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Intraspecific competition in larvae of the larger grain borer, Prostephanus truncatus (Horn) within maize grains

Published online by Cambridge University Press:  19 September 2011

Kwame A. Vowotor*
Affiliation:
Food Research Institute (CSIR), P. O. Box M20, Accra, Ghana
William G. Meikle
Affiliation:
Plant Health Management Division, International Institute of Tropical Agriculture BP 08–0932, Cotonou, Bénin
Jonathan N. Ayertey
Affiliation:
University of Ghana, Crop Science Department P. O. Box 44, Legon, Accra, Ghana
Christian Borgemeister
Affiliation:
Plant Health Management Division, International Institute of Tropical Agriculture BP 08–0932, Cotonou, Bénin
Richard H. Markham
Affiliation:
Plant Health Management Division, International Institute of Tropical Agriculture BP 08–0932, Cotonou, Bénin
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Abstract

The effects of egg clutch size on development and survivorship of the larger grain borer, Prostephanus truncatus (Horn) (Col.: Bostrichidae) on maize were measured in the laboratory using single grains of the white maize variety, TZSR-W, at 30 ± 2°C and 70 ± 5% RH. Varying numbers of P. truncatus eggs (1, 2, 4, 8, or 16) were introduced into a hole drilled into a single maize grain. Destructive sampling was used at regular intervals to obtain data on immature developmental parameters, the location of immatures within the grain and the weight and sex of any emerged adults. First instars fed mainly on the floury endosperm tissue whereas the second and third instars preferred the germ tissue. Mortality due to competition was highest in first instars. At high initial densities (> 4 per kernel), some P. truncatus larvae reduced competition by moving out of the grain. A maximum of 6 adults emerged from a single grain. The mean number of adults that emerged per grain for initial egg densities of 8 and 16 were 3.3 and 3.5, respectively. Prostephanus truncatus adult weight at emergence was not significantly influenced by initial egg density except in the case of clutch size 16. The sex ratio of emerged adults was also unaffected by competition, and was always 1:1. Complete developmental period within grains ranged between 28 and 32 days.

Résumé

Les effets de la taille de la fournée d'oeufs déposés par le grand capucin, Prostephanus truncatus (Horn) (Coleoptera: Bostrichidae), sur son développement et sa survie, ont été étudiés au laboratoire sur les graines isolées du maïs blanc, variété TZSR-W, à une température de 30 ± 2°C et une humidité relative de 70 ± 5%. Un nombre différent d'oeufs (1,2, 4,8 ou 16) de P. truncatus a été introduit dans un trou foré dans chaque graine de maïs. Une méthode destructive a été utilisée à des intervalles réguliers pour recueillir les données sur les paramètres de développement larvaire, la localisation des stades immatures à l'intérieur de la graine ainsi que le poids et le sexe des adultes émergés. Les premiers stades larvaires se nourrissaient principalement de l'endosperme tandis que les second et troisième stades larvaires préféraient se nourrir sur le germe. La mortalité due à la compétition nutritionnelle était très élevée chez les larves du premier stade. A des densités initiales élevées (> 4 individus par grain), certaines larves de P. truncatus évitaient cette compétition en sortant de la graine. Un maximum de 6 adultes a émergé d'une seule graine. Avec des densités initiales de 8 et 16 oeufs par graine, la moyenne d'adultes émergés étaient respectivement de 3,3 et 3,5. Le poids moyen des adultes à l'émergence n'était pas significativement influencé par la densité initiale d'oeufs, sauf dans le cas de 16 oeufs par graine. Le rapport de mâles et femelles adultes n'était pas affecté par la compétition et il est resté tout le temps de 1:1. Le développement complet de l'insecte à l'intérieur des graines se rangeait entre 28 et 32 jours.

Type
Research Articles
Copyright
Copyright © ICIPE 1998

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