Scientists removed insects from fields of primrose for several years.
In just a few generations the primrose relaxed it’s defenses against insects and devoted more energy to competing for space and resources.
In the study, 16 identical plots were set up that contained the same relative numbers of 18 unique genotypes of native evening primrose. During each growing season, half the plots were treated biweekly with an insecticide; the other half were not.
The offspring of evening primrose are mostly clones of the parent due to self-pollination and other factors in primrose reproduction.
Of the genotypes that remained in the plots without insects, the researchers found more plants with relaxed defenses. By 2010 and even more in 2011, there was a shift toward plants that flowered earlier. When insects are present, later-flowering plants do better due to the timing of insect development, where larvae tend to eat the fruits of early flowering plants. Also, over time, there was a shift toward primroses with lower amounts of insect-deterring chemicals in the fruits, suggesting that in the wild, selection had been strongest for defense against flower and fruit eating insects.
Finally, without insects, primroses were better able to compete against dandelions – primrose genotypes that led to larger plants were favored when compared to the controls.
“The effects of insect pests can have immediate consequences for plant health and also sweeping consequences for evolution of entire communities,” Agrawal said.