Biodegradable Insecticides in Forestry
159
the forest manager with a choice of registered insecticides as part of an integrated
pest management program for suppression of major forest pest problems. The
approach used by the Forest Service to make the transition from DDT to the
present use of conventional biodegradable insecticides is the focus of this review.
To stress the importance of the environmental aspect of pesticide R&D, a
former chief of the Forest Service (McGuire, 1976) has said:
The solutions to our problems are becoming more difficult to achieve and will continue
to become increasingly complex because of environmental considerations; but this is
only proper. We must be responsive to the environmental impacts associated with our
programs and the programs of others. We must broaden our responsibilities to include
all aspects of environmental quality as it affects the health and vitality of forest stands.
7.2. NEED FOR INSECTICIDES
In the United States, native and introduced insect populations in forests at
times cause considerable economic damage (NAS, 1975b). Most of the significant insect damage to forests is done by defoliators and bark beetles. The most
important defoliators are the spruce budworm [Choristoneurafumiferana (Oem.)],
western spruce budworm (Choristoneura occidentalis Freeman), Douglas fir
tussock moth [Orgyia pseudotsugata (McDunnough)], and gypsy moth [Lymantria dis par (L.)]. Other defoliators are serious pests at times on specialty sites
(e.g., Christmas tree farms) (NAS, 1975b).
The most destructive cambium-phloem-feeding insects are the bark beetles.
Predominant species creating major economic losses are the western pine beetle
(Dendroctonus brevicomis Le Conte), spruce beetle [Dendroctonus rufipennis
(Kirby)], mountain pine beetle (Dendroctonus ponderosae Hopkins), and southern pine beetle (Dendroctonus frontalis Zimmerman). The trees lost from these
cryptic insects are highly visible because of changes in coloration. Such changes
are associated with impending death in trees.
Impact of forest insects is hard to assess (NAS, 1975a,b) and is a major
part of future programs to develop technology in impact assessment of defoliators
(CANUSA. 1979; USDA, 1977b, 1978b) and bark beetles. The impact of insect
defoliators on growth and mortality of trees has been reviewed (Kulman, 1971).
Radial growth ceases only if defoliation is complete (Rose, 1958). Partial defoliation, as associated with most coniferous insect defoliators, results in a reduction in radial growth and may cause top-kill and dieback. The major impact
of insect defoliation or growth of conifer trees more closely correlates with
utilization than with production of photosynthate, since stored carbohydrate is
often present but not utilized in the absence of plant hormones. Usually, the
greatest and first observable effects are noted in the living crown where hormones
are produced (Kulman, 1971). Trees in Minnesota forests infested with jack pine
159
the forest manager with a choice of registered insecticides as part of an integrated
pest management program for suppression of major forest pest problems. The
approach used by the Forest Service to make the transition from DDT to the
present use of conventional biodegradable insecticides is the focus of this review.
To stress the importance of the environmental aspect of pesticide R&D, a
former chief of the Forest Service (McGuire, 1976) has said:
The solutions to our problems are becoming more difficult to achieve and will continue
to become increasingly complex because of environmental considerations; but this is
only proper. We must be responsive to the environmental impacts associated with our
programs and the programs of others. We must broaden our responsibilities to include
all aspects of environmental quality as it affects the health and vitality of forest stands.
7.2. NEED FOR INSECTICIDES
In the United States, native and introduced insect populations in forests at
times cause considerable economic damage (NAS, 1975b). Most of the significant insect damage to forests is done by defoliators and bark beetles. The most
important defoliators are the spruce budworm [Choristoneurafumiferana (Oem.)],
western spruce budworm (Choristoneura occidentalis Freeman), Douglas fir
tussock moth [Orgyia pseudotsugata (McDunnough)], and gypsy moth [Lymantria dis par (L.)]. Other defoliators are serious pests at times on specialty sites
(e.g., Christmas tree farms) (NAS, 1975b).
The most destructive cambium-phloem-feeding insects are the bark beetles.
Predominant species creating major economic losses are the western pine beetle
(Dendroctonus brevicomis Le Conte), spruce beetle [Dendroctonus rufipennis
(Kirby)], mountain pine beetle (Dendroctonus ponderosae Hopkins), and southern pine beetle (Dendroctonus frontalis Zimmerman). The trees lost from these
cryptic insects are highly visible because of changes in coloration. Such changes
are associated with impending death in trees.
Impact of forest insects is hard to assess (NAS, 1975a,b) and is a major
part of future programs to develop technology in impact assessment of defoliators
(CANUSA. 1979; USDA, 1977b, 1978b) and bark beetles. The impact of insect
defoliators on growth and mortality of trees has been reviewed (Kulman, 1971).
Radial growth ceases only if defoliation is complete (Rose, 1958). Partial defoliation, as associated with most coniferous insect defoliators, results in a reduction in radial growth and may cause top-kill and dieback. The major impact
of insect defoliation or growth of conifer trees more closely correlates with
utilization than with production of photosynthate, since stored carbohydrate is
often present but not utilized in the absence of plant hormones. Usually, the
greatest and first observable effects are noted in the living crown where hormones
are produced (Kulman, 1971). Trees in Minnesota forests infested with jack pine