1Laboratoire d';Ecologie Moléculaire, Université de Pau, 64000 Pau, France.
2Centro de Edafologia y Biologica Aplicada del Segura (CEBAS), Consejo Superior de Investigaciones Cientificas (CSIC), Murcia, Spain.
Acanthoscelides obtectus is a cosmopolitan beetle and one of the most damaging insect pest. It attacks the beans in the fields as well as stored seeds and can adapt to several Leguminosae species: its host plant, the kidney bean (Phaseolus vulgaris ) and also other originally non host-plants (Vigna unguiculata, Cicer arietinum etc.), but not to Glycine max. Soya bean seeds contain a widespread range of antinutritional and toxic compounds (saponins, amino-acids, proteins) which contribute to its defence. They also include a high content in flavonoids. These allelochemicals have been identified to play a role in plant resistance against pathogens and phytophagous insects. The aim of this work is to study if some polyphenolic compounds could be involved in the non adaptability of Acanthoscelides obtectus to the soya bean seeds. After rearing the beetle with several Leguminosae species (P. vulgaris, V. unguiculata, C. arietinum, Vicia faba, Pisum sativum, G. max), we compared the polyphenolic patterns of non host and host plant seeds by HPLC. The main difference between soya bean and the others was a large amount of isoflavonoid glycosides (daidzin, glycitin, genistin) and derived compounds. These compounds were isolated and included in artificial seeds to observe if they could inhibited the reproduction of the beetle. Statistical studies showed a significant activity for glycitin derived compounds but not for the others. So, it seems that some isoflavonoids could participated to the soya bean defence against the bruchid. A structure-activity relationships of the compounds is discussed.