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Spring 2012

Urban Jungle

The changing natural world at our doorsteps | Illustration and text by Patterson Clark      

May 29, 2012


The scent of commencement

For many students, their first breath of summer freedom is thick with the heavy fragrance of white-blossomed Ligustrum, or privet, which is commonly planted on school campuses. Perfuming many an outdoor graduation ceremony, the scent invites attendees to close their eyes and drift into a languid torpor.

Privet odor has a stimulating effect on moths, which at night will actively seek out the highly visible flowers. During the day, bees and butterflies are also drawn to the nectar-laden blooms in May and June.

Scientists have closely studied the alluring effect that privet perfume has on the small cabbage white, an invasive butterfly from Europe, Asia and North Africa.

More than 30 compounds comprise the plant's floral scent, and five of those chemicals attract the cabbage white. Two of the most powerful attractants are well-known aromatic compounds:

Phenylacetaldehyde, also found in chocolate, has a honeylike odor. Scores of insects generate the compound on their own to communicate with other insects.

Phenethyl alcohol has an aroma that is also present in orange blossoms and in the flowers of hyacinths. The compound, used as a fragrance in personal care products, is also deployed by many insects as an attractant.

Although each chemical by itself can attract cabbage whites, the most powerful draw happens when all five compounds are combined, creating a synergistic effect.

The butterfly reveals its interest by uncoiling its proboscis, anticipating a sip of late spring's dizzy nectar.

SOURCES: Journal of Chemical Ecology, Environmental Working Group, pherobase.com

Japanese Ligustrum and Small Cabbage White, Ligustrum japonicum and Pieris rapae

A small cabbage white, Pieris rapae, prepares to land on Japanese privet, Ligustrum japonicum.