Daily egg production in Pantala flavescens in relation to food intake (Odonata: Libellulidae)

摘要

The migratory dragonfly, Pantala flavescens (Fabricius, 1798), arrives in Japan from tropical regions every spring. Although the population increases as autumn nears, it dies in the winter cold. The adults often form foraging swarms above open grasslands when feeding on small insects, while oviposition occurs at diverse open water bodies throughout the day. Although oogenesis requires a daily intake of nutrition from prey, there has been little consideration of the relationship between food intake and, the number of eggs produced. In the early morning, females of reproductive age were captured from foraging swarms in grasslands. Immediately after capture, an artificial oviposition technique was applied to each female to release all mature eggs loaded. Then, the females were kept until death, up to 5 days, in envelopes in the laboratory. They were starved but hydrated daily, and the dry weight of faeces excreted during 24 h after capture was measured. Females excreted 8.4 mg of faeces within 24 h after capture. Then, they released about 840 mature eggs at 24 h after capture, suggesting that when females take in a sufficient amount of daily food, they can oviposit a large number of eggs every day. The rapid egg production might enable the population of P. flavescens to grow. A positive correlation was found between the food intake on the previous day and the number of eggs produced within a 24 h of capture. The act of ingesting fresh nutrients derived from the prey might promote rapid release of reserves in the female fat body, resulting in the oogenesis. Females able to encounter available foraging sites might produce a large number of mature eggs in the subsequent day to be laid.