Copal Resin Ecology Project
COPAL PROJECT RESEARCH UPDATE: SUMMER 2007
This summer the copal project focused on two new aspects. The first involved taking our first close look at the harvest of copal resin by bees. We had seen these activities the previous summer and knew that many bees use resin in building their nests. Our goals were to identify which types of bees were harvesting copal resin and begin estimating how much resin they were collecting. This summer, Italo’s brother Melaneo joined the regular copal research team.
In the first type of observation, one team member sat next to a tree with fresh resin for an entire day. Their job was to note what kind of bee arrived at a resin patch and record the length of its visit. Once we had a basic idea of these patterns, we then expanded our coverage by having an observer spend his day rotating between three trees every 20 minutes. Bees and relatives we saw collecting copal resin included tiny, medium and large sized stingless bees (including Trigona and at least four other genera), iridescent green and gold orchid bees (genus Euglossa), and a large brown wasp (family Sphecidae). The most interesting observations were of a group of large orchid bees (genus Eulaema) with fuzzy brown and yellow striped abdomens. Individuals sometimes spent 20-30 minutes scraping at little hardened resin patches without depositing any on their legs. The surprise came when one bee implanted itself on a fresh resin lump and emitted an unusual loud buzz. This attracted considerable and often aggressive attention from other bees. One possible explanation for this behavior was that the bees were using the resin lump (made by a weevil attack) as a mating site. These types of observations make field ecology irresistibly fascinating.
It was easy to capture most bees hovering near a copal tree for the purpose of identifying them. It was a lot harder to capture a bee (or a large wasp!) just before it flew away with a full load of resin. The next challenge was to remove the resin from its hind legs carefully enough to weigh it separately. It took a lot of trial and error to develop a method that worked reasonably well for the large bees. We’re still trying to figure out how to do this with small ones.
In various parts of Mexico and Central America, perhaps where weevils don’t stimulate large resin lumps, forest people wound copal trees and collect the fresh resin that drips down the trunk. Since we know that weevil formation of resin lumps is a slow process that often removes the larvae responsible for it, we launched a manual wounding resin harvest in one of the copal plantations at Jenaro Herrera. We used a knife to cut a shallow half-dollar size wound in the bark. Depending on the size of the tree, they were given one, two or three cuts. Italo and Melaneo are now refreshing the cuts once a week – each time making the cut a little bit higher to allow the bottom edge to heal. Since we quickly found that some bees are very attracted to this fresh resin, we covered the wounds on half of the trees with wire mesh so we can measure resin production with and without the impact of bee harvest. This experiment will continue at least through early 2008 so we can compare the results during both a dry and rainy season.