Local folks are singing the “blueberry blues” this year. A June 30, 2007 article in the Gainesville Sun summed up the situation nicely. The “slim pickings” for both growers and general u-pick customers it says are due to several factors, including late freezes, drought and lack of pollination. The article focuses mostly on the first two, which growers generally are aware of and can be somewhat controlled. The farms doing the best appear to have had irrigation systems in place to provide both needed soil moisture and also freeze protection (spraying water on the berries creates ice on the surface protecting the entrails from freeze damage).
Pollination was mentioned only in passing as it usually is, one reason I wrote an article some time in the past emphasizing pollination as the “forgotten agricultural input.” Fortunately, the furor about honey bee losses is creating good visibility for pollinators and the value of their contributions as I noted in my last column, which emphasized activities surrounding National Pollinator Week.
The southern blueberry pollination story is fascinating and may be quite different based on variety grown. Visiting the fields during blooming, one can hear audible, short buzzing sounds coming from the many insects attracted to the blossoms. It is this sound, emanating from vibrations given off by the pollinators, that literally shakes the pollen from the flowers. This “buzz pollination” is essential to the process, but not every critter is accomplished at this important task.
Perhaps the champion buzz pollinator is the southeastern blueberry bee, Habropoda laboriosa. This insect resembles a small bumblebee. It also forages from early morning to sunset and is not drawn to flowers which compete with blueberries for pollinating attention, making it a true specialist or “obligate” pollinator. In spite of its effectiveness, however, Habropoda does not produce colonies of numerous individuals needed to pollinate large stands of blueberries. The solitary females dig tunnels in the soil to lay their eggs and there is only one generation per year.
Bumblebees are also major pollinators of blueberries, but their numbers are usually very low early in spring during the bloom. The technology does not exist to produce either bumblebees or southeastern blueberry bees in enough abundance to take care of the pollination requirements of large acreages, although there is currently some grower effort in this area..
All this adds up to a complex situation. Blueberry growers with small acreages have the best opportunity to get their plants pollinated because fewer individual bees are needed and these can come from the efficient pollinating population. However, as field size increases, the sheer number of flowers overwhelms the ability of these pollinators to do the required task. Because there is no way to culture these populations, pollination becomes a hit or miss affair based on the ebb and flow of natural conditions. In some years, the efficient, native bees are more numerous; in others few can be seen.
That brings us to honey bees. Many blueberry growers contract rental of these colonies for their assistance from beekeepers as a kind of quasi pollination insurance policy. In spite of the large numbers, however, honey bees are not efficient pollinators of blueberries. They don’t buzz the pollen out and also will actively work around the bloom, assisted by other bees, which are also found in fields. Carpenter bees (Xylocopa sp.) it seems cannot get to the nectar except by slitting the flower (corolla) at the base. The nectar then leaks out, which the carpenter bee sucks up. These permanent holes, however, become magnets for honey bees to use and, thus is born what many agriculturalists fear most, a “side worker” honey bee, one that gets rewarded with nectar, but its visit results in no pollination.
Given this situation, what’s a respectable blueberry grower going to do? For a predicable managed pollination force, there is only one answer, bring in more honey bees. For even if inefficient, the large number of honey bees in the field can usually mean the difference between a bad and good crop. Unfortunately, the answer to the question concerning how many colonies to rent varies each year depending on the number of native bees, both efficient (southeastern blueberry bees and bumblebees) and inefficient (carpenter bees and honey bees) in the field.
This pollination situation represents a classic case where both plant and honey bee breeding might help. Plant breeders could begin to select blueberry varieties that are attractive to honey bees or do not require buzz pollination. Bee breeders could explore the possibility of developing a population that would buzz pollinate and prefer blueberries. There is precedent for both these approaches. It has been found that there is enough variability in onion and bee populations to select for increased onion pollination. In the past, one of the major achievements in bee breeding was development of a stock of bees that preferred to collect pollen from alfalfa, notorious for developing huge populations of honey bee “side workers.”
To conclude, pollination is far more important to southern blueberry growers than often thought. Native, specialized bees are much more efficient pollinators than honey bees, but their small numbers and variable living conditions work against them in large-scale plantings. The honey bee continues to be the managed pollinator growers and consumers will depend on for a local, reliable, plentiful blueberry supply.