Laboratory assessment of toxic activity of purified peptides extracted from chickpea seeds to two strains of the rice weevil Sitophilus oryzae (L.) (Coleoptera: Curculionidae)

Several peptides with entomotoxic properties were extracted from seeds of different chickpea varieties, by either aqueous or alcoholic phase extraction. The extracts were purified by anion-exchange chromatography followed by membrane dialysis. The toxicity of the purified extracts was tested on two different strains of the rice weevil, Sitophilus oryzae: a French strain feeding only on cereal grain and sensitive to pea phytotoxins (SS strain) and a Chinese strain naturally breeding on split pea (RS strain). The toxic activity of the different fractions isolated from the purified extracts was evaluated by the 'artificial kernel method', incorporating the fraction into a reconstituted ('artificial') kernel made from whole wheat flour. The toxicity of the fractions was assessed by determining the mortality of young adults of each S. oryzae strain after 7 and 14 d feeding. With the more toxic acidic fraction incorporated into the artificial kernel, the mortality rate of SS strain weevils was 83% and 100% after 7 and 14 d feeding, respectively. With all the alcoholic fractions, mortality of the SS strain remained very low. With RS strain weevils, mortality was negligible after 7 d or 14 d feeding on any peptide fraction of the extracts.