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Bees are pushed hard to pollinate multiple crops, and some crops might not provide adequate nutrition.

Bees are pushed hard to pollinate multiple crops, and some crops might not provide adequate nutrition.

Dr. Zachary Huang, Michigan State University

Approximately 130 crops grown in the United States depend on honeybees for pollination. Examples of bee-pollinated fruits include almonds, apples, cherries, blueberries, pears, peaches, strawberries, raspberries, and the melons (squashes, cucumbers, pumpkins, and watermelons). Vegetable seed productions that require bees include asparagus, broccoli, onions, cabbages, and radishes.

A Cornell study in 2001 estimated the total value of pollination to these crops in the United States to be about $15 billion per year. This value far exceeds the value of honey or other bee products (propolis, pollen, beeswax, and royal jelly) combined.

Loss of bees

Starting around October 2006, some beekeepers observed the rapid loss of bees in many colonies. For example, a colony full of 40,000 workers on one day, after a week suddenly has only one queen and a few hundred young bees left, with five to six frames of sealed brood (immature stages of bees, including eggs, larvae, and pupae). No dead adult bees are found inside the hive or in close proximity. Furthermore, these colonies are not invaded by opportunistic pests such as wax moth or small hive beetles, which attack weak colonies or empty hives. Nor are the very weakened colonies "robbed" by nearby honeybees. Robbing is a behavior by honeybees to remove honey from nearby, usually weaker, colonies when resources are scarce. Scientists termed this ailment CCD, shortened for colony collapse disorder, because it was not clear what caused these symptoms and whether it was a disease or simply a symptom from stresses or pesticide poisoning.

Possible causes

The cause for CCD remains illusive, but several important stresses might play roles. Most scientists believe there is a combination of various factors, much like a "perfect storm" when several factors come together, causing bee colonies to collapse. The following is a list of possible elements, but none of them alone has been proven to cause CCD.

Varroa and viruses—By far the worst threat to honeybee health, in the United States and worldwide, is the ectoparasite varroa mite (Varroa destructor ). This mite, formerly referred to as Varroa jacobsoni in the literature, was introduced into the United States around 1987. Varroa mite has been known to transmit many types of bee viruses, including deformed winged virus, cloudy wing virus, Kashmir virus, slow paralysis virus, and acute bee paralysis virus. In 2007, the new Israeli acute paralysis virus was found to have a tight association with CCD and was considered a possible cause. Later, it was found that the Israeli virus had actually been in the United States for at least seven to eight years. Given that CCD only happened the last two years, it was thought that the Israeli virus could not have been the sole cause for CCD, although it might be a contributing factor.

Nosema disease— Nosema apis , a fungal parasite (previously considered a protozoan) that infects the midgut cells of bees, causes nosema disease. Colonies often die during winter because sick bees defecate inside the hive and spread the disease. In the summer, infected workers forage earlier and live shorter lives, causing reduced honey yield. In 1996, a new species of Nosema was discovered in Asia and named Nosema ceranae because it was thought that it only infected the Asian hive bees, Apis cerana . But recently, scientists in Taiwan and Europe found the parasite infecting Western honeybees. Some scientists, especially those in Spain, consider the new species as the main culprit causing massive bee die offs, possibly the cause for CCD. In the United States, scientists have found the new species in samples that were eight to ten years old, thus, again, Nosema ceranae by itself cannot be the sole cause of CCD.

Pesticides—Beekeepers have been putting many pesticides, including pyrethroids, organophosphates, organic acids, and essential oils, into bee colonies, mostly to control varroa. Some of these chemicals will stay stable inside beeswax for a long time, and become slowly released into larval food. Studies have shown that insecticides inside beeswax can decrease the survival rate and the body weight of queens and reduce sperm numbers in drones. It is not clear how these chemicals affect the learning and memory of worker bees. Pesticides applied externally to the hive—those used on crops and on ground covers—also affect honeybees. Pesticides sprayed onto flowers directly can be picked up by bees visiting those flowers. Also, systemic insecticides are absorbed by plants and then transported to nectar and pollen that are collected by bees. French beekeepers observed the mysterious "mad bee disease" around 1999, when foragers became disoriented and had trouble finding home. Beekeepers suspected the pesticide Gaucho (imidacloprid) as the culprit. At high concentrations, the chemical can disrupt learning and memory of bees, but numerous studies between 2000 and 2003 concluded that there is not enough imidacloprid in the nectar and pollen from the seed-treated plants to have caused behavioral changes or toxic effects.

Environmental and/or nutritional stresses—Environmental and nutritional factors could also play a role in CCD. Bees are trucked long distances across many time zones, climate is changing due to global warming, bees are pushed very hard to pollinate multiple crops, and some of the crops perhaps do not provide adequate nutrition (especially protein) to bees. Moreover, some beekeepers feed bees high fructose corn syrup, which in some instances has high amounts of hydroxymethylfurfuraldehyde, a chemical that is toxic to bees.

Grower implications

The CCD crisis did impact California almond growers. They are now paying an average price of $175 per colony, compared to $125 about four years ago. Although apple and cherry growers are currently paying much less ($45 to $70 per colony), there has been a slight increase the last two years, most likely due to CCD.

As a grower, you should try to maintain a long-time relationship with your beekeeper and sign a pollination contract about six to eight months before you need the bees. has a "beebase" with which you can search for a beekeeper close to you.