Abstract
To evaluate the effectiveness of an egg parasitoid, Trichogramma chilonis Ishii, in suppressing numbers of the diamondback moth (DBM), Plutella xylostella (L.), three types of experiments, the response of T. chilonis to host density within a plant, the response of T. chilonis to host density among plants, and the fluctuation of DBM populations with and without T. chilonis, were carried out in a laboratory and in a greenhouse. T. chilonis attacked more host eggs as their density increased. The number of eggs parasitized was higher and the variation in the parasitism was lower when the number of parasitoids released was larger. However, the number of parasitized eggs per parasitoid decreased as the number of parasitoids released increased. Results of releasing experiments in the greenhouse showed that the behavior of parasitoids toward the DBM eggs is nearly random. A multiple regression analysis suggested that to realize 80 percent parasitism, the release of more than 60 parasitoids per plant is required. The release experiments indicated that T. chilonis has a suppressive effect on DBM density.
