Adverse Effects on Birds of Phosphamidon Applied to a Montana Forest

Abstract

A field trial of Phosphamidon applied by aircraft in Montana against spruce budworm (Choristoneura fumiferana) had immediate adverse effects on birds. A 5,000-acre block of forested land was sprayed at the rate of 1 pound per acre. Some birds, including blue grouse (Dendragapus obscurus), were killed by the insecticide. Bird activity on the sprayed plot dropped to about one-quarter of the prespray level of activity while it increased on an unsprayed plot. Two sick blue grouse were caught by hand and held in captivity; one died and the other recovered. Analysis of grouse blood samples showed a marked inhibition of cholinesterase activity in the sick birds, followed by return of cholinesterase to normal in the surviving bird. The spruce budworm continues to be one of the most destructive forest insects in North America (U. S. Forest Service 1964:2), and is the object of large-scale aerial spraying. Although DDT has long been the standard insecticide for use against this pest, its hazard to fish (Cope 1961) and the high residues accumulated in the tissues of big game animals from treated forests (Pillmore and Finley 1963) have aroused growing concern. In 1963, the U. S. Forest Service tested several short-lived insecticide formulations of the organophosphate group against the spruce budworm in hopes of finding an effective replacement for DDT. Phosphamidon (2-chloro-2-diethylcarbamoyl-1methylvinyl dimethyl phosphate) was an attractive candidate material because it has a much lower toxicity to fish than DDT and a relatively short residual life. The commercial distributor's assessment of Phosphamidon's possible hazard to wildlife was highly optimistic (Dever and Wessel 1962). Feeding tests at the Patuxent Wildlife Research Center indicated a high toxicity to bobwhite quail (Colinus virginianus) but a much lower toxicity to ring-necked pheasants (Phasianus colchicus) and mallards (Anas platyrhynchos) (DeWitt et al. 1963:88). A field trial of Phosphamidon was conducted on 5,000 acres of Douglas fir (Pseudotsuga menziesii) forest in western Montana in order to test its effectiveness against the spruce budworm and to evaluate its possible hazard to wildlife, particularly birds. Personnel of the U. S. Forest Service, the U. S. Bureau of Sport Fisheries and Wildlife, and the Montana Department of Fish and Game participated in the study. This content downloaded from 207.46.13.176 on Mon, 20 Jun 2016 07:29:48 UTC All use subject to http://about.jstor.org/terms EFFECTS OF PHOSPHAMIDON ON BIRDS * Finley, Jr. 581 I am grateful to Tom T. Terrell, U. S. Forest Service entomologist and Phosphamidon project coordinator, for technical information and help on numerous occasions. The advice and aid of David Scott and Merle Gee in planning the study are much appreciated. Merle L. Richmond's assistance with all phases of the fieldwork was indispensable to the success of the study. Dr. Robert Eng, Thomas Mussehl, Philip South, and Wesley Woodgerd assisted in searches for grouse after the spray application. Robert Greene, manager of the State Game Farm at Warmsprings, kept captive grouse from the study area and took some of the grouse blood samples required. Measurements of blood cholinesterase were made by Charles W. Hall, chemist, of the Denver Wildlife Research Center.