Biodegradable Pesticides in Public Health Entomology
211
are also toxic to mOSQuito larvae (Roberts, 1967). Applied to the water surface
Metarrhizium is effective against Anopheles: some strains are highly virulent to
culicines in fresh, brackish, or organically polluted waters (WHO, 1977). M.
anisopliae has shown survival but not replication in mammals (WHO, 1977).
According to Laird (1977), M. anisopliae has been mass-produced and used in
the field in the USSR without any reported adverse health or environmental
effects. However, its wide host range compared to that of most entomopathogens--more than 200 species being susceptible in a variety of insect orders-would appear to be a factor limiting its use in some integrated-control programs.
As the fungus is not normally associated with mosquitoes, repeated applications
would be necessary (Roberts, 1970).
Lagenidium giganteum (= L. culicidum) (Umphlett, 1973) is a promising
mosquito control agent. A saprophyte, it should be propagatable by fermentation
techniques similar to those for bacteria. Anopheles are susceptible (Couch and
Romney, 1973) as well as virtually all freshwater culicines (McCray, 1973, and
others). Larval death is usually simultaneous with sporangial formation and
occurs about 60 hr after ingestion of motile zoospores (McCray, 1973). Young
larvae are more susceptible than older ones, but more than 80% of larvae of all
stages are killed at high dosages (Umphlett and Huang, 1972). By modifications
of its life cycle, the fungus recycles in both permanent water and intermittently
flooded areas, and field tests by McCray et al. (1973) in both types of situations
resulted in dramatically reduced mosquito populations. No infections were found
in 1400 nontarget organisms (small crustaceans and insects) sampled from the
treated sites. WHO has assigned high priority to studies on L. giganteum with
emphasis on in vitro propagation and finding methods for storage and transportation of the zoospores (WHO, 1977).
8.6.5. Protozoa
The main impact of Nosema algerae (= N. stegomyiae) is on the longevity
and reproductive capacity of adult mosquitoes [An. albimanus (Anthony et al.,
1972, 1978); An. stephensi (Undeen and Alger, 1975); C. fatigans (Reynolds,
1971)]. High larval mortality sometimes occurs in anophelines (Savage and
Lowe, 1970). Anthony et al. (1978) found that first and second instars were only
slightly more susceptible to infection (100%) than were third and fourth instars
(88% and 92%, respectively) when exposed to 5 x lQ4 spores/ml of water.
From their data on the number of viable eggs produced, they estimated that N.
algerae introduced into populations consisting of mixed larval instars could
reduce the FJ progeny of infected females by 54%. Anthony et al. (1972)
proposed a population model showing that an infection of N. algerae that reduced
the female LT-90 by 50% (as shown by laboratory data) would reduce malaria
transmission by 85-97%.
211
are also toxic to mOSQuito larvae (Roberts, 1967). Applied to the water surface
Metarrhizium is effective against Anopheles: some strains are highly virulent to
culicines in fresh, brackish, or organically polluted waters (WHO, 1977). M.
anisopliae has shown survival but not replication in mammals (WHO, 1977).
According to Laird (1977), M. anisopliae has been mass-produced and used in
the field in the USSR without any reported adverse health or environmental
effects. However, its wide host range compared to that of most entomopathogens--more than 200 species being susceptible in a variety of insect orders-would appear to be a factor limiting its use in some integrated-control programs.
As the fungus is not normally associated with mosquitoes, repeated applications
would be necessary (Roberts, 1970).
Lagenidium giganteum (= L. culicidum) (Umphlett, 1973) is a promising
mosquito control agent. A saprophyte, it should be propagatable by fermentation
techniques similar to those for bacteria. Anopheles are susceptible (Couch and
Romney, 1973) as well as virtually all freshwater culicines (McCray, 1973, and
others). Larval death is usually simultaneous with sporangial formation and
occurs about 60 hr after ingestion of motile zoospores (McCray, 1973). Young
larvae are more susceptible than older ones, but more than 80% of larvae of all
stages are killed at high dosages (Umphlett and Huang, 1972). By modifications
of its life cycle, the fungus recycles in both permanent water and intermittently
flooded areas, and field tests by McCray et al. (1973) in both types of situations
resulted in dramatically reduced mosquito populations. No infections were found
in 1400 nontarget organisms (small crustaceans and insects) sampled from the
treated sites. WHO has assigned high priority to studies on L. giganteum with
emphasis on in vitro propagation and finding methods for storage and transportation of the zoospores (WHO, 1977).
8.6.5. Protozoa
The main impact of Nosema algerae (= N. stegomyiae) is on the longevity
and reproductive capacity of adult mosquitoes [An. albimanus (Anthony et al.,
1972, 1978); An. stephensi (Undeen and Alger, 1975); C. fatigans (Reynolds,
1971)]. High larval mortality sometimes occurs in anophelines (Savage and
Lowe, 1970). Anthony et al. (1978) found that first and second instars were only
slightly more susceptible to infection (100%) than were third and fourth instars
(88% and 92%, respectively) when exposed to 5 x lQ4 spores/ml of water.
From their data on the number of viable eggs produced, they estimated that N.
algerae introduced into populations consisting of mixed larval instars could
reduce the FJ progeny of infected females by 54%. Anthony et al. (1972)
proposed a population model showing that an infection of N. algerae that reduced
the female LT-90 by 50% (as shown by laboratory data) would reduce malaria
transmission by 85-97%.