Effect of trap cropping on the egg parasitism of Riptortus clavatus (Thunberg) in soybean fields

The integration of several pest management techniques can minimize the use of chemical pesticides. Experiments were conducted to determine the effect of trap cropping on the egg parasitism of Riptortus clavatus (Thunberg) (Heteroptera: Alydidae) in the field level. Each soybean field was separately treated with trap cropping, trap cropping with nectar (buckwheat), and control; Daewon was the main soybean variety in each of these soybean fields. Egg parasitism of R. clavatus was compared among treatments. Ooencyrtus nezarae (Ishii) (Hymenoptera: Encyrtidae) and Gryon japonicum (Ashead) (Hymenoptera: Scelionidae) (Ishii) are parasitoids that were found in the experimental fields in Andong, south-eastern part of the Republic of Korea and the sex ratios of O. nezarae and G. japonicum were 0.78 and 0.67, respectively. The eggs of R. clavatus were parasitized by more than one O. nezarae. One to six O. nezarae emerged from a single host egg, averaging 3.0 per egg. Total egg parasitism was higher in trap crop fields than in trap crop with nectar (buckwheat) or control fields, with parasitism levels of 83%, 75%, and 70%, respectively. Parasitism of O. nezarae was highest in trap crop fields (52%), whereas it was lowest in trap crop with nectar fields (20%). However, no significant differences were found among the parasitism rates of G. japonicum in the three treatments. Furthermore, a negative relationship was found between the parasitism levels of O. nezarae and G. japonicum. The hatchability of R. clavatus eggs was higher in control fields (22%) and lower in trap crop fields (11%). This study suggests the use of trap cropping for the enhancement of biological control agents.