Biodegradable Insecticides in Forestry
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stricted to those periods of the season when they are available. Most toxicology
laboratories establish colonies of insects needed for conducting bioassays and
screening tests. Laboratory-reared insects are acceptable if they are continually
compared with field populations and found to behave similarly. Field collections
are used only when the toxicological effort is short-term or rearing procedures
cannot be established. Insect toxicologists have succeeded in establishing rearing
procedures for gypsy moth (Singh, 1977) and spruce budworm (Lyon et al.,
1972a,b; Robertson, 1979). The procedure for spruce budworm has been adapted
for fall cankerworm [Alsophila pometaria (Harris)] (Lyon and Brown, 1970) and
Douglas fir tussock moth (Lyon and Flake, 1966).
7.6.1.1. Analytical and Statistical Procedures
Analytical and statistical techniques for evaluating results include probit
analysis, the preferred method of evaluating dose response data (Russell et al.,
1977; Savin etal., 1977). A computer program forprobit analysis, POLO (Probit
Or LOgit analysis), is a data-handling and statistical tool (Robertson et al., 1980;
Russell and Robertson, 1979). POLO has been used for several years by the
Forest Service and appears to have broad acceptance.
7.6.1.2. Basic Screening for Relative Toxicity
The kinds of toxicity tests currently conducted are contact toxicities on
larvae or adults by direct application to the insect or in spray chambers and
feeding toxicity on foliage dosed in a spray chamber or on a spiked artificial
diet. Similar procedures and tests are used by the Forest Pest Management
Institute in Canada (Nigam 1977, 1978). Toxicological evaluation of this kind
provides toxicity data which ultimately lead to qualified judgments about the
most promising candidate materials and formulations and provide guidelines for
selecting rational dosage levels and other variables in field tests (Lyon, 1976).
The possible actions of candidate chemicals are mortality (acute and latent),
knockdown, sterilization, interference with growth and development, alteration
of behavior, disease enhancement, synergism, and potentiation.
7.6.1.3. Topical Tests on Insects
Topical (contact) toxicity tests for a broad spectrum of the most commonly
available insecticides and many experimental insecticides have been conducted
against larvae of the western spruce budworm. The pyrethroids structurally related to isomers of decamethrin and cypermethrin are among the most toxic
compounds to sixth-stage budworm larvae. Highly effective pyrethroids from
these classes are NRDC-168S (d,cis-dichlorochrysanthemic acid + 3-cyano-
169
stricted to those periods of the season when they are available. Most toxicology
laboratories establish colonies of insects needed for conducting bioassays and
screening tests. Laboratory-reared insects are acceptable if they are continually
compared with field populations and found to behave similarly. Field collections
are used only when the toxicological effort is short-term or rearing procedures
cannot be established. Insect toxicologists have succeeded in establishing rearing
procedures for gypsy moth (Singh, 1977) and spruce budworm (Lyon et al.,
1972a,b; Robertson, 1979). The procedure for spruce budworm has been adapted
for fall cankerworm [Alsophila pometaria (Harris)] (Lyon and Brown, 1970) and
Douglas fir tussock moth (Lyon and Flake, 1966).
7.6.1.1. Analytical and Statistical Procedures
Analytical and statistical techniques for evaluating results include probit
analysis, the preferred method of evaluating dose response data (Russell et al.,
1977; Savin etal., 1977). A computer program forprobit analysis, POLO (Probit
Or LOgit analysis), is a data-handling and statistical tool (Robertson et al., 1980;
Russell and Robertson, 1979). POLO has been used for several years by the
Forest Service and appears to have broad acceptance.
7.6.1.2. Basic Screening for Relative Toxicity
The kinds of toxicity tests currently conducted are contact toxicities on
larvae or adults by direct application to the insect or in spray chambers and
feeding toxicity on foliage dosed in a spray chamber or on a spiked artificial
diet. Similar procedures and tests are used by the Forest Pest Management
Institute in Canada (Nigam 1977, 1978). Toxicological evaluation of this kind
provides toxicity data which ultimately lead to qualified judgments about the
most promising candidate materials and formulations and provide guidelines for
selecting rational dosage levels and other variables in field tests (Lyon, 1976).
The possible actions of candidate chemicals are mortality (acute and latent),
knockdown, sterilization, interference with growth and development, alteration
of behavior, disease enhancement, synergism, and potentiation.
7.6.1.3. Topical Tests on Insects
Topical (contact) toxicity tests for a broad spectrum of the most commonly
available insecticides and many experimental insecticides have been conducted
against larvae of the western spruce budworm. The pyrethroids structurally related to isomers of decamethrin and cypermethrin are among the most toxic
compounds to sixth-stage budworm larvae. Highly effective pyrethroids from
these classes are NRDC-168S (d,cis-dichlorochrysanthemic acid + 3-cyano-