Insecticidal Activity of Chitosans of Different Molecular Weights and Chitosan-metal Complexes against Cotton Leafworm Spodoptera littoralis and Oleander Aphid Aphis nerii

摘要

BADAWY M.E.I., EL-ASWAD A.F. (2012): Insecticidal activity of chitosans of different molecular weights and chitosan-metal complexes against cotton leafworm Spodoptera littoralis and oleander aphid Aphis nerii. Plant Protect. Sci., 48: 131-141. As an alternative to synthetic pesticides, chitosan has received much attention as a biopolymer active against some agricultural pests. The, insecticidal activity of chitosans of four molecular weights (2.27 x 10(5), 3.60 x 10(5), 5.97 x 10(5), and 9.47 x 10(5) g/mol) was investigated against two species of arthropod pests: oleander aphid Aphis nerii and cotton leafworm Spodoptera littoralis. In addition, the most active chitosan of 2.27 x 10(5) g/mol was chemically modified with metals of Ag(I), Cu(II), Ni(II), and Hg(II) to give corresponding chitosan-metal complexes. Larval mortality, growth inhibition, and antifeedant activities for third instar larvae of S. littoralis were evaluated at 4 g (a.i.) chitosan/kg diet. Chitosan of 2.27 x 10(5) g/mol and its complexes with Ni and Hg were the most active compounds. The results against A. nerii indicated that chitosans of 3.60 x 10(5) and 5.97 x 10(5) g/mol showed high activity among the different molecular weights in leaf-dip bioassay after 24 h of treatment with 48 and 49% mortalities, respectively, at 1000 mg/l. All compounds had a systemic effect against A. nerii. Chitosans of 2.27 x 10(5), 3.60 x 10(5), and 5.97 x 10(5) g/mol showed the highest efficacy at all concentrations tested; however, chitosan-Cu was significantly the most active among the complexes.