Effects of 7 concentrations of chlorpyrifos (Dursban 50W), halofenozide (Mach 2) and spinosad (Conserve SC) were tested on bigeyed bugs (Geocoris spp.: Heteroptera: Geocoridae) in bioassays with or without turfgrass as a potential moderating influence. Survival of bigeyed bugs was recorded at 1, 3, 7 and 10 d posttreatment. In a bioassay without turfgrass, the lowest chlorpyrifos dose of 62.5 ppm resulted in 100% adult bigeyed bug mortality; however, significantly more fifth-instar nymphs survived than first to fourth instars, whereas none of the adults survived. Spinosad at the recommended rate significantly reduced bigeyed bug density compared with the untreated check. Similarly, halofenozide influenced bigeyed bug survival only at the full-recommended rate in Petri dish assays. Effects of the same 6 concentrations of insecticides described above were studied on geocorids when 3 turfgrass genotypes, ‘Cavalier’ zoysiagrass (Zoysia japonica von Steudel and Z. matrella L. Merrill), ‘Sea Isle 1’ seashore paspalum (Paspalum vaginatum Swartz), and ‘TifSport’ bermudagrass (Cynodon dactylon L. × C. transvaalensis Burtt-Davy), were present. Chlorpyrifos affected survival of geocorids even at 62.5 ppm in all turfgrass genotypes evaluated at 1 or 3 d posttreatment. More bigeyed bugs survived on ‘Cavalier’ zoysiagrass than other turfgrass genotypes treated with chlorpyrifos. None of the turf-mediated residual concentrations of spinosad caused predator mortality. Insecticide-induced nontarget mortality is influenced by turfgrass genotype and may depend on mode of action of insecticide, type of host plant resistance and plant morphology and architecture.
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Vol. 47 • No. 3