Relative toxicity of spirotetramat on Riptortus pedestris (Hemiptera:Alydidae) and its egg parasitoids

Spirotetramat is lipid biosynthesis inhibitor effective against sucking insect pests and harmless to natural enemies. Due to these advantages, spirotetramat has potential to be registered for the management of soybean pests such as soybean aphid in Korea. We evaluated this insecticide against bean bug Riptortus pedestris (F.), one of the most important soybean pest now in Korea, and its two egg parasitoids Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and Gryon japonicum (Ashmead) (Hymenoptera: Platygastridae). Five concentrations of spirotetramat, i.e., 1.00, 0.50, 0.25, 0.13, and 0.06 ml/l were tested. The insects were fed with those insecticide solutions for 24 h after 12 h of starvation. The lethal median dose (LD₅₀) of second instar of bean bug was calculated as 0.25 ml/l after 48 h whereas that of forth instar and adult was 1.0 and 19.0 ml/l, respectively. The median lethal time (LT₅₀) of bean bug when exposed to the concentration of 0.50 ml/l was 1.2-1.5 times higher than that of control whereas in G. japonicum and O. nezarae was 1.1-1.2 times of control. These results show that spirotetramat is harmless to egg parasitoids of bean bug and would be applied in integrated soybean pest management.

Keywords: biological control, bean bug, toxicity, systemic insecticide, Ooencyrtus nezarae, Gryon japonicum