Biodegradable Pesticides in Public Health Entomology
215
to more than 25 days of control with granular chlorpyrifos applied as a posthatch
treatment at the rate of 0.1 lb/acre, and more than 30 days at the same rate
applied as a preflood treatment. Temephos at a similar dosage was comparatively
ineffective.
Chlorpyrifos has exhibited especially long-lasting residual activity in organically polluted waters. McNeill et al. (1968) observed an average of 72 and
108 days of complete control of C. quinquefasciatus larvae in septic ditches in
Texas when chlorpyrifos granular and EC, respectively, were applied at the rate
ofO.5Ib/acre. They attributed the residual activity to absorption of the insecticide
on organic matter in the ditches. In waste disposal lagoons in Louisiana, chlorpyrifos at 1 ppm (EC) provided 144 days of complete control of C. quinquefasciatus compared to only 18-20 days for temephos and several other insecticides, and only 2 days for malathion (Steelman et al., 1967). In Oregon log
ponds, chlorpyrifos at 0.1 lb/acre gave 23 days of control of C. p. pipiens
compared to 14 days for fenthion (Lewis et al., 1966). Against four species of
Culex in sewage oxidation ponds in California, chlorpyrifos EC at 0.3-0.4 lb/
acre gave complete control for 77 days compared with 28 + days for temephos
and 7-21 days for fenthion (Mulla et al., 1970).
A consequence of the increasing dearth of effective residuals that are economically practical for wall spraying in malaria control has forced a move toward
greater consideration of larvicides. Fontaine and Rosen (1973) found that temephos, in floating granule formulations, was effective for about 27 days at 1
ppm against An. gambiae in northern Nigeria during the dry- to wet-season
transition period. During the wet season, temephos 1 % sand granules and emulsion formulations at 1 ppm prevented larvae from developing beyond the first
instar for a 24-day period, suggesting a sorption-release mechanism as described
above for chlorpyrifos.
Larvicidal oils, including some newly developed ones, are receiving increased usage, especially where resistance to organic insecticides is high, such
as in California. Flit MLO is effective against larvae and pupae of Anopheles
and Culex at only 1 gal/acre compared to 1~0 gal/acre for older formulations.
Resistance to Flit MLO was not induced in C. fatigans in 20 generations of
selection pressure (Micks et al., 1968).
The NAS Public Health Study Team (NAS, 1976) made a plea for the
resurrection of Paris green as a larvicide more readily available for mosquito
control. They detailed the excellent safety record of the insecticide when it was
used in large quantities worldwide for malaria control (Bishopp, 1940, 1949);
its rapid disappearance when added to soil or water (Rathburn, 1966); the development of formulations that made it effective against culicines (Rogers and
Rathburn, 1958, 1960a,b) as well as against anophelines; and the failure of
mosquitoes to develop any significant tolerance to it (Rathburn and Boike, 1973).
The study team suggested that Paris green might well be the method of last resort
215
to more than 25 days of control with granular chlorpyrifos applied as a posthatch
treatment at the rate of 0.1 lb/acre, and more than 30 days at the same rate
applied as a preflood treatment. Temephos at a similar dosage was comparatively
ineffective.
Chlorpyrifos has exhibited especially long-lasting residual activity in organically polluted waters. McNeill et al. (1968) observed an average of 72 and
108 days of complete control of C. quinquefasciatus larvae in septic ditches in
Texas when chlorpyrifos granular and EC, respectively, were applied at the rate
ofO.5Ib/acre. They attributed the residual activity to absorption of the insecticide
on organic matter in the ditches. In waste disposal lagoons in Louisiana, chlorpyrifos at 1 ppm (EC) provided 144 days of complete control of C. quinquefasciatus compared to only 18-20 days for temephos and several other insecticides, and only 2 days for malathion (Steelman et al., 1967). In Oregon log
ponds, chlorpyrifos at 0.1 lb/acre gave 23 days of control of C. p. pipiens
compared to 14 days for fenthion (Lewis et al., 1966). Against four species of
Culex in sewage oxidation ponds in California, chlorpyrifos EC at 0.3-0.4 lb/
acre gave complete control for 77 days compared with 28 + days for temephos
and 7-21 days for fenthion (Mulla et al., 1970).
A consequence of the increasing dearth of effective residuals that are economically practical for wall spraying in malaria control has forced a move toward
greater consideration of larvicides. Fontaine and Rosen (1973) found that temephos, in floating granule formulations, was effective for about 27 days at 1
ppm against An. gambiae in northern Nigeria during the dry- to wet-season
transition period. During the wet season, temephos 1 % sand granules and emulsion formulations at 1 ppm prevented larvae from developing beyond the first
instar for a 24-day period, suggesting a sorption-release mechanism as described
above for chlorpyrifos.
Larvicidal oils, including some newly developed ones, are receiving increased usage, especially where resistance to organic insecticides is high, such
as in California. Flit MLO is effective against larvae and pupae of Anopheles
and Culex at only 1 gal/acre compared to 1~0 gal/acre for older formulations.
Resistance to Flit MLO was not induced in C. fatigans in 20 generations of
selection pressure (Micks et al., 1968).
The NAS Public Health Study Team (NAS, 1976) made a plea for the
resurrection of Paris green as a larvicide more readily available for mosquito
control. They detailed the excellent safety record of the insecticide when it was
used in large quantities worldwide for malaria control (Bishopp, 1940, 1949);
its rapid disappearance when added to soil or water (Rathburn, 1966); the development of formulations that made it effective against culicines (Rogers and
Rathburn, 1958, 1960a,b) as well as against anophelines; and the failure of
mosquitoes to develop any significant tolerance to it (Rathburn and Boike, 1973).
The study team suggested that Paris green might well be the method of last resort