eurosta biology page

Eurosta Page

The female Eurosta is about 7 to 9 mm long.

The male is of slightly smaller size and lacks an ovipositor on the end of it's abdomen. The one shown here was video-taped in one of the plastic cup cages, that we use for mating flies. In nature, male flies take-up a position on a goldenrod bud. If a female approaches, the male will attempt to attract her by performing a mating display. This display consists of rapid side-to-side rocking movements. If the female is receptive, the male mounts her from the rear and clasps her with his front and middle legs. The male then inserts his aedeagus into her ovipositor. The time required for copulation ranges from about 15 minutes to over an hour, with an average of about 40 minutes. In order to produce large numbers of offspring with known parentage (for genetic and evolutionary research), Abrahamson laboratory researchers use small cages made from plastic cups and window screening. Small wooden sticks are mounted in the cups to provide an artificial "goldenrod bud." Usually, one female is placed in the cup with one to three males, to increase the probability that a mating will occur. Once mating takes place, the excess males are moved to other cages. Often, after mating the males are stored for future genetic analysis, while females are moved to larger cages containing goldenrods for oviposition. In this way the Abrahamson laboratory can conduct experiments which determine whether there is a genetic basis for some trait of interest. {To make the illustration above, a Canon XL-1 DV camcorder and EF 50mm macro lens was used to "film" the insect and then captured this still with a Canopus DV Raptor card in a PC. It is from one of our early experiments in macro video and the lighting isn't the best...}

After mating the female fly leaves to search for acceptable goldenrods in which to oviposit her eggs. Research has shown that Eurosta solidaginis has distinct host races which show a high degree of fidelity to their specific host species of goldenrod. While one race only oviposits on Solidago altissima, the other only oviposits on Solidago gigantea. The initial selection is probably done visually, but final selection is done by "taste." The female fly walks over the bud "tasting" it with chemical sensors on her feet and antennae. If the plant is acceptable, she will then attempt to ovipuncture the bud. By using a "tricky" experiment, researchers in our lab have shown that the female also "tastes" the plant with her ovipositor. By wrapping the bud of a fly's non-host species with a leaf from the fly's host species, the researcher was able to trick the female fly into attempting to ovipuncture the bud. However, once her ovipositor had penetrated the wrapper and touched the non-host bud, the female fly would reject the bud.

Young galls become apparent about three weeks after oviposition. The fly larva excretes chemicals which induce the plant to produce a gall. The gall has a complex structure with a hard corky exterior and interior of specialized nutritive tissues. These latter tissues are the gall fly's only food, as they do not feed as adults.

As the gall grows, the fly larva excavates a central chamber in which it will live until the following spring. The mature galls are nearly the size of a golf ball and are a common sight in old fields throughout eastern North America.

In the fall, as the plants, stems, and galls sencense and turn brown, the larva excavates an emergence tunnel before going into diapause for the winter.

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