Larvae of the Tailed Green Oakblue feed on old mango leaves, adults feed on rotting fruit; invasive alien species status remains to be clarified
Tailed Green Oakblue arrives in Taiwan, mango growers beware! In October, the Neiliau Community Development Association of Keelung City discovered a butterfly they had never seen before at the Neiliau wetland in Keelung. Experts identified it as the Tailed Green Oakblue (Chilades pandava), commonly found in Southeast Asia, which depends on mango trees for survival from larva to adult but does not harm ripe fruit. It is currently only found in Keelung. Chen Hung-po, head of the Plant Protection Division of the Bureau of Animal and Plant Health Inspection and Quarantine, said whether it is an invasive species or an alien species remains to be clarified, and no reports have been received so far. (For the complete photo series of the six-instar changes of the Tailed Green Oakblue, please see the end of the article.)
A common sight on Hong Kong, China street trees, arriving from afar from Xiamen
Shen Chin-feng, standing director of the Keelung Wild Bird Society, said butterflies generally rely on nectar for their survival, and very few do not feed on nectar; the Tailed Green Oakblue is one of them.
When it was discovered recently, Shen Chin-feng could not find it in Taiwan butterfly field guides, so he forwarded the photos to Huang Hsing-chi, a teacher at the Taiwan Butterfly Conservation Society, for help with identification, and it turned out to be the Tailed Green Oakblue, distributed in Southeast Asia and South China in mainland China.
Shen Chin-feng said the closest record of the Tailed Green Oakblue to Taiwan is in Xiamen, and mango trees are a common street tree species in Hong Kong, China, where the butterfly is also seen.
As for how the Tailed Green Oakblue came to Taiwan, Shen Chin-feng and experts and scholars believe it arrived by ship, with two possible routes: the first is the "COSCO Star" passenger ferry that regularly runs between Xiamen and Keelung every week, and the second is shipping containers. However, some experts believe butterflies are strong fliers and may have flown across the sea.
Still in Keelung, but it may fly to all of Taiwan
Shen Chin-feng's continued tracking and observation found traces of the Tailed Green Oakblue on more than 50 mango trees, mainly in Zhongzheng District, Xinyi District, Zhongshan District and Anle District of Keelung City. The bite marks on the leaves are L-shaped, and the larvae are hard to spot on the leaves, but pupal molts and female butterflies have already been found on several mango trees.
Shen Chin-feng will continue surveying Ren'ai District, Qidu District and Nuannuan District in the near future. Bite marks have now also been seen on mango trees in Xizhi District, and he speculates it has already spread to the Taipei-Keelung metropolitan area. According to the literature, the Tailed Green Oakblue has multiple generations per year and six larval instars. (For the complete life process, please see the end of the article.)
Hsu Yu-feng, a professor in the Department of Life Science at National Taiwan Normal University, said the Tailed Green Oakblue is currently only seen near Keelung and has not yet spread, but generations have already overlapped, and spreading across all of Taiwan is only a matter of time.
The Tailed Green Oakblue loves only mango trees; the kids eat old leaves, the parents eat rotting fruit
Hsu Yu-feng said the Tailed Green Oakblue depends on mango trees for survival; the larvae eat old mango leaves, while the adults eat rotting fruit, but they do not harm ripe mangoes. "I have never seen a mango tree die because of this butterfly," Hsu Yu-feng said. He believes the feeding habits of the Tailed Green Oakblue will not harm commercial crops; even the leaf-chewing larvae eat only a small amount of old leaves, and both larvae and adults die if they take in even a little pesticide.
He said the Tailed Green Oakblue is no different from ordinary leaf-eating insects, and there is no need to worry at present.
Chen Hung-po, head of the Plant Protection Division of the Bureau of Animal and Plant Health Inspection and Quarantine, said the mango trees in Keelung are not a local commercial crop, and whether this is an invasive species or an alien species remains to be clarified; no reports have been received so far.
"Life Process of the Tailed Green Oakblue" recorded by Shen Chin-feng
