Relative Toxicity of Spirotetramat to Riptortus pedestris (Hemiptera: Alydidae) and its Egg Parasitoids

Spirotetramat, a lipid biosynthesis inhibitor, is effective against sucking insect pests but harmless to insect natural enemies. As spirotetramat can be registered for the management of sucking insect pests such as aphids and bugs in soybeans, we evaluated the insecticide against Riptortus pedestris (Fabricius) (Hemiptera: Alydidae), one of the most important soybean pests in Korea, as well as its effect on two of its important egg parasitoids, Ooencyrtus nezarae Ishii (Hymenoptera: Encyrtidae) and Gryon japonicum (Ashmead; Hymenoptera: Platygastridae). Oral toxicities of five concentrations of spirotetramat (1.00, 0.50, 0.25, 0.13, and 0.06 ml/liter) were tested by feeding these test solutions to insects for 24 h after 12 h of starvation. The lethal median concentration (LC50) for second instars of the bean bug was 0.3 ml/liter after 48 h while values for fourth instars and adults were 9.2 and 19.0 ml/liter, respectively. The median lethal time (LT50) for bean bugs when exposed to a concentration of 0.50 ml/liter was 1.2-1.5 times less than that of the control, while in G. japonicum and O. nezarae it was 1.1-1.2 times less than the control. These results show that spirotetramat is less toxic to the egg parasitoids of bean bug than to bean bug itself and would thus be useful in an integrated management program for this pest.