244
J. R. Plimmer
fumigant or other toxicologically significant molecules can be quantitatively
determined.
9.3. PROTECTANTS
The use of protectants to limit the occurrence of insects in stored products
is a widespread practice. Malathion, which will be discussed in some detail, has
been used for a long time to control a variety of insect pests; however, the
problem of resistance to malathion makes it necessary to continue the search for
alternatives that provide residual activity without hazardous effects. Other compounds that have been examined include fenitrothion, primiphos-methyl, bioresmethrin, and chlorpyrifos-methyl, alone or in combination. All of these except
bioresmethrin are organophosphate insecticides. Currently malathion, methoxychlor, and pyrethrins are among the chemicals used in the U.S. for application
to storage bins as residual sprays. The only readily available insecticide approved
in the U.S. for direct application to grain is malathion. Pirimiphos-methyl has
been approved for this purpose in Great Britain and France.
Malathion. Malathion (O,O-dimethyl phosphorodithioate of diethyl mercaptosuccinate) may be formulated as a 57% emulsifiable liquid (0.6 kg A.I.!
liter), 25% wettable powder, or 4% dust. In the U.S. it has been registered for
use on stored grains (including wheat, oats, rice, com, barley, grain sorghum,
and field or garden seeds) against the confused flour beetle (Tribolium conjusum
Jacquelin duVal), rice weevil [Sitophilus oryzae (L.)] , granary weevil [Sitophilus
granarius (L.)], sawtoothed grain beetle [Oryzaephilus surinamensis (L.)], flat
grain beetle [Cryptolestes pusillus (SchOnherr)], red flour beetle [Tribolium castaneum (Herbst)], rusty grain beetle (CryptolestesJerrugineus Stephens)], lesser
grain borer [Rhyzopertha dominica (F.)], and Indianmeal moth [Plodia interpunctella (Hiibner)]. The emulsifiable liquid is diluted and sprayed over the
surface of the uninfested grain. It may also be used to spray boxcars before they
are used for transportation of packaged flour or cereals. Other stored products
may also be protected by applications of malathion.
Malathion is one of the least toxic of the currently available insecticides
and is extremely versatile. For these reasons, it has been widely used throughout
the world. It is used on a large scale by the World Health Organization for
control of malaria vectors. The U.S. product volume in 1972 was estimated at
about 11 million kg A.I., of a total of 124 million kg of insecticides produced
in the U. S. in that year (von Rumker et al., 1974). The other leading insecticides
were toxaphene, carbaryl, and methyl parathion, of which 34.5, 24.0, and 23.2
million kg A.I., respectively, were produced in 1972. A further 69,800 kg of
J. R. Plimmer
fumigant or other toxicologically significant molecules can be quantitatively
determined.
9.3. PROTECTANTS
The use of protectants to limit the occurrence of insects in stored products
is a widespread practice. Malathion, which will be discussed in some detail, has
been used for a long time to control a variety of insect pests; however, the
problem of resistance to malathion makes it necessary to continue the search for
alternatives that provide residual activity without hazardous effects. Other compounds that have been examined include fenitrothion, primiphos-methyl, bioresmethrin, and chlorpyrifos-methyl, alone or in combination. All of these except
bioresmethrin are organophosphate insecticides. Currently malathion, methoxychlor, and pyrethrins are among the chemicals used in the U.S. for application
to storage bins as residual sprays. The only readily available insecticide approved
in the U.S. for direct application to grain is malathion. Pirimiphos-methyl has
been approved for this purpose in Great Britain and France.
Malathion. Malathion (O,O-dimethyl phosphorodithioate of diethyl mercaptosuccinate) may be formulated as a 57% emulsifiable liquid (0.6 kg A.I.!
liter), 25% wettable powder, or 4% dust. In the U.S. it has been registered for
use on stored grains (including wheat, oats, rice, com, barley, grain sorghum,
and field or garden seeds) against the confused flour beetle (Tribolium conjusum
Jacquelin duVal), rice weevil [Sitophilus oryzae (L.)] , granary weevil [Sitophilus
granarius (L.)], sawtoothed grain beetle [Oryzaephilus surinamensis (L.)], flat
grain beetle [Cryptolestes pusillus (SchOnherr)], red flour beetle [Tribolium castaneum (Herbst)], rusty grain beetle (CryptolestesJerrugineus Stephens)], lesser
grain borer [Rhyzopertha dominica (F.)], and Indianmeal moth [Plodia interpunctella (Hiibner)]. The emulsifiable liquid is diluted and sprayed over the
surface of the uninfested grain. It may also be used to spray boxcars before they
are used for transportation of packaged flour or cereals. Other stored products
may also be protected by applications of malathion.
Malathion is one of the least toxic of the currently available insecticides
and is extremely versatile. For these reasons, it has been widely used throughout
the world. It is used on a large scale by the World Health Organization for
control of malaria vectors. The U.S. product volume in 1972 was estimated at
about 11 million kg A.I., of a total of 124 million kg of insecticides produced
in the U. S. in that year (von Rumker et al., 1974). The other leading insecticides
were toxaphene, carbaryl, and methyl parathion, of which 34.5, 24.0, and 23.2
million kg A.I., respectively, were produced in 1972. A further 69,800 kg of