Dose-response relationships of clothianidin, imidacloprid, and thiamethoxam to Blissus occiduus

Neonicotinyl insecticides (imidacloprid, clothianidin, and thiamethoxam) are generally highly effective against a variety of turfgrass pests, particularly phloem-feeding insects. Imidacloprid and thiamethoxam, however, have shown only moderate to poor control of the western chinch bug, Blissus occiduus Barber. To better understand the intrinsic toxicity of these insecticides, systemic and contact bioassays were conducted to document their dose-response relationships against B. occiduus. Third and fourth instars and adult B. occiduus were exposed to buffalograss treated with technical grade imidacloprid, clothianidin, and thiamethoxam to document systemic activity at lethal and sublethal concentrations. A companion study evaluated the contact activity of these insecticides. In this study, third and fourth instars and adult B. occiduus were placed in scintillation vials treated with technical grade imidacloprid, clothianidin, thiamethoxam, and bifenthrin, a synthetic pyrethroid considered a commercial standard for chinch bug control. In the nymphal systemic and contact bioassays, clothianidin was the most toxic neonicotinyl insecticide, followed by imidacloprid and thiamethoxam. In the adult bioassays, thiamethoxam exhibited the greatest toxicity. A concurrent study assessed insecticide levels in buffalograss leaf tissues. Buffalograss field plots were treated with labeled rates of Arena 0.5 G (clothianidin) at 89.7 kg/ha, Meridian 25 WG (thiamethoxam) at 19.1 kg/ha, and Merit 75 WP (imidacloprid) at 9.6 kg/ha. Leaf tissue was harvested from the blades and stems at 3, 7, 14, and 28 days after treatment. The concentrations of insecticides were analyzed using high pressure liquid chromatography (HPLC). Results will be presented at the 2009 Annual Meeting of the ESA.