Some insects have the ability to manipulate plants to produce new organs known as galls, which manifest as abnormal growths on leaves, branches, or twigs. These galls provide insects and their offspring with food and shelter. Insects are also able to redirect the plant's nutrients, such as sugar, toward their galls, sometimes leaving the plant malnourished.

This competition for nutrition between the gall and the rest of the plant makes some of these insects a serious pest. In the 1800s, the galling insect phylloxera nearly decimated grapevine in Europe and another, the Hessian fly, caused a severe cereal shortage in the United States. Galling insects are master manipulators with the potential for widespread damage.

A team of scientists from the University of Toledo, University of Missouri and Northern Arizona University studied the relationship between galling insects and poplar trees and found that poplars that resisted these insects had higher levels of defense hormones. They also found that resistant poplars had a lower amount of a class of growth hormones called cytokinins. Last, they discovered that hormone changes in response to insect feeding are inherited.

This study, published in Molecular Plant-Microbe Interactions, is the most complete study to date about the role of hormones in galls, measuring 15 plant hormones belonging to 5 different classes. These findings can be used as a model for pest management and could help the agriculture and forestry industries better understand what makes plants resistant to pests.