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Forecasting the Severity of Armyworm Seasons in East Africa from Early Season Rainfall

  • M. R. Tucker
Article

Abstract

—The relationship between seasonal numbers of outbreaks of African armyworm (Spodoptera exempta) in Kenya and Tanzania, and early season rainfall in source areas has been examined using records for 21 seasons. Significant inverse relationships were found between numbers of Kenya outbreaks and early season rains in the Kisumu area, and between numbers of Tanzania outbreaks and early season rains in the Morogoro and Mtwara areas. Total Kenya and Tanzania outbreak numbers were significantly inversely related to early season rainfall for 8 areas combined. These results suggest that early season rainfall totals, either from specific likely source areas or countrywide, could be used in January to give a seasonal forecast of likely numbers of armyworm outbreaks during the rest of the season. Seasons with more than average numbers of outbreaks often follow poor early season rains and visa versa. Further work is needed to establish biological causes of this apparent relationship.

Key Words

Spodoptera exempta rainfall Kenya Tanzania seasonal forecasts 

Résumé

—Le rapport entre les chiffres d’attaques au Kenya et en Tanzanie par la chemille légionnaire africain (Spodoptera exempta) et la pluviosité du début de saison a été examiné en utilisant des données pour 21 saisons. Des rapports inverses significatifs ont été trouvés entre le nombre d’attaques au Kenya et des pluies précoces dans la région de Kisumu et pareillement entre le nombre d’attaques en Tanzanie et des pluies précoces dans les régions de Morogoro et Mtwara. La totalité des attaques au Kenya et en Tanzanie se trouvait en rapport inverse significatif avec les pluies précoces dans une combinaison de huit régions. Ces résultats offrent la perspective d’utiliser au mois de janvier des chiffres globaux de pluviosité précoce dans les régions éventuellement génératrices des attaques, ou bien dans les pays entiers, pour prévoir le nombre probable d’attaques par la chemille légionnaire pendant le reste de la saison. D’habitude les attaques se révélent plus nombreux dans les saisons ou les pluies précoces sont rares, et réciproquement. La détermination des raisons biologiques de ce rapport apparent exige des travaux complémentaires.

Mots Clès

Spodoptera exempta pluie Kenya Tanzania prévisions saisonnière 

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Copyright information

© ICIPE 1984

Authors and Affiliations

  • M. R. Tucker
    • 1
  1. 1.Tropical Development and Research InstituteLondonUK

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