A modified two queen system

"A modified two queen system: “Tower” colonies allowing for easy for drone brood removal. An Interim Report February 2006 Dennis vanEngelsdorp1, Shane Gubauer2, and Robyn Underwood1 1Pennsylvania Department of Agriculture 2Better Bee Inc. There are many ways to manage varroa mite populations including cultural and chemical controls. Beekeepers commonly use hard chemicals, but the mites are now developing resistance to them. There is also the concern that these chemicals contaminate comb. A more sustainable option is the use of integrated pest management (IPM), which involves using a combination of several mite reduction techniques. A cultural control technique that may be useful as part of an IPM program is drone brood removal. This method of removing capped drone brood, and with it varroa mites, can be very effective (Schmidt-Bailey et al., 1996, Calderone, 2005). Varroa mites tend to invade drone brood more readily than worker brood so drone brood can act as a trap for the mites. Removing the capped drone brood can greatly reduce the number of mites in infested colonies. However, drone brood removal requires the beekeeper to remove honey supers regularly to access the brood chamber. Removing full honey supers is hard work! If there were a way of managing hives so it is easier to access the brood, drone brood removal would be a much more feasible option. Some beekeepers use a two-queen system (Cale, 1963). Colonies are maintained with two laying queens in one hive, with the two queens kept in different brood boxes by placing queen excluders between them. This management technique is thought to increase the honey bee population and, subsequently, the honey yield. In addition, if one queen dies, the colony survives without an interruption in brood production. In this small-scale study, we tried a new hive configuration that took advantage of a two-queen system and permitted easy drone brood removal. The results suggest that we were able to keep the daily varroa mite drop from dramatically increasing over the summer without using chemicals and with very little effort. We used a small number of colonies, but our data are convincing enough that we think it is worth having beekeepers give it a try. Following is a description of the experiment we performed and preliminary conclusions. This is followed by a protocol we hope some beekeepers will try. If enough beekeepers do try this experiment, collect the data, and send it to us, we will be able to confidently say if drone removal works in this system, and what impact, if any, this type of twoqueen hive system will have on honey production. Methods We started with 16 colonies in an apiary located at Betterbee Inc. in Greenwich, NY. The colonies were started from packages in May 2005. These colonies were randomly assigned to one of two treatments: 1) normal management with a double brood chamber, queen excluder, and supers or 2) management in a “tower” marrangement.

The tower arrangement consisted of two colonies in double brood chambers side-by-side with a queen excluder and supers over the center of these two (Fig. 1). The exposed half of each brood chamber was covered by a half-size migratory cover that allowed easy access to the frames on that side of the brood chamber. This essentially created a two-queen system and enabled us to add and remove drone comb for mite trapping. In addition, part of the brood nest could easily be inspected. Figure 1: Colonies in the tower configuration.

Figure 2: Placement of a drone frame (green) in the exposed half of the brood chamber tower. A one-piece plastic drone frame was added to each tower colony (Fig. 2) and the first supers were added to all colonies on 10 June 2005. Sticky boards were put in place in all of the hives that day as well, and were replaced every 7 days until 12 August 2005. On 5 and 28 July, drone brood frames, containing capped drone brood, were removed and replaced with drone foundation. On 23 August 2005, drone brood frames were removed and replaced with drone comb that had been frozen from the previous replacement period. When possible, brood of the proper age from the removed frame was examined for varroa mites. The goal was to examine 50 capped drone brood cells per frame for the presence of varroa mites to quantify how many mites were being removed. The total amount of drone brood present on the frame was also estimated. A final sticky board was in place for 3 days from 9 to 12 September 2005. On 31 October, the honey was harvested from all of the colonies and the removed supers were weighed. The presence of the queen was also observed and the readiness of the colony for winter assessed.

Results
Because of the small sample sizes used in this study, statistical tests did not show differences between our treatment groups. However, our numerical results are suggestive, and so we present them here. It is likely that had our sample sizes been larger, significant differences would have been detected. In the normal colonies (without having drone comb removed), average daily varroa mite drop increased from 3.2 ± 0.8 mites per day at the beginning of the study to 25.8 ± 6.7 mites per day over the course of the experiment (Fig. 3). In contrast, mite drop in the tower colonies only increased from 1.9 ± 0.5 to 8.0 ± 2.9 mites per day for each colony (3.8 ± 1.0 to 16.0 ± 5.8 mites per day for each tower). That means that the tower colonies went into the fall with much lower varroa mite populations than the control colonies. In addition, the colonies from the two treatments produced equivalent amounts of honey with the normal colonies producing an average of 37.9 ± 10.9 lb and the tower colonies producing 33.4 ± 9.3 lb each or 66.8 ± 18.5 lb per pair. On average, each drone frame removed from a tower colony contained 1650 capped drone cells. Between 0 and 9 % of the drone cells that were opened contained varroa mites.

Discussion
Management of colonies in a tower configuration utilizing drone brood removal and a twoqueen system reduced varroa mite population growth over the course of the summer. Colonies managed in a tower configuration contained fewer mites in early September than those that were managed normally. While this system would not likely permit beekeepers to forgo alternative mite treatment methods, it would keep mite levels below economic injury levels for longer periods of time. This management technique was easy to use and allowed bees to collect equivalent amounts of honey as compared to normally-managed colonies. In general, 2005 was a bad year for honey in New York and these colonies were started from packages, possibly contributing to the low yields in colonies from both treatments. In addition, the packages were started from frames of foundation and so the bees had to draw out comb, an activity that reduces honey production. We feel that the addition of drone brood removal to an IPM program using a tower configuration will be advantageous, but requires further investigation. We are presently seeking beekeepers that are willing to try this experiment on their own bees and share the results with us. Beekeepers interested in helping conduct this experiment should contact www.betterbee.com/resources/newsevents.html for more information."

Literature Cited
Calderone, N. W. 2005. Evaluation of drone brood removal for management of Varroa destructor (Acari: Varroidae) in colonies of Apis mellifera (Hymenoptera: Apidae) in the Northeastern United States. J. Econ. Entomol. 98:645-650. Cale, G. H. 1963. Management for honey production. In The Hive and the Honey Bee, Dadant & Sons, Inc. Hannibal, Missouri, Pp. 249-302. Schmidt-Bailey, J., S. Fuchs, and R. Buchler. 1996. Effectiveness of drone brood trapping combs in broodless honeybee colonies. Apidologie 27:293-294. Figure 3: Mean (± SE) number of mites falling per day onto sticky boards in colonies managed normally or in the tower configuration



 

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