Seasonal dynamics of the development of the diamondback moth, Plutella xylostella and its hymenopteran parasitoids on cabbages in the Dakar region (Senegal, West Africa)

Between June 2000 to May 2001 a survey has been conducted at 3 sites located in the suburbs of Dakar to determine the composition of the complex of hymenopteran parasitoids attacking P. xylostella and the pattern of the seasonal and spatial dynamics of the pest and its parasitoids. Four species of parasitoids have been reported: Oomyzus sokolowskii, Apanteles litae, Brachymeria sp. and Cotesia plutellae. To our knowledge, Cotesia plutellae has been reported for the first time on cabbage in Senegal. Field populations of P. xylostella are attacked year-round with high rates of parasitism. The highest level of parasitism was observed between September and November (39-49%) and the lowest in April (12.6%). The dynamics of P. xylostella and its hymenopteran parasitoids are also greatly influenced by environmental factors. In Senegal it seems that P. xylostella is mainly attacked by hymenopteran parasitoids (mainly Oomyzus sokolowskii) which are responsible for the mortality of immature stages. Several attempts to isolate microsporidia and other entomopathogens have failed (Diarra, 1988). (Résumé d'auteur