A new study by a University of California - Riverside (UC) Riverside-led team shows pollutant metal kills honey bees or delays their development. The health of honey bees is adversely impacted by selenium. Traditionally, honey bee research has focused on environmental stressors such as pesticides, pathogens and diseases. Interestingly, some honey bee farmers raise honeybees part of the year on their rooftops and return the bees to their hives at certain times of the year.
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). You may wish to check out the study results that appear in the October 2013 issue of the journal Environmental Toxicology and Chemistry.
The researchers found that the four main forms of selenium (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, according to the October 3, 2013 news release, Health of honey bees adversely impacted by selenium. "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."
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. The researchers found that the four main forms of Se in plants -- selenate, selenite, methylselenocysteine and selenocystine -- caused mortality and delays in development in the honey bee.
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 Selenium (Se)-accumulating plants. Selenium (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 selenium 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 in the October 3, 2013 news release, Health of honey bees adversely impacted by selenium. "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. Also see the article, Corn insecticide linked to great die-off of beneficial honeybees.
"Mortality within the hive can reduce the number of workers and foragers overall," she said in the news release. "The forager's ability to tolerate high concentrations of selenium may act against the colony as a whole. Honey bees are social animals and their first line of defense against environmental stressors is the foraging bees themselves. High concentrations of Se will not kill foragers outright, so they can continue to collect contaminated pollen and nectar, which will be stored and distributed throughout the colony."
Besides areas surrounding coal-fired power plants, petroleum refineries, copper refineries, and mining activities, areas around industrial plants producing glass, pigments, inks, and lubricants, can all be anthropogenic sources of Se. In the United States, the well-established toxicity of Se to wildlife and humans has resulted in this element being regulated by the Toxic Substances Control Act and the Clean Water Act.
"Selenium occurs naturally in many places around the world, but it also is a byproduct of many industrial activities, and finding ways of recovering and recycling it is key to minimizing the damage to the environment," Hladun said in the news release. "Currently, researchers are exploring its use in solar energy technologies."
According to Hladun, knowing which contaminants are the most important to regulate is key to minimizing the exposure of honey bee hives to contaminants
"Beekeepers can take steps to prevent bees from foraging during flowering periods of plants that have exceptional pollutant levels or to move hives away from contaminated areas," she said in the news release. "Also, better management of weedy plant species that are known to be Se-accumulators can prevent them from becoming a route of exposure."
Currently the researchers are conducting experiments feeding honey bee colonies with selenium (Se)-laden food. They will monitor the bees for changes in survival and behavior. In addition, they are exploring the effects of other metal pollutants (cadmium, copper, and lead in particular) that have been found in honey bee hives, especially the ones located near urban or industrial areas.
The research was funded by a three-year grant from the US Department of Agriculture, National Institute of Food and Agriculture, awarded in 2012. Hladun was joined in the study by Osman Kaftanoglu, a research apiculturalist at Arizona State University; David Parker, a professor in the Department of Environmental Sciences at UCR; and a UCR undergraduate student, Khoa Tran. UCR's John Trumble, a distinguished professor of entomology, is the principal investigator on the project.
The real reason to worry about bees
Honeybees should be on everyone's worry list, and not because of the risk of a nasty sting, an expert on the health of those beneficial insects said here last month at the 246th National Meeting & Exposition of the American Chemical Society (ACS), the world's largest scientific society. Set aside the fact that the honeybee's cousins — hornets, wasps and yellow jackets — actually account for most stings, said Richard Fell, Ph.D. Despite years of intensive research, scientists do not understand the cause, nor can they provide remedies, for what is killing honeybees.
"Some estimates put the value of honeybees in pollinating fruit, vegetable and other crops at almost $15 billion annually," Fell said in the September 11, 2013 news release, The real reason to worry about bees. "Without bees to spread pollen from the male parts of plants to the female parts, fruit may not form. That would severely impact consumers, affecting the price of some of the healthiest and most desirable foods."
Farmers use honeybees to pollinate more than 100 different fruit and vegetable crops around the country in an approach known as "managed pollination." It involves placing bee hives in fields when crops are ready for pollination.
"The biggest impacts from decreased hive numbers will be felt by farmers producing crops with high pollination requirements, such as almonds. Consumers may see a lowered availability of certain fruits and vegetables and some higher costs," explained Fell in the news release, The real reason to worry about bees.
He discussed the ongoing decline in honeybee populations in the U.S. and some other countries — a condition sometimes termed colony collapse disorder (CCD). Although honeybees have been doing better in recent years, something continues to kill about 1 in every 3 honeybees each year. He spoke at a symposium on the topic. Abstracts of other presentations appear at the end of this press release.
"There is a good bit of misinformation in the popular press about CCD and colony decline, especially with regard to pesticides," Fell said in the news release, The real reason to worry about bees. He is an emeritus professor of entomology at Virginia Tech, and an authority on colony decline in bees. "I think it is important to emphasize that we do not understand the causes of colony decline and CCD and that there are probably a number of factors involved. Also, the factors that trigger a decline may be different in different areas of the country and at different times of year."
Some of the leading theories about the cause of CCD include the use of certain pesticides, parasites, diseases and overall hive nutrition
Beekeeper and other organizations are pushing to stop the sale of certain neonicotinoids, insecticides that some regard as the main culprit of CCD. However, Fell said that would be premature. The U.S. Environmental Protection Agency recently reviewed the situation and concluded that there is no scientific evidence that the neonicotinoids are causing serious problems with bee colonies.
Honeybees are not the only species of bee that can be used in managed pollination. If colonies continue declining, Fell believes that there will be an increase in the use of other species, including the bumble bee and alfalfa leafcutter bee. There are, however, measured declines in these species' populations as well. In addition, they are not as easily managed for pollination as the honeybee.
"The major advantages of using honeybees are ease of movement, both in and out of orchards or fields, as well as the ability to manage colonies for higher populations. Honeybee colonies can be moved from one crop to another in a single season, something that cannot be done easily with bumble bees or solitary bee species such as the alfalfa leafcutter bee," explained Fell in the news release. "If we can gain a better understanding of the factors causing honeybee decline, we may be able to apply this knowledge to protecting other species."
Fell cited funding from the Virginia Department of Agriculture and Consumer Services, the National Honey Board, the Virginia Agricultural Council and the U.S. Department of Agriculture National Institute of Food and Agriculture.