To escape winter’s doldrums recent episodes of Bug of the Week visited tropical realms to meet rainforest recyclers, stinging ants, fungus farmers, large spiders, creepy cave dwellers, and blood-sucking flies. With the passing of the spring equinox and hopefully Old Man Winter’s last snowy gasp, it is time for us to return from tropical sojourns and seek adventure in the wilds of suburban Maryland.
On a visit this week to the banks of the Patuxent River I was dazzled by a carpet of early season bloomers including snow drops and winter aconite. Assurances from scholarly websites such as Cornell University’s Growing Guide relieved my angst in admiring these Eurasian beauties that were described as non-invasive and non-aggressive. Despite a bit of a chill, pollen-laden honey bees busily worked the aconite in the afternoon sunshine. It seemed only fitting that these early bloomers from across the sea would be some of the first blossoms to be visited by our hard-working pollinators from Europe.
As I watched the honey bees, I wondered how they fared this winter. The appearance of a deadly phenomenon called Colony Collapse Disorder, or CCD, grabbed national attention in 2007 when many commercial beekeepers reported unusually large losses of honey bee colonies in several locations in the United States. When CCD strikes a hive, worker bees simply disappear leaving behind the queen, a few young workers, and colonies with plenty of food and brood. One of the defining characteristics of CCD is the absence of dead bees in the colony. Without a full contingent of hardy workers, the queen and brood are doomed and the colony collapses. Soon after CCD was discovered national surveys of beekeepers were conducted to determine the magnitude of the problem. Between September 2006 and March 2007, beekeepers lost approximately 32% of their hives. During a similar period in 2007 and 2008, beekeepers in general lost about 36% of their colonies.
One important trend in the colony loss phenomenon has been a reduction in losses attributed to CCD. In 2007 beekeepers that met the definition for CCD lost 45% of their colonies, but by in the winter of 2010-2011 only about 26% of beekeepers surveyed lost colonies with the symptom of “no dead bees in the hive or apiary.” Results of the survey reported in May, 2014 had some good news. During the winter of 2013 to 2014 overall losses of managed honeybee colonies were about 24%. Although this number was markedly lower than losses recorded in previous years, it still exceeded levels of beekeeper acceptable winter losses of about 19%.
What are some of the factors connected with loss of honey bee colonies in the US? The causes of CCD and hive loss are not fully understood, but researchers have made great progress identifying some of the culprits in this mystery. At a recent meeting of the Entomological Society of America, Dennis vanEngelsdorp, one of the foremost experts on pollinator health, identified three clusters of factors contributing to CCD and honey bee decline. With the introduction of Varroa mite and tracheal mite in the 1980’s and their rapid spread, many hobbyist beekeepers, including the Bug Guy, lost their hives. Varroa mites have been described as baby vampires, infesting honeybees and sucking blood from larvae, pupae, and adults, particularly that of male bees. Not surprisingly, this weakens bees and predisposes them other serious diseases. Varroa mites have also been implicated in transferring viruses that attack or cripple bees, such as acute bee paralysis virus and deformed wing virus.
The second galaxy of factors debilitating honey bees is their nutrition. Often commercial honeybees are placed in large crop monocultures such as almonds or apples to provide the important ecosystem service of pollination for these crops. Recent studies indicate that diets of monofloral pollen (pollen from one plant species) may impair the normal immune function of honeybees compared to diets of pollen from many plant species (polyfloral diets). Many of the pollen-rich fattening grounds for honey bees in the upper mid-west have been plowed under and planted in corn and soybeans. Poor diets may result in weakened immune systems and reduce the ability of honey bees to fight off the aforementioned viral pathogens and others pathogens including Nosema, a nasty unicellular fungus associated with colony failure that attacks the gut of honey bees. Scientists have also suggested that the use of honey substitutes such as high-fructose corn syrup may d reduce the ability of honey bees to deal with pathogens and pesticides.
The third major culprit in the triumvirate of honey bee threats is pesticides. Pesticides are regularly used to manage pests of crops, and honey bees may encounter residues in nectar and pollen. As bees return with nectar and pollen, pesticides can accumulate in the waxy comb and leach out, exposing bees to chronic residues. Even pesticides used to combat Varroa mites may accumulate in beeswax in the hive. Beyond the outright acute effects of pesticides that result in rapid bee death, pesticides may have sublethal effects that reduce their ability to forage, navigate, learn and remember locations. Pesticides are thought to further stress bees and weaken their immune system, predisposing them to disease. While much of the national attention has focused on the role of one class of insecticides, the neonicotinoids, as the primary contributor to pesticide associated losses, recent studies of honey bees in real world settings suggest otherwise. An important study by Pettis and his colleagues revealed fungicides to be the single most common category of pesticide brought back to the hive by worker bees across seven crop systems including almond, apple, blueberry, cranberry, cucumber, pumpkin, and watermelon. More importantly, fungicide laden pollen was more likely to result in infections by Nosema when fed to bees that were exposed to the pathogen.
Where did neonicotinoids fit into the study? In terms of the amounts brought back to the hive, they trailed behind other classes of insecticides such as organophosphates and carbamates, classes of insecticides well known for their toxicity to honeybees and other beneficial insects. In addition, the neonicotinoids along with several other insecticides were associated with a reduced risk of Nosema infections rather than an increased risk of infection. An article published last week by Galen Dively and his colleagues found a dose-dependent response in measures of colony health and winter survival of honeybees to chronic exposure of pollen laced with a neonicotinoid insecticide. However, at the lowest dose of insecticide, one likely to be encountered by honey bee foragers in the fields of seed-treated crops, little or no deleterious effects were observed. Both Pettis et al. and Dively et al. stressed the need for additional research efforts on effects of fungicides and other chemicals, acting singly and in concert, in both short and long-term studies under realistic field conditions.
With most feral colonies of bees extirpated by mites and other factors and ever declining numbers of hobbyist beekeepers, the loss of commercial honeybee colonies is significant and places extreme demands on remaining hives to complete the important job of pollinating our crops. Later this spring, scientists will complete another survey with beekeepers and we will learn what happened with losses to honey bees during this long chilly winter. We hope it will be a better one for our besieged honey bees. Finding better ways to safeguard our honey bees and native bees is a national priority, for these sturdy workers help make our food and keep our natural ecosystems cruising.
Bug of the Week thanks Dennis vanEngelsdorp and the Bee Informed Partnership for providing inspiration and information used in this episode. Several references were consulted, including “Diet effects on honeybee immunocompetence” by C. Alaux, F. Ducloz, D. Crauser, and Y. Le Conte; “Influence of Pollen Nutrition on Honey Bee Health: Do Pollen Quality and Diversity Matter?” by G. Di Pasquale, M. Salignon, Y. Le Conte, L. P. Belzunces, A. Decourtye, A. Kretzschmar, S. Suchail, J. Brunet, and C. Alaux;“Honey constituents up-regulate detoxification and immunity genes in the western honey bee Apis mellifera” by W. Maoa, M. A. Schuler, and M. R. Berenbaum; “Crop Pollination Exposes Honey Bees to Pesticides Which Alters Their Susceptibility to the Gut Pathogen Nosema ceranae” by J. S. Pettis, E. M. Lichtenberg, M. Andree, J. Stitzinger, R. Rose, D. vanEngelsdorp; and “Assessment of Chronic Sublethal Effects of Imidacloprid on Honey Bee Colony Health” by G. P. Dively, M. S. Embrey, A. Kamel, D. J. Hawthorne, and J. S. Pettis.
To learn much more about honey bees and their travails, visit the bee informed web site on a regular basis: http://beeinformed.org/