Irrigation Stress to Wheat at Sensitive Growth Stages: Tri-trophic Effects and Implications for Aphid Control

Abstract

Weather extremes can have profound impact on plant physiology. The altered physiology of stressed plant can also modify trophic interactions in that plant environment. Aphids are important pests of wheat crop causing direct or indirect injury to the crop. The pest is routinely managed through use of insecticides. Insecticides due to their toxic effects are mostly not desired for use on food crops. Thus, alternative approaches such as biological and cultural control are more desirable. This research explores irrigation stress impacts on wheat aphids, predators, and yield characteristics under field conditions. The wheat crop was stressed at any of the tillering, booting, heading or grain formation stages by skipping irrigation during entire length of each stage. Unstressed wheat enjoyed irrigation at all four stages. Schizaphis graminum (Rondani) was the most abundant aphid species and coccinellids, the most abundant predators. S. graminum was least on unstressed or tillering stressed wheatbut was the most on wheat stressed at booting, heading, and grain formation stages. Irrigation stress reduced chlorophyll contents (5-25%) and wheat yield (kg/ha) (6-31%) when compared with unstressed wheat. The irrigation stress changed coccinellid abundance and predator-prey ratio. Altered plant physiology and a weaken plant defense under irrigation stress attracted feeding by more aphids which resultantly reduced chlorophyll amount. The abundant prey attracted more predation in the stressed wheat. The aphids and predator’s preference change under irrigation stress are clear in our findings. We also discuss tri-trophic effects and implications of current study toward wheat aphid control.