216
Gene R. DeFoliart
for control of resistant larvae if petroleum derivatives should be declared environmentally unacceptable. Also, its use as a larvicide could prolong the life of
residual organic insecticides by delaying the development of resistance.
8.7.1.1. Controlled-Release Formulations
The terms controlled release and slow release have been used rather indiscriminately for various methods of prolonging toxicant release, from adsorption or absorption on clays, silicas, or charcoal, to incorporation or encapsulation
in elastomeric or plastic matrices. Cardarelli (1976) restricted the term controlled
release to formulations that deliver the proper dosage at a constant rate over a
long period of time, in contrast to slow release of toxicant at variable rates over
a long period.
Controlled-release technology has not only added greatly to the potential
of juvenoids and other IGRs, for which timing of application is critical, but has
been used to increase the residual of OP compounds such as temephos and
chlorpyrifos. In one of the earliest semifield evaluations, chlorpyrifos in various
plastic-based formulations demonstrated effective control for 21 to more than
24 weeks in outdoor artificial pools (Miller et al., 1973; L. W. Roberts et al.,
1973). At dosages effective for larval control, nontarget populations of gerrids,
chaoborids, and chironomids were reduced but not eliminated (D. R. Roberts
et al., 1973). More recently, Nelson et al. (1976) tested a 10.6% controlledrelease formulation of chlorpyrifos against P. confinnis in Arkansas rice plots.
In plots treated at 0.25, 0.5, 1.0, and 2.0 ppm based on a theoretical total release
of all active ingredients, average mortalities over an ll-week period were 22,
58, 79, and 99% respectively. Chlorpyrifos residues recovered from test water
averaged 0.0004,0.0006,0.0009, and 0.0014 ppm, respectively.
Keenan (1978) reported excellent control of larvae, including several species, in southern Maryland with a controlled-release formulation of chlorpyrifos
(Dursban® 10 CR). Control lasted throughout the entire 12-18 weeks of observation when pools and ditches were treated to yield a dosage rate of 1.5 ppm.
Except on one overdosed sewage basin, where notonectids were killed and did
not reappear for 4 weeks, no adverse effects were noted on nontarget organisms.
Against adult mosquitoes, long-term control (2-4 months) has been obtained
by dichlorvos formulated in wax, polyvinyl chloride resins, and permeable plastic
in storm sewer catch basins (Brooks et al., 1963, 1965) and in huts (Schoof et
al., 1963).
One disadvantage of controlled-release and slow-release formulations is that
a considerable amount of sublethal dosing is probably unavoidable. A result is
an increased potentiality for development of resistance among target species.
Gene R. DeFoliart
for control of resistant larvae if petroleum derivatives should be declared environmentally unacceptable. Also, its use as a larvicide could prolong the life of
residual organic insecticides by delaying the development of resistance.
8.7.1.1. Controlled-Release Formulations
The terms controlled release and slow release have been used rather indiscriminately for various methods of prolonging toxicant release, from adsorption or absorption on clays, silicas, or charcoal, to incorporation or encapsulation
in elastomeric or plastic matrices. Cardarelli (1976) restricted the term controlled
release to formulations that deliver the proper dosage at a constant rate over a
long period of time, in contrast to slow release of toxicant at variable rates over
a long period.
Controlled-release technology has not only added greatly to the potential
of juvenoids and other IGRs, for which timing of application is critical, but has
been used to increase the residual of OP compounds such as temephos and
chlorpyrifos. In one of the earliest semifield evaluations, chlorpyrifos in various
plastic-based formulations demonstrated effective control for 21 to more than
24 weeks in outdoor artificial pools (Miller et al., 1973; L. W. Roberts et al.,
1973). At dosages effective for larval control, nontarget populations of gerrids,
chaoborids, and chironomids were reduced but not eliminated (D. R. Roberts
et al., 1973). More recently, Nelson et al. (1976) tested a 10.6% controlledrelease formulation of chlorpyrifos against P. confinnis in Arkansas rice plots.
In plots treated at 0.25, 0.5, 1.0, and 2.0 ppm based on a theoretical total release
of all active ingredients, average mortalities over an ll-week period were 22,
58, 79, and 99% respectively. Chlorpyrifos residues recovered from test water
averaged 0.0004,0.0006,0.0009, and 0.0014 ppm, respectively.
Keenan (1978) reported excellent control of larvae, including several species, in southern Maryland with a controlled-release formulation of chlorpyrifos
(Dursban® 10 CR). Control lasted throughout the entire 12-18 weeks of observation when pools and ditches were treated to yield a dosage rate of 1.5 ppm.
Except on one overdosed sewage basin, where notonectids were killed and did
not reappear for 4 weeks, no adverse effects were noted on nontarget organisms.
Against adult mosquitoes, long-term control (2-4 months) has been obtained
by dichlorvos formulated in wax, polyvinyl chloride resins, and permeable plastic
in storm sewer catch basins (Brooks et al., 1963, 1965) and in huts (Schoof et
al., 1963).
One disadvantage of controlled-release and slow-release formulations is that
a considerable amount of sublethal dosing is probably unavoidable. A result is
an increased potentiality for development of resistance among target species.