208
Gene R. DeFoliart
8.6.1. Larvivorous Fish
Many successful instances of the use of Gambusia and other larvivorous
fish can be cited. Green and Imber (1977) recently reported excellent control of
C. pipiens for a distance of 3 miles from stocking sites in two urban polluted
stream systems in New Jersey. In India, for control of the urban malaria vector,
An. stephensi, breeding in wells, Sitaraman et al. (1975) found G. affinis as
effective as either pure petrol or Paris green, and use of fish resulted in a
considerable cost reduction. Menon and Rajagopalan (1977) studied the mosquito
control potential of 13 species of indigenous fishes and found 2 of them to have
advantages in certain situations over G. affinis against An. stephensi in wells.
Oryzias melastigma and Aplocheilus blochii demonstrated higher tolerances for
temperature, salinity and pollution than did Gambusia.
The introduction of exotic fish can have a heavy impact on an aquatic
ecosystem and, as the longest-used antimosquito biocontrol agent, Gambusia is
illustrative of the types of considerations that come into play, both as to effectiveness and environmental impact, in the choice of a living organism for insect
control. The following advantages and disadvantages are summarized from NAS
(1976) and Legner et al. (1974): A surface feeder (1) is generally less effective
against culicines than against Anopheles; (2) lives easily in the confined water
of artificial containers, making it effective against such species as Ae. aegypti;
(3) grazes selectively on zooplankton in small habitats, thereby causing phytoplanktonic blooms, which in turn may cause other undesirable side effects such
as odor; (4) has high reproductive capacity and the capability of existing at high
population densities; (5) has fair pollution tolerance, but not as good as that of
the common guppy, Poecilia reticulata; (6) tolerates a fairly wide temperature
range but has insufficient cold tolerance for year-round survival in northern
temperate zones; (7) has good shoaling behavior-into shallow water after larvae-but is less able to penetrate algal mats and some aquatic weed growths
than are some other fish, such as Heterandriaformosa, a very small live-bearer
that penetrates these readily; (8) has been known to eliminate native fish species;
and (9) has caused significant reductions in native invertebrate predators such
as notonectids, dytiscids, and hydrophilids by predation upon them.
Studies have shown that Gambusia is fairly tolerant to insecticides used as
larvicides and is therefore compatible with larvicides in an integrated mosquito
control program. Malathion is toxic to Gambusia at larvicidal levels (70% mortality 48 hr posttreatment at 0.5 Ib/acre) (Mulla and Isaak, 1961), but temephos,
fenthion, and chlorpyrifos (Darwazeh and Mulla, 1974; Ferguson et al., 1966)
have appeared safe (Table 8.4). Chlorpyrifos, however, was shown to produce
some fish toxicity at only two to four times larvicidal rates, so caution would
be necessary to avoid overdosing with this insecticide in areas where fish are
present (Darwazeh and Mulla, 1974).
Gene R. DeFoliart
8.6.1. Larvivorous Fish
Many successful instances of the use of Gambusia and other larvivorous
fish can be cited. Green and Imber (1977) recently reported excellent control of
C. pipiens for a distance of 3 miles from stocking sites in two urban polluted
stream systems in New Jersey. In India, for control of the urban malaria vector,
An. stephensi, breeding in wells, Sitaraman et al. (1975) found G. affinis as
effective as either pure petrol or Paris green, and use of fish resulted in a
considerable cost reduction. Menon and Rajagopalan (1977) studied the mosquito
control potential of 13 species of indigenous fishes and found 2 of them to have
advantages in certain situations over G. affinis against An. stephensi in wells.
Oryzias melastigma and Aplocheilus blochii demonstrated higher tolerances for
temperature, salinity and pollution than did Gambusia.
The introduction of exotic fish can have a heavy impact on an aquatic
ecosystem and, as the longest-used antimosquito biocontrol agent, Gambusia is
illustrative of the types of considerations that come into play, both as to effectiveness and environmental impact, in the choice of a living organism for insect
control. The following advantages and disadvantages are summarized from NAS
(1976) and Legner et al. (1974): A surface feeder (1) is generally less effective
against culicines than against Anopheles; (2) lives easily in the confined water
of artificial containers, making it effective against such species as Ae. aegypti;
(3) grazes selectively on zooplankton in small habitats, thereby causing phytoplanktonic blooms, which in turn may cause other undesirable side effects such
as odor; (4) has high reproductive capacity and the capability of existing at high
population densities; (5) has fair pollution tolerance, but not as good as that of
the common guppy, Poecilia reticulata; (6) tolerates a fairly wide temperature
range but has insufficient cold tolerance for year-round survival in northern
temperate zones; (7) has good shoaling behavior-into shallow water after larvae-but is less able to penetrate algal mats and some aquatic weed growths
than are some other fish, such as Heterandriaformosa, a very small live-bearer
that penetrates these readily; (8) has been known to eliminate native fish species;
and (9) has caused significant reductions in native invertebrate predators such
as notonectids, dytiscids, and hydrophilids by predation upon them.
Studies have shown that Gambusia is fairly tolerant to insecticides used as
larvicides and is therefore compatible with larvicides in an integrated mosquito
control program. Malathion is toxic to Gambusia at larvicidal levels (70% mortality 48 hr posttreatment at 0.5 Ib/acre) (Mulla and Isaak, 1961), but temephos,
fenthion, and chlorpyrifos (Darwazeh and Mulla, 1974; Ferguson et al., 1966)
have appeared safe (Table 8.4). Chlorpyrifos, however, was shown to produce
some fish toxicity at only two to four times larvicidal rates, so caution would
be necessary to avoid overdosing with this insecticide in areas where fish are
present (Darwazeh and Mulla, 1974).