Selenium seen as a bee killer
Traditionally, honey bee research has focused on environmental stressors such as pesticides, pathogens and diseases. Now a research team led by entomologists at the University of California, Riverside has published a study that focuses on an anthropogenic pollutant: selenium (Se).
The researchers found that the four main forms of Se in plants—selenate, selenite, methylselenocysteine and selenocystine—cause mortality and delays in development in the honey bee.
“Metal pollutants like selenium contaminate soil, water, can be accumulated in plants, and can even be atmospherically deposited on the hive itself,” said Kristen Hladun, the lead author of the study and a postdoctoral entomologist. “Our study examined the toxic effects of selenium at multiple life stages of the honey bee in order to mimic the chronic exposure this insect may face when foraging in a contaminated area.”
Study results appear in the Oct. 2013 issue of the journal Environmental Toxicology and Chemistry.
The honey bee is an important agricultural pollinator in the United States and throughout the world. In areas of Se contamination, honey bees may be at risk because of the biotransfer of the metal from Se-accumulating plants.
Se contamination is a global problem originating from naturally contaminated soils and a multitude of anthropogenic sources including mining and industrial activities such as petroleum refining and coal-power production, as well as where agricultural runoff is collected and can concentrate Se from the surrounding soils.
Low Se concentrations are beneficial to many animals; in particular, it is a critical component of an antioxidant enzyme. Slightly higher concentrations, however, are toxic. Several insect species suffer toxic effects from feeding on Se-contaminated food.
In the case of the honey bee, Se enters the body through ingestion of contaminated pollen and nectar. Organic forms of Se can alter protein conformation and cause developmental problems, and inorganic forms of Se can cause oxidative stress.
“It is not clear how selenium damages the insect’s internal organs, or if the bee has the ability to detoxify these compounds at all,” Hladun said. “Further research is necessary to examine the cellular and physiological effects of selenium.”
Hladun explained that honey bees may also be more susceptible than other insects due to a lack of detoxification enzymes that other insects still possess. Further, honey bees at the larval stage are more susceptible to selenium relative to other insect species.