Effect of synthetic aggregation pheromone of Riptortus clavatus on densityand parasitism of egg parasitoid Ooencyrtus nezarae Ishii (Hymenoptera : Encyrtidae) in soybean fields

(E) -2-Hexenyl(Z)-3-hexenoate (E2HZ3H), a component of a synthetic aggregat ion pheromone (pheromone) of the bean bug, Riptortus clavatus, attracts fem ales of the bug's main natural enemy, the egg parasitoid Ooencyrtus nezarae . The effect of E2HZ3H on the density of O. nezarae, and its parasitism of R. clavatus, was studied in soybean fields. When fields were treated with E 2HZ3H, O. nezarae tended to migrate into them before they were invaded by R . clavatus. O. nezarae also reached higher densities in treated than in unt reated fields. In addition, E2HZ3H did not increase the density of R. clava tus. On the other hand, both R. clavatus and O. nezarae migrated into phero mone-treated fields earlier than usual and reached higher densities than in untreated fields. However, E2HZ3H did not increase the percentage parasiti sm of R. clavatus eggs placed artificially on soybean plants. Eggs close to E2HZ3H or the pheromone were not parasitized to any greater extent by O. n ezarae than more-distant eggs.