Plants are having less sex, and it’s our fault.

I came to this conclusion earlier this month after reading a January 4 New York Times article about a study of Johnny-jump-ups. It showed that the plants have been forced to learn to self-pollinate because the population of insects that should be doing the job has plunged.

The plant – its scientific name is Viola arvensis, or you may know it as the European field pansy – is not native to Maine. Its native territory includes most of Europe, and parts of Asia, Siberia and North Africa. It is, however, very common in Maine and closely related to the native violets that have, with permission, taken over my own backyard.

Plant sex requires other participants. Bees, other insects and hummingbirds feed on nectar from one plant, accidentally pick up pollen, and then carry it to the next plant. That is the sexual act for plants. Sometime later seeds are produced, which will drop to the ground and create a new plant.

Over the last century or so, the population of pollinating insects has declined sharply, according to the scientific study cited by the Times. It was published by the New Phytologist Foundation and based on research at the University of Montpellier in France. But you probably know from your own experience the decline is not limited to France. (Readers who are old enough will remember when car windshields used to get covered with smashed insects.)

A University of Maine Cooperative Extension pamphlet on native blueberries also notes the decimation of insects: “However, because of the alarming decline in native bee numbers over the past several decades (due to bee habitat loss, fragmentation, and pesticide use) farmers have relied more and more on managed bees.”

Lily Calderwood, an Extension wild blueberry specialist and an assistant professor of horticulture at the University of Maine, said that Viola arvensis is considered a weed (which some blueberry growers pretty much define as anything that is not a blueberry).

“Plenty of these plants we call weeds are native and/or good pollinator plants,” Calderwood said. “As the New York Times article mentions, this plant is pollinated by bumblebees, which we have many of in wild blueberry fields.”

But far fewer than there used to be.

The French study found that because insects – bumblebees especially – were not no longer able to do a good enough job of pollinating the Johnny Jump-ups, the plants have figured out how to self-pollinate. The plants use their own pollen to fertilize themselves, a process the study called “selfing.”

That process requires less energy for the plant than creating large flowers and lots of nectar to attract bumblebees, so it makes some sense for a plant aiming to preserve its own energy and live longer. Unfortunately, it may mean problems for the existence of the plant species long term.

Sex is beneficial for plants because it gives the offspring of that sexual contact genes from two sets of parents. Two sets of genes translates to better disease resistance, growth rates and overall vigor. It’s really not so different from humans. Incest is illegal in part because it can produce genetic abnormalities (such as hemophilia among the European royal families in the 19th century).

Among the less-than-ideal results of “selfing,” the study found, is that the self-pollinating plants are reducing the size of the corolla and individual petals that make up the plant blossoms. These are part of what attracts pollinating insects in the first place. Similarly, they’re reducing the amount of scent they produce, another attraction for pollinating insects. Most critically, they are producing less nectar, which is a primary food for all pollinating insects, including about 270 native Maine bees, Calderwood said. With inadequate nectar, insects may starve.

Insecticides are among the reasons for pollinator death. Here in Maine, we must reduce the amount of insecticides we use. They not only kill pest insects, the intended targets, but the chemicals also kill the pollinators that are vital to the natural world – the natural world that we humans depend on. Without pollinators to fertilize crops, what would we eat? The shortage of these beneficial insects, it turns out, weakens the plants, too.

That is far too big a price to pay.

Tom Atwell is a freelance writer gardening in Cape Elizabeth. He can be contacted at: tomatwell@me.com.

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