The white grub beetle, Dasylepida ishigakiensis (Niijima et Kinoshita), is a serious pest of sugarcane in the Miyako Islands of Okinawa, Japan. Two evident electroantennographic (EAG) responses were observed by solid-phase microextraction sampling from female secretion and subsequent gas chromatography-electroantennographic detection (GC-EAD) analyses. These were identified as 2-propanol and 2-butanol by GC-MS analyses. GC-EAD on a chiral column showed two evident EAG signals corresponding to 2-butanol enantiomers, but the ratio and amounts could not be determined because of the small amounts. (R)-2-Butanol elicited the strongest EAG response, followed by (S)-2-butanol and 2-propanol, which showed 1/10 and 1/100 of the response of the first compound, respectively. In the field, only (R)-2-butanol attracted feral males when it was baited as 1 ml water solution of 1–100 μg of this compound, (S)-2-butanol, racemic mixture or 2-propanol on cotton ball lures (ca. 1.5 cm diameter) in vane-traps. When 2-propanol was blended with 10 μg/ml of (R)-2-butanol solution on cotton ball lures, male catches decreased as the amount of 2-propanol increased. From these results it was concluded that (R)-2-butanol was a component of the sex attractant pheromone of D. ishigakiensis while (S)-enantiomer and 2-propanol showed inhibitory effects when they were blended with the first compound.

Precopulatory behavior of the white grub beetle, Dasylepida ishigakiensis, was observed under laboratory conditions to determine the environmental factors controlling mating behavior, which is synchronized among individuals at dusk in the field. When light intensity was gradually decreased, both females and males sequentially started moving their antennae, legs and abdomen, then walking, and females rhythmically extruded their abdomen while males opened the elytra to fly. Pheromone release by females was suggested in a wind tunnel assay in which males oriented themselves to both intact and crushed bodies of females, but not of males. When illumination was suddenly turned off, precopulatory behavior of females and males was similarly induced but the frequencies of calling and flying behaviors were significantly reduced as compared with those observed when light intensity was gradually reduced. This result may suggest that gradual darkening is an important factor for their synchronized appearance from the soil and subsequent mating behaviors, including pheromone release in females and orientation flight in males. These behaviors were significantly suppressed at low temperatures below 18°C. This result supports our previous conclusion that temperature is the primary factor controlling the emergence and mating activity of sexually mature beetles in the field.

Mating behavior of the green chafer Anomala albopilosa sakishimana Nomura (Coleoptera: Scarabaeidae) was observed in Miyako Island, southwestern Japan from 28 to 29 May 2003. Females and males were present on patches of the beach naupaka, Scaevola sericea Vahl, throughout this time and showed clumped distribution within the patches. Males were observed to mount the backs of females for several hours during a day and successfully defend females from intruding males. Copulations took place only from 19:00 to 20:00 (JST) and most frequently at 19:40 (light intensity: 24 lx). Mean copulation duration was 18.1±2.6 min (mean±SD, N=16). After mating, both sexes remained on the same leaf to feed. When females guarded by males were collected before mating time and subsequently reared in the laboratory, about 65% (11/17) laid fertilized eggs. This indicated that most of the females mounted by males are not virgin. In laboratory observations, several females mated more than once on different days, indicating A. a. sakishimana females are polyandrous. Since mounted males successfully defended the females from intruding males in the laboratory, long-lasting mounts appear to comprise precopulatory mate-guarding behavior. This is the first record of precopulatory mate guarding in scarab beetles.