Over the past couple of years we’ve been looking at how populations of European honeybees (Apis mellifera) evolve in response to emergent diseases, focusing primarily on a population near Ithaca, NY. It seems that the Ithaca population evolved in relative isolation, but elsewhere in the range of the bees in the United States, the arrival of the parasitic mite Varroa destructor also led to extensive gene flow from Africanized bees. Although bees from Africa were first introduced to Brazil in the 1950, they arrived in the Southern U.S. in the early 1990s:
This arrival took place at the same time that Varroa swept through the US, causing large-scale introgression of African genes into the previously European populations. This is likely due to the fact that African bees are inherently more Varroa-resistant than European bees, and are also better adapted to hot weather conditions.
The above figure from Pinto et al. 2005 shows how in one population in Texas, after the arrival of mites in the early 1990s (they were first detected in 1995), the proportion of African mitochondrial DNA has increased rapidly. Such introgression seems to have been ubiquitous throughout the Southern United States. But what genes have driven it? This question is of great importance for beekeeping around the world, since European honeybee colonies have to be treated for Varroa several times a year, so that they will survive.
As it happens, we’ve already obtained samples of wild honeybees from Texas and Arizona from before the arrival of Varroa, and shortly after its arrival. We would like to compare them with the bees that live there now, in the presence of the mites, to try identify which genes may be involved in resistance. So, this means we had to get some bees from near Tucson, a population that has been studies for many decades (we also have a population from Texas, but that’s another story). In the desert, where there are no trees, bees nest in rock crevices and you can sometimes even see the comb sticking out. Thanks to Gerry Loper, who has worked for the USDA bee lab for many decades, and still visits his bee populations, we were able to locate 40 colonies in the course of just a couple of days.
The Africanized bees are not friendly, and can pursue you for hundreds of meters if you get them really mad, so a bee suit is necessary for this sort of work, though it gets a bit hot in the Arizona desert sun (temperatures in the high 30s). We had to start our days at 6am, at sunrise.
This was a great trip, and I am really grateful to Gloria Degrandi-Hoffman and USDA Carl Hayden Bee Research Center for hooking me up with a field vehicle and two excellent techs, as well as for giving me a opportunity to give a talk about my research.
Mona, Henry and Gerry.