Population dynamics of Plutella xylostella (Lepidoptera : Yponomeutidae) and its parasitoids in the region of Brasilia

The diamondback moth Plutella xylostella (L.) is the most serious pest of Brassicaceae in the world. It is resistant to many insecticides which has led to a search for alternative techniques of control, principally biocontrol based pest management. The impact of P. xylostella and its parasitoids was analysed in a six-month study of cabbage crops in the Brasilia region of Brazil, from June to November 1998. The population of the pest and its guild of parasitoids were quantified on two experimental plots at the Embrapa-Hortaliças research station by weekly samplings. In the first cropping (June to early September) populations of P. xylostella followed a logistic growth curve leading to the destruction of the crops. In the second cropping the rains prevented development of P. xylostella. Seven species of parasitoids were observed, Diadegma leontiniae (Brethes) and Apanteles piceotrichosus (Blanchard) being dominant. Cotesia plutellae (Kurdjumov) and Actia sp., previously more abundant, became very minor parasitoids. Significant differences were observed in specific parasitism rates between the plots. The combined parasitism rates were identical on both plots (around 23%) and were insufficient to regulate the populations of P. xylostella. Six species of hyperparasites were reared from Diadegma leontiniae and Apanteles piceotrichosus, showing a high diversity of natural enemies in this region of recent colonisation by P. xylostella. (Résumé d'auteur