Abstract
Toxicity, anticholinesterase properties, elimination and metabolism of carbofuran applied to the larvae of fruit stalk borer, Oryctes elegans were investigated. Larvae given 10 or 20 ppm of carbofuran did not show any observable signs of acute toxicity. The LC50 values were 82, 62, and 48 ppm following 24, 48, and 72 hrs, respectively. The activity of brain cholinesterase of the treated larvae at 10 ppm level initially decreased during the first three hrs (63.3%), and then the enzyme recovered at the end of the experiment (72 hrs).
Carbofuran was readily absorbed within 24 hrs following its application at 20 ppm level. The amounts of carbofuran increased to peak value of 20.3, 6.6, and 31.3 μg/g in brain, fat body and midgut at 10, 7, and 10 days, respectively. These values decreased with time and at the end of the experiment (21 days) reached at 4.9, 2.9, and 12.4 μg/g levels, respectively. Carbofuran was metabolized to 3-hydroxy- carbofliran, 3-ketocarbofuran and 3-ketocarbofuranphenol in the tissues. These metabolic conversions resulted in the formation of highly polar products which facilitated their elimination from the insect body. The daily rate of elimination of carbofuran increased with time following its application. The amount of carbofuran eliminated was 42.9 μg after one day and then increased to 163.6 μg at the end of experimental period (21 days). This indicates that there was no tendency of the compound to accumulate in the insect tissues. Thus carbofuran and its metabolites were rapidly excreted soon after application.