The Amateur Naturalist: Chamisa Bushes as Insect Nurseries

The Amateur Naturalist
Chamisa Bushes as Insect Nurseries
By ROBERT DRYJA

Early summer is a good time to observe the emergence of two kinds of insects on chamisa, also called rabbit bush. The larvae of the picture-winged fly (Aciurina bigeloviae) have been patiently nesting in galls on the chamisa for the past winter. The larvae of a leaf beetle that live specifically on the chamisa also emerge.

Adult picture-winged flies with their brightly patterned wings emerge from their galls in May and promptly lay the next generation of eggs on chamisa plants. The larvae that emerge from the eggs then burrow into the stem of the chamisa plant.

Galls on chamisa. Photos by Robert Dryja

These larvae release a chemical stimulant that causes the chamisa plant to start growing a gall. This gall conveniently grows around a larva and serves the larva in two ways. The gall provides a protective home, hiding the larva inside a white, cottony ball that typically is about half an inch in diameter by late summer. The cotton surrounds a green and harder ball and this ball provides food for the larva. A round nest is at the center of the ball and this where the larva can be found. A chamisa gall therefore is a protective and nourishing home.

A picture-winged fly larva inside of a gall Photo by Robert Dryja

A gall can be cut or broken into halves to see the larva. It is a small worm-shaped creature. It is brownish-white and moves only slowly, as if just waking up. It grows to be about a quarter of an inch in length over the summer and then settles down for a long winter’s nap. It becomes active again in the spring, entering the chrysalis stage in April.

A brown cocoon now is seen if a gall is opened. The adult fly burrows its way from the cocoon to the surface of the gall to start the next generation in May. Even so, these galls do not appear to harm the chamisa plant.

A picture-winged fly chrysalis. Photo by Robert Dryja

The picture-winged fly is a member of the fruit fly family. Biology students may be familiar with the red-eyed fruit fly used in genetic studies. By contrast, the picture-winged fly has green colored eyes. Its wings are transparent except for a distinctive pattern of black lines and dots.

An adult green-eyed picture-winged fly. Photo by Robert Dryja

The chamisa leaf beetle, unlike the picture-winged fly, has no elaborate home to protect itself. Instead, it relies on the chemicals it accumulates inside of itself by eating the leaves of the chamisa.

The scientific name of the chamisa plant is Ericameria nauseosa, referring to the sickening effect that occurs from eating it. It also has an unpleasant smell.

Chamisa leaf beetle larvae on a chamisa plant. Photo courtesy/Whitney Cranshaw for Forestry Images

Inexperienced predators of the leaf beetle learn not to eat it after an initial distasteful or even nauseating meal. The dark metallic blue-green color of the beetle larvae also provides a visually distinctive warning. The caterpillar and adult stages of the monarch butterfly use similar defenses.

Chamisa leaf beetle larva. Courtesy/Whitney Cranshaw for Forestry Images

The adult leaf beetle lays its eggs in the soil beneath a chamisa plant in the fall. The larvae emerge in the spring and spend the summer eating the chamisa leaves until they metamorphose into adults.

The adult beetle continues to eat the chamisa leaves for the remainder of summer. Indeed, some chamisa bushes may be eaten very extensively by the leaf beetle.

Adult chamisa leaf beetle. Courtesy/Whitney Cranshaw for Forestry Images

Would you like to see chamisa galls and leaf beetles yourself?  Even though chamisa bushes grow around Los Alamos County, you could also take a great trip to the Leonora Curtin Wetland Preserve (under the auspices of the Santa Fe Botanical Garden). It  provides a good habitat for these insects due to its creek, pond, and numerous chamisa plants.

To find directions and open hours, visit http://www.santafebotanicalgarden.org/visit-us/leonora-curtin-wetland-preserve/.

LOS ALAMOS

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