ALLIUM SULFUR-COMPOUNDS - BIOLOGICAL-ACTI VITIES IN INSECTS AND BIOSYNTHESIS

Allium plants produce very specific sulfur compounds. Cysteine derivat ive amino-acids are converted by enzymatic splitting when leaves are b roken in sulfenic acids and thiosuffinates which evolve into numerous substances. These various compounds are wellknown for their biological properties : gustative, pharmacologic (antibiotic, anticoagulant), al lelopathic (growth inhibitor ...) and pesticide (nematicide, fongicide , insectide). They have an important ecological activity on several or ganisms living around Allium, particularly on insects. It is the case in Allium-Onion fly and Allium-Leek moth-entomophage relationships. Su lfur compounds mediate host searching, oviposition and phagostimulatio n of specialist phytophages and also in phytophage-parasitoid relation s. These sulfur compounds are present in soil and in feces of phytopha gous larvae as well. Microorganisms seem to interfere in their product ion and transformation, particularly when amino-acid precursors are co nverted in volatiles.