Antennal olfactory receptor neuron responses in the scarab beetle Phyllophaga anxia (LeConte) were investigated using tungsten microelectrodes. Morphological investigations revealed that antennal sensilla are distributed on the entire antennal club lamellae. The female-produced pheromones, L-valine and L-isoleucine methyl esters, were shown to affect two types of olfactory receptor neurons differently. One type of olfactory receptor neurons was excited with increasing pheromone concentrations at low doses (0.01–1 μg), but inhibited at higher doses. The second type was excited only at the high pheromone doses (100–1,000 μg stimulus loading). Both receptor neuron types were affected in the same way by the two pheromone components.