Researchers in the Department of Entomology, University of California, Davis, have discovered that the fruit fly has a native odorant receptor that detects the silkworm moth’s sex pheromone, and that it’s “amazingly more sensitive” than the moth’s odorant receptor. Their work could open research doors for insect-inspired biosensors.

PROFESSOR WALTER LEAL (left) and postdoctoral scholar Zain Syed examine the leaves of a mulberry tree, planted on the Briggs Hall lawn in memory of professor Susumu Maeda. The scientists use the tree to rear silkworm moths for their studies on insect olfaction. (Photo by Kathy Keatley Garvey.)

The odor detector (OR) is a means of chemical communication that helps insects find mates. The olfactory link between silkworm moths (Bombyx mori) and fruit flies (Drosophilia melanogaster) is remarkable, said the UC Davis researchers Walter Leal, professor of entomology and postdoctoral scholar Zain Syed.

“Many insect species, including silkworm moths, release sex pheromones or chemical signals to attract a mate,” Leal said. “Female silkworm moths release a sex pheromone, bombykol, to attract males. Males detect the scent with ORs from miles away. That’s how they find one another.”

In a serendipitous discovery, Leal and Syed found that the fruit fly’s odor detector not only detects bombykol, but responds to bombykol with high sensitivity. Their groundbreaking research, Bombykol Receptors in the Silkworm Moth and the Fruit Fly, was published in the Proceedings of the National Academy of Science (PNAS).

“The fruit fly’s odor detector is amazingly sensitive to the sex pheromone of the silkworm moth,” Leal said. “Since the identification of bombykol as a sex pheromone five decades ago for the silkworm moth, hundreds of sex pheromones have been identified from lepidoteran species.”

Leal described the female-produced sex pheromone, a fatty acid-derived semiochemical “unique to chemical communication in moths.”

A single molecule of bombykol is sufficient to activate the olfactory receptor neurons (ORN) in the male antennae of the silkworm moth, the scientists said.

“These species-specific communication channels seem to have evolved under a strong evolutionary pressure into a sophisticated signal-receptor system,” Leal said.

The researchers said the fruit fly’s ORN is housed in “ab4 basiconic sensilla in the antennae” of the insect.

“Scientists have long been amazed by the incredible ability of male moths to detect females of their own species from far away,” said ecologist and evolutionary biologist Fred Gould of North Carolina State University, not affiliated with the research. “We have known for some time that the male's receptor proteins for the females pheromones were highly specialized for this purpose, but Syed and Leal have now clearly demonstrated that the specific hairs on the male antennae that house these receptors have other machinery that amplifies the sensitivity of males to these volatile compounds.”

“The work of Syed and Leal also provides important guidance and tools for other researchers who want to explore the pheromone communication systems of other species, or who want to further dissect the mechanisms within the specialized hairs of silkworms that enable this high sensitivity.”

Earlier (2006) the Leal lab and the lab of UC Davis genetics researcher Deborah Kimbrell published research in PNAS that found that genetically engineered fruit flies responded to the silkworm moth scent of a female — but they now they have identified the exact odorant receptor.

Bombykol was the first sex pheromone ever identified in an insect. Male moth detection of the sex pheromone was considered the “gold standard” in olfaction or chemical communication and paved the way for numerous research.

In collaboration with UC Davis geneticist Artyom Kopp, they went one step further and asked how the fly would respond to bombykol when the silkworm moth’s receptor is incorporated in the fruit fly’s trichoid sensilla, which are the detectors for the fruit fly sex pheromone. Surprisingly, the trichoid sensilla in the flies with the moth’s receptor responded to bombykol with comparable sensitivity to the moth’s sensilla.

“These discoveries pave the way for using flies as biodetectors with broader potential application,” Leal said.

Their research is funded by the National Science Foundation.