If a male Japanese beetle is unable to detect the sex pheromone released by a female, he won't be able to locate her and reproduce. UC Davis researchers have discovered how a key enzyme interacts with those pheromones in the beetle's sophisticated olfactory system, a finding that may lead to important applications for controlling this damaging, invasive pest.

The findings of the team of chemical ecologists, led by Professor Walter Leal of UC Davis' entomology department, are published this week in the June 16 issue of the Proceedings of the National Academy of Sciences.

The researchers probed how the male Japanese beetle distinguishes between two sex pheromones using a smelling mechanism located on its antennae. The beetle has two olfactory receptor neurons housed in the same highly sensitive structures of the antenna, one detecting the pheromone of a female Japanese beetle and the other tuning in to a female pheromone of the closely related Osaka beetle.

"If the Japanese beetle smells the other species, it shuts down," Leal said. "It's like a stop sign."

Previous studies by the Leal group showed that the Japanese beetle uses an enzyme or protein in its antenna to inactivate pheromones by chemically breaking them down.

In this newly published study, the UC Davis researchers isolated, identified, cloned and expressed an enzyme known as PjapPDE. They demonstrated that this enzyme interacts with the pheromones from the Japanese beetle and from the Osaka beetle, quickly inactivating the pheromone of a female Japanese beetle and slowly degrading the pheromone from the female of the other species.

Leal's goal is to find ways to slow down pheromone degradation by inactivating the enzyme, thus interfering with the ability of male Japanese beetles to detect the pheromone and locate female Japanese beetles.

The Japanese beetle was first detected in the United States in 1916 at a New Jersey nursery. It now infests some 22 states east of the Mississippi River and is spreading west. Isolated infestations have popped up in California, Wisconsin and Oregon. In its larval stages, the beetle is considered the most widespread turf-grass pest in the United States. The adult beetle feeds on the foliage and fruits of several hundred species of fruit trees, ornamental trees, shrubs and vines, as well as field and vegetable crops.

This research was funded by the U.S. Department of Agriculture's National Research Initiative and the National Science Foundation.

More information and photos related to this study are available at the Department of Entomology Web site at: http://entomology.ucdavis.edu/news/pnaspaperlealishida.html.