IUCN SSC Mid-Atlantic Island Invertebrates Specialist Group


BackArgyresthia minusculella Rebel, 1940

Argyresthia minusculella Rebel, 1940

Small ermine moth (English); Traça (Portuguese)

  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Class: Insecta
  • Order: Lepidoptera
  • Family: Yponomeutidae
EN Endangered
IUCN Red List Status:

Countries of Occurrence:
Portugal - Azores


Danielczak, A.

Nunes, R. & Lamelas-Lopez, L.

Facilitators / Compilers/s:

Assessment Rationale:

Argyresthia minusculella is an endemic species present in Flores, Pico and Terceira islands (Azores, Portugal) (Borges et al. 2010). It has a relatively large extent of occurrence (EOO =  8,889 km²), but a small area of occupancy (AOO = 28 km²). Currently Argyresthia minusculella is under threat due to degradation of the habitat by urban development and agriculture, but also due to invasive plants Pittosporum undulatum and Hedychium gardnerianum that are changing some of the areas and decreasing the quality of the habitat. Based upon the small area of occupancy, decreasing quality of the habitat and low number of populations it is assessed as Endangered.

Geographic Range:

Argyresthia minusculella is an endemic species present in Flores, Pico and Terceira islands (Azores, Portugal) (Borges et al. 2010), known from the Natural Forest Reserve of  Mistério da Prainha (Pico). The extent of occurrence (EOO) is ca 8,900 km² and the maximum estimated area of occupancy (AOO) is 28 km².

Portugal - Azores
Extent of Occurrence (EOO):
8900 (km2)
Area of Occupancy (AOO):
28 (km2)
Elevation Lower Limit:
50 (m)
Elevation Upper Limit:
800 (m)
Biogeographic Realms:
Endemic Azores


The species occurs in native forest from three islands, but in two of the island the historical localities were highly modified in the last decades. The species is particularly rare in terms of abundance in all these islands. This species is assessed here as severely fragmented, as it occurs in three isolated patches, one in each island (Flores, Pico and Terceira). At least 50% of its population can be found in subpopulations/in habitat patches that are 1) smaller than would be required to support a viable population, and 2) separated from other habitat patches by a large distance. In fact, the species occurs in three natural forest fragments that are isolated in a sea of pastures and Cryptomeria japonicaplantations. At least two of the locations will be under severe threat in the next 10 years due to the aggressive spread of the invasive plant Hedychium gardnerianum.

Habitat and Ecology

This species occurs mainly in the Azorean native forest. Possibly it is a specialist phytophagous that feeds preferentially on Ericaceae plants. The moth flies in June and July (Rebel 1940). Altitudinal range: 50-800 m.

Major Threat(s):

In the past, the species has probably strongly declined due to changes in habitat size and quality, mostly the creation of pastures  (Triantis et al. 2010). Two of the historical localities were recently highly modified by degradation of the habitat by urban development and agriculture. Currently invasive plants Pittosporum undulatum and Hedychium gardnerianum are changing some of the areas and decreasing the quality of the habitat. These changes are decreasing the relative cover of endemic plants and changing the soil cover (decreasing the cover of bryophytes and ferns). Based on Ferreira et al. (2016) the habitat will further decline as a consequence of climate change (increasing number of droughts).

Conservation Actions

The species is not protected by regional law. Its habitat is in regionally protected areas (Natural Parks of Flores and Pico). Degraded habitats should be restored and a strategy needs to be developed to address the future threat by climate change and ongoing impact of invasive species. It is necessary a monitoring plan for the invertebrate community in the habitat in order to learn about the ecological requirements of the species and the feeding substrate of the larva, and contribute to the conservation of this species. A habitat management plan with associated education outreach initiatives is needed and anticipated to be developed during the coming years. Further research is needed into its ecology (population size, distribution & trends) and life history in order to find extant specimens in additional sites. Monitoring every ten years using the BALA protocol will inform about habitat quality (see e.g. Gaspar et al. 2010). A taxonomic revision of Azorean Argyresthia, which should also include a comparisson of the DNA barcodes,  is needed to show how many species are present in the Azores islands.