Published online by Cambridge University Press: 19 September 2011
Cotesia sesamiae (Cameron) (Hymenoptera: Braconidae) is an indigenous, gregarious, larval endo/parasitoid which is widely distributed in Africa and attacks mid- to late instars of stemborers. There is renewed interest in using Co. sesamiae for biological control to reduce the problems caused by stemborers. However, Wolbachia sp., a bacterial symbiont of some populations of Co. sesamiae, poses some threat to the successful use of the parasitoid for stemborer control. This bacterium's common effect is cytoplasmic incompatibility between infected males and uninfected females. Polymerase chain reaction (PCR) tests were carried out on parasitoid samples collected from 5 locations in Kenya and 8 other countries in eastern Africa. Wolbachia presence was detected in Co. sesamiae populations from Coast and Machakos in Kenya, and from samples collected from 6 other eastern and southern African countries. No infection was detected from western Kenya, Uganda and Malawi. Cross mating among 3 infected populations (North Coast, South Coast and Machakos) and 2 uninfected populations (Kitale and Kuja) was done to establish which populations were reproductively compatible. Biological parameters, such as brood size and percent females were compared among the different crosses. One-way incompatibility, indicative of Wolbachia infection, was observed from the crosses between males of either Mombasa or Machakos arid females from Kitale. Selection of compatible Co. sesamiae populations is critical to successful augmentation biological control programmes.
Cotesia sesamiae (Cameron)(Hymenoptera: Braconidae) est un parasitoïde endémique grégaire des larves de foreur de tiges de céréales. Il est reparti sur toute l'Afrique. Il y a un renouvellement d'intérêt pour l'utilisation de Co. sesamiae dans la lutte biologique contre les foreurs. Toutefois, la bacterie symbiotique, Wolbachia sp:, présente chez certaines populations du parasitoïde est une menace pour l'utilisation efficace de Cotesia sesamiae. Cette bacterie cause généralement une incompatibilité sexuelle entre les mâles infectés et les females non infectées. Les tests par les réactions en chaîne de polymerase (PCR) ont été effectués sur 5 populations différentes du Kenya et des populations collectées dans 8 pays de l'Afrique de l'est. Au Kenya, la bacterie a été détectée chez les populations de la còte et de Machakos et aussi dans les échantillons venant de 6 pays d'Afrique de l'est et du Sud. Aucune infection n'a été observée dans les populations de l'ouest du Kenya, du Malawi et de l'Ouganda. Les croisements génétiques entre les 3 populations infectées (Côte Nord, Côte Sud et Machakos) et les 2 populations non infectées (Kitale et Kuja) ont été effectués pour établir quelles populations étaient incompatibles. Des parametres biologiques tels que le nombre de descendants, et le pourcentage de females ont été comparés pour les differents croisements. Une incompatibilité unidirectionelle charactéristique de l'infection par Wolbachia a été observé dans les croisements où les mâles venaient de Mombasa ou de Machakos et les females de Kitale. La selection des populations compatibles de Co. sesamiae est essentielle au succes des programmes de lutte biologique.
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