Our fall honey bee health, disease, and pest monitoring on hives that have the potential to become breeders has now officially come to an end but will resume again in mid-January. A hiatus from field work provides the opportunity to explore bees in a different way….
Ten percent of all the samples we collect get processed at the Butte County Cooperative Extension in Oroville, CA (the other 90% are shipped to the USDA Bee Research Lab in Beltsville, MD). Samples are processed in our lab to determine levels of Varroa, Nosema, and white nodules while autopsies are performed on individual bees that grade the tissues housed within the abdominal cavity. We are now in the process of examining the abdomens of bees for white lumps known as white nodules. These white nodules are thought to be made of tyrosine a non-essential amino acid. Why are they important? Data suggests that colonies which contain bees exhibiting white nodules are more likely to survive then those that do not. Figures 1 and 2 illustrate how the hunt for white nodules is undertaken. Recently, ten workers from each of 160 samples were carefully examined for the presence of white nodules under the plates of the abdomen with the naked eye using only the light provided by the fluorescent bulbs in the drop ceiling of our lab.
The trait does not appear in all bees and can only be observed after they have been placed in alcohol for an amount of time in excess of three days. All of the samples we take to determine Varroa and Nosema levels contain roughly 300 bees from the brood nest and are collected in 70% ethanol to preserve them over time. A 10 bee sub-sample is taken from each sample to determine the prevalence of white nodules. Later autopsies are performed on each of the corpses. Although samples are always stored in 70% ethanol, white nodules have been observed in bees stored in concentrations ranging from 50-90% ethanol. White nodules can be found within the abdominal cavity of workers (Figures 3-10), drones (Figures 11-14), and queens (Figure 15-17). They have been found in nearly every cohort of honey bee workers from newly emerged to foragers. White nodules can range in size from relatively large (Figures 3-7 and 10-17) to significantly smaller like the ones pictured in Figures 8 and 9. For a more accurate idea of their size see Figures 15-17.
At this point we cannot be sure exactly what the white nodules mean but one hypothesis is that they may be a reaction in defense of some foreign body that has invaded the bee. The bee recognizes this foreign body within its own and floods that site with tyrosine. The tyrosine encapsulates the foreign body and prevents it from moving freely throughout the rest of the abdomen. The tyrosine becomes dehydrated once the bee becomes saturated with alcohol and forms what we see as white nodules in the areas where the amino acid has formed an encapsulation. Attempts to examine the cell structure of white nodules using the transmission electron microscope have failed but we were able to capture some scanning electron images of the site of an infection where tyrosine may have been deployed to encapsulate a foreign body. Figures 18–21 show the surface of the malpighian tubules or kidneys of a worker bee from a colony that was known to contain a high prevalence of the trait white nodules. The grape like structures clustering around the tubules are what we think is the beginning of what might eventually transform into white nodules.