facilities for the entomologist but that the limitations introduced by the problem of target recognition have yet to be defined.
Article
1. Comparison of dominant wind directions with seasonal redistribution of Spodoptera exempta caterpillar outbreaks in East Africa provides further circumstantial evidence to support the hypothesis of downwind migration by adult moths. 2. Calculated backward and forward tracks for sixty-nine nights during the 1973–74 and 1974–75 seasons, when there were sudden increases in numbers of moths caught at six light traps, illustrate the variability of downwind movement due to the effects of temporary atmospheric disturbances. 3. Comparison of calculated tracks with known outbreaks before and after the nights of increased moth catch suggests that some outbreaks are derived from unreported sources, especially eariy in the season, and it is therefore unwise to link new outbreaks only with known earlier ones.
Article
1. If synoptic-scale wind systems are important in determining long-distance movements of butterflies, a portion of the variation in daily counts of migrants at a site should be explainable by prior winds. 2. Using special flight traps near Gainesville, Florida, U.S.A., from 29 August until 12 November 1978, we made replicated, continuous counts of four migrant species: Phoebis sennae, Urbanus proteus, Agraulis vanillae and Precis coenia. 3. Significant SSE-ward flights occurred for one or more of the four species on 47 days between 5 September and 6 November (Fig. 1). 4. Seasonal changes in numbers of migrants were similar for the four species (Fig. 1). Median fall migrants were trapped between 22 September (A.vanillae) and 1 October (U.proteus and P.sennae). 5. Daily fluctuations in total numbers of migrants were largely attributable to local weather, viz temperature, wind speed and cloud cover (Fig. 2). 6. Neither local wind direction (Fig. 3) nor back-tracking the positions of air parcels (Fig. 4) helped explain the daily fluctuations. 7. The characteristic autumn weather patterns of south-eastern U.S.A. and the day-to-day steadiness of the numbers of migrants are incompatible with the hypothesis that synoptic-scale wind systems are important in determining butterfly migrations through Gainesville, Florida, in the autumn.
Article
A new apparatus was developed for studies on flight behaviour of the African armyworm, Spodoptera exempta (Wlk.), to record the time and duration of all flights continuously for up to several days. A technique for attaching the mounting bracket to the pharate adult before eclosion allowed flight recording to commence within 1–2h of emergence without the need for anaesthesia. Results obtained using the apparatus indicate that migratory flight does not occur on the night of emergence. The time of take-off of tethered moths in the laboratory agrees closely with observations of flight behaviour in the field.
Article
1) Studies were made in Kenya of the flight behaviour of African armyworm moths which had emerged from areas previously infested with ‘gregarious’ caterpillars. The use of radar and an infra-red optical detector permitted quantitative, direct observations of the flying moths, over all of their flight altitudes, without disturbing their behaviour. 2) Almost all of the successfully emergent moths climbed to altitudes of several hundred metres above ground level and migrated from the emergence sites. Their migratory flights sometimes started on the night of emergence, but on other occasions the moths remained roosting in trees until dawn, then engaged in short dispersal flights, concealed themselves during the day. and commenced migration in mass flights at dusk the following night. 3) The onset of these ‘dusk flights’ occurred when the irradiance level fell on average to 2.7 × 10−5Wm−2 nm−1 in the 450–800 nm range (in the photometric units appropriate for human vision this corresponds approximately to 2 lux). The ‘dawn flights’ began with the first sustained increase in irradiance at dawn, and terminated at the end of dawn twilight. 4) Migratory flight in the strong, easterly winds which usually occurred during the first half of the night resulted in rapid, down-wind displacement to the west. Observations of groups of flying moths passing successively over two radars demonstrated that these migrations could cover at least 20 km. 5) In the second half of the night, winds were usually weak and variable, and up-wind or cross-wind directions of displacement were sometimes observed. 6) Moths were observed to disperse rapidly during their migration, so that the mass influxes which lead to outbreaks must be a consequence of subsequent reconcentration. The importance of meso-scale wind convergence zones in reconcentrating flying moths, and the role of rainfall in inducing descent, and possibly landing, are discussed.
Article
Zusammenfassung Es wurden mit gas-chromatographischer Elektroantennogramm-Methode (Z)-9-tetradecenyl-1-acetat und (Z)-9, (E)-12-tetradecadienyl-1-acetat als die Sexuallockstoffe weiblicherSpodoptera exempta (Wlk.) identifiziert.
Large Whire Birtterfly
  • J Feltwell
Feltwell, J. (1982) Large Whire Birtterfly. Dr W. Junk Publishers, The Hague.
Spruce budworm moth flight and dispersal: new understandings from canopy observations, radar, and aircraft. Memoirs of the Entomological Society of Canada
  • D O Greenbank
  • G W Schaefer
  • R C Rainey
Greenbank, D.O., Schaefer, G.W. & Rainey, R.C. (1980) Spruce budworm moth flight and dispersal: new understandings from canopy observations, radar, and aircraft. Memoirs of the Entomological Society of Canada, No.. 110.
The ecology of Locusta in the semi-arid lands and seasonal movements of populations. Locusta
  • J T Davey
Davey, J.T. (1959) The ecology of Locusta in the semi-arid lands and seasonal movements of populations. Locusta, No. 7.
Field tests with the synthetic sex pheromone of the African armyworm Spodoptera exempta (Wlk.). Centre for Overseas Pest Research
  • D G Campion
  • P O Odiyo
  • A M Mushi
  • D R Hall
  • R Lester
  • B F Nesbitt
Campion, D.G., Odiyo, P.O., Mushi, A.M., Hall, D.R., Lester, R. & Nesbitt, B.F. (1976) Field tests with the synthetic sex pheromone of the African armyworm Spodoptera exempta (Wik.). Centre for Overseas Pest Research, Miscellaneous Report No. 25. London.
Migration: Paths through Time and Space
  • R R Balcer
Balcer, R.R. (1982) Migration: Paths through Time and Space. Hodder & Stoughton, London.
Route of the seasonal migration of the oriental armyworm moth in the eastern part of China as indicated by a three-year result of releasing and recapturing of marked moths
  • K-P Li
  • H-H Wong
  • W-S Woo
Li, K-P., Wong, H-H. & Woo, W-S. (1964) Route of the seasonal migration of the oriental armyworm moth in the eastern part of China as indicated by a three-year result of releasing and recapturing of marked moths. Acta Phytophylactica Sinica, 3, 101-110.
Proceedings of the International Workshop on Heliothis Management
  • J.R. Raulston
  • W.W. Wolf
  • P.D. Lingren
  • A.N. Sparks
Synoptic weather associated with outbreaks of African armyworm, Spodoptera exempta (Walker) (Lepidoptera, Noctuidae), in Zimbabwe during 1973 and 1976f77
  • B W Blair
  • D J W Rose
  • A B Law
Blair, B.W., Rose, D.J.W. & Law, A.B. (1980) Synoptic weather associated with outbreaks of African armyworm, Spodoptera exempta (Walker) (Lepidoptera, Noctuidae), in Zimbabwe during 1973 and 1976f77. Zimbabwe Journal of AKricultural Research, 18, 95-110.
Migration of Laphygma exigua Hb. (Lep.: Noctuidae) in northwestern Europe in 1964
  • K. Mikkola
  • P. Salmensuu
Movement of Highly Mobile Insects
  • A.N. Sparks
Migration as a factor in Heliothis management
  • J R Raulston
  • W W Wolf
  • P D Lingren
  • A N Sparks
Raulston, J.R., Wolf, W.W., Lingren, P.D. & Sparks, A.N. (1982) Migration as a factor in Heliothis management. Proceedings of the International Workshop on Heliothis Management (ed. by W. Reed), pp. 61-73. ICRISAT, Patancheru, India.
Centre for Overseas Pest Re search (Overseas Development Administration
  • J R Riley
  • D R Reynolds
  • M J Farmery
Riley, J.R., Reynolds, D.R. & Farmery, M.J. (1981) Radar observations of Spodoptera exempta, Kenya, March-April 1979. Miscellaneous Report No. 54. Centre for Overseas Pest Research (Overseas Development Administration), London.
An introduction to the status, current knowledge and research on movement of selected Lepidoptera in. south-eastern United States
  • A N Sparks
Sparks, A.N. (1979) An introduction to the status, current knowledge and research on movement of selected Lepidoptera in. south-eastern United States. Movement of Highly Mobile Insects (ed. by R.L. Rabb and G. G. Kennedy), pp. 382-385. North Carolina State University.