title: Horizontal and trophic transfer of diflubenzuron and fipronil among grasshoppers (Melanoplus sanguinipes) and between grasshoppers and darkling beetles (Tenebrionidae).
abstract: The possibility of horizontal transmission of diflubenzuron and fipronil was assessed in rangeland grasshoppers. Laboratory studies of Melanoplus sanguinipes demonstrated that fipronil was horizontally transferred at lethal levels (p < 0.05) via cannibalism through four passages when the initial dose applied to a food source was 250 times the label rate for rangeland grasshopper and locust control (label rate is 4 g AI/ha). Mortality was 100% on the first three passages through cannibalism. At 25 and 1 times the label rate, fipronil was lethal (p < 0.05) only on the first cannibalistic passage. Diflubenzuron generated significant (p < 0.05) mortality via horizontal transmission through two passages when the initial dose applied to a food source was 2,000 times the label rate for rangeland grasshopper control (label rate is 8.71 g AI/ha). There was 100% mortality in the first passage via cannibalism. At 250 and 25 times the label rate, diflubenzuron was lethal only on the first cannibalistic passage. Field applications of these two acridicides followed by collection of cadavers (Amphitornus coloradus and Ageneotettix deorum) that were fed to M. sanguinipes in the laboratory revealed that fipronil (25 times the label rate) generated significant (p < 0.05) mortality through two passages and diflubenzuron (label rate) caused no mortality via necrophagy. Tenebrionid beetles fed grasshopper cadavers collected from the field application of fipronil yielded 45% mortality, compared with 25% mortality in the controls. These findings suggest that horizontal and trophic transfer probably play a nominal ecotoxicological role in rangeland grasshopper control programs with diflubenzuron, but the transfer of fipronil to grasshoppers, scavengers, and natural enemies via necrophagy may increase both the efficacy of control programs and their environmental affects.
authors.affiliation: Entomology Section, Department of Renewable Resources, University of Wyoming, Laramie, WY 82071-3354, USA. dsmith@uwyo.edu
authors.forename: D I
authors.initials: DI
authors.lastname: Smith
authors.forename: J A
authors.initials: JA
authors.lastname: Lockwood
mesh_terms: D000818:Animals; D002190:Cannibalism; D001517:Coleoptera / Q000502:physiology*; D004132:Diflubenzuron / Q000633:toxicity*; D005247:Feeding Behavior / Q000502:physiology*; D006110:Grasshoppers / Q000502:physiology*; D007300:Insect Control / Q000379:methods*; D011720:Pyrazoles / Q000633:toxicity*
chemical_list: D011720:Pyrazoles; D004132:Diflubenzuron; C082360:fipronil