Life history, life table, habitat, and conservation of Byasa impediens (Lepidoptera: Papilionidae)

This article investigates the biology of Byasa impediens, presenting its life-table data and analyzing its habitat requirements and the key factors threatening the survival of this species. This study also aims to detect specific protection methods to guarantee the long-term survival of Byasa impediens in Baishuijiang Reserve. Byasa impediens is bivoltine in Baishuijiang Reserve. The pupae overwinter on shrubs or on branches of trees. The eclosion of the first generation starts in mid-April. The adults of the first generation emerge in large numbers in mid-late May, and the second generation emerges from late June to mid-July. The two generations overlap. The adult males emerge 7–10 days earlier than the adult females. Their flight behavior is determined by factors such as perching along small rivers and gullies, and visiting flowers. The males are strong fliers. On the contrary, the flying ability of the females is weak; therefore, they just visit flowers, mate, and lay eggs near the natal area. The ratio of female to male is 1:4.1. The maximum lifespan of the males is 26 days, with an average of 6.9 days, whereas the maximum lifespan of the females is 21 days, with an average of 7.6 days. The pregnant eggs per female are 31.5 on average. The incubation period of the first generation is 12–14 days, whereas that of the second generation is 7–9 days. The larvae feed mainly on Aristolochia heterophylla. The larval period of the first generation lasts for 30 days with five instars and that of the second generation lasts for 30–40 days with five or six instars. The pupal period of the first generation begins in early June and lasts for 20–26 days whereas for the second generation, it begins between late July and late September. The adults prefer the following nectar plants: Albizzia julibrissin, Bauhinia glauca, Clerodendrum bungei, and Sambucus chinensis. The plant Aristolochia heterophylla is distributed at an altitude of 900–1680 m, and the most suitable range is 1200–1500 m. The host plants grow mainly along the paths and along the borders of forests where the canopy is rather open and shrubby undergrowth is found. The plant can hardly be found when the canopy density of the forest is greater than 80%. The elevation range most suitable for the larvae is 1200–1500 m. The ideal habitat of host plants also seems to be the ideal habitat of Byasa impediens. The key factors that adversely affect the population of Byasa impediens are loss and deterioration of habitats. The loss and deterioration of the habitats result in a decrease in the numbers of host plants and a more restricted distribution of the potential habitats. The habitat is easily influenced by anthropogenic activities, such as herding, cultivating, and using pesticides, which in turn influences the growth of the host plant Aristolochia heterophylla and the larvae of butterflies. Abnormal climatic conditions and natural enemies are the key factors affecting population density. The hot and dry weather in summer and the heavy rain in autumn considerably reduce the survival rate of eggs and larvae. The ichneumon parasitoids reduce the survival rate of the over-wintering pupae. The primary natural enemies of the larvae include spiders, earwigs, wasps, bugs, and ichneumon parasitoids. Other natural enemies of pupae and adults are birds. The most important conservation measures are preservation and reconstruction of the natural habitat, which includes rebuilding forests, enhancing management, enforcing existing laws, and developing eco-tourism. Creating a core-patch near all patches at a central area is also an important measure for conservation. In the most ideal habitat, appropriate shrub cutting can increase the growth of host plants, thereby promoting expansion of the Byasa impediens population.