Influence of Population Density and Plant Water Potential on Russian Wheat Aphid (Homoptera: Aphididae) Alate Production

Little information is presently available on the \nenvironmental variables causing alate production in the Russian \nwheat aphid, Diuraphis noxia (Mordvilko). Our objectives were to \ndetermine if population density of aphids affects alate production \nand to determine the relationship between water potential of \nwheat and production of alates. Response to crowding was tested \nusing a low density treatment of 10 - 20 aphids and a high \ndensity treatment of 150 - 200 aphids. No significant difference \nwas found between the low and high density treatments. A \npressure chamber was used to quantify the amount of water \nstress in wheat. Wing pad formation began within the range of \n-0.5 and -0.6 MPa and ended within the range of -1.21 and -1.31 \nM Pa. From this range in water potential values, six water \npotential treatment ranges were established. Our results show a \npositive correlation between alate production and the leaf water \npotential of wheat, with maximum alate production occurring \nbetween -0.79 and -1.03 MPa. These data suggest that a response \nof the host plant which, in part, results from feeding damage is \ncausing the production of alates. \nKey Words: Russian wheat aphid, water potential, crowding, alate \nproduction