Environmental Science 15th Edition by Scott Spoolman,Tyler Miller

Exercise 8

HONEYBEE LOSSES: A SEARCH FOR CAUSES
Each winter since 2006, 30-35% of the U.S. population of European honeybees has disappeared because of colony collapse disorder ( Core Case Study ). This problem also occurs in parts of Europe, China, and India.
Scientific research has found a number of possible of reasons for this decline, including:
•The varroa mite, a parasitic insect, can weaken and kill honeybee adults by feeding on their blood and larvae. It has killed millions of bees since it appeared in the U.S. in 1987-probably from infected bees imported from South America.
•Harmful interactions between viruses and fungi found in European honeybees and in almost all bee colonies suffering from colony collapse disorder can kill bees by weakening their immune systems.
•Pesticides. As honeybees forage for nectar, they can come into contact with insecticides that they sometimes carry back to their hives. Some research indicates that several types of widely used neonicotinoids, which are derived from nicotine that tobacco plants use as a natural insecticide, may play a role in CCD. These pesticides are deliberately incorporated into food plants so they end up in the nectar and pollen that the bees take back to their colonies. Some studies suggest that exposure to trace amounts of these chemicals can disrupt the nervous systems of bees, decrease their ability to find their way back to their hives, weaken their immune systems, and make them more susceptible to mites, viruses, and fungi. The explosive growth in the use of neonicotinoids since 2005 has roughly tracked the rise in CCD since 2006. Pesticide manufacturers deny that the levels of neonicotinoids and other pesticides that bees are exposed to are high enough to cause harm if the chemicals are used as directed.
•Stress and poor nutrition, for some of the bees that are transported long distances around the United States for the industrial pollination business (Figure 8.A), can weaken the bees' immune systems and make them more vulnerable to death due to mites, viruses, fungi, and pesticides.
•Lack of natural foraging areas. Widespread conversion of grasslands to crop fields has dramatically reduced the diversity of natural plants on which bees naturally thrive.
The growing consensus among bee researchers is that the likely cause of colony collapse disorder is a combination of the often-interacting factors listed here. Some scientists see the decline of honeybees as an indicator of the environmental degradation of our life-support system.
Critical Thinking
Can you think of some ways in which commercial beekeepers could lessen one or more of the threats described here? Explain.

FIGURE 8.A European honeybee hive boxes in an acacia orchard. Each year, commercial beekeepers rent and deliver several million hives by truck to farmers throughout the United States.