Polinización en arándanos

Como podemos ir viendo a través de la encuesta que está realizando LATINBERRIES, problemas de polinización fueron para muchos la causa de disminución en la producción de berries durante el año 2007. Parece que en algunos lugares de Florida ha pasado lo mismo. A pedido de los lectores agregamos aquí una nota interesante de la Universidad de Florida y de Alabama para que la próxima campaña no encuentre a los productores desprevenidos.

Last year was not a good season for blueberry pollination in Florida.Although all the evidence is not in yet, many are saying that a big problemwas lack of bee pollination. Growers renting honey bee colonies did not getthe fruit set they wished and are asking why. J.H. Cane and J.A. Paynerecently published some information through the Alabama Agricultural Experiment Station which gives a good beginning in estimating how real this problem may be and suggesting a solution.

It seems that blueberry flowers are so constructed that pollen is held internally in the anther and can only exit through the small pores at the tip. The pollen pours out when the anthers are vibrated by buzzing bees. Most native beespecies "buzz-pollinate" blueberries when foraging for nectar.Unfortunately, both the honey bee and the carpenter bee do not. If that isn't enough, it seems that carpenter bees get blueberry nectar by making as lit in the corolla, further by passing the flower's sexual parts. These holes then attract honey bees and so both species become even less efficient in pollinating the blooms!

Most native bumblebees are excellent pollinators of rabbiteye blueberries;however, the southeastern blueberry bee, Habropoda laboriosa, is the most effective according to the authors. These resemble small bumblebees. They will not use the robbery holes and buzz-pollinate flowers. They also forage from early morning to sunset and are not drawn to flowers which compete with blueberries for pollinating attention. In spite of its effectiveness,however, Habropoda is not a colonial insect and, therefore, does not producecolonies 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 majorpollinators of blueberries, but their numbers are usually very low early inspring during the bloom. The technology does not exist to produce eitherbumblebees or southeastern blueberry bees in enough abundance to take careof the pollination requirements of large acreages.All this adds up to a complex of problems that might occur in rabbiteyeblueberry pollination. Growers with small acreages have the best opportunity to get their plants pollinated because fewer individual bees are needed andthese can come from the wild pollinating population.

However, as field size increases, the sheer number of flowers overwhelms the ability of native pollinators. Because there is no way to culture these native populations,pollination becomes a hit or miss affair based on the ebb and flow of natural conditions. In some years, the bees are numerous, in others few can be seen. An additional factor is the presence or absence of carpenter bees which either increase or decrease the number of slit corrolas present each season. Fortunately, the carpenter bee, like the southeastern blueberry bee,is solitary and very large populations are exceptional.

This brings us to the role of honey bees in pollinating blueberries.Although the individual insects are not as efficient as wild native bees,each colony can be induced to put out a huge number of foragers. If thereare no competing plants, if the blueberry flowers are attractive by providing enough nectar and if carpenter bee slits are minimized, there will be so many bees out there that pollination must occur in spite of the inefficiencies mentioned above. Thus, the same recommendation is made for other crops which are difficult to get pollinated: "bring in more colonies of honey bees." Unfortunately, the question concerning how many colonies is enough varies each year depending on the number of native bees, both beneficial (bumblebees) and inefficient (carpenter bees), that will be in the field.These pollination problems represent a classic case where plant and honeybee 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 apopulation that would buzz pollinate and prefer blueberries. There isprecedent for both these approaches. Recently, it has been found at the ARS Carl B. Hayden Bee Laboratory that there is enough variability in onion and bee populations to select for increased onion pollination. In the past, oneof the major achievements in bee breeding was development of a stock of beesthat preferred to collect alfalfa pollen.