Recently, the Wildlife Disease Laboratories received an interesting request from Seth Menser, a senior horticulturist at the San Diego Zoo, asking if we could take pictures of plant parts under the microscope. “I would really like to do a couple of shots of a fig cut in half with the fig wasps still inside. I have the figs needed for the shots. And, if you have never seen inside a fig, with the fig wasps, it is a very incredible thing to look at!” We were curious, so agreed to help.
Seth brought up several figs from a Ficus macrophylla, commonly known as a Moreton Bay fig. These trees originate in the subtropical rain forest of eastern Australia but do well in frost-free climates such as ours. These majestic trees can reach up to 200 feet (60 meters) with long, aerial roots providing the tree with additional support to hold up the immense canopy. Seth brought several figs ranging from green and firm to dark maroon with spots on the outside. He explained the life cycle of the fig and the fig wasp as he cut them in half, and we set up the cameras.
Ficus trees are unique because the flowering parts of the plants are inside the fruiting parts (figs), making it difficult for insects to pollinate the trees. Thus begins the cooperative relationship with the fig wasp. The fig provides refuge and a food source for the wasps, and, in turn, the wasps pollinate the tree.
To begin the cycle, a tiny female fig wasp enters into a narrow opening (ostiloe) at one end of the fig. While wiggling into this small hole, she often looses a wing or antenna. Safely inside, she lays her eggs. As she is wandering through the fig, she spreads pollen from the fig she hatched in, thus helping the fig tree produce viable seeds. The cycle of the female wasp is complete, and she dies. Her eggs hatch, and the young wasps grow, finding food and refuge in the fig. Interestingly, only female wasps grow wings and leave the fig. The males live their entire life in the fig. Their function is to mate with the females and chew small openings through the fig’s wall for the females to escape, and the cycle begins again.
We were totally fascinated by the story. Using a dissecting scope with a camera attachment and a macro lens on a photo stand, we were able to capture the intertwined life cycles of the fig and the wasp. We photographed the narrow ostiole of the immature smooth fig where the female enters. Mature figs looked completely different on the inside. They were soft and fleshy, with delicate flower structures and seeds lightly attached to the inner walls. Each mature fig contained several wingless male wasps, and Seth was lucky enough to find one female flighted wasp.
At first glance, theses tiny wasps are difficult to see. The magnification helps, but a keen eye is needed to see them. How many can you find?
April Gorow is a senior pathology technician with the San Diego Zoo Institute for Conservation Research. Read her previous post, We Never Stop Learning.