Vive les Bourdons!* As we learn more about the status of North American bumble bees, more questions arise that require solutions. From our 3-year interdisciplinary study of changing distributions, genetic diversity and pathogen infection in bumble bee populations across the United States (see Newsletter essay 2007-2008), we have found that the relative abundances of four species (a fifth we couldn’t actually study because it is at or near extinction status) have declined by up to 96% and their surveyed geographic ranges have contracted by 23-87%, some within the last 20 years. We have also found that declining populations have significantly higher infection levels of the microsporidium Nosema bombi and lower genetic diversity compared to co-occurring populations of non-declining species. A couple of interesting aspects of the pathogen findings: first, four of the five declining North American species belong to the same species group, indicating a strong genealogical component in the species decline. Secondly, there seems to be a rather convincing temporal correlation between the population declines and the development of commercial bumble bee rearing in the U.S. One compelling hypothesis suggests that an invasive Nosema bombi strain escaped into wild populations from commercial bumble bee facilities in the western U.S. during the mid- to late 1990s and spread easterly to infect related species. But we have no idea to date whether this is true. All we know is that declining species in the U.S. have higher N. bombi infections than species with stable populations. So our team is on the hunt to find out first, whether there are genetic differences between North American and European N. bombi, second, whether N. bombi existed in North American bumble bee populations before commercial producers came in, and third, how the population genetic structure of bumble bees could contribute to the spread of a pathogen.
These questions took some of our team to France this summer. We were only three from the U.S, Robbin Thorp from UC Davis, my postdoc, Jeff Lozier, and me. Our host was Pierre Rasmont, an intrepid bee biologist from Belgium and his wife Ann. Although it was hard to compete with the likes of Sturgis bike week and the Badlands of SD from prior summers spent chasing bees around the U.S., we managed to pull off some pretty interesting collecting experiences in France. We began in the hills of Provence at Pierre’s beautiful summer “camp”, draped in orange trumpet vine situated in the hills near the village of Gonfaron. This region, in the Department of Var just north of the Mediterranean Sea, is reminiscent of California oak woodlands, but two native species stood out. The cork oak (Quercussuber) with its thick, craggy bark was once an important link in the area’s wine-growing economy– the wines are the wonderful Côte de Provence. And the Chestnut tree (Castanea), which occurs in dense groves throughout the hills of Provence, is magnificent; its nuts are turned into the candied chestnuts (marrons glacé) renowned across the region. And then there was Lavender. You’ve all seen those idyllic scenes of French Lavender fields in the hilly regions of Provence– red earth, sunny skies, mountains in the distance– well, that’s exactly what it looks like. As it turned out, Lavender was the most important plant in our search for Bombus terrestris (and it’s internal pathogen, Nosema bombi). Not only were the vast fields of the purple stuff a haven for hungry bees, but also just about every one of the ten million roundabouts in southern France sprouts Lavender as a landscaping feature. So when no bees could be found in the wild, all we had to do was head for a village roundabout and, voilà, there were the bees en masse. This was a bit taxing during rush hour with Citroens whizzing by, but in typical French fashion, we were mostly ignored. Ann’s meals were our reward at the end of the day, and morning tea and coffee were accompanied by fresh croissants and café au lait.
After 10 days of collecting across these ancient hills, in temperatures soaring into the mid-90s F, we left for the Pyrenees and the little Catalan village of Eyne, perched about 2,000 m in the Pyrénées Orientales, population 127. This idyllic cluster of old dwellings, a site inhabited since the Neolithic (3000-4000 BC), with stunning views of the mountains surrounding the Cerdagne basin, was our base for travel to collecting sites near the coastal city of Perpignan. If we thought the hills of Provence were hot, we were in for a real treat coming down from the cool, temperate mountain climate to the ovens of coastal Catalan. At some sites known for their abundant B. terrestris populations we found nary a bee-- not a fit day out for man nor bees. But the turquoise waters of the Mediterranean provided refreshing respite. And when all else failed, there were always the roundabouts with Lavender. By early evening we were back in heavenly Eyne. After-dinner walks along mountain paths behind Eyne, past the ancient dolmen (Neolithic burial tomb), still standing in the open meadow after 4,000 years, sun setting behind an infinite horizon alight with complementary colors, closed the day. Side trips to some of the best-preserved 15th century fortresses in Europe, including Mont Louis just down the road from Eyne, and Villefranche set high in the Catalan hills, sampling the Catalan cuisine and strolling through flower-filled meadows were special experiences to remember. We left Eyne to return to Paris on the eve of Bastille Day, and arrived in Limoges at dusk to see a spectacular fireworks display in the Le Champ de Juillet. Just outside of Paris we stopped one last time, to visit the medieval town of Chartres with its soaring cathedral spires and magnificent stained glass windows. We had our last lunch in France just off the cathedral square and drove the 80 km into Paris on Bastille Day, a fitting end to our Tour de France in search of les Bourdons.