Insecticides weaken plants

This is an evening primrose video.

From the National Science Foundation in the USA:

Why We Need InsectsEven “Pesky” Ones

At first blush, many people would probably love to get rid of insects, such as pesky mosquitoes, ants and roaches. But a new study indicates that getting rid of insects could trigger some unwelcome ecological consequences, such as the rapid loss of desired traits in plants, including their good taste and high yields.

Specifically, the study–described in the Oct. 5, 2012 issue of Science and funded by the National Science Foundation showed that evening primroses grown in insecticide-treated plots quickly lost, through evolution, defensive traits that helped protect them from plant-eating moths. The protective traits lost included the production of insect-deterring chemicals and later blooms that gave evening primroses temporal distance from plant-eating larvae that peak early in the growing season.

These results indicate that once the plants no longer needed their anti-insect defenses, they lost those defenses. What’s more, they did so quickly–in only three or four generations.

Anurag Agrawal, the leader of the study and a professor of ecology and evolutionary biology at Cornell University, explains, “We demonstrated that when you take moths out of the environment, certain varieties of evening primrose were particularly successful. These successful varieties have genes that produce less defenses against moths.”

In the absence of insects, the evening primroses apparently stopped investing energy in their anti-insect defenses, and so these defenses disappeared through natural selection. Agrawal says that he was “very surprised” by how quickly this process occurred, and that such surprises, “tell us something about the potential speed and complexities of evolution. In addition, experiments like ours that follow evolutionary change in real-time provide definitive evidence of evolution.”

Agrawal believes that his team’s study results are applicable to many other insect-plant interactions beyond evening primroses and moths. Here’s why: The ubiquitous consumption of plants by insects represents one of the dominant species interactions on Earth. With insect-plant relationships so important, it is widely believed that many plant traits originally evolved solely as defenses against insects. Some of these anti-insect plant defenses, such as the bitter taste of some fruits, are desirable.

“This experimental demonstration of how rapid evolution can shape ecological interactions supports the idea that we need to understand feedbacks between evolutionary and ecological processes in order to be able to predict how communities and ecosystems will respond to change,” said Alan Tessier, a program director in NSF’s Directorate for Biological Sciences.

“One of the things farmers are trying to do is breed agricultural crops to be more resistant to pests,” said Agrawal. “Our study indicates that various genetic tradeoffs may make it difficult or impossible to maintain certain desired traits in plants that are bred for pest resistance.”

In addition, oils produced by evening primroses have been used medicinally for hundreds of years and are beginning to be used as herbal remedies. Agrawal’s insights about pests that attack these plants and about chemical compounds produced by these plants may ultimately be useful to the herbal and pharmaceutical industries.

Agrawal says that most previous real-time experiments on evolution have been conducted with bacteria in test tubes in laboratories. “One of things we were excited about is that we were able to repeat that kind of experiment in nature. You can expect to see a lot more of this kind of thing in future. We will keep our experiment running as a long-term living laboratory. “

More information about this study is available from a Cornell University press release.

Pest evolves better resistance to insecticidal GM crops: here.

A first-of-its-kind study used herbarium specimens to track insect herbivory across more than a century, and found that, across four species — shagbark hickory (Carya ovata), swamp white oak (Quercus bicolor), showy tick trefoil (Desmodium canadense) and wild lowbush blueberry (Vaccinium angustifolium) — specimens collected in the early 2000s were 23 percent more likely to be damaged by insect herbivores than those collected in the early 1900s: here.

11 thoughts on “Insecticides weaken plants

  1. A most excellent post! Reminds me of a quote by E.O. Wilson: “If all mankind were to disappear, the world would regenerate back to the rich state of equilibrium that existed ten thousand years ago. If insects were to vanish, the environment would collapse into chaos.”


  2. Petrel41, My problem is deer. They eat all the flowers or buds the minute they appear. Do you know if the deer repelents (usually a mixture of dead fish, eggs and a few other horrible ingredients) are of any harm to flowers? I am ready to douse the new spring plants and buds with some commercial deer repellent such as “Not tonight deer” or “deer be-gone.” Any knowledge on these liquids? Thanks, Wally


    • Hi, deer are a bit of a different issue than insects. I am not by any means an expert on deer repellents. I would tend to think that organic material like dead fish would not be as hazardous as some chemical repellents. Though too much organic material like dung, or fertilizer, will kill flowers which need a “nutrient poor” soil, like violets.

      Maybe a fence around the flowers, or a net above them, might prevent deer from eating the flowers?


      • The deer are agressive. They lean on or jump on netting and have been known to get over six foot fences. On violets, the deer are more than welcome to any they find. My grass lawn is invaded by violets and their horrible root systems. I wish to protect my flower garders; lillies, roses, peonies, fox gloves (which they normally don’t bother) and I have a section of blood root which they do not seem to care for either. Some Hibiscus they ignore and others they eat right down to the root. Thanks for your advice. I can’t do much more to the flowers than the deer do. I will take your advice and continue to avoid the chemicals. Thanks again, Wally


  3. Pingback: Saving English woodland birds | Dear Kitty. Some blog

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