Milionia zonea 橙帶藍尺蛾 in Hong Kong

Lots of postings to various social media and citizen science websites pertaining to Hong Kong’s wildlife of late, quite a few of which have illustrated either larvae or adults of the distinctive, brightly coloured, diurnal (day flying) looper moth Milionia zonea Moore, 1872 (Lepidoptera: Geometridae, Ennominae, a.k.a. 橙帶藍尺蛾). Links summarised later . . .

What’s it look like?

Here’s some pictures to help:

1st up, the larva. It munches (quite rapidly) through the Bhuddist Pine, Podocarpus macrophylla, in Hong Kong. It doesn’t eat alone – usually there are lots of larvae feeding on one plant, sometimes defoliating trees.

2nd: the adult moth. A fairly large moth, with a wingspan in the region of 50 mm (2 inches), seen flying by day. It has a very dark metallic blue background colour, with broad orange stripe crossing the forewing, extending along the termen and dorsum of the hindwing. There is nothing like it in Hong Kong.

What’s all the fuss about?

Two points.

(1) – this species wasn’t known in recent history to have been seen in Hong Kong. The first documented observation occurred in January 2016.

(2) – because the larvae are somewhat voracious diners on Podocarpus, the larvae have a pretty bad PR problem. Podocarpus is an expensive horticultural asset linked to good fung shui in Hong Kong. A small tree costs thousands of HK$ !

Are these points related?

That’s a matter of opinion. Here’s some background info.

(1) Taxonomy: Jeremy Holloway (1993 [1994]), in his work on the Borneo ennomine moth fauna, illustrated Milionia zonea and wrote up an entry for it and a sister species, Milionia basalis, under the latter name, which at that time was considered the only species of the two, zonea being thought of either as a junior synonym (e.g. by Holloway) or as a subspecies (e.g. by Japanese taxonomists). In the updated Borneo moth book list (Holloway, 2011), Milionia zonea is listed as a valid species, agreeing with the review of the genus Milionia written by Prof. Inoue (2005), wherein zonea was promoted to (or removed from synonymy with basalis, depending upon one’s view) the rank of species.
(2) Geography: Holloway (2011) gives the natural distribution of zonea as “N.E.Himalaya, Taiwan, Japan to Sundaland, Philippines” and of basalis as “Sundaland” (i.e. Borneo, Java, Sumatra and peninsular Malaya). The wide distribution of zonea already encompasses Hong Kong, and one should thus regard Hong Kong as being within the natural distribution of zonea.
(3) Horticultural trade: the larval host, Podocarpus macrophylla, is also a native species in Hong Kong, BUT due to its fung shui significance it is also an important horticultural plant, being traded across the border (both to and from, not always legally) with mainland China.
(4) Ages old human impact on Hong Kong’s vegetation: most of Hong Kong’s pre-human civilisation vegetation was sub-tropical monsoon forest (Dudgeon & Corlett, 2011), most of which went under the axe from over three thousand years ago until around four hundred years ago. It is likely that when Hong Kong’s pre-human landscape was forested with primary forest (i.e. not human disturbed), Milionia zonea would have been one of the thousands of moth species present here. There are other primary forest moth species found close to Hong Kong that are absent here in Hong Kong now (e.g. Brahmeidae, many Notodontidae, many lichen moths (Erebidae, Arctiinae, Lithosiini)), which adds credibility to this opinion.
(5) Milionia zonea is a very easy species to see. So easy that I cannot believe that the many people who have been photographing butterflies in the better vegetated parts of Hong Kong for the last 20 years prior to the end of 2015) could have failed to observe a single M. zonea. Yet in the last 18 months there have been dozens of sightings, by both butterfly photographers and general public hiking in the countryside, as well as even stunned observers in urban areas (e.g. Central and Causeway Bay).

Hypothesis.

Milionia zonea has recolonised Hong Kong  in late 2015 after an absence of at least some 400 years.

Howcome?

Probably through the horticultural trade, through the undetected importation of larvae on Podocarpus being sold in HK for fung shui purposes. Alternatively, or even additionally, M. zonea could also be undergoing a population expansion in Guangdong province due in part to the popularity of Podocarpus as a fung shui “asset” (due to its retail price), and has reached Hong Kong under its own powers of flight dispersal. Once here, it has found a plethora of pines (sorry, couldn’t resist!) as breakfast, lunch and dinner for lots of larvae. Consequently M. zonea has undergone a rapid population increase, to the point at which many people are actually seeing both larvae and adults of this species.

Defoliation – is this a problem?

There’s no getting away from it, M. zonea larvae can defoliate Podocarpus. In May 2016, staff at Kadoorie Farm & Botanic Garden [KFBG] manually picked off bucket loads of larvae from rapidly defoliating Podocarpus trees growing at higher elevations of the Farm. The trees later (a month or so) underwent a complete regrowth of leaves, indicating that there has been a longer evolutionary battle playing out between these two species. More recently (a couple of weeks ago), just around the hillside from KFBG at Kadoorie Centre, (The University of Hong Kong), I observed small Podocarpus “trees” that had dozens of M. zonea larvae on them, and some 30 to 50% defoliation. Strange part was that ALL the larvae were dead, not from insecticide, but from a bacterial infection (photo below). So nature has its own population control for this defoliator…..

M zonea with bacterial infection (for blog)

So if you love your Podocarpus, and see the colourful blue-black and orange adult moth flying around your prize / expensive tree(s), or (perish the thought) see the blue-black, orange & white larvae having the audacity to much their way through your Podocarpus(es), panic ye not! Podocarpus trees can regrow their leaves if you find they’ve been defoliated. Don’t be afraid to pick the larvae off the tree (though I’d advise wearing gloves, just in case those bold colours are advertising a poisonous skin). Your local koel or plaintive cuckoo might help remove the larvae for you, too.

Acknowledgements and thanks to all the Hongkongers who have posted observations of Milionia zonea adults and larvae on iNaturalist, Hong Kong Wildlife Net (forum and Facebook group), as well as through direct reports to me by e-mail or even the good old-fashined phone call! Additional thanks to Kadoorie Farm & Botanic Garden for providing personal communications on the status of M. zonea @ KFBG.


References

Dudgeon D. & Corlett R. (2011). The Ecology and Biodiversity of Hong Kong. Lions Nature Education Foundation & Cosmos Books, Hong Kong. 344 pp (revised 2nd edition).

Holloway, J.D. (1993 [1994]). The Moths of Borneo: part 11; Geometridae, subfamily Ennominae. Malayan Nature Journal 47: 1-309

Holloway, J.D. (2011). The Moths of Borneo: part 2; Families Phaudidae, Himantopteridae and Zygaenidae; revised and annotated checklist. Malayan Nature Journal 63 (1-2): 1-548.

Inoue, H. (2005). Illustrated and annotated catalogue of the genus Milionia and allied genera (Insecta: Lepidoptera, Geometridae, Ennominae). Tinea 18 (Suppl. 2): 27 pages + 49 plates.


Copyright
Text and photographs © 2017, R.C.Kendrick.
All rights reserved.
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