The chemical analysis of spring and autumn leaves of plum can give important informations for the relation between chemical components and the susceptibility of plum leaves to be infested with aphid. So, spring and, autumn leaves from the local plants Prunus domestica L. were subjected to chemical analysis to isolate the flavonoid coumarins which are phenylpropanoid in origin especially those formed by ring closer to a C₆-C₃ compound such as o-hydroxy cinamic acid.  Results revealed that spring and summer leaves, have been containing either hydroxy or oxy-coumarin (HC or OC) in the C₃,  propane unit.  Whereas the autumn leaves contain coumarin with C₃, unsaturated propane unit. When the commercial coumarins were tested against adults of the aphid.  Hyalopterus arundinis (Fabr) through stretched membrane on synthetic diet, coumarin gave feeding stimulants at 2X10^-3 molar while the other two compounds  (HC and OC) changed the effect of the molecule on aphid feeding from stimulatory to inhibitory. Hydroxy coumarin was very feeding inhibitor at 2.5 X 10^-3 molar while oxy-coumarin was lethal at 1.5 X 10³ molar. That may, in part, explain why aphid harboured abundantly plum plants in autumn, since the leaves are containing coumarin which used as an antifrost agent and protected them with their adults, from severe cooling during winter. On the contrary, the spring and summer leaves have been containing hydroxy and oxy-coumarin. In Egypt, aphids protect themselves against the low temperature of winter by feeding on Handaquoq and sweet clover in which they have coumarin.