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Rediscovery of Ischnura rufostigma (Selys, 1876) in Hong Kong after half a century

Ischnura rufostigma, known to be a historical odonate record of Hong Kong, was rediscovered by a member of the public earlier this month. A male of this species was observed by Patrick Leung in a barren field in the western New Territories on 20 March 2020. With his assistance in collecting the specimen, the Dragonfly Working Group has confirmed that the species was Ischnura rufostigma.

Ischnura rufostigma is common and widely distributed across the Himalayan belt from India to eastern part of China (including Guangdong and Fujian). It is thought to be a species complex or contain several subspecies (Mitra 2010), but the population in China is currently treated as a single species (Sanmartín-Villar et al 2016; Zhang 2019). 

In Hong Kong, the species was once commonly found in Fanling, Ho Chung and Kam Tin in the 1960s (Asahina 1965; Lai 1971). Lai (1971) mentioned that the species was usually found in slow-flowing sections of low-elevation streams with grassy waterside and furrows in agricultural fields. Elsewhere the species can also be found in ponds with emergent plants. However, since then there had been no further records of the species in Hong Kong and its findings are considered as historical records.

The colour of male Ischnura rufostigma is spectacular: synthorax apple green with three black stripes; segments 2-6 orange red; segments 7-10 black with a typical dorsal blue spot on segment 8.

This individual was recorded next to a somewhat grassy and muddy nullah, with no water bodies nearby. Given that this is a single record found in a habitat not typical for I. rufostigma, whether or not the species has successfully re-colonised Hong Kong needs further observation. 

Acknowledgement: We would like to thank Patrick Leung for sharing his finding and providing assistance.

Male Ischnura rufostigma

 

References

Asahina, S. (1965). The Odonata of Hong Kong. Kontyû 33(4): 493-506.

Lai, Y.L., (1971). An introduction to the Odonata of Hong Kong. New Asian College Academic Annual 13: 1-48. (Chinese with an English summary)

Mitra, A. (2010). Ischnura rufostigma. The IUCN Red List of Threatened Species 2010: e.T167489A6356820.https://dx.doi.org/10.2305/IUCN.UK.2010-4.RLTS.T167489A6356820.en. Downloaded on 21 March 2020.

Sanmartín-Villar, I., Zhang, H.M. and Cordero-Rivera, A. (2016). Colour polymorphism and ontogenetic colour changes in Ischnura rufostigma (Odonata: Coenagrionidae). Odonatologica 45:77-86.

Zhang, H.M. (2019). Dragonflies and Damselflies of China. Chongqing: Chongqing University Press.