The Department of Applied Ecology welcomed Marla Spivak, Distinguished McKnight Professor at the University of Minnesota on Thursday, March 28. A world-renowned entomologist, Spivak studies honey bee and pollinator health, including breeding and genetics, social immunity, community ecology, and landscape ecology. In 2010 she received the prestigious MacArthur Foundation “genius grant” for her research.
“To be supportive and collaborative in a competitive world such as academic research, that is the very definition of genius,” said David Tarpy, professor and extension apiculturist, while introducing Spivak at the department seminar.
Spivak detailed her research on the role of propolis in honey bee colonies. Long before propolis was understood, beekeepers gave it a name. This brown-ish, sticky substance acts as a glue, irritating beekeepers by cementing removable frames inside a Langstroth hive. Propolis was first believed to be a substance made by honey bees, similar to wax. It has since been discovered that propolis is antimicrobial tree resin that is collected by worker female bees and brought back to the hive. Spivak described how the bees line their nest with resin, creating a “propolis envelope.”
Today, we know what propolis is, but why do honey bees use it? Foraging for tree resin is energetically costly for worker bees, and the resin does not offer a direct reward. Honey bees do not use resin for food. If the goal is to waterproof the nest or fill in cracks, why not use wax? Spivak, through her research, has sought to understand how the propolis envelope affects colony health and determine if bees self-medicate with tree resin.
There are several fatal honey bee diseases including chalkbrood (fungal) and American foulbrood (bacterial). In research trials, Spivak and her team introduced these diseases to bee colonies in Langstroth hives with and without a propolis envelope painted on the interior walls. Spivak found the disease load of both chalkbrood and American foulbrood to be significantly less in colonies with a propolis envelope. The mechanism of this revelation is still unknown, and while the propolis envelope does not act as a cure, it reduces the number of sick bees.
The propolis envelope also appears to impact bee immune systems. By conducting PCR tests throughout the season, Spivak found that bees living in a hive with a propolis envelope had stable immune systems while bees without propolis-lined walls had immune systems that fluctuated wildly over the course of several months. Spivak believes that propolis acts as an external immune system, sanitizing the environment before bees come into contact with disease. In further experiments, it was documented that worker bees collect more tree resin when a disease is introduced to the colony. In this way, bees are self-medicating (or more correctly, social-medicating as bees work for the health of the colony as a whole rather than themselves as individuals).
From this research, special Langstroth hive boxes with grooved interior sides are being created for beekeepers. The grooves encourage bees to collect more tree resin, as their natural behavior is to fill cracks with propolis. These boxes have been shown to increase colony size in commercial almond pollination.
“It’s just heartwarming, especially for the students to see really hard work then go to the industry and have it work”, says Spivak.
The Applied Ecology department welcomes you to attend the weekly, in-person seminars and the subsequent social hour at the Raleigh Brewing Company.