Rhyssomatus subtilis (Coleoptera: Curculionidae) Impact in Soybean Plant Stands

Abstract  The black soybean weevil, Rhyssomatus subtilis (Fiedler), is an important but infrequently studied insect pest of soybean, Glycine max (L.) Merrill, in South America. Severe crop damage occurs when the adult weevils attack soybean seedlings, resulting in reduced plant stands, and when weevils feed on and oviposit in seedpods. The objectives of this 3-yr study were to quantify early-season damage caused by R. subtilis to terminal buds and plant stands in soybean and evaluate insecticide seed treatments under field conditions relative to this damage. Terminal bud damage is the most consistent criteria for determining early-season damage by R. subtilis to soybean. The results indicated that R. subtilis can cause as much as 36% plant stand loss in soybean. Thiamethoxam and a mixture of ethiprole + fipronil provided significant levels of control of R. subtilis damage, with the higher doses of each product tending to provide longer-lasting protection.