Field studies were carried out in Honduras on the natural parasitism of the yponomeutid Plutella xylostella by the ichneumonid Diadegma insularis in cabbages. Parasitism was examined in plots treated with conventional chemical insecticides, the microbial pesticide Bacillus thuringiensis [as Dipel] and an untreated control. Fourth-instar larvae and prepupae of the pest were collected from 2 sites on a weekly basis between June 1988 and January 1989. Mean parasitism levels for each site were: 23.2 and 18.5% for the conventional treatments; 26.9 and 23% for B. thuringiensis treatment; and 29.3 and 28.5% in untreated controls. none