POPULATION BIOLOGY OF AN HERBIVOROUS LADY BEETLE

在日本中部志贺县西北部的两个地点（A和F）调查了取食蓟的雌甲虫的产卵时间的适应意义。我跟踪了一个季节生产的队列，并测量了终身健康的四个组成部分：卵存活率，幼虫存活率，从羽化到次年繁殖季节的雌性成虫存活率，以及终身繁殖力。在同一种群中，不同种群间的终生适应度差异较大，但在种群适应度模式上存在明显差异。在A点，在一个季节早期出生的队列比晚出生的队列具有更高的终身健康，而在F点，晚出生的队列往往具有更高的终身健康。这些站点间差异的主要原因是由于节肢动物捕食和寄主植物退化引起的虫卵和幼虫死亡强度的季节性变化。野外观测结果表明，a点产卵早，f点产卵晚，雌虫较长的生殖寿命是造成f点产卵时间较长的主要原因。室内实验结果与野外观测结果一致，并提出了雌虫产卵时间的遗传基础。各地点的繁殖模式与后代终生适合度的相关性表明，对产卵时间的选择提高了雌性的终生繁殖成功率。

The adaptive significance of the timing of oviposition in the thistle-feeding lady beetle Epilachna niponica was investigated at two localities (site A and Site F) in the northwestern part of Shiga Prefecture, central Japan. I followed cohorts produced over a season and measured four components of lifetime fitness : egg survival, larval survival, female adult survival from emergence to the reproductive season in the following year, and lifetime fecundity. Large variation in lifetime fitness was evident among cohorts within a population, but the two local populations showed a clear difference in patterns of cohort fitness. At site A, cohorts produced early in a season had higher lifetime fitness than later cohorts, whereas at site F, later cohorts tended to have higher lifetime fitness.The major causes of these between-site differences were seasonal variation in intensity of egg and larval mortalities fue to arthropod predation and host plant deterioration. Field observations revealed a significant difference in oviposition phenology between the two sites : early reproduction at site A and delayd reproduction at site F.The relatively longer reproductive life-span of females was responsible for the prolonged reproduction at site F.Results of a laboratory experiment which eliminated environmental variables agreed with the field observations, and suggested a genetic basis for the oviposition schedules. Correlation of reproductive pattern at each site with higher lifetime fitness of offspring suggests selection on the timing of oviposition to improve the lifetime reproductive success of females.