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Mating
During the mating season, Asian Swallowtail butterfly males will fly through the foliage of trees in search of a mate. If he encounters a female resting on a plant with her wings open and horizontal, he will approach her from a distance of 1-1.5 meters and examine her through contact of his fore legs with the tips of her wings. If the female is a virgin, the male will continue with copulation. Like the males of the Queen Butterflies (Danaus gilippus berenice), White Cabbage butterflies (Pieris rapae crucivoria), and Fritillary butterflies (Argynnis paphia), male Asian Swallowtail butterflies rely on specific visual cues to help conduct their mating rituals. While the aforementioned species’ males base their mating practices on the generalities of their respective female’s color scheme, observational experiments suggest that the males of P. xuthus select their mates based on the specific coloring of their wings with a particular attraction to closely spaced yellow patches. Researchers at the Tokyo University of Agriculture and Technology first established that females with red patches on their wings, as opposed to yellow, did not entice the males to approach her. In the second portion of their study, researchers it was found that only specific patterns of yellow patches would excite the male butterflies enough to approach the “female” model to attempt to mate. While a stripe pattern excited males enough to approach, in contrast to a patch pattern, it was observed that many males left the female without contacting it. Through this same experiment, researchers observed that the male’s initial approach of the female was conspecific and visually motivated, irrelevant of sex.

Most females of the Asain Swallowtail butterfly will mate more than once in their life. This behavior is typical of many other swallowtail butterflies including P. glaucus, P. helenus, and P. protenor. In a study conducted by Mamoru Watanabe and colleagues of Mie University’s Department of Biology in Japan, it was found that females that had never mated before increasingly produced eggs in the week following her emergence, culminating in about thirty mature eggs.

With increased mates, the female is able to increase the genetic diversity of her offspring. Females will oftentimes also lay eggs in between her multiple matings. Furthermore, once a female had mated once, the second time she mated, the number of mature eggs she was able to produced increased significantly. Despite this large increase in singularly mated females from non-mated females, while females who had mated more than once (twice or even three times) did increase in the number of mature eggs produced, there was not as significant a jump as that between non-mated and singularly mated females. Therefore, it was concluded that the more a female mated, the more eggs she deposited. There was also evidence suggesting that the sperm obtained from the most recent mating appeared to be dominant.

Development and Population Dynamics
P. xuthus is the most common of swallowtail butterflies in suburban areas of Japan. Despite its wide distribution, the population maintains a stable, relatively low, level. There are typically four to five generations every year with the adults of the first generation emerging from mid April to early may and adults of the second generation emerging in the middle of June. P. xuthus will lay single eggs on leaves of host plants, allowing hatched larvae to feed on Poncirus trifoliata, Zanthoxylum ailanthoides, and various citrus species. The larval stage lasts for approximately three to five weeks while the pupal stage is around two weeks.

According to an observational study conducted in a suburban area of Fukuoka, Japan between 1970 and 1972, it was concluded that the population fluctuation of the Asian Swallowtail butterfly was surprisingly stable compared to that of various other insects. The stability of the population appeared to be regulated by the population of egg parasitoids, Trichogramma, and pupal parasitoids, P. puparum, who maintained shorter life spans and generation-times than the egg of the P. xuthus. When the entire population of butterflies reaches a high density, because of the shorter generation times of the parasites, intergeneration responses of the parasites are faster than those of the P. xuthus, resulting in an responding increased growth of the parasites. This creates an evolutionary stable system to keep the population of both the parasites and the host in check. It was also found that amongst the subpopulations studied, exchanges between each subpopulation helped to maintain the stability of the entire population as a whole.

Oviposition
Females released into a specific subhabitat will disperse across various other subhabitats to lay their eggs according to sun exposure. Female butterflies govern the number of eggs deposited in each subhabitat is mainly governed by the quality of the subhabitat, the existing adult population in the area, the quantity of young leaves in the vicinity, and the degree of sun exposure (females prefer sunnier areas). There was also no notable significant statistical difference made in the observational study determining female preference for host plant height when ovipositing.

Mortality factors
It has been suggested that other insects may suck the larvae out of their eggs before they hatch. During an observational study, the grasshopper Oeanthus longicauda was seen attacking various P. xuthus eggs. Once the larvae hatch, they were also observed to be attacked by the ant Lasius niger. Researchers also observed that primarily ants, spiders, and various other bugs prayed upon the first and second instar larvae. Occasionally, some larvae were killed by rain. Polistes wasps consistently attacked the fourth through fifth instar larvae. In each generation of a study done by Mamoru Watanabe, the wasp Trogus mactator was seen to parasitize the second and third instar larvae while Pteromarus puparum was seen to attack the fourth or fifth instart larvae. This contributed to the main mortality rate of P. xuthus during the pupal stage. The wasp was observed emerging from the host pupa four or five days after the predicted date of emergence of the host.

Aside from predation, larval mortality rate was also affected by disease that appeared to correlate with duration of the rainy season. Long days of rain in autumn led to the rot of infected larvae.