Abstract:
The fall armyworm (FAW), Spodoptera frugiperda is a recent invasive pest that has
successfully established in Sri Lanka where it continues to disrupt agriculture, particularly
corn production. Management of fall armyworm using agrochemicals has led to the
development of resistance against many insecticides and the accumulation of toxic
residues on agricultural products. Therefore, the utilization of plant extracts which are
wealthy in bioactive compounds for the control fall armyworm has become a developing
pattern. This study was undertaken to screen the effectiveness of Adathoda vassica,
Dathura metal, and Tagetes erecta crude extracts against fall armyworm. Shade dried
leaves were used for the extraction which was done by the Soxhlet method using
methanol and ethyl acetate as solvents. Bioefficacy of crude extracts was studied against
third instar larvae of S. frugiperda using 4000, 2000 and 1000 ppm concentrations to test
the contact toxicity by topical application method, antifeedant activity by leaf disc no
choice assay and repellency effect from the dual choice method. Commercially available
insecticide, collagen was used as a positive control. The crude extracts from T.
erecta (LD50 - 186.63µg/g) and D. metel (LD50 - 256.44µg/g) showed significantly (p <
0.05) high mortality (100%) rate within twelve hours even compared with the positive
control. The results revealed that the methanolic extract of T. erecta showed the highest
significant (p < 0.05) antifeedant activity (92.09%) at 4000 ppm compared with other
plant extracts. All plant extracts provoked a notable decrease in feeding with the
increment of their concentration. Methanolic extract of T. erecta showed the highest
significant repellency (66.65%). Therefore, it can be concluded that methanolic extracts
of D. metel and T. erecta have the power of damaging fall armyworm and are suitable
candidates for the development of bio-insecticide for the local use.
Keywords: Fall armyworm, Adathoda vassica, Dathura metel, Tagetes erecta
