D3073: Populations of Plutella xylostella and parasitism by Diadegma insulare on cultivated and weedy Brassicaceae

The diamondback moth, Plutella xylostella (DBM), is the primary pest in the production of Brassicaceae like cabbage, cauliflower, Brussels sprouts and broccoli. The control of DBM is based on synthetic insecticides. There are few studies on weeds of the same family (like wild mustard and rockets) as hosts of DBM. An efficient natural control of DBM are parasitoids like Diadegma spp. (Braconidae). The role of weeds and crops in the Brassicaceae, on population dynamics of DBM and Diadegma insulare   was studied. Larvae of P. xylostella were collected from three of the most abundant Brassicaceae weeds, as well as from cabbage. Data were taken from plants exposed to sunlight and in shaded conditions. DBM numbers and level of parasitism were influenced both by host plant species and by sunlight. In the weeds Sisymbrium irio and Eruca sativa a high level of parasitism of D. insulare on P. xylostella is shown in shade conditions. In Lepidium virginicum, on the other hand, the parasitoid appears to maintain similar levels of parasitism regardless of the conditions under which the plants were collected. Regarding the larvae collected from Brassicacea oleracea var. capitata, in these there was a higher level of parasitism in sunny conditions compared to shaded conditions. This study indicates the importance of weeds and environmental conditions (sunlight) in the population dynamics of DBM. Furthermore, these data indicate the importance of weeds as a reservoir of the parasitoid D. insulare.