Reduced wind strengthens top-down control of an insect herbivore

Abstract

Global wind speeds have decreased 5-15% over the last 30 years and are expected to continue decreasing in the future. However, little is known about how wind affects species and their interactions within communities. I experimentally tested the effects of wind on predator-prey interactions using soybean aphids and predatory multicolored Asian ladybeetles. First, I examined the direct effect of wind on aphids in a greenhouse without predators under three treatments: no wind, wind (oscillating fan), or simulated wind movement. Aphid abundances did not differ among treatments. Next, I conducted a field experiment in soybean plots assigned to either control or wind-block treatments. Predators were more abundant in wind-block treatments and reduced aphid abundance by 40% compared to control plots. To elucidate why wind indirectly increased aphid density in open plots, I conducted a feeding trial with ladybeetles foraging for aphids on plants that were assigned to either control or simulated wind movement treatments. Plant movement doubled the amount of time it took predators to begin consuming aphids and decreased predation rate by two-thirds. These experiments illustrate how wind can have indirect effects on prey by altering predator behavior and show the importance of this under-studied effect of global change.