Although both phosphatase and carboxyesterase activity are present in 
insects, it is the lower activity of the carboxyesterases and the higher pro- 
duction of malaoxon that apparently accounts for the higher insect toxicity 
GLI, 3005) 3017 203. "816 2 817, 8839. 868.9 937. 94286976. 142. 1475). dn fives 
resistant to malathion, the carboxyesterase activity was higher. Concomitant, 
there was significantly higher activity in degrading malathion to its mono- 
carboxylic acid analog both in vivo and in vitro (941). 
Studies have shown that enzyme systems are present in various tissues 
of aesert locust, Schistocerca gergaria F., which can activate malathion. 
Activity was highest in fat bodies and gut and least in thoracic muscles, 
ovaries and head. $35 and H%-labeled malathion in mineral oil was applied 
to mature male locusts, Schistocerca gregaria. At varying intervals insect 
and excreta were analyzed. The authors felt that the data indicated acti- 
vation of malathion and formation of malaoxon in the locust body wall (96/7). 
After exposure of two-spotted spider mites to malathion, phosphate, 
diethyl malate, diethyl mercaptosuccinate, 0,0-diethylphosphorothionate 
and malaoxon were detected (943). 
The soil fungus, Trichoderma viride, apparently degraded malathion 
via two paths that did not include the oxidation product malaoxon. The 
presence of powerful carboxyesterases was suggested by the fact that the 
carboxylic acid derivatives of malathion constituted the major portion of 
the metabolites. Some variants of T. viride also showed high desmethy- 
lation activity. Diethylmalate and some unidentified hydrolysis products 
were also observed (935). 
Malaoxon and three other products of malathion breakdown were re- 
covered from lettuce sprayed with malathion (290). In other studies, di- 
methyldithiophosphate was found in plants treated with malathion (1415). 
When malathion treated maize and wheat was stored in sealed jars for six 
months and analyzed monthly, dimethyl phosphorothiolate, malathion mono- 
acid, and malathion di-acid were identified by thin-layer chromatography. 
Other studies showed that wheat grain converted malathion to dimethyl 
phosphate and malaoxon. Malathion breakdown appeared, however, to be 
principally hydrolytic rather than oxidative (1244, 1245). Oxidation of 
the malathion to malaoxon occurred in the seed coats and germs of the wheat 
grains whereas the hydrolyses occurred in the germ and endosperm (1247). 
In rice bran, the rate of disappearance of malathion was greater in 
those samples having the higher acid content. Hydrolysis proceeded, 
apparently, by both enzymatic and chemical routes. Dimethyl phosphorothionate 
and dimethyl phosphorothiolothionate were found (1249). 
UV Irradiation of malathion dusts and emulsions showed the latter 
to be less stable (1104). 
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