Biodegradable Insecticides in Forestry
171
throughout the ponderosa pine forests of the northwestern United States and
British Columbia. Tests to determine contact toxicity to larvae showed that
resmethrin, pyrethrins, chlorpyrifos-methyl, methomyl, and chlorpyrifos were
effective insecticides (Lyon and Brown, 1971). Pyrethroids were toxic to two
eastern hardwood defoliating insects-the spring cankerworm [Paleaerita vernata (Peck)] (Page et al., 1974) and the elm spanworm [Ennomos subsignarius
(Hubner)] (Robertson and Lyon, 1973a). The most toxic insecticides were ethanoresmethrin, resmethrin, pyrethrins, mexacarbate, and phoxim (Robertson and
Lyon, 1973a).
A comparison of the relative contact toxicity of insecticides to two subspecies of western tent caterpillar [Malaeosoma ealifornieum luteseens (Neumoegen and Dyar) and M.e. ealifornieum (Packard)] showed that resmethrin,
ethanoresmethrin, pyrethrins, mexacarbate, and methomyl were effective (Robertson and Gillette, 1973; Page and Lyon, 1975). Results of contact toxicity
tests for the forest tent caterpillar (Malaeosoma disstria Hubner) larvae were
very similar to those for the western tent caterpillar (Lyon et al., 1972a).
A major pest of eastern North America which is destructive to pine reproduction is pales weevil [Hylobius pales (Herbst)]. Insecticides for use against
this pest should be persistent within the growing seedling and toxic enough to
kill feeding weevils for one year or more (Hobart, 1977). Topical tests against
the adult weevil showed that fospirate, chlorpyrifos, bioethanomethrin, methomyl, and pyrethrins were effective (Robertson et al., 1975).
The relative toxicities of the pyrethroids would seem to suggest that they
would have promise for field testing. However, less than 1000 acres were sprayed
from 1945 to 1974 with pyrethroids (NAS, 1975b).
Contact toxicity to defoliators and beetles is usually greatest with the pyrethroids. Most control programs use organophosphates and carbamates at the
present time. The real potential of the pyrethroids remains to be realized in forest
pest management. If the new halogenated pyrethroids can meet the challenge of
environmental safety, they may have a future in forestry.
One environmental concern has been the impact of pyrethroids on aquatic
biology. Permethrin applied by aircraft to small lakes at 35 g active ingredient
per acre caused significant, but short-lasting, effects on zooplankton and bottom
fauna. Native fish suffered essentially no mortality (Kingsbury, 1976). Some
fish biologists have been concerned about the reported high toxicity of pyrethroids
to fish (Mauck et al., 1976). However, the results with permethrin to date are
encouraging.
7.6.1.4. Feeding Toxicities
Feeding toxicities of a broad spectrum of the most commonly available
insecticides and some experimental materials have been determined for some
forest insect pests. According to Gillette et al. (1978) and Robertson (1978b)
171
throughout the ponderosa pine forests of the northwestern United States and
British Columbia. Tests to determine contact toxicity to larvae showed that
resmethrin, pyrethrins, chlorpyrifos-methyl, methomyl, and chlorpyrifos were
effective insecticides (Lyon and Brown, 1971). Pyrethroids were toxic to two
eastern hardwood defoliating insects-the spring cankerworm [Paleaerita vernata (Peck)] (Page et al., 1974) and the elm spanworm [Ennomos subsignarius
(Hubner)] (Robertson and Lyon, 1973a). The most toxic insecticides were ethanoresmethrin, resmethrin, pyrethrins, mexacarbate, and phoxim (Robertson and
Lyon, 1973a).
A comparison of the relative contact toxicity of insecticides to two subspecies of western tent caterpillar [Malaeosoma ealifornieum luteseens (Neumoegen and Dyar) and M.e. ealifornieum (Packard)] showed that resmethrin,
ethanoresmethrin, pyrethrins, mexacarbate, and methomyl were effective (Robertson and Gillette, 1973; Page and Lyon, 1975). Results of contact toxicity
tests for the forest tent caterpillar (Malaeosoma disstria Hubner) larvae were
very similar to those for the western tent caterpillar (Lyon et al., 1972a).
A major pest of eastern North America which is destructive to pine reproduction is pales weevil [Hylobius pales (Herbst)]. Insecticides for use against
this pest should be persistent within the growing seedling and toxic enough to
kill feeding weevils for one year or more (Hobart, 1977). Topical tests against
the adult weevil showed that fospirate, chlorpyrifos, bioethanomethrin, methomyl, and pyrethrins were effective (Robertson et al., 1975).
The relative toxicities of the pyrethroids would seem to suggest that they
would have promise for field testing. However, less than 1000 acres were sprayed
from 1945 to 1974 with pyrethroids (NAS, 1975b).
Contact toxicity to defoliators and beetles is usually greatest with the pyrethroids. Most control programs use organophosphates and carbamates at the
present time. The real potential of the pyrethroids remains to be realized in forest
pest management. If the new halogenated pyrethroids can meet the challenge of
environmental safety, they may have a future in forestry.
One environmental concern has been the impact of pyrethroids on aquatic
biology. Permethrin applied by aircraft to small lakes at 35 g active ingredient
per acre caused significant, but short-lasting, effects on zooplankton and bottom
fauna. Native fish suffered essentially no mortality (Kingsbury, 1976). Some
fish biologists have been concerned about the reported high toxicity of pyrethroids
to fish (Mauck et al., 1976). However, the results with permethrin to date are
encouraging.
7.6.1.4. Feeding Toxicities
Feeding toxicities of a broad spectrum of the most commonly available
insecticides and some experimental materials have been determined for some
forest insect pests. According to Gillette et al. (1978) and Robertson (1978b)