R. A. Farrow

The migration of Nilaparvata lugens (stål) (delphacidae) and other hemiptera associated with rice during the dry season in the Philippines: a study using radar, visual observations, aerial netting and ground trapping

The migratory flight behaviour of Nilaparvata lugens (Stal), other delphacid and cicadellid pests of rice and some of their heteropteran predators was investigated during the dry-season crop in an irrigated rice-growing area of the Philippines. A combination of radar (including an X-band and a newly-developed Q-band system (8 mm wavelength)), aerial netting, ground trapping and visual observations was used to determine diel changes in aerial density and composition of arthropods in flight over the study site. The most abundant migrant caught in the aerial nets was Cyrtorhinus lividipennis Reuter (a mirid predator of N. lugens ), with Nephotettix spp. and Nilaparvata lugens the next most abundant species. Flight activity in all migrants was found to be very largely confined to periods of about 30 min at dusk and dawn, with minimal activity at other times of the day and night. Migration distance in the dusk flight was generally limited to 6–30 km, depending on wind speed, and the dawn migration covered shorter distances due to the lighter winds. Small numbers of rice cicadellids and delphacids including N. lugens were occasionally detected later in the night, and these may have had the potential to migrate longer distances.

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

Abstract. 1. The spring migration of the oriental armyworm moth, Mythimna separata (Walker), and other insects into northeastern China was observed by radar at a site in central Jilin province. Samples of the migrants were obtained in a net flown from a kite, and M.separata populations in the surrounding region were monitored with a trap network.

The nocturnal migration of the Australian plague locust, Chortoicetes terminifera (Walker) (Orthoptera: Acrididae): quantitative radar observations of a series of northward flights

Night migrations of insects above the surface boundary layer were studied by direct observations with an entomological radar, and by direct aerial sampling with a kite-borne net, in an area in New South Wales inhabited by large fledging populations of Chortoicetes terminifera (Wlk.). The aerial catches and radar echo-modulation observations suggested that the majority of migrants detected by the radar were locusts, and this conclusion was supported indirectly by light-trap catches and by observations of take–off at dusk. Night flights of locusts began at dusk with a mass take-off and continued on a diminishing scale until about midnight. Displacements were all approximately downwind and to the north, under the influence of a southerly airflow which prevailed throughout the six-day study period. A quantitative radar observation procedure was used to estimate locust aerial densities and migration rates, and to observe the variations of these quantities with height and time; typical and extreme values for all the principal migration quantities are presented. The flight paths of the locusts were estimated from radar observations of target tracks, and probable source areas at distances of up to 200 km to the south were identified; a major overflight which probably originated 150 km away was detected on one occasion. Northward movements of C. terminifera during anticyclonic conditions may help to explain how populations are redistributed in the periods between the long-range southward invasion movements for which this species is well-known.

Method of using kites to carry tow nets in the upper air for sampling migrating insects and its application to radar entomology

Insects migrating above the surface boundary layer were efficiently and economically sampled over long periods using a large diameter tow net suspended beneath a kite. In a series of trials in Australia, sequential samples were obtained by day and night at predetermined altitudes, in the range 50–500 m. The net was raised and lowered independently of the kite, so that when conditions were calm in the lower atmosphere the kite could remain aloft in the geostrophic airflow. Potential contamination of insects flying below the sampling height was minimised during net ascent, by reducing the airflow through the net. A radio-operated net-closing and releasing mechanism prevented contamination during the free fall of the net. The catch was converted to absolute values of aerial density and migration rate or flux. Aerial sampling was originally developed to identify upper air migrants under observation by the CSIRO entomological radar and to provide quantitative measurements of those species too small to be individually detected by radar. The technique was subsequently operated independently of radar to quantify microinsect migrations, but not those of macroinsects because of their relatively low catch rate.

The ‘aerial plankton’ and atmospheric convergence

Airborne migration is one of the most common adaptations for surviving and exploiting habitat variability. One weather feature that airborne migrants sometimes encounter, convergence, has the potential to concentrate populations in localities where climatic conditions have made a habitat temporarily favourable. Studies of migratory insects have now begun to establish which of several forms of atmospheric convergence are most likely to affect population processes.

Migration strategies and outbreaks of noctuid pests in Australia.

Cutworms, semiloopers, budworms and armyworms in the genera Agrotis, Chrysodeixis, Heliothis, Mythimna, Persectania and Spodoptera are important pasture and crop pests in Australia. They comprise both cosmopolitan species, such as A. ipsilon, H. armigera, M. separata and 5. tiexempta and endemic species such as A. infusa, H. punctigera, M. convecta, P. ewingii and P. dyscrila. Although the cosmopolitan species are major pests of parts of Asia and Africa, they are, with the exception of H. armigera, less important agricultural pests in Australia than their endemic counterparts. The latter are widely distributed outside cropping areas, because they breed on a wide range of native host plants as well as on introduced crops and pastures and also have the potential to invade cropping areas from native habitats. The cosmopolitan species are largely confined to tropical and subtropical summer crops and improved pastures of north and east Australia where chronic infestations often develop although major outbreaks and migration out of cropping areas are rare. Periodic outbreaks of endemic species result from an unusually favourable growth of vegetation in early autumn, following drought-breaking rains in the inland. Moths arrive in the rain-affected areas as a result of migration and concentration by rain-bearing troughs and depressions. Southward migration of their progeny occurs in spring on warm northerly airflows produced ahead of eastward-moving cold fronts and results in invasions of temperate crops and pastures. Migration also occurs in anticyclonic conditions, resulting in an extensive redistribution of populations and is adapted to the erratic distribution of rainfall in inland Australia. Among cosmopolitan species, only Spodoptera spp. cause outbreaks which are infrequent and occur with the onset of summer rains in coastal and sub-coastal areas. Most movements of cosmopolitan species are confined within cropping areas although migration from coastal to inland crops, under the influence of prevailing SE winds, and in frontal systems, troughs and storm outflows, is also suspected.RésuméLes larves de Lépidoptères des genres Agrotis, Chrysodeixis, Heliothis, Mythimna, Persectania et Spodoptera sont d’importants prédateurs des cultures et des pâturages en Australie. Elles englobent des espèces cosmopolites, telles que A. ipsilon, H. armigera, M. separata, S. exempta et des espèces endémiques, telles que A. infusa, H. punctigera, M. convecta, P. ewingii and P. dyscrita. Bien que les espèces cosmopolites soient des prédateurs majeurs dans certaines aires d’Asie et d’Afrique, elles sont, à l’exception de H. armigera, moins importantes comme pestes d’agriculture en Australie que les espèces endémiques. Ces dernières sont largement distribuées hors des régions de culture, parce qu’elles se reproduisent sur un grand nombre de plantes indigènes, aussi bien que sur les cultures et les pâturages d’espèces introduites, et elles ont la capacité d’envahir les surfaces cultivées à partir de leurs habitats. Les espèces cosmopolites sont largement resteintes aux cultures d’été des tropiques et des sous-tropiques et aux pâturages améliorés du nord et de l’est d’Australie ou les infestations chroniques se dévèloppent souvent, quoique les pullulations majeures et les migrations hors les aires de culture soient rares. Des pullulations périodique d’espèces endémiques se produisent lorsque le début d’autumne est exceptionnellement favorable à la croissance de la végétation, après les fortes pluies suivànt une période de sécheresse. Les lépidoptères arrivent dans les aires arrosées par les pluies, du fait de trous d’air et dépressions atmosphériques porteurs de pluie, qui en provoquent la concentration et le migration. Ils produisent une nouvelle génération qui migre vers le sud au printemps, transportée par les vents chauds qui se forment à l’avant de fronts froids, et qui se déplacent vers l’est. Ainsi se produit l’invasion des cultures et pâturages des zones tempérées. Les migrations ont aussi lieu en conditions anti-cycloniques causant une redistribution importante des populations. Ceci est une adaptation à l’irrégularité de la répartition des pluies à l’intèrieur en Australie. Parmi les espèces cosmopolites, seule les spodoptères causent des pullations, mais rarement, à l’arrivée des pluies d’été dans les régions côtières et sub-côtières. Les déplacements des espèces cosmopolites sont généralement confinés aux aires de culture bien que les migrations vers l’intèrieur à partir des côtes soient également suspectées, en cas de de vents de sud-est dominants et dans les fronts atmosphériques, les trous d’air ou les courants orageux.

The development of the 1983 outbreak of the common armyworm, Mythimna convecta, in eastern Australia.

A large outbreak of common arymworm began in spring 1983, 6 months after the conclusion of a nation-wide drought, and occurred throughout the major cereal-growing regions of E Australia. Probable source areas were in the extensive grasslands of inland Australia, particularly SW and C Queensland. Population increase appeared to follow a complex sequence of overlapping, complementary generations. Although some generations were initiated directly by the drought-breaking rains, others appeared to arise from isolated thunderstorms which preceded them by several weeks in late summer. Moth emergence occurred in early April, late May, late July, and from late August to November. In each case, except late May, it was hypothesized that there were both local and long-range movements of adults on the synoptic airflows, resulting in moths spreading progressively from several isolated sources into the flourishing grasslands of E Australia. Multitemporal satellite data were used to identify areas of potential armyworm habitat in an inland source area of SW Queensland. Very small patches of suitable habitat were identified during the drought whilst, after the drought broke, 36% of the area comprised green grasses ideal for colonization. The subtropical grasses dried off by late winter and emigration by newly emerged moths on prefrontal airflows enabled the spring populations to colonize the temperate grass regions of inland New South Wales.

Effects of changing land use on outbreaks of tropical migratory locust, Locusta migratoria migratorioides (R. & F.)

In the major breeding areas of tropical migratory locust, Locusta migratoria migratorioides (R. & F.) in Mali, Chad, Sudan and Madagascar, man has played a vital role in maintaining locust numbers above the levels found in undisturbed environments, through his agricultural and pastoral activities. Recent rapid agricultural development, particularly broad-acre cultivation of monocotyledonous summer crops in areas climatically suitable for migratory locust, has caused population upsurges in new areas, which have occasionally led to outbreaks and plagues. Some outbreaks appear to have been a reaction to the initial disturbance and have never recurred while others recur when meteorological conditions are favourable. Continued agricultural development in tropical and sub-tropical areas of the Old World will bring the risk of further upsurges of tropical migratory locust.RésuméDans les principales regions de forte reproduction du criquet migrateur Locusta migratoria migratorioides (R & F), au Mali, Chad, Soudan et Madagascar l’homme, par ses activités agricoles et pastorales, a joué un rôle important dans le maintien du nombre de criquets au dessus des niveaux trouvés dans les terres non cultivées.Le dévelopement récent et rapide de l’agriculture, particulierement les grandes cultures des mono-cotylédones d’été, dans des régions oú le climat est favorable aux criquets migrateurs a permis l’apparition de populations dans de nouvelles regions. Des domages ont été parfois enregistrés. Certains sont apparus par réaction aux pertubations initiees et n ont jamais pu étre réparés alors que dautres s’estompent quand les conditions météorologiques sont favorables.Le dévelopement continu de l’agriculture dans les régions tropicales et sub-tropicales du Vieux Monde amène le risque d’autres catastrophes causé par le criquet migrateur.

New austral records of massive swarming by a chloropid fly, Chloromerus striatifrons (Diptera: Chloropidae)

Mass aggregations, including aerial swarms, of a yellow swarming chloropid fly are reported from Australia. The species, Chloromerus striatifrons (Becker), is endemic to south‐eastern Australia and has been reported swarming only once previously, 40 years ago.