Geographic variation of temperature effects on initial colony development of Lasius japonicus (Hymenoptera: Formicidae)

Abstract

For Lasius japonicus Santschi (Hymenoptera: Formicidae), a common ant species in Japan, diapause induction is temperature dependent. To elucidate the geographic variation of its temperature dependence, new L. japonicus queens were collected immediately after nuptial flight from four sites at different latitudes: Kitami (44.1°N), Hakodate (41.8°N), Shizuku-ishi (39.7°N), and Okayama (34.7°N). The collected queens were reared for 100 days at four constant-temperature conditions (25 °C, 20 °C, 17.5 °C, and 15 °C) under a 12L:12D photoperiod. The queens began founding colonies immediately in all conditions. For all temperature conditions, daily change patterns of the average numbers of eggs, larvae, and pupae were similar among the Hakodate, Shizuku-ishi, and Okayama populations, but the development patterns of the Kitami colonies differed from those of the other three sites. Low temperatures strongly suppressed colony development of the Kitami population; development was weak even at moderate temperatures. For new queens of L. japonicus, solitary overwintering without rearing larvae is regarded as serving an important role in successful colony foundation under cool climate conditions. Results reported herein suggest that local temperatures exert important selective pressure on the timing of diapause induction and on colony development in northern populations.