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LABORATORY EVALUATION OF MICROENCAPSULATED FORMULATIONS OF CHLORPYRIFOS-METHYL AGAINST BLACK FLY LARVAE (DIPTERA: SIMULIIDAE) AND SELECTED NONTARGET INVERTEBRATES1

Published online by Cambridge University Press:  31 May 2012

C. S. Rodrigues
Affiliation:
Department of Enviromental Biology, University of Guelph, Guelph, Ontario, CanadaN1G 2W1.
N. K. Kaushik
Affiliation:
Science Service, New York State Museum, The State Education Department, Albany, New York 12230.
D. Molloy
Affiliation:
Department of Enviromental Biology, University of Guelph, Guelph, Ontario, CanadaN1G 2W1.

Abstract

Laboratory tests were conducted under simulated stream conditions to determine the efficacies of microencapsulated formulations of chlorpyrifos-methyl (Reldan® 10–10) against Simulium and Prosimulium late-instar larvae. In tests with eight formulations, no correlation was evident between efficacy and formulation stability (i.e., cross-linking ratio). The most effective formulations were 34-75-50A, 119-75-6A, and 119-75-6C. The LC50 and LC90 values of 34–75–50A against S. vittatum were 5.5 μg/L and 24 μg/L/10 min. respectively. The formulations 119-75-6A and 119-75-6C were statistically not different from 34-75-50A. Prosimulium magnum was less susceptible (LC50 = 36μg/L, LC90 = 205 μg/L). Susceptibility among S. vittatum larvae varied inversely with size. Treatment with formulation 34-75-50A at 237 μg/L/10 min (the observed LC100 for S. vittatum) severely affected nymphs of the mayfly Baetis sp. and the stonefly Taeniopteryx burksi, but had a minimal effect on most other detritivores, filter-feeding caddisflies (Hydropsyche betteni and Brachycentrus sp.), and predators. Mortality increased significantly in some of these latter species, however, when exposed to 492 μg/L/10 min (the observed LC100 for P. magnum). Tests indicated that there was some leakage of active ingredient from the microcapsules into the water. Although the microencapsulated formulations of chlorpyrifos-methyl were designed to have selective toxicity to black fly larvae, our laboratory tests indicated that they were not as safe towards nonfilter feeders as had been expected.

Résumé

Des tests de laboratoire simulant des conditions de ruisseaux ont été effectués afin de déterminer l'efficacité de certaines formules microcapsulaires du chlorpyrifos-méthyle (Reldan® 10–10) contre les larves âgées de Simulium et de Prosimulium. L'essai de 8 formules n'a révélé aucune corrélation entre l'efficacité et la stabilité des formules (c.-à-d. l'incidence de liaisons croisées). Les formulations les plus efficaces étaient les numéros 34-75-50A, 119-75-6A et 119-75-6C. Les valeurs des CL50 et CL90 de 34–75–50A contre S. vittatum étaient 5.5 μg/L et 24 μg/L/10 min, respectivement. Les formules 119-75-6A et 119-75-6C ne différaient pas statistiquement de 34-75-50A. Prosimulium magnum est moins sensible (CL50 = 36 μg/L, CL90 = 205 μg/L). La sensibilité a varié inversement avec la taille chez les larves de S. vittatum. Le traitement avec la formule 34-75-50A à 237 μg/L/10 min (la CL100 observée pour S. vittatum) a affecté sévèrement les naiades de l'éphémère Baetis sp. et du plécoptère Taeniopteryx burksi, mais a eu peu d'effet sur la plupart des autres détritivores, sur les larves filtrantes de trichoptères (Hydropsyche betteni et Brachycentrus sp.) et sur les prédateurs. Cependant la mortalité chez certaines de ces espèces a augmenté significativement lorsqu'elles furent exposées à 492 μg/L/10 min (la CL100 observée pour P. magnum). Les tests ont indiqué qu'il y a libération dans l'eau de l'ingrédient actif à partir des microcapsules. Bien que ces formules microcapsulaires du chlorpyrifos aient été conçues dans le but d'une toxicité sélective à l'endroit des larves de mouches noires, nos tests de laboratoires ont montré qu'elles n'étaient pas aussi sécuritaires qu'espéré pour les organismes non-filtrants.

Type
Articles
Copyright
Copyright © Entomological Society of Canada 1983

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