European bumblebees pollinating the crops. Image credits: Wikimedia Commons
During the duration of the research, B. ruderatus extended its geographical distribution up to 434 kilometers, while B. terrestris extended up to 1,320 kilometers. In another 20-year study of pollinators visiting the native flower Alstroemeria aurea in northern Patagonia, Aizen and colleagues found that the two exotic species had replaced the native pollinator B. dahlbomii, which had pollinated the flower for generations. Some interesting statistics can be highlighted from this evidence. This southern extension of its distribution was accompanied by a retreat of B. dahlbomii.
The study ‘ Alien parasite hitchhikes to Patagonia on invasive bumblebee ’ (Arbetman et al., 2013), published in Biological Invasions , tested bumblebees collected before and after the arrival of B. terrestris for the pathogenic protozoan Apicystis bombi . The article by Morales et al. states quite directly what this particular case study implies for future actions in other places: given how rapidly an invasive bumble bee displaces its native congener, introducing non-indigenous pollinators in areas inhabited by endangered bee species should be done much more carefully than was done in Chile in 1982. The genetic analysis revealed that the parasite belonged to the European lineage, which means that the parasite had most probably been brought in alongside the commercial bees.
This bee has not been classified in terms of its inclusion in the IUCN Red List yet, according to the information provided by the IUCN species account. Range expansion alone does not fully explain how quickly the native bee vanished from so many locations. A second line of research points to disease as a compounding factor. In the absence of the invasion, not a single specimen of B. ruderatus or B. dahlbomii was infected by the parasite. Following the establishment of B. terrestris in the area, the situation drastically altered. Nearly one in two B. terrestris specimens tested positive for the parasite, as did just over one in two B. ruderatus specimens and about one in nine B. dahlbomii specimens. As noted in the study discussed above, this was the first recorded instance of Apicystis bombi infecting B. ruderatus or B. dahlbomii in the whole world. This combination of factors that are competition, the accelerated colony turnover rate of the invader and spillover pathogens has been very costly. Species B. dahlbomii has gone extinct in certain areas it used to inhabit, such as some portions of the Challhuaco Valley that scientists had been monitoring for decades. This example demonstrates the necessity of implementing regulations concerning non-indigenous pollinators.
