Wednesday, 27 April 2011

Moths with flightless females: two New Zealand examples.

New Zealand is unique in the world, having a large number of endemic moth species with flightless females. During the midterm break I was lucky enough to see one of these when I went down to Riverton in Southland for a family reunion. After arriving in Southland with my father, step mum and new baby brother, we decided to go out to Tiwai Point to do some serious moth collecting before settling into our rental accommodation. After arriving at a coastal spot with low native vegetation, we proceeded to put out a light trap. This consisted of a Mercury Vapour light positioned on a white sheet and powered by a portable generator. While we were hoping for some moth species to come into light, me and my father walked down to the strip of grassland beside the beach and looked for a very unique moth species. The moth we were looking for was Asaphodes frivola and only known from a handful of localities in costal Southland. One male of this species was caught by Alfred Philpot, a New Zealand entomologist, around 100 years ago. It was then described in the UK by Edward Merick where the original specimen is now thought to be. Subsequent New Zealand entomologists such as George Hudson (famous for inventing day light savings) mentioned this species in one of his books, but because he didn’t have access to a specimen was not able to provide an illustration. Without an illustration and much information on its ecology, Asaphodes frivola remained un-collected for around 70 years, until in 1981, when it was rediscovered at Otatara by Brian Patrick (my Dad). Unlike the male which looks like a fairly typical moth, he found that the female had thin, scrunched up wings that can’t be used to fly with. Anyway, back at Tiwai point I was able to; with the help of my father find several males of Asaphodes frivola at the bases of native tussocks. These flew up once I had disturbed them and settled on the ground a few meters from where they had been disturbed. After a long search, I eventually located several of the well camouflaged females sitting in the tips of the native tussocks. When we arrived back at the light trap, we found that no moths had come into light. Only two flies were present. This demonstrates how some knowledge of an insect’s ecology can greatly increase the chance of finding it in the field.

Photograph 1: A female of Asaphodes frivola sitting on the lawn of our rental house in Riverton.

Other New Zealand moth species with flightless females include ghost moth and tiger moth species. The reason for the evolution of flightlessness is thought to be due to females maximising their egg laying potential as when you fly you need to worry about having a large, heavy egg-fulled body. The downside to flightlessness is that it can be harder to find mates. Females of the New Zealand ghost moths overcome this by releasing pheromones; these are picked up by male antennae (feelers) and followed to the highest concentration, to the female. It is thought that this species also used pheromones to attract males. One of the New Zealand ghost moths with a flightless female is Aoraia macropis. I was lucky enough to find this species in March of this year up the Old Man Range in Central Otago. At 1300m above sea level on a roadside wetland, a male of this species was observed. After several hours of searching, I was able to locate five females that were moving over the wetland depositing eggs every few seconds as they were walking. These females where then placed into a container with no lid. After a short time, many of the usually fast and hard to catch males flew close to the container and started to fly around it before eventually entering the container and trying to mate with the females located inside. As well as making the males more catchable, this demonstrated how the female uses pheromones to attract males. In the course half an hour, around 30 males came in showing the effectiveness of this strategy. 

Photograph 2: Two males (upper and lower left) and two females (upper and lower right) of Aoraia macropis collected up the Old Man Range.

Because these moths have flightless females, they are not as fast as species with flighted females at invading new habitats and reinvading ones that they have become locally extinct at. It is therefore of the upmost importance that the habitat of these moths is preserved.

You can find further information on the two moth species mentioned in the flowing references;
Asaphodes frivila: Patrick B. 1981. Notes on an interesting moth Asaphodes oraria at otatara near Invercargill. Weta 4, page 23. Asaphodes frivola is mentioned at the end of this paper where it was referred to as Asaphodes sp. Only after the publication of this paper was it figured out that it was a species that had already been named.

Aoraia macropis:
Dugdale J.S. 1994. Hepialidae (Insecta: Lepidoptera). Fauna of New Zealand 30, 164 pages. I also recommend taking a look at any of books written by George V. Hudson. Despite working in a post office he was a prolific entomologist and produced books on a large variety of New Zealand insects. These books contain magnificent plates.