August 5, 2011
A couple weeks ago we had the second round of our North Campus insect survey. Fifteen Museum staff tromped around the North Campus to see what insectuous wonders we could collect. Although we found some notably large specimens, the largest being a 3-inch bird grasshopper (Schistocerca sp.), the most interesting find was actually something a lot smaller. Much, much smaller in fact: a minute fig wasp about 2 millimeters in length!
Female Fig Wasp, Pleistodontes sp. Fig wasps belong to the wasp family Agaonidae and as their name implies, they have a life history intricately linked with fig trees, family Moraceae. In fact fig trees can not produce figs without the wasps, and the wasps can't reproduce without the figs! The way this mutually beneficial relationship works is quite astonishing, especially if you take a journey to the core of a ripening fig! Journey to the Center of the Fig It all starts when a mature female fig wasp enters the synconium (an immature fig if you will) through its natural opening, called the ostiole. This sounds really easy when you think how small these wasps are, but nature has not made it easy on the fig wasp, as the opening is actually too small for the adult wasp to enter without damaging herself. It's so small that the fig wasp often loses her wings and much of her antennae as she struggles through the opening. To enable passage through the ostiole, the underside of her head is also equipped with spines that help to get a grip as she's going through the hole (see image above). Once inside the synconium she passes over the fig's female flowers and inadvertently deposits pollen from the male flowers of her original host tree. She then deposits her eggs in the cavity. Her business being done, she dies. The Pleistodontes fig wasp we found is, interestingly, not a pollinator of edible figs. Instead, it is a pollinator of ornamental figs which can be found in backyards and parks across Los Angeles. Once pollinated, the fig fruit begins to develop, consuming the wasp's dead body in the process. The eggs hatch and the larvae consume small parts of the developing fig. After the larva eat enough fig, they pupate and finally emerge as adult male and female wasps. The wingless male wasps have only two functions to perform in their short lives—to mate and to escape! Finding a mate inside the fig isn't too difficult for the male wasp as all of his sisters are stuck inside the fig with him (remember how small the ostiole opening is). After he mates with at least one of his siblings (or offspring from another wasp), he begins digging a tunnel to exit the fig. This tunnel is the escape route that the female wasp uses to exit the fig, but not before she picks up pollen from the male flowers. This pollen will eventually pollinate the developing fig she visits to lay her own eggs in, and thus the life cycles of both fig and fig wasp continue. All I can say is WOW! Nature is weird, wonderful, and so cool! Thanks to entomology curator Brian Brown for identifying and photographing the wasp.