Cheryl Briggs, a doctoral student at UC Santa Barbara, has been spending quite a bit of time at Big Creek. She is setting up an experiment to study how tiny parasitic wasps control equally tiny flies. The flies she is studying are a species of gall midge (about 1/25″ long). They lay their eggs in growing shoots of Coyote Brush. Upon hatching, the tiny fly maggots cause the plant to grow round galls about 3/4″ across, within which the maggots grow into adult flies. If midge reproduction goes unchecked, galls will cover the plant within a year. In nature this usually does not happen. Tiny parasitic wasps (also 1/25″ long) usually come along and lay their eggs in the galls. The wasp eggs hatch and kill the maggots, preventing the midges from reproducing while making new wasps. The wasps are called “parasitoids” because they begin life as a parasite of the host midge but, unlike a true parasite, they eventually kill their host.This intricate relationship is an example of a field of study known as “parasitoid-host interactions.” Understanding these interactions is crucial if we are to control insect pests without excessive use of pesticides. What Cheryl has done at Big Creek is to discover a natural example of this type of system, and to study the interaction under natural conditions. For example, Cheryl has found two species of parasitoid wasps attacking the Coyote Brush midges. After studying the details of the life cycles she developed mathematical equations, which describe how effectively the wasps should control the midges. The equations predict that the two species of wasp will be a less effective control than one species alone. The caging experiments are designed to see if this is actually true by putting one species of wasp in some cages and two species in others, and then counting the rate of gall formation. Using the data she gets, Cheryl will be able to modify the equations so as to give more accurate predictions. The equations can then be used in developing a general theory of how multiple parasitoids affect their hosts.
Cheryl’s research demonstrates the use of nature reserves as places to test theories about the natural world. In her case the knowledge gained will be useful for deciding how many species of parasitoid wasps to release (when trying to control a pest), as well as improving our understanding of natural creatures. Big Creek Reserve is ideal for such work because (1) all the natural predators and competitors are present in a complex “balance,” (2) Cheryl can set up her cages in the field without danger of their being vandalized, and (3) we can help support her work by providing grant funds.
Other notes: After five years of drought the flow in Big Creek is low. The March rains made a difference, though. For example, this September the creek is about 2/3 of an inch deeper than last September, which means 1-2 gallons per second more water. During the recent rains the creek rose about 8″ for a short time and fell back quickly to base flow.
During October, deer moved into the reserve in large numbers. Many are feeding on tanoak acorns. We have not yet seen numerous mountain lion tracks but I expect the lions will move down from the high country soon. The other day I saw a doe and fawn run up a slope and almost collide with a bobcat hiding in the brush. They jumped sideways and ran down slope, the bobcat watching their progress. The bobcat then ran off the opposite direction. In Florida bobcats frequently eat deer, but the cats there are big and the deer very small. Here, I suspect only a very large bobcat would attack anything larger than a small fawn, but we have no data. One student (Tye DePena) is collecting cat scats on the reserve. He may shed some light on this question when he analyzes the dietary remains.
This fall the monarch butterflies seem very abundant, or perhaps they are just more active because of the warm weather. We have marked over 300 individuals this year (writing a small “BC” on the wings with a soft black “sharpie” pen). Please tell me if you spot these or any marked butterflies. Last season two of our marked monarchs were found, one at Esalen (4 miles north) and one at Plaskett Creek (15 miles south). This data is useful in understanding how much the butterflies move along the coast during the winter, one objective of a study undertaken by Walt Sakai of Santa Monica College. (11/7/91)