Optimal Pollination

By , |

Optimal Pollination

Honey bees play a critical role in U.S. agriculture, thanks to their large numbers, easy transportation, and special adaptation for efficient foraging for pollen.

Without honey bees to supply pollination services, most fruit and vegetable producers would be forced out of business. Nationally, the value of honey bees due to pollination is estimated to be around $14.6 billion per year.

Parasite Problems

Despite the importance of honey bees, the beekeeping industry has been in decline since two parasitic mites, varroa and tracheal mites, invaded the U.S. in the 1980s. Varroa mites (Varroa descructor) have nearly wiped out the feral (unmanaged) honey bee population in the U.S., and managed honey bee colonies have been declining mainly due to more complicated management because of the mites.

The most recent crisis in honey bee population is the so-called CCD (colony collapse disorder), which received national attention. The disorder has the symptoms of bees “disappearing,” and a colony seemingly healthy in September would have no bees left, or a handful of bees left with the queen, around October or November.

This disorder is large in scale, and it has been reported in 36 states. The disorder is also severe, with large beekeepers (5,000 to 9,000 colonies) losing up to 90% of their colonies. The cause is still unknown, and honey bee scientists all over the country are studying the problem. The report that the Israeli Acute Paralysis Virus (IAPV) could be the cause of CCD is now in doubt, as the virus was found in bee samples as early as 2002.

Work In Tandem

In light of these problems, growers are urged to work even more closely with beekeepers to ensure good pollination results. Here are some steps that can help growers optimize their fruit and vegetable pollination.

- Understand basic honey bee biology and behavior. Understanding some basic bee biology and beekeeping will facilitate your inspection of the hives, gauging of quality/strength of the hives, and help maximize the use of bees for your pollination.

- Understand the social structure. Honey bees are social insects and only the sterile female workers do all the in-hive and outside work. The queen’s only job is to lay about 2,000 eggs per day and release queen mandibular pheromone to let the workers know that she is present and healthy.
The male (drone) has only one job: mate with queens. A typical colony of bees has about 30,000 workers: one queen and a few to hundreds of drones. About one-third of these workers are foragers. Foragers show flower constancy so they tend to focus on flowers of a single species, resulting in more efficient pollination.

- Pay attention to internal factors affecting foraging behavior. To provide adequate pollination, honey bee colonies must be of sufficient strength, free of diseases, have a laying queen, and enough “brood” (immature stages which include eggs, larvae, and pupae). A newly installed package bee colony, with 2 pounds of bees, would have about 9,000 to 11,000 workers and is considered on the weaker side. Such a colony would concentrate heavily on brood rearing and only have about 1,000 to 2,000 foragers. Only strong colonies (25,000-plus workers) would send out about 30% of bees as foragers.

- Environmental factors affect honey bee foraging. Bees do not work in the rain and work less on cloudy days. Foraging activity is positively related to temperature, with a linear relationship from 60°F to 90°F. Bees also slow down when it gets too hot (above 90°F). High winds (above 20 mph) will inhibit flying activity. Bees tend to fly lower when winds are high.

- Bees do not like to get wet while in flight. They also will avoid visiting flowers filled with water. In addition, too much water getting into the flowers will disrupt pollen germination. For these reasons, it is better to sprinkle the crops at night or early in the morning before honey bees are actively foraging, or use drip irrigation.

- Find a beekeeper near you. There is a database of beekeepers who are willing to provide pollination services with more than 430 beekeepers registered: http://cyberbee.net. Click beebase on the left, then click #2 “For beekeepers providing pollination services,” and you have a choice to search beekeepers by area code, county, zip code, or a last name.

- Pay attention to pest management during pollination. Do not apply broad-spectrum insecticides when flowers are open. Bee hives should be removed immediately after pollination if post-bloom pesticide applications are planned. By monitoring for pest problems carefully during bloom, growers can help minimize the need for pest control. If an insecticide application is necessary during bloom, the compounds that are least toxic to bees should be used, with careful observation of the pollinator-restrictions on the label. In general, dust form is more harmful to honey bees, and morning or day applications are not as safe for bees as evening applications.

Inform the beekeeper before a spray so that colonies can be shut down for one to two days with wetted burlap blocking entrances, if highly toxic insecticides have to be sprayed.

- Employ different strategies for different crops. Use the early strategy for vine crops. Cucurbit flowers (cucumber, squash, pumpkin, melons) are open for only one day, and unpollinated female flowers will abort and drop off if pollen is not received on that same day.

For pickling cucumbers, honey bees are crucial because most varieties now are gynoecious (mostly female flowers, with another variety to provide pollen), and mechanical harvest requires quick fruit set and more even ripening. Honey bee colonies should be moved into the field or on its border two to three days before the first female flowers are to bloom.

- Take note of hive density recommendations. Because Varroa mites had wiped most of our feral (unmanaged) honey bee populations, recommended rates for pollination prior to 1987 have to be increased to compensate for the lack of “free” honey bees. 

From an economic point of view, it is best to start with the highest hives you can afford, then cautiously reduce it next year to see if your yield is affected. An alternative method is to stock different densities and determine if yield is different later.   

Huang is in the Department of Entomology at Michigan State University.

Pett is in the Department of Entomology at Michigan State University.

Leave a Reply