Environmental and pheromonal control of precopulatory behavior for synchronized mating in the white grub beetle, Dasylepida ishigakiensis (Coleoptera: Scarabaeidae)

Abstract

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.

Identification of (R)-2-butanol as a sex attractant pheromone of the white grub beetle, Dasylepida ishigakiensis (Coleoptera: Scarabaeidae), a serious sugarcane pest in the Miyako Islands of Japan

“…2) in repeated GC-EAD analyses. This may have been affected by their physiological condition such as age and diapause status (Tanaka et al, 2008) as well as environmental factors, including light intensity and temperature (Fukaya et al, 2009). The range of the releasing amount of this compound by females, however, appears to be below the lower detection limit of GC and GC-MS instruments.…”

“…The initial light bulb voltage was 100 V, which was reduced by 10 V every 3 min until it reached 30 V, resulting in stepwise reduction of light intensity from 175 to 0.9 lx, which was measured on the table using an illuminometer (TL-1; Minolta Camera Co., Ltd., Tokyo, Japan). This gradual change of light intensity was roughly equal to that encoun-tered when mating behavior was observed in a sugarcane field (Arakaki et al, 2004;Fukaya et al, 2009). The number of males that (1) took off for flight (take-off) and (2) hovered for more than 2 s within 5 cm from the net cage on the leeside (hovering) was recorded.…”

“…SPME samples were taken 1 h before lights off. Five or 10 field-collected D. ishigakiensis females were introduced to a 100-ml glass beaker, of which opening was then covered completely with aluminum foil to make it dark inside to stimulate pheromone release at 22°C in the laboratory (Fukaya et al, 2009). A piece of wire mesh was used to separate the sampling area from the insects.…”

“…The flight tunnel was the same as described in previous studies (Yasuda, 1996;Fukaya et al, 2009). Fresh air was supplied at a flow rate of 10 cm/s to the tunnel (18.5 cmϫ 18.5 cmϫ60 cm long) made of transparent acrylic plates, and exhausted to the outside.…”

“…They metamorphose there to pupae in October and then to adults in November. The adults stay in the soil for another two months and appear for mating for just a short time in the evening during the coldest time of the year (Tanaka et al, 2008;Fukaya et al, 2009).…”