Biodegradable Pesticides in Public Health Entomology
217
8.7. 1.2. Ultra-Low- Volume Application
The unique feature of ultra-low-volume (ULV) application methodology in
public health entomology is that it provides an efficient "last-resort" tool for
aborting impending epidemics. The common mosquito adulticides are usually
applied at rates of 3 fl oz/acre or less (compared to 32-192 fl ozlacre formerly
in aerial sprays), and this permits the treatment of large areas in a short period
of time. The reduced volumes also result in greatly reduced costs because of
increased payloads.
The practicality of UL V for disease control was first demonstrated during
an outbreak of St. Louis encephalitis in Dallas, Texas, in 1966. Malathion, at
3 fl oz/acre, was applied by aircraft to 475,000 acres during an 8-day period,
with a consequent reduction of 90-95% in the density of the vector, C. quinquefasciatus (Kilpatrick and Adams, 1967). An even more spectacular demonstration of the efficacy of ULV in an emergency situation was, as referred to
earlier, the application of malathion to more than 8 million acres during the 1971
outbreak of VEE in Texas.
Lofgren (1970) reviewed the use of UL V -applied insecticides against mosquito adults and larvae and discussed technical and operational considerations
related to droplet size, application equipment and conditions of application. Since
then there have been many reports of improved techniques of application; operational, technical, meteorological, and environmental conditions that influence
the results obtained; evaluations of newer insecticides; nontarget effects; and
additional tests of the old standards, malathion, naled, and fenthion. A few
representative examples will suffice to indicate results that can be expected and
the variability encountered in field tests.
The results of Mount et al. (1972) (Table 8.6) against rice field mosquitoes
in Arkansas are typical of what can be expected from UL V applications against
mosquito species that disperse readily and, therefore, can rapidly infiltrate a
treated area. They tested malathion, naled, and chlorpyrifos against the rice field
mosquito, P. confinnis at Lonoke, Arkansas. All three compounds gave good
control at 1-2 hr posttreatment (86-100%) applied as ground aerosols but at 24
hr posttreatment, applications every other night and every night, averaged only
66% and 87% control, respectively. The authors concluded that nightly applications would be necessary for satisfactory control.
The salt marsh mosquitoes, Ae. taeniorhynchus and Ae. sollicitans, also
disperse rapidly. Mount and Lofgren (1967) compared conventional sprays of
naled, fenthion, and malathion with ULV against these species in citrus groves
located near salt marshes in Florida. Naled gave about the same cpntrol with
both methods, and neither method gave residual control. A dosage rate of 0.2
Ib/acre was required to obtain more than 90% control 6 hr after application.
217
8.7. 1.2. Ultra-Low- Volume Application
The unique feature of ultra-low-volume (ULV) application methodology in
public health entomology is that it provides an efficient "last-resort" tool for
aborting impending epidemics. The common mosquito adulticides are usually
applied at rates of 3 fl oz/acre or less (compared to 32-192 fl ozlacre formerly
in aerial sprays), and this permits the treatment of large areas in a short period
of time. The reduced volumes also result in greatly reduced costs because of
increased payloads.
The practicality of UL V for disease control was first demonstrated during
an outbreak of St. Louis encephalitis in Dallas, Texas, in 1966. Malathion, at
3 fl oz/acre, was applied by aircraft to 475,000 acres during an 8-day period,
with a consequent reduction of 90-95% in the density of the vector, C. quinquefasciatus (Kilpatrick and Adams, 1967). An even more spectacular demonstration of the efficacy of ULV in an emergency situation was, as referred to
earlier, the application of malathion to more than 8 million acres during the 1971
outbreak of VEE in Texas.
Lofgren (1970) reviewed the use of UL V -applied insecticides against mosquito adults and larvae and discussed technical and operational considerations
related to droplet size, application equipment and conditions of application. Since
then there have been many reports of improved techniques of application; operational, technical, meteorological, and environmental conditions that influence
the results obtained; evaluations of newer insecticides; nontarget effects; and
additional tests of the old standards, malathion, naled, and fenthion. A few
representative examples will suffice to indicate results that can be expected and
the variability encountered in field tests.
The results of Mount et al. (1972) (Table 8.6) against rice field mosquitoes
in Arkansas are typical of what can be expected from UL V applications against
mosquito species that disperse readily and, therefore, can rapidly infiltrate a
treated area. They tested malathion, naled, and chlorpyrifos against the rice field
mosquito, P. confinnis at Lonoke, Arkansas. All three compounds gave good
control at 1-2 hr posttreatment (86-100%) applied as ground aerosols but at 24
hr posttreatment, applications every other night and every night, averaged only
66% and 87% control, respectively. The authors concluded that nightly applications would be necessary for satisfactory control.
The salt marsh mosquitoes, Ae. taeniorhynchus and Ae. sollicitans, also
disperse rapidly. Mount and Lofgren (1967) compared conventional sprays of
naled, fenthion, and malathion with ULV against these species in citrus groves
located near salt marshes in Florida. Naled gave about the same cpntrol with
both methods, and neither method gave residual control. A dosage rate of 0.2
Ib/acre was required to obtain more than 90% control 6 hr after application.