title: Effects of the herbicides hexazinone and triclopyr ester on aquatic insects.
abstract: Experiments were conducted to measure acute lethal response of aquatic insects to hexazinone (Velpar L) and triclopyr ester (Garlon 4) in flow-through laboratory bioassays, and to determine lethal and behavioral effects of these herbicides on insects in outdoor stream channels. No significant mortality (chi 2 P greater than 0.05) occurred in 13 test species exposed to hexazinone in laboratory flow-through bioassays (1-hr exposure, 48-hr observation) at the maximum test concentration of 80 mg/liter. The survival of insects exposed to 80 mg/liter hexazinone in outdoor stream channels was likewise unaffected. Significant drift (chi 2 P less than 0.001) of Isonychia sp. occurred during a hexazinone treatment of the stream channels, but only at the maximum concentration of 80 mg/liter, and survival of the displaced Isonychia sp. was not affected. In flow-through bioassays with triclopyr ester, 10 of 12 test species showed no significant mortality at concentrations greater than 80 mg/liter. Survival of Isogenoides sp. and Dolophilodes distinctus was significantly affected at less than 80 mg/liter. Lethal concentrations were estimated by probit analysis of concentration-response data (1-hr exposure, 48-hr observation) for Simulium sp. (LC50 = 303 mg/liter), Isogenoides sp. (LC50 = 61.7 mg/liter), and D. distinctus (LC50 = 0.6 mg/liter). Triclopyr ester applications to the stream channels resulted in significant drift and mortality of D. distinctus at 3.2 mg/liter (no effects at 0.32 mg/liter), Isogenoides sp. at 32 mg/liter, and Hydropsyche sp. and Epeorus vitrea at 320 mg/liter. The risk to aquatic insects of these herbicides used in forest vegetation management is discussed.
authors.affiliation: Forestry Canada, Forest Pest Management Institute, Sault Ste. Marie, Ontario.
authors.forename: D P
authors.initials: DP
authors.lastname: Kreutzweiser
authors.forename: S B
authors.initials: SB
authors.lastname: Holmes
authors.forename: D J
authors.initials: DJ
authors.lastname: Behmer
mesh_terms: D000818:Animals; D005618:Fresh Water; D006016:Glycolates / Q000633:toxicity*; D006540:Herbicides / Q000633:toxicity*; D007313:Insecta / Q000187:drug effects*; D007928:Lethal Dose 50; D014227:Triazines / Q000633:toxicity*
chemical_list: D006016:Glycolates; D006540:Herbicides; D014227:Triazines; C032742:triclopyr; C025641:hexazinone