Migrations and dispersal in a South American plague grasshopper, Rhammatocerus schistocercoides Rehn 1906 and impact on management strategies

Lecoq Michel. 2000. Migrations and dispersal in a South American plague grasshopper, Rhammatocerus schistocercoides Rehn 1906 and impact on management strategies. In : XXI International congress of entomology. Gazzoni D.L. (ed.). EMBRAPA-Soja, SEB. Londrina : EMBRAPA, Résumé, p. 37. (Documentos Embrapa Soja, 143) International Congress of Entomology. 21, Foz do Iguaçu, Brésil, 20 August 2000/26 August 2000.

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Abstract : For several years, Brazil (Mato Grosso State), Colombia and Venezuela ("llanos" area) have been facing severe outbreaks of the grasshopper Rhammatocerus schistocercoides. This species shows a very marked gregarious behaviour (but apparently with no phase transformation), and forms dense hopper bands and adult swarms covering several hectares. The study of the flight behaviour of these swarms in the state of Mato Grosso shows that this species has a limited displacement ability (a few kilometers per day), contrary to what was previously hypothesised. In Mato Grosso, outbreaks are mainly a local phenomenon and swarms are not a threat for other Brazilian States. Regular eastward migration of this grasshopper - as often hypothesised during the last ten years - seems completely impossible, given its flying behaviour and local wind and weather conditions. In contrast, the structure of the biotopes, meteorological conditions (the regular alternation, during the dry season, of north or northeast and south winds and the absence of west or east winds), and the existence of (( barriers)) constituted by gallery forests, create small ecological units more or less isolated one from each other. As a result, swarms can only wander locally on a mainly north-south/south-north direction. These displacements show characteristic migratory behaviour - obligatory flight regardless of the biotope quality - but on a restricted scale. Damage to crops is mainly a result of local grasshopper outbreaks (in natural vegetation not far from the crops, areas that are generally not visited by farmers) rather than of long-range migrations of locusts as it was thought previously. As a result, the new control strategy focuses mainly on local monitoring and preventative actions. The situation is very different in the north of Amazonia where swarms are formed in a remote area at the border between Colombia and Venezuela. Given the permanent northeast direction of winds in this region, swarms move relatively fast in a southwest direction. They may not return northward, to the area of their origin. Here is a true invasion phenomenon with a one-way and long distance emigration. In Venezuela, unfavourable winds make the invasion more localized and limited to the vicinity of the source area. (Résumé d'auteur)

Mots-clés Agrovoc : Rhammatocerus schistocercoides, Migration animale, Dynamique des populations, Écologie animale, Lutte antiravageur

Mots-clés géographiques Agrovoc : Brésil

Classification Agris : L20 - Animal ecology

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