On 26 Jul. 1969, imagos were observed emerging form an open park near Las Cruces, New Mexico, between 1800 and 2000 h (MST). Males were flying in a zig-zag pattern, 10 to 50 cm above ground level, with their lamellate antennae extended. In three of the 22 copulations observed, males helped the female to dig her way out of the soil. Females emerged briefly, mated, than returned to their emergence burrows and disappeared. Only males were captured at lights, suggesting that females emerge only to mate. On 16 occasions, more than one male was attracted to the emergence hole, resulting in jostling for copulatory positions. After on male successfully engaged the female genitalia, the other males dispersed. Three newly emerging females were captured before copulation and placed in small screen cages. When placed on the ground, each of these cages attracted a minimum of five males within a 5-min time period. Males also landed and investigated emergence holes into which newly mated females had returned. All of these observations support the presence of sex pheromones in Polyphylla diffracta, and suggest that the females mate only once.