Immunity Deficiency In Bumblebees And Neonicotinoid  Pesticides

This feature is a continuation of an article by Dr Rosemary Mason and Palle Uhd Jepsen. To go to the beginning of the feature, click HERE.


Bumble bees in the US

Massive declines in wild bumble bees in the US and Canada were reported in the late 1990s. Colla (2008) in Ontario, previously a ‘hot spot’ for bumble bees, sampled sites for three summers, 2004-6, in eastern North America [38]. Out of the 14 species that had been present in the same areas in 1971-73, three had disappeared completely and five of the remaining 11 were in steep decline. Of the species that had been fourth most common in the 1970s (14%), she found only one male. In 2008, the Xerces Society for Invertebrate Conservation reported that “bumble bee researchers across the continent have established that at least four species of formerly common North American wild species have experienced catastrophic declines over the past decade - two of them may be on the brink of extinction” [39].

Massive declines in wild bumble bees in the US and Canada were reported in the late 1990s. Colla (2008) in Ontario, previously a ‘hot spot’ for bumble bees, sampled sites for three summers, 2004-6, in eastern North America [38]. Out of the 14 species that had been present in the same areas in 1971-73, three had disappeared completely and five of the remaining 11 were in steep decline. Of the species that had been fourth most common in the 1970s (14%), she found only one male. In 2008, the Xerces Society for Invertebrate Conservation reported that “bumble bee researchers across the continent have established that at least four species of formerly common North American wild species have experienced catastrophic declines over the past decade - two of them may be on the brink of extinction” [39].

In a status review by the Xerces Society and Dr Robbin Thorp (UC Davis), three formerly common species of bumble bee “went from being widespread and commonly found to rare or absent within a relatively short period of time (about 7-10 years).” They were found to be infected with a series of unusual pathogens that entomologists attributed to unregulated movement of commercial bumble bees from Europe to pollinate greenhouses. Developments in bumble bee breeding techniques in the previous 10 years or so had become “an essential part of modern agriculture” and allowed pollination in commercial greenhouses to take place out of season.

In 2008, Ottenstatter & Thompson (Toronto) devised mathematical models and laboratory work to estimate ‘spillover’ of the pathogen Crithidia bombi from greenhouses where imported bumble bees were being used for pollination [40]. They monitored wild bumble bee populations in the vicinity and found that the prevalence of C. bombi in wild bumble bees near to greenhouses appeared to support their model.

In fact many bumble bee scientists became convinced that infections in imported bumble bees were at the heart of the declines in the wild population. A petition was sent in Jan 2010 from the Xerces Society, the Natural Resources Defense Council, Defenders of Wildlife and Dr Robbin Thorp to the USDA’s Animal and Plant Health Inspection Service (APHIS) asking them to regulate the movement and health of commercial bumble bees to safeguard wild, native bumble bee pollinators. By Feb 2010, the situation was so bad that a broad coalition of 67 scientists (many of them bumble bee experts), sent a letter to The Hon Tom Vilsack, Secretary USDA in Washington and the Administrator of APHIS. However, Cameron and her colleagues (2011) were unconvinced by this ‘spillover’ theory [41].

In a 3-year interdisciplinary study, they looked at changes in distribution, population genetic structure and levels of pathogen infection in bumble bee populations across the US. Comparing results with museum records of bumble bees they showed that the relative abundances of four species had declined historically by up to 96%. Geographical ranges had contracted by 23-87%, some within the past two decades. Those species that had declined had significantly higher infection levels of the pathogen Nosema bombi and had low genetic diversity compared with those that had not. They concluded that “cause and effect remain uncertain” for these “alarming patterns of decline in North America.” However, in the discussion, the authors said: “These observations are reminiscent of reports of other introduced fungal pathogens that pose widespread threats to some taxa” including frogs and bats.


Bumble bees in mainland Europe and UK

As noted above, breeding of bumble bees for use in commercial greenhouses, to increase yield and quality of vegetables, is now commonplace.


According to scientists from Turkey “thousands of colonies are reared in the laboratories and they are being shipped to different countries over the last 10 years.” The development of breeding techniques has allowed pollination to be controlled “especially during the off seasons.”

Health concerns by the importing countries led them to investigate pathogens in wild populations of bumble bees [42].

In 2006 they collected 578 mated Bombus terrestris queens from different regions in Turkey and found a wide range of bacterial and parasitic infestations, both internal and external. Infestations in wild populations ranged from 9% to 41% and the authors observed that heavily infested queens cannot establish colonies. In 2008 Goulson, Lye & Darvill reported bumblebee declines in the UK, but at that stage, they were not as drastic as in the US [43].

In 2009 Williams and Osborne confirmed the declines of some species in Europe, North America and Asia, and suggested that pathogens may be having a stronger effect for a few species in some regions [44].

They said that variations in susceptibility to threat factors, such as pesticides, “have yet to be studied.”

Continues.... butterflies and moths



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