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“Preliminary results showed that 30 per cent of Alberta bees died during the 2006-2007 winter,” says Dr. Medhat Nasr, provincial apiculturist with Alberta Agriculture and Food, Edmonton. “The reported winterkill appears to be twice the long-term average over wintering loss in Alberta. It has also been reported that 15 per cent of the survived colonies were weakened considerably. The recovery of these weak colonies was hindered by the late cold spring and the production of these colonies in 2007 is questionable.”
The survey included a detailed list of questions about management practices conducted during 2006 and the spring of 2007. Questions were asked concerning management practices, bee health and environmental conditions. The purpose of these questions was to determine any common possible factors that could explain the causes of the high winterkill.
“In addition to the questionnaire, hundreds of the affected bee colonies were examined and sampled in the field,” says Nasr. “Preliminary results of examined colonies revealed that symptoms of the colony collapse disorder (CCD) as described from the USA have not been found in Alberta. Data collected in the survey and winter killed bee colony samples are under analyses. Once these analyses are completed, a full report will be released.”
Wintering losses have plagued beekeepers for decades, but the losses experienced this year are substantially higher across various regions in Alberta. Even within individual bee operations, one side of the operation may have suffered heavy losses, but on the other side the winter mortality were considered average.
“This year, losses may be attributed to one or a combination of several potential causes,” says Nasr. “There were several unusual weather conditions that affected the 2006 bee season and the production of winter bees. Some regions of Alberta suffered from lack of rain in the early summer, which affected the canola honey crop and the bee biological cycle. Then in mid- to late-summer, good rainfall was reported in several regions which prolonged the nectar flow of clover, particularly the second cut. Beekeepers in the regions of late nectar flow were able to make an above average honey crop. However, these bees were not able to produce winter bees because brood chambers were plugged with honey. This resulted in queens not having room to lay eggs.
“On top of these problems, the fall season was very short and was followed by an early winter. The unusual climate conditions caused the bees’ cycle to be out of sync with the season. Consequently, summer bees remained for wintering, and not enough bees developed for winter.”
Winter bees, reared from August into October, do not immediately begin hive work. They are physiologically adapted to survive winter and they have a life expectancy of about six months.
“If the colony population that survives winter is comprised of summer bees, the result is that as the summer bees get older, they die and leave only a small cluster of bees. When this happens, the bees loose their ability to thermo-regulate their cluster and the colony dies. In addition, the prolonged winter, with no break in the cold weather through to late March and early April, has aggravated the problem in northern and central regions of Alberta.”
Another contributing factor to the decline in bee populations is the reported failure of chemical control of Varroa mites. In the fall of 2006, in some beekeeping operations, Alberta bee inspectors, examining bees to issue health certificates, reported this failure of chemical control of Varroa mites. Varroa mites unexpectedly developed resistance to applied miticides. Consequently, mite populations were higher than normal in bee colonies and these mites had enough time to damage the winter bees.
“When doing inspections, bee inspectors found that in some operations mites were resistant to Apistan and CheckMite,” says Nasr. “This has made it very difficult to treat Varroa in an acceptable time to protect the winter bees. These damaged bees could not withstand the winter and this resulted in an increased rate of viral infections in the bee colonies.”
Nosema is another factor that is often responsible for winter loss, late winter and early spring dwindling and supercedure. In the spring of 2007, beekeepers reported higher than normal colonies with Nosema-like symptoms. In some of the operations, though beekeepers feed medicated sugar syrup in the fall to control Nosema, the chemotherapy did not work. The failure of this treatment is under investigation. In addition, the prolonged, cold winter also contributed to the increased the incidences of Nosema in the northern and central regions of Alberta.
“Viruses and other secondary infection pathogens, such as sac brood and chalk brood were found in weak colonies that survived winter,” says Nasr. “These colonies could not withstand the cold 2007 spring. The population of bees in a large percentage of these colonies continued to decline, queens superseded and eventually died.”
All of these factors are being examined. Data collected in Alberta Agriculture and Food survey along with the provincial apiculturist’s investigation and analyses of collected samples will be used to shed more light on the causes of the high winterkill.
Contact: Dr. Medhat Nasr (780) 415-2314
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