Mating behavior of the scarab beetle Dasylepida ishigakiensis was observed in a sugar cane field in Miyako Is., Okinawa, Japan. In field observations of tethered females on 6 February 2002, calling behaviors were observed only within 30 min of sunset time (18:25-18:55, JST), when light intensity decreased from ca. 500 lx to 1 lx. Mating was strongly affected by temperature: adults appeared and subsequent mating occurred when the temperature at 18:00 was higher than 18°C. Females appeared from the soil, flew to settle on sugar cane leaves and commenced rhythmical abdominal expansion and contraction. Males were attracted to the calling females from leeward, landed on or near the calling female, and immediately mounted. After genital connection, the male raised his legs and suspended himself with his genitalia. Mating lasted for ca 2 h. Most mated D. ishigakiensis females neither appeared from the soil nor attracted males until the end of March, so are considered monogamous. In contrast, males appeared from the soil after mating on evenings warmer than 18°C and probably repeat mating if females are available.
The life history of the white grub Dasylepida sp. was surveyed in a sugarcane field in Miyako Is., Okinawa, Japan. Adult flights were observed from early February to mid-March in 2001. Adults commenced flight just after sunset (at around 18:30) and mated. Sampling from the pots placed in the field on 19 April yielded 41.8% eggs and 58.2% first stadium larvae. Larvae sampled on 20 June, 2000 were found to consist of 33.3% and 66.7% of the first and second stadium larvae, respectively. On 22 August, 87.5% of larvae were second stadium and the remainder (12.5%) were third stadium larvae. The proportion of third stadium larvae increased and attained 100% by 30 November. In an excavation survey on 26 November, 2001, 11 adults (three females and eight males) and five pupae were found in the soil at a depth of around 45 cm. Pupae were found in the tunnel cavities. We believe that adults remain in the tunnels until the next February. In the rearing experiments at 25°C in the laboratory, the egg period was 23.6 d and the larval periods of the first, second and third stadia were 80.9, 91.8 and 335.8 d, respectively. These facts indicated that Dasylepida sp. has a two-year life cycle.
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 mg 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 mg/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.
Although in mark‐recapture experiments traps are useful to estimate the dispersal distance of organisms, they cause a dilemma that may be called a kind of Heisenberg effect: a large number of traps should be placed to yield a precise estimate of mean dispersal distance, while these traps shorten the mean dispersal distance itself by intercepting organisms that should have dispersed for further distances. We propose a procedure to solve this dilemma by placing traps uniformly in a lattice pattern, and by assuming a random movement and a constant rate of settlement for organisms. We applied this procedure to estimate the dispersal distance of the sugarcane wireworm Melanotus okinawensis Ohira (Coleoptera: Elateridae). The estimated mean dispersal distance was 143.8 m. Through the use of a conventional method of estimation, the mean dispersal distance was estimated to be 118.1 m. Thus, it was shown that the conventional estimate of dispersal distance was 18% smaller than the corrected estimate in our experiment.
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