On farms, chemical application changes the biophysical cues that plants use to attract pollinators, according to a recent British study. Spraying flowers with synthetic fertilizer, altered their electrical voltage, disrupting the electrical fields that bumblebees use for navigation. This is the first study to show how fertilizer impacts pollinator visitation to flowers. With less pollination, farms can’t produce as much food, impacting the availability of important fruits and vegetables to our diets.

In non-organic farming, farmers typically use synthetic chemicals on their crops to curb diseases and provide nutrition to the plants. Studies have shown that pollinator visits decrease after pesticide application. If the sprays don’t immediately kill beneficial insects, research shows these chemicals are harmful long-term in sublethal amounts to pollinator activity and vitality.

Flowers use physical and chemical cues such as color, odor, and electrical fields, to guide pollinators towards them. This study explored the biophysical alterations in flowers caused by agrochemical application of synthetic fertilizer and a common neonicotinoid pesticide: imidacloprid neonicotinoids. Specifically, they measured potential impacts on flower color, odor, and electrical voltage, utilizing a variety of flowers, and bumblebees as model pollinators.

To measure the impacts of fertilizer on each response variable, researchers compared fertilizer solution to a negative control of demineralized water. Researchers examined the color of each solution by measuring their light reflectance across the color spectrum and compared it to colors of high bumblebee photosensitivity. To the effect of odor, researchers observed bumblebee consumption behavior, spraying a platform with water or fertilizer solution and supplying a stack of sugar for the bees to eat.

Researchers applied several methods in exploring the effects of the application of fertilizer and common pesticides on electrical fields. They monitored electrical voltage on and near the plant, at relevant distances for foraging bees. Electrostatic-colored powder was applied to flowers after fertilizer spray, sticking to areas with negative electric voltages. Lastly, researchers observed bee activity while artificially applying electrical voltage to flowers in the field.

The application of fertilizer drastically altered flower electrical fields. Upon spraying, the resting potential of the flower spiked, from negative to positive. This change was reflected by the electrostatic paint, adhering more successfully onto unsprayed flower petals and revealing their more negative charge. The electrical voltage took 12.5 minutes on average to fall to pre-application levels. Researchers hypothesize that the modification in electric fields is due to agrochemical sprays carrying a large number of charged particles, designed to stick to the plants.

Bumblebees responded to artificial modifications in plant voltage, displaying less pollinating behavior towards plants whose electric voltage scientists artificially raised. For unmodified plants, bees landed on over 80% of flowers they approached, however less than 50% of approaches towards a positively charged plant resulted in a successful landing. Electric fields guide bumblebee activity, so modifications to them disrupt pollination.

There was no significant difference between the color of fertilizer solution and water, each holding similar reflectance spectra. Additionally, there was no difference in sugar consumption when exposed to fertilizer solution, indicating that fertilizer application’s effect on pollinator behavior is neither visual nor aromatic.

Successful pollination enhances both the plants of a farm’s ecosystem and the pollinator population. While it has been well documented that the application of chemical sprays in conventional farming results can dramatically reduce the abundance and diversity of pollinators on farms and in nearby areas, which reduces their pollination services to the crops. This novel study shows that seemingly harmless ammonia fertilizer as well as common pesticides can reduce the effectiveness of pollinators. This can impact not only crop yields, but also the health of this important biodiversity.

Banner Photo Credit: Joran Quinten: https://unsplash.com/photos/a-bee-on-a-flower-BnMyDiJOue8