174
Carl E. Crisp
Lyon, 1973a-c). Generation mortality in response to pyrethrins, mexacarbate,
and DDT has been investigated in depth (Robertson et al., 1976). No significant
change in the pattern of response to mexacarbate throughout the period of rearing
to the nondiapausing colony could be established.
Development of resistance by forest insect defoliators is not expected to
occur. since the frequency of application is only once or twice per 10-year period
and seldom more than once per season. Genetic stress of such low magnitude
is not expected to produce resistance. On the other hand, if the frequency of
application increases then genetic stress may follow.
7.6.2. Bioassay Studies
Bioassays with laboratory-reared and field-collected insects are used to
obtain an LDso or LCso that can be used to characterize other responses. Some
examples of bioassays for special uses are bioassays of field-collected plant parts
to determine residues (Barger, 1978; Hopewell, 1977; Markin et al., 1978),
rainfastness (Robertson, 1979b), anatomical susceptibilities (Roberts et al., 1976),
evaluations of insecticides for systemic activity in plants (Crisp, 1972), testing
synergism (Lang, 1970; Roberts et al., 1972), and juvenile hormones (Richmond,
1972). Bioassays have been used to evaluate structure-activity relationships
(Look et al., 1976; Miskus et al., 1968) and to evaluate the impact of fungi and
bacteria on insects (Lewis and Filer, 1977). Bioassays have been found useful
for evaluating the toxicity of insecticide metabolites generated by various in vivo
and in vitro techniques (Roberts et al., 1969, 1978). Even the shelf life of
insecticides can be checked with bioassays (Page and Robertson, 1976).
7.6.3. Individual Tree Evaluations
The use of single trees for insecticide efficacy tests has had mixed acceptance
among forest entomologists (Lyon, 1976). In Canada, after laboratory testing,
candidate insecticides are generally tested on individual trees, then on tens of
thousands of acres of trees. In the United States, individual tree tests are not
generally conducted before aerial tests, (Lyon, 1976). The major rationale against
individual tree tests is that the statistical sample is too small, insect populations
within trees and between trees are highly variable with respect to stage of development and density, and field parameters such as drop spectrum, spray volume, and coverage are difficult to simulate on individual trees. In spite of these
limitations, individual tree tests have yielded a wealth of useful information.
Three basic application methods used in single-tree treatments are hydraulic,
aerial application to potted trees placed on airport runways, and simulated aerial
spray tests.
Carl E. Crisp
Lyon, 1973a-c). Generation mortality in response to pyrethrins, mexacarbate,
and DDT has been investigated in depth (Robertson et al., 1976). No significant
change in the pattern of response to mexacarbate throughout the period of rearing
to the nondiapausing colony could be established.
Development of resistance by forest insect defoliators is not expected to
occur. since the frequency of application is only once or twice per 10-year period
and seldom more than once per season. Genetic stress of such low magnitude
is not expected to produce resistance. On the other hand, if the frequency of
application increases then genetic stress may follow.
7.6.2. Bioassay Studies
Bioassays with laboratory-reared and field-collected insects are used to
obtain an LDso or LCso that can be used to characterize other responses. Some
examples of bioassays for special uses are bioassays of field-collected plant parts
to determine residues (Barger, 1978; Hopewell, 1977; Markin et al., 1978),
rainfastness (Robertson, 1979b), anatomical susceptibilities (Roberts et al., 1976),
evaluations of insecticides for systemic activity in plants (Crisp, 1972), testing
synergism (Lang, 1970; Roberts et al., 1972), and juvenile hormones (Richmond,
1972). Bioassays have been used to evaluate structure-activity relationships
(Look et al., 1976; Miskus et al., 1968) and to evaluate the impact of fungi and
bacteria on insects (Lewis and Filer, 1977). Bioassays have been found useful
for evaluating the toxicity of insecticide metabolites generated by various in vivo
and in vitro techniques (Roberts et al., 1969, 1978). Even the shelf life of
insecticides can be checked with bioassays (Page and Robertson, 1976).
7.6.3. Individual Tree Evaluations
The use of single trees for insecticide efficacy tests has had mixed acceptance
among forest entomologists (Lyon, 1976). In Canada, after laboratory testing,
candidate insecticides are generally tested on individual trees, then on tens of
thousands of acres of trees. In the United States, individual tree tests are not
generally conducted before aerial tests, (Lyon, 1976). The major rationale against
individual tree tests is that the statistical sample is too small, insect populations
within trees and between trees are highly variable with respect to stage of development and density, and field parameters such as drop spectrum, spray volume, and coverage are difficult to simulate on individual trees. In spite of these
limitations, individual tree tests have yielded a wealth of useful information.
Three basic application methods used in single-tree treatments are hydraulic,
aerial application to potted trees placed on airport runways, and simulated aerial
spray tests.