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Life tables, key factor analysis and density relations in natural populations of the legume pod borer Maruca testulalis Geyer (Lepidoptera: Pyralidae) in Western Kenya

Published online by Cambridge University Press:  19 September 2011

J. B. Okeyo-Owuor  and
G. W. Oloo
J. B. Okeyo-Owuor
Affiliation:
The International Centre of Insect Physiology and Ecology (ICIPE), Mbita Point Field Station, P. O. Box 30, Mbita, Kenya
G. W. Oloo
Affiliation:
The International Centre of Insect Physiology and Ecology (ICIPE), Mbita Point Field Station, P. O. Box 30, Mbita, Kenya
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Abstract

Data from regular field samples throughout the life cycle for five generations of the legume pod borer, Maruca testulalis on cowpea crops at one site, and three generations at another, were used to construct life tables and through key factor analysis to determine the key mortality factor. The total mortality from egg to adult was 98.4–98.6% at site 1 and 98.2–99.4% at site 2. At both sites the highest mortality occurred between the eggs and the third instar larvae, whilst the fourth instar larvae suffered the lowest mortality. The commonest cause of mortality was classified as disappearance, followed by disease. Parasitism contributed minimally to M. testulalis mortality. At site 1 disappearance at the egg stage was the key mortality factor and was significantly correlated with the total generation mortality. At site 2, disappearance operating at the larva 1 and 2 stage was tentatively identified as the key mortality factor. The data from site 1 showed no significant correlation between population density and mortality at the same stage. This study provides the first detailed analysis of M. testulalis populations and should contribute towards developing control strategies for this important pest of cowpea.

Résumé

Les données receuillies à partie des échantillons réguliers le long du cycle de vie de cinq générations des insectes térébrants de cosses de pois Maruca testulalis, données enregistrées grâce à la récolte faite dans un site, et sur 3 générations dans un autre, étaient utilisées pour établir des tables de longévité et a travers des analyses des facteurs-clés en vue de déterminer le facteur clé de mortalité. Le taux de mortalité entre l'ovulation et l'état adult était de 98.4 à 98.6% au site 1 et 98.2 à 99.4% au site 2. Dans tous les 2 sites la mortalité la plus élevée a eu lieu entre l'ovulation et la 3ème phase à l'état pupal, tandis que la 4ème phase pupale connaissait le taux de mortalité le plus bas. La cause la plus commune de mortalité envisagée était la disparition, suivie par la maladie. Le parasitisme contribuait très peu à la mortalité chez le M. testulalis. Au site 1, la disparition à la phase ovulaire était le facteur clé de mortalité et était étroitement liée à la mortalité globale de la génération. Au site 2, la disparition se passant lors des phases 1 et 2 était identifiée comme la raison principale de la mortalité. Les données obtenues du site n'ont montré aucune corrélation entre la densité de la population et la mortalité au même phase. Cette étude fournit la première analyse détaillée des populations M. testulalis et devrait contribuer au développement des stratégies de contrôle de cette bête qui détruit les cosses de pois.

Keywords

Maruca testulalislife tableskey factor analysisdensity dependence
Type
Research Articles
Information
International Journal of Tropical Insect Science , Volume 12 , Issue 4 , August 1991 , pp. 423 - 431
Copyright
Copyright © ICIPE 1991

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