Lower Shore Agronomy Day Looks at Factors Affecting Declining Population
SALISBURY, Md. — Anyone who has been listening to the news lately should know that bees are declining in numbers and that their decline is a threat to the food supply.
Nut-bearing trees, fruit trees, berry bushes and vines, even corn and wheat, depend on bees to transfer pollen between the male and female part of the plants enabling them to bear “fruit.”
In the course of picking up pollen, however, the bees pick up other things that are not good for bees.
Agriculture experts, such as Mike Embrey, a University of Maryland Extension apiculturist, are increasingly grim when they talk about colony collapse disorder, or CCD.
“CCD is not a disease but a symptom of another problem,” Embrey told attendees at the annual Lower Shore Agronomy Day, held Jan. 29 at Christ United Methodist Church, Salisbury.
Figuring out which problem is not always easy, because it could be a number of different environmental factors. Embrey, who has participated in research trials designed to determine which factors are contributing to the problem, said three types of bees play a role in pollinating the grains and vegetables that fill our plates as well as help to feed the animals whose meat we enjoy. These are bumble bees, alfalfa leaf cutter bees and mason bees.
There are 2.5 million managed bee colonies, half of which are in California. California almond trees require vast numbers of bees to do the job when they are in flower, so many that hives have to be imported. There just aren’t enough bees in California to do the job.
Hives are transported from all over the country to do the pollination of numerous crops. Transporting the bees causes stress to the hive. Depending on the time of their arrival, and the flowering of the crop, the bees may be held with only sugar as a food source and bees like (and need) variety.
Big agriculture means large-scale monoculture farming operations that not only reduce the variety of nutrients available to bees, making it difficult for bees to get what they need to survive, but also cause habitat destruction. In recent years, farms have become almost devoid of hedgerows. Hedgerows are natural bee habitat with some species nesting and feeding in hedgerows.
Parasitic mites introduced from Asia in the late 1980s added another stressor that has reduced bee populations, Embrey said. Transport and environmental conditions reduced the bee population 10 to 15 percent before the mites were introduced. The loss escalated to 20 to 25 percent since before leveling somewhat.
The incidence of CCD jumped to 32 percent in California. Last year was the first year in which there was a drop in the number of hives lost.
CCD resulting from mite infestations is not the major problem in Maryland, which tends to suffer bee loss due to adverse weather conditions. Maryland is losing 30 percent of its bee population, as indicated by a rapid loss of worker bees and the presence of small clusters of bees with a queen present, Embrey said. Few or no dead bees at the entrance of the hive, excess brood and food stores and higher pathogen (bacteria, virus, fungi) counts have also been noted.
Pesticides are among the easiest problem substances to trace. They can be detected in the wax produced by the bees. But as with many other concerns that threaten human habitation, it is partly our destruction of wildlife habitat that threatens our own subsistence. We have removed much of the bee’s natural habitats and there probably are not too many urban dwellers eager to share their immediate surroundings with bees, he said.
Although pesticides present a certain risk to bees, University of Maryland Extension Service scientists have found no pattern of exposure to pesticide levels that raises alarms.
Many Americans worry about toxic chemicals contained in pesticides and herbicides, but Embrey said that that science and perception are not the same.
“Toxicity does not equal risk,” he said. “Risk equals hazard (toxicity) multiplied by exposure. Toxicity is a constant regardless of use. Exposure depends on the conditions of use.”
Reducing exposure has proved to be beneficial, he said.
“Bees are flying dust mops,” Embrey said. “Their forage range is 8,000 acres or a two-mile radius of the hive or nest.”
Because most farms in Maryland are nowhere near 8,000 acres, bees will be affected by the practices of neighboring farmers as well as that of their home farm. Applications of pesticide and herbicide can drift onto nonflowering vegetables and grain and increase potential bee exposure after a heavy dew by leaving a residue in the nectar, pollen or extra-floral nectaries. Some pesticides remain active up to two years after application, he said.
Secondary routes that expose bees to harmful chemicals include spills or contaminated (often standing) water. The residue that remains in the nectar and pollen of rotational crops that are planted more than once during the growing season is also a problem, Embrey said.
And treated seed dust may be deposited on- or off-site onto flowering vegetables that attract bees, such as cucumbers, melons, pumpkins, squash and watermelon, which cause a higher incidence of bee exposure because of increased applications of pesticide. Embrey cited as potential culprits neonicotoid insecticides that are widely used as seed dressings and for home gardening.
The risk to bees can be greatly reduced by reducing the incidence of exposure. In layman’s terms that means it’s all in the timing. Because die-outs of worker bees represent a serious threat to the health of the hive, etymologists in Maryland are looking at whether current practices also affect worker bees still in the larval stage. They know that chronic exposure, over time, does the most damage.
At the USDA-Beltsville Agricultural Research Center, Embrey participated in experiments with various treatment regimens and helped to conduct residue sampling five weeks after planting by collecting flowers in the field so that nectar and pollen could be analyzed.
They used mass spec analysis to prove that the residue was higher if the pesticide was applied close to or during pollination. The best results occurred when they treated planting or bedding trays.
Embrey said that while many farmers are independent-minded and not eager to get “outsiders” involved in their farming operation, the bee problem will not be solved without cooperation.
“The EPA needs kill reports so they can investigate to pinpoint cause and effect,” he said. Researchers identify “suspects” by analyzing beeswax. It’s an expensive chemical test. Embrey urged farmers to let the EPA do it on their nickel.
Not all chemical contaminants come from external forces. Beekeepers use chemicals such as fulminate and coumaphos that are toxic in high concentrations. When these substances are detected in the beeswax, it can usually be traced to the beekeeping operation.
Some chemical substances, including pesticides, are more lethal when combined than when used alone, he said.