Radar-based studies of the migratory flight of grasshoppers in the middle Niger area of Mali.

ABSTRACT Some grasshopper species are pests of subsistence agriculture in the Sahelian zone of West Africa. Formulation of effective control strategies against these pests requires some knowledge of their migratory ability. In this paper a study is described in which radar was used to observe aspects of the nocturnal migratory behaviour of grasshoppers in the middle Niger delta. Mass take-off at dusk, layering and common orientation were regularly observed. Layering appeared to be related to air temperature. Mean orientation was often downwind but at other times crosswind headings occurred which added to the southerly component of the insects' displacement. Probable source areas of insects overflying the radar were identified by calculations of the insects' back-trajectories.

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    ABSTRACT: Insects can serve as useful radar targets for determining aspects of the structure and kinematics of the atmosphere, but it is necessary sometimes to know more about insect behaviour in order to have confidence in the meteorological interpretations. A variety of meteorological radars situated at Chilbolton in southern England have been used to investigate the nature of multiple shallow clear-air echo layers that were detected at heights between 1.0 and 2.5 km in the vicinity of an elevated daytime thunderstorm (mesoscale convective system). Multi-wavelength and polarization measurements were used to confirm that the layers were due in large part to insects. The layers were within potentially warm air near the top of a cold undercurrent of surface air. The convective updraught of the thunderstorm was fed by air from just above the cold undercurrent. Some of the insect layers were within air destined to ascend into the storm's convective updraught and some were within undercurrent air that was forced to ascend only temporarily as the storm approached. Initially the layer echoes ascended with the airflow but then, close to the storm, their intensity weakened despite continuing updraughts, mainly as a result of the insects dropping downwards. Far ahead of the storm the insects showed a strong preference to remain within their individual shallow layers but, even close to the storm, where they started dropping out, insects still retained a preference to be within these layers. As a result, some layers continued to be discernible as they followed the ascending airflow towards the storm, thereby continuing to serve as useful meteorological tracers of the perturbed flow in the vicinity of the thunderstorm. Copyright © 2011 Royal Meteorological Society
    Quarterly Journal of the Royal Meteorological Society 04/2011; 137(656):723 - 735. · 3.33 Impact Factor
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    ABSTRACT: Radar has been applied to the study of insect migration for almost 40 years, but most entomological radars operate at X-band (9.4 GHz, 3.2 cm wavelength), and can only detect individuals of relatively large species, such as migratory grasshoppers and noctuid moths, over all of their flight altitudes. Many insects (including economically important species) are much smaller than this, but development of the requisite higher power and/or higher frequency radar systems to detect these species is often prohibitively expensive. In this paper, attention is focussed upon the uses of some recently-deployed meteorological sensing devices to investigate insect migratory flight behaviour, and especially its interactions with boundary layer processes. Records were examined from the vertically-pointing 35 GHz ‘Copernicus’ and 94 GHz ‘Galileo’ cloud radars at Chilbolton (Hampshire, England) for 12 cloudless and convective occasions in summer 2003, and one of these occasions (13 July) is presented in detail. Insects were frequently found at heights above aerosol particles, which represent passive tracers, indicating active insect movement. It was found that insect flight above the convective boundary layer occurs most often during the morning. The maximum radar reflectivity (an indicator of aerial insect biomass) was found to be positively correlated with maximum screen temperature.
    Meteorlogical Applications 12/2009; · 1.32 Impact Factor
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    ABSTRACT: Large tracts of millet fields in the Sahel are sprayed with chemical insecticides to control the grasshopper Oedaleus senegalensis, but it is difficult to assess the impact of these pesticide applications on the grasshopper's population dynamics due to its migratory behaviour. The grasshoppers migrate along a route which runs from south to north. Therefore, a simulation model that can simulate population development and migration on a simple south–north transect was used to assess the impact of treatment with pesticides, including the biopesticide Green Muscle®, in terms of grasshopper control on two south–north transects in the Sahel. The results indicate that the various actual pesticide treatments had a considerable overall impact on local grasshopper pressure but had little impact on sites further along the transect, because they were only carried out curatively in the millet fields themselves. The results however suggest that preventive treatment of both grassland and millet fields in the south would be more efficient, and thereby represents an alternative strategy. It would, moreover, appear that this could represent an environmentally sensitive alternative if carried out using Green Muscle, but even preventive use of a traditional chemical pesticide would be more environmentally sensitive than spraying pesticides solely on millet fields curatively and over a larger area.
    International Journal of Pest Management 04/2009; 55(2):113-120. · 0.72 Impact Factor