Life history of Phonarellus ritsemai (Orthoptera: Gryllidae)(1) Egg development and egg period

クロツヤコオロギ Phonarellus ritsemai(Orthoptera: Gryllidae)の生活史(1)卵発育と卵期間

Life history of Phonarellus ritsemai (Orthoptera: Gryllidae)(1) Egg development and egg period

Creators ARAI Tetsuo

Creators Watanabe Uichi

Adult field crickets, Phonarellus ritsemai, were collected in Oimachi, Kanagawa Prefecture (35.3 degree north latitude, 139.2 east longitude, elevation about 98m) on July 7, 2012, June 28, 2014, July 12, 2015, and June 24, 2017. Thereafter, adults were bred in a laboratory close to natural conditions in Osaka Prefecture’s Mino City (34.8 north latitude, 135.5 east longitude, elevation about 81m). Eggs used for the experiments were collected within 24 hours of oviposition. Adult females laid eggs from their collection date until early August, peaking in early July. Eggs that were kept at a constant temperature of 35ºC or 15ºC all died. However, 70% or more of the eggs hatched　successfully when they were kept at 30ºC, 25ºC, or 20ºC. Mean incubation period was at 30ºC in 16.8± 1.04 days, 25ºC in 25.6±1.05 days, and 20ºC in 52.4±2.42 days. Thus the developmental zero point was estimated at 15.1ºC with the development of 254.7 cumulative growing degree-days. Egg length along the major axis tended to increase with adult female body size, while the opposite trend was observed for the minor length, but this difference was not significant. Egg size seemed unrelated to adult age as both positive and negative correlations were observed for the different females. At a constant temperature of 25ºC, eggs exhibited punctuated growth from oviposition to eclosion, growing rapidly for four days along both the minor and major axes from the 6th to 9th day after oviposition, and changing little thereafter until hatching. P. ritsemai is distributed from west of Ibaraki Prefecture on Honshu to the Nansei Islands. In the area north than Kyushu, the species has a univoltine life cycle with overwintering nymphs. In Oimachi, adults begin to emerge from late May to early June, and considered to lay eggs from mid-June to early or mid-August. Their eggs do not undergo diapause and are though to hatch from early/mid-July to early/mid-September.

[ISSN]2189-4825