1 - Pollinators at PI
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(Apis mellifera L.)
Honey bees were introduced to the U.S. by European colonists. Traditionally honey bees have been used to pollinate a wide variety of crops; this holds true at NCRPIS as well. Honey bees have been used to pollinate many accessions of most curatorial holdings with the exception of cultivated type Helianthus and Zea mays. These bees are used in ca 700 cages annually.
Honey bees are social insects (many bees live and work together in a single colony with one queen whose primary function is to lay eggs). A honey bee colony contains non-reproductive females called "workers" and productive males called "drones" along with the single productive female (the queen). Honey bee colonies are potentially "perennial" as the queen may live for more than one year.
Honey bees forage best from 60 to 90 F (15 to 32 C). They are considered aggressive and may sting when they feel threatened. Rearing of honey bees is well established but costly due to the equipment and continuous care required.
At NCRPIS, honey bees are maintained for pollination in small queen-right colonies referred to as "nucleus hives" or "nucs" which are constructed of pine wood. The bottom board features a unique sliding entrance which allows the bees to fly either within the cage only or outside of the cage (Ellis et al, 1981). This slide also allows for the bees to be held within the nuc box for short periods of time (e.g. for transport of nuc or pesticide applications to caged plants). Because of limited food supplies for bees within the cages, a feeding hole in the nuc lid allows for supplementary feeding.
Each nuc contains six 15.9 cm frames. Two of the frames contain honey and pollen, three frames contain brood; the final frame contains empty drawn comb. In addition there are ca 2000 workers and a mated queen bee.
Nucs are obtained through one of two methods. The first is the division of an over-wintered two story nuc in the spring several weeks after the hives are moved outdoors. One of the stories maintains the queen from the previous year, while the second story will have a grafted queen introduced shortly after the stories are separated.
The second method of obtaining nucs is to use three story honey bee hives referred to as "parent colonies"; the majority of nucs produced annually are created with this method. From April to August, nucs are established from parent colonies as follows: remove three frames of brood and adhering bees, provide two stored frames of honey and pollen and one frame of empty comb, and insert one ripe queen cell produced via standard queen-rearing techniques (Spivak and Reuter, 1997). Before nucleus hives are inserted into the cages for pollination, it is ensured that they are queen-right (i.e. the queen bee is producing new brood or eggs and young bee larvae).
Once nucs are ready for use and have been requested by curatorial staff, they are transported to field cages early in the morning. Nucs are placed in the northwest corner of small field cages. This encourages bees to traverse the entire cage as they are attracted to the southeast side, closest to the spring/summer sun. The cage screen is wrapped around the midpoint of the box leaving the feeding hole outside the cage. The screen is secured around the box with a polypropylene strap; soil is placed at both sides and on top of the nuc box to ensure bees are retained inside the cage.
Double story nucs are prepared for use in large field cages. In a double story nuc, the bottom box contains two frames of honey and four frames of brood; the top box contains four frames of honey and two frames of empty drawn comb. Double story nucs are placed entirely inside of a cage; the cage opening is normally positioned at the north end, so the nuc is placed in either the northwest or northeast corner of these cages. Beekeepers must enter the large cages to feed these hives.
The nucs are fed a 3:1 solution of high fructose corn syrup and water on a weekly basis through the field pollination season. Pollen patties (mix of bee pollen, soy flour, and undiluted corn syrup) are provided every other week.
At curatorial direction, nucs are removed from cages, and transported to bee yards where the bees are allowed to forage freely until needed for another cage or prepared for winter. When nucs are pulled from the cages, screening is secured with soil to prevent seed loss to rodents and birds.
At the end of the field pollination season, all colonies are prepared for over-wintering. Several feedings of diluted corn syrup are provided to assure adequate food stores within the hives. In December, hives are moved to an indoor over-wintering facility. This facility is maintained at ca 45 F (6 C), RH 60 %, 24 hour dark.
In both the spring and the fall as hives are prepared for the upcoming season, they are examined for diseases such American foul brood and mites. Affected hives are treated appropriately.
Ellis, M.D., G.S. Jackson, W.H. Skrdla, and H.C. Spencer. 1981. Use of honey bees for controlled interpollination of plant germplasm collections. HortSci. 16:488-491.
Spivak, M. and G.S. Reuter. 1997. Successful queen rearing. Short course by University of MN Dept. of Entomology and University of MN Extension Service.
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