By Nneka Nwogwugwu
A new study has revealed a type of insecticide made for commercial plant nurseries that is harmful to a typical bee even when applied well below the label rate.
Chemically similar to nicotine, neonicotinoids are insecticides that protect against plant-consuming insects like aphids, but seriously harmful to bees. They are widely used by commercial growers.
The study was published on July 28, 2021, in the journal Proceedings of the Royal Society B: Biological Sciences.
Much research has focused on their use in food crops like canola, in which they are typically applied at low doses.
However, this study is one of the few to examine neonicotinoid application in potted ornamental plants, which can represent more potent, acute sources of exposure to the toxin for bees.
“Neonicotinoids are often used on food crops as a seed treatment,” explained UCR entomologist and lead study author Jacob Cecala.
“But they’re usually applied in higher amounts to ornamental plants for aesthetic reasons. The effects are deadly no matter how much the plants are watered.”
Cecala said he was surprised by this result, given that neonicotinoids are water soluble.
Going into the study, Science Tech says he assumed that more water would dilute the amount of harm they caused the bees.
The researchers were also curious whether increased watering could benefit bees despite insecticide exposure by increasing the quantity or quality of nectar offered by the plants.
To test these assumptions, the researchers raised bees on flowering native plants in pots that either received a lot of watering, or a little. Plants were selected based on their popularity at nurseries, drought tolerance to ensure blooming even without much water, and their attractiveness to bees. In addition, half the plants were treated with the insecticide.
Though increased water decreased the pesticide’s potency in the nectar of the flowers, the negative effects on bees were still observed.
“Unfortunately, we observed a 90% decrease in the bees’ reproduction with both high and low levels of irrigation,” Cecala said.
This study is also one of the few to examine neonicotinoid effects via ornamental plants on solitary bees, which make up more than 90% of native bee species in North America, and an even higher percentage in California.
The researchers recommend that nurseries quantify the amount of pesticides that are making their way into flowers given their watering and pesticide regimes, and consider alternative management practices that reduce harm to bees and the ecosystems dependent on them.
