Some of our rarest bumblebees could be at greater risk of extinction because of inbreeding among their now small and isolated populations, ecologists are warning. Speaking at the British Ecological Society Annual Meeting at the University of Leeds, Penelope Whitehorn (right) from the University of Stirling revealed new results on inbreeding and its effects in the moss carder bumblebee.

Research into insect immunity is rarely carried out under field conditions and this is the first study to investigate inbreeding and immunity in wild bees. Working on nine Hebridean islands off the west coast of Scotland, Ms Whitehorn – a PhD student with world-leading bumblebee expert Professor Dave Goulson – measured moss carder bumblebees' immune systems and recorded whether or not they suffered from any parasitic infections.

Comparing this data with information on genetic diversity previously gathered by (left) Professor Goulson's team, Ms Whitehorn was able to show that, while inbreeding does not seem to be affecting the bumblebees' immune systems, making them more susceptible to parasitic infection.

According to Ms Whitehorn: “We found that isolated island populations of the moss carder bumblebee with lower genetic diversity have an increased prevalence of the gut parasite trypanosome Crithidia bombi (right: size about 10 µm) that causes failure of colony foundation in bumblebees. 

"Our study suggests that as bumblebee populations lose genetic diversity the impact of parasitism will increase, which may increase the extinction risk of threatened populations.”

The findings are important because populations of several bumblebee species have declined dramatically over recent decades. Efforts to conserve bumblebees are vital as their pollination services are of major ecological and commercial importance, so ecologists need a better understanding of the factors affecting bumblebee populations.

The results also have wider significance because many species' populations are becoming increasingly isolated due to fragmentation of habitats and climate change. Even though these species may not, like the moss carder bumblebee, live on actual offshore islands, many are now effectively marooned on habitat islands, between which there is limited migration.

“Investigating how inbreeding impacts parasitism and immunity in real island populations provides a proxy to understand the impacts of inbreeding in habitat islands on the mainland. Our findings may be useful for informing conservation efforts to protect threatened insect species whose populations are declining,” Ms Whitehorn explains.

Using the Hebrides as a model island system, the next stage of her research will be to find out whether the relationship between inbreeding and parasite prevalence is also affecting other bumblebee species.

Across the world the silversword bee
Rob Robichaux,  professor in the University of Arizona’s Dept of Ecology  & Evolutionary Biology, has worked primarily on the restoration inHawaii of a unique subspecies silversword plant found only on Mauna Kea’s upper slopes in Maui  Taking some 10 to 50 years to mature, silverswords eventually sprout a single stalk, approximately 5-6 feet tall, covered with hundreds of tiny, sunflower-like blossoms. Having produced the next generation seed, the plant dies.

An enclosure built in the vicinity of the last remaining natural silversword population on Mauna Kea afforded some protection from grazing animals, and the silversword population began its slow comeback. Between 1973 and 1982, the State of Hawai‘i began outplanting young silversword seedlings into the enclosed reserves.
Silverswords (left) are pollinated by yellow-faced bees (right) that are endemic to Hawaii, Robichaux explains.


“The decline in the yellow-faced bee population is probably linked to the introduction of aggressive, non-native ants that feed on bee larvae," he says. " Without these bees to pollinate them, the silverswords face the possibility of diminished reproduction, which in turn could lead to their extinction."

Last year and this, the Xerces Society for inverebrate protection, petitioned the US Fish and Wildlife Service that the yellow faced bees be listed as endangered and that a critical habitat be designated for the species.  The Wildlife Service  is now to take a year to review the bee status.

Perhaps yellow face bee parasitic immunity should also be on that review agenda?