The Biological Consequences of Lingering Fenitrothion Residues in Conifer Foliage – A Synthesis

Conifer foliage is a sink for fenitrothion, with a limited capacity for accumulation. Fenitrothion, not derivatives or metabolites, is retained from year to year in foliage on the tree and for at least one year in foliage in forest litter. Translocation can occur but has not been demonstrated to new foliage from foliage treated the previous year.Among forest animals, only insects have been identified as confined entirely to a diet of conifer needles. Among insects tested and observed, diprionid sawflies are most sensitive to fenitrothion poisoning. Diprionids and conifer-feeding pamphiliid sawflies are most threatened because most eat old foliage and, in New Brunswick, may have to feed on contaminated foliage even in years when spraying does not occur.Vertebrates that feed extensively on conifer foliage (none does exclusively) are deer, moose, snowshoe hares, and spruce grouse; spruce grouse is probably the most sensitive to fenitrothion. It is estimated that a 550-g grouse would have to eat 29 kg of foliage containing 1 ppm fenitrothion to ingest a dose lethal to 50% of a test population and that significant sublethal effects are unlikely.