Effect of temperature on queen oviposition and seasonal colony development in Lasius japonicus (Hymenoptera: Formicidae)

Although day length plays a critical role in the seasonal development of many temperate insects, this study showed that this variable is less important than temperature for seasonal regulation of an ant’s life cycle. Here, we examined the effects of temperature on queen oviposition and seasonal colony development of Lasius japonicus Santschi. Queens were collected soon after their nuptial flight and were reared under constant laboratory conditions; colony development was analyzed. The percentage of larvae- and pupae-emerged colonies was reduced in low rearing temperatures, indicating that temperature is the primary environmental factor for the regulation of seasonal development. Larval diapause was induced at higher temperatures than the reproductive diapause of queens. Larvae need to enter diapause before winter; nevertheless, eggs that were still unhatched in late autumn would not necessarily be wasted because they could be eaten by queens. Cyclic fluctuation in the egg number was observed. At 25 °C, the second increase in egg number was synchronized with pupation, suggesting a social effect on queen oviposition. In contrast, at 20 and 17.5 °C, the clear second peak of oviposition was found in colonies wherein larvae did not emerge, suggesting that endogenous rhythmicity is involved in the regulation of queen oviposition.