Nuttapon Theskayan. The study of potential elimination of a common cutworm (Spodoptera litura, Farbr) by cyanide extracted from cassava . Master's Degree(Appropriate Technology for Resources and Environmental Development). Mahidol University. : Mahidol University, 2006.
The study of potential elimination of a common cutworm (Spodoptera litura, Farbr) by cyanide extracted from cassava
Abstract:
The study of potential elimination of a common cutworm (Spodoptera litura, Farbr)
by cyanide extracted from cassava was investigated. The peel of root and the leaves of
cassava Kasetsart 50 variety with two kinds of solvents; 95% ethanol and distilled water,
were used in this study. The weight by volume ratio between the cassava and the solvent
were 1:1, 1:2, 1:3, 2:1, 2:2, 2:3, 3:1, 3:2, and 3:3, respectively. The extraction times were
24, 48, and 72 hours. The results obtained from 95% ethanol extraction of the peel of root
and the leaves of cassava were in the range of 156.7 - 715.4 and 78.1 - 591.2 mg CN-/kg dry
weight, respectively, whereas those obtained from distilled water extraction of the peel of
root and the leaves of cassava were in the range of 85.5 – 406.1 and 81.8 - 631.2mg CN-/kg
dry weight, respectively. From the results, it was found that the optimum condition for the
extraction was obtained from the extraction of the peel of the root by using 95% ethanol at
the ratio of 2:2 and an extraction time of 48 hours. The yield was 715.4 mg CN-/kg dry
weight. Therefore, this optimum condition was selected to be used for the extraction of
cyanide from cassava. The cyanide obtained from the extraction was used for further study
on the stability of the cyanide extract, the potential of the cyanide extract on common
cutworm elimination, and the toxicity effect of cyanide extract on the environment.
The stability study of the cyanide extract was investigated at room temperature
(about 30oC) and at 4oC for a period of seven days. The results showed that cyanide extract
deteriorated continuously for the whole period of seven days; the concentration of cyanide
extract decreased by 30% and 38%, respectively.
The potential of the cyanide extract on common cutworm elimination was studied
by testing the mortality rate of 2nd-3rd stage common cutworm after being fed with Chinese
kale leaf in cyanide extract at various concentrations. It was found that the mortality rates of
common cutworm were 36.7 - 63.3% at 48 hours. The highest concentration of cyanide
extract was 246.7 mg CN-/l. At this highest concentration, the mortality rate of common
cutworm was 63.3% with the LC50 (at 95% level of confidence) of 140.8 mg/l at 48 hours.
The mortality rate of common cutworm obtained from the cyanide extract was compared
with that obtained from Cypermetrin, which is the widely used insecticide for common
cutworm elimination, it was found that the mortality rate of 93.3% at 24 hours was obtained
from Cypermetrin. This mortality rate was higher than that obtained from the cyanide
extract. However, there is a potential of the cyanide extract to be used at a certain level for
common cutworm elimination.
The toxicity effect of cyanide extract on the environment was studied by using Nile
tilapia as a representative. The concentrations of cyanide extract used in this study were
24.7 and 14.6 mg/l. The results showed that the LC50 was 12.3 mg/l for cyanide extract at
both concentrations, at 95% level of confidence, and at both 48 and 72 hours. The mortality
rate of Nile tilapia exposed to the cyanide extract was compared with that obtained from
exposed to potassium cyanide at a concentration of 16 mg/l, it was found that the fish
exposed to potassium cyanide had a 100% mortality rate within 15 minutes. Therefore, it
can be concluded that potassium cyanide is very toxic whereas the cyanide extract from
cassava has a relatively low toxicity to the environment. However, if the cyanide extract
from cassava is used, it should be used with care.