Bees are required to pollinate hundreds of flowering fruit, vegetable, seed and nut crops. Without bees, these crops are unable to produce.

During the last quarter century, honeybees in the U.S. have been exposed to at least six major diseases and parasites.

In addition, they have lost habitat to urban expansion and high grain prices are driving pasture conversion to row crops that are not attractive to bees.

Together, these factors have severely stressed colonies, said a University of Nebraska-Lincoln entomologist.

"Collectively, these things are taking a toll on bees and beekeepers," said Marion Ellis, UNL entomologist in the Institute of Agriculture and Natural Resources.

The problems facing beekeepers have been in the news for the last two years. National advertising campaigns by companies that rely on hive products such as Burt's Bees, Haagen Dazs, L'Oreal Paris and J.W. Dundee Brewing Company also are putting them in the spotlight.

Ellis said he doubts that one thing can be blamed for the bee population reduction and suggests that improving honeybee health will require addressing more than one problem.

It started in 1984 with the appearance of the tracheal mite, an organism that lives in the respiratory system of the honeybees.

This was followed by the arrival of varroa mites in 1987 and Africanized bees in 1990. In 1998, the small hive beetle was discovered, followed by the Nosema ceranae parasite and the Israeli acute paralysis virus in 2007.

A rapid increase in the acreage of insect-pollinated crops, especially almonds in California, compounds the problem, Ellis said.

"Beekeepers are being asked to move their hives much more frequently than in the past," he said.

"Last year was the first time in U.S. history that beekeepers earned more income from moving their hives to California to pollinate almonds than from all the honey produced in the U.S."

The U.S. is the leading producer and exporter of almonds and supplies the vast majority of the world's almonds.

Half of the country's bees are needed to pollinate almonds, which need two colonies of bees for each acre.

With the new orchards that will come into production in the next four years, almonds alone will need three-fourths of the bee population.

"Either we need to find a way to provide healthy bees to pollinate those crops, or those farmers are going to go belly up," he said.

Most of the honeybee colonies that produce honey in Nebraska and other north central states travel to California each winter to meet the demand for pollination.

There are things Nebraskans can do to help the bees. When possible, instead of having all grass pastures, lawns, parks and golf courses, incorporate some blooming plants.

Bees need resources throughout the season and diverse resources are better than monocultures. Some forbs that are highly attractive to bees include clovers, vetches, alfalfa, sunflowers, various mints and most native prairie wildflower mixes. Beneficial trees and shrubs include pussy willow, linden, black locust, butterfly bush and Russian sage.

The single most important thing people can do is have a diverse set of resources that bloom throughout the growing season, Ellis said.

"You can have 100 acres of a blooming crop, but once the blooms are gone, bees have to look for something else," he said. "In a natural setting, there is succession of blooming things to benefit pollinating insects."

It also would be helpful in Conservation Reserve Program acres to incorporate native blooming plants. This not only would help pollinators, but also other beneficial insects that prey on crop pests, since many beneficial species use blooming plants for feed and cover.

Finally, it's important that people use insecticides carefully read and follow all label directions and don't spray during blooming periods. It is illegal to spray most insecticides when plants are in bloom.

To shed some light on this problem, UNL recently received $140,000 as part of a multi-state grant from the U.S. Department of Agriculture. Sixteen different scientists from around the country are looking at stress on bees from several perspectives, including diseases, pests, loss of diversity, exposure to chemicals and nutrition.

At UNL, the Sustainable Solutions to Problems Affecting Honeybee Health grant will allow Ellis and entomologist Blair Siegfried to investigate abiotic stress due to chemical exposure and its impact on honeybee health. They will focus on synergistic interactions and effects on reproduction fitness.