Resistance of faba bean to the African bean aphid A-craccivora Koch (Hom.: Aphididae) caused by parasitic broomrape Orobanche crena

In Egypt, from our field observations, faba bean (Vicia fabae) when parasitized with broomrape (Orobanche crenata) becomes resistance to the african bean aphid A. craccivora (Koch). Suggesting that the cause of this type of resistance to that aphid may be, in part, due to either in the lack of free amino acids contents of the plant sap, soil texture or to the effects of produced stress metabolises as result of parasitism of broomrape from type phenylethylamine alkaloids. So, the unparasitized and parasitized foliages of laba bean with broomrape were subjected to chemical extractions to isolate those alkaloids. Results revealed that the parasitized foliage have been containing para aminophenylalanine, N-methyltyramine and mescaline. Whereas the unparasitized foliage with broomrape was free from those compounds. When the commercial chemicals of those three compounds were tested against young adults of A. craccivora through stretched membrane on synthetic diet, para aminophenylalanine gave feeding deterrent at 0.7 x 10(-3) molar while N-methyllyramine was very feeding inhibitor at 1.2 x 10(-3) molar but mescaline was lethal at 1.3 x 10(-3) molar after 24 hrs under laboratory conditions. LD50's were 0.6 x 10(-3) molar (mescaline), 1.0 x 10(-3) molar (N-methyltyramine) and 1.7 x 10(-3) molar (p-aminophenylalanine) after 24 hrs. Artificial infestation by prisoned young adult aphids under leaf cages on faba resistant plant in the field during Feb.-March 1997 resulted 100\% mortality after 48 hrs, that may be due to either the direct toxicity effect of those extracted alkaloids on aphids or their effects on aphid symbionts. That may explain why aphid did not harboured faba plants parasitized with broomrape, since their foliage are containing these stress metabolises as a plant defence against aphids.