Feeding by the aphid Sipha flava produces a reddish spot on leaves of Sorghum halepense: an induced defense?

Feeding by the aphid Sipha flava produces a reddish spot on mature leaves o f Sorghum halepense. The present work is aimed at determining whether this plant response entails induced resistance against the aphid. Old and young leaves showed the same response to aphid Feeding (reddish coloration). Wate r-stressed plants displayed a similar reddish coloration to aphid-infested plants. This was verified by evaluation of absorbance peaks of the respecti ve leaf extracts. Aphid fecundity was reduced on previously infested (and h ence reddish colored) leaves. However, aphid fecundity was not affected on water stressed plants. Furthermore, aphid survival was not different on art ificial diets containing increasing concentrations of the reddish pigment. It is concluded that the reddish spot is correlated with. bur is not itself responsible for, the observed induced resistance of S. halepense against S . flava.