268
C. R. Krishna Murti and T. S. S. Dikshith
growing fields of India under flooded conditions and the role of microorganisms
in its degradation have been investigated. After the first application to a flooded
soil, parathion degradation proceeded via nitro group reduction to aminoparathion. But after the second application, substantial hydrolysis occurred in addition
to reduction. After the third application, the pathway was essentially one of
hydrolysis. Thus, the metabolism of parathion shifted from reduction to hydrolysis after repeated applications (Sethunathan et al., 1975).
Three-day-old larvae of the silk worm Bombyx mori L. were used to monitor
the persistance of fensulfothion in soil under laboratory conditions (Sheela and
Vasantharajan, 1978a). Paper chromatographic and TLC analysis revealed that
fensulfothion and its oxygen analogue were the predominant breakdown products.
Compatibility of fensulfothion, chlorfenvinphos, and chloropyriphos was studied
with NPK fertilizers. The degradation of fensulfothion was 6-10% in the first
100 days. Chloropyriphos degraded anywhere from 8.9-34.8%, whereas chlorfenvinphos showed the highest degradation rate, 37.5-94.6% (Anonymous, 1978b).
In general, monocrotophos and dicrotophos, when mixed with fertilizers,
degraded faster than did phorate and disulfoton mixed with fertilizers. Thus in
120 days at 30°C the rate of degradation of the former was 10-40% as compared
to 8-30% of the latter. An increase in temperature from 30° to 50°C was found
to enhance the amount of insecticide degraded in all cases. The effect of temperature was, however, more pronounced (1- to 1.5-fold increase) on monocrotophos and dicrotophos than on phorate and disulfoton. Addition of moisture at
the 5% level increased the rate of degradation by 1.5- to 3.5-fold at 30°C and
1.5- to 5-fold at 50°C (Anonymous, 1978b).
Fruits of tomato sprayed with carbaryl contained very little residue, suggesting a quick degradation of the insecticide (Singh and Singh, 1970). No
residue was detected in the stem, or on cobs of maize and on cauliflower treated
with carbaryl (Deshmukh and Saramma, 1971). Abelmoschus esculantus (Bhindi,
okra) showed no residues of the insecticide 3 days after spraying, indicating
faster dissipation (Raghuraj et al., 1973).
Carbofuran has been used for the control of the sorghum shoot fly in India.
Straw as well as grain contained no residues of carbofuran, indicating fast dissipation (Gupta and Dewan, 1974). Baygon (2-isopropoxyphenyl-N-methylcarbamate) was degraded to 2-isopropoxy phenol by Pseudomonas sp. (Gupta et
al., 1979).
10.4. INSECTICIDES OF PLANT ORIGIN
Attempts have been made to identify and utilize plant products as insecticides. About 2000 species of plants have been known to offer products possessing
C. R. Krishna Murti and T. S. S. Dikshith
growing fields of India under flooded conditions and the role of microorganisms
in its degradation have been investigated. After the first application to a flooded
soil, parathion degradation proceeded via nitro group reduction to aminoparathion. But after the second application, substantial hydrolysis occurred in addition
to reduction. After the third application, the pathway was essentially one of
hydrolysis. Thus, the metabolism of parathion shifted from reduction to hydrolysis after repeated applications (Sethunathan et al., 1975).
Three-day-old larvae of the silk worm Bombyx mori L. were used to monitor
the persistance of fensulfothion in soil under laboratory conditions (Sheela and
Vasantharajan, 1978a). Paper chromatographic and TLC analysis revealed that
fensulfothion and its oxygen analogue were the predominant breakdown products.
Compatibility of fensulfothion, chlorfenvinphos, and chloropyriphos was studied
with NPK fertilizers. The degradation of fensulfothion was 6-10% in the first
100 days. Chloropyriphos degraded anywhere from 8.9-34.8%, whereas chlorfenvinphos showed the highest degradation rate, 37.5-94.6% (Anonymous, 1978b).
In general, monocrotophos and dicrotophos, when mixed with fertilizers,
degraded faster than did phorate and disulfoton mixed with fertilizers. Thus in
120 days at 30°C the rate of degradation of the former was 10-40% as compared
to 8-30% of the latter. An increase in temperature from 30° to 50°C was found
to enhance the amount of insecticide degraded in all cases. The effect of temperature was, however, more pronounced (1- to 1.5-fold increase) on monocrotophos and dicrotophos than on phorate and disulfoton. Addition of moisture at
the 5% level increased the rate of degradation by 1.5- to 3.5-fold at 30°C and
1.5- to 5-fold at 50°C (Anonymous, 1978b).
Fruits of tomato sprayed with carbaryl contained very little residue, suggesting a quick degradation of the insecticide (Singh and Singh, 1970). No
residue was detected in the stem, or on cobs of maize and on cauliflower treated
with carbaryl (Deshmukh and Saramma, 1971). Abelmoschus esculantus (Bhindi,
okra) showed no residues of the insecticide 3 days after spraying, indicating
faster dissipation (Raghuraj et al., 1973).
Carbofuran has been used for the control of the sorghum shoot fly in India.
Straw as well as grain contained no residues of carbofuran, indicating fast dissipation (Gupta and Dewan, 1974). Baygon (2-isopropoxyphenyl-N-methylcarbamate) was degraded to 2-isopropoxy phenol by Pseudomonas sp. (Gupta et
al., 1979).
10.4. INSECTICIDES OF PLANT ORIGIN
Attempts have been made to identify and utilize plant products as insecticides. About 2000 species of plants have been known to offer products possessing