IUCN SSC Mid-Atlantic Island Invertebrates Specialist Group

Species

BackDrouetius borgesi Machado, 2009

Drouetius borgesi Machado, 2009

True weevil (English); Gorgulho (Portuguese)

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

Countries of Occurrence:
Portugal - Azores

Archipelago(s):
Azores

Reviewer/s:
Danielczak, A.

Contributor/s:

Facilitators / Compilers/s:


Assessment Rationale:

Drouetius borgesi is an endemic species with three subspecies: D. b. borgesi present in Terceira island; D. b. centralis present in Faial, Pico, S. Jorge and Graciosa islands and D. b. sanctmichaelis restricted to S. Miguel island (Azores, Portugal). It has a relatively large extent of occurrence (EOO = ca 11,600 km²) but a small area of occupancy (AOO = 92 km²).  The several populations are highly fragmented and located at mid to high altitudes mostly in natural habitats but also in some exotic plantations. Based on Ferreira et al. (2016) the habitat will further decline as a consequence of climate change (increasing number of droughts). Based upon the small area of occupancy, the decline in AOO and number of populations, the decreasing extent and quality of habitat, the species is assessed as Endangered (EN).

Geographic Range:

Drouetius borgesi is an endemic species with three subspecies: D. b. borgesi present in Terceira island; D. b. centralis present in Faial, Pico, S. Jorge and Graciosa islands and D. b. sanctmichaelis restricted to S. Miguel island (Azores, Portugal) (Borges et al. 2010). D. borgesi is known from Natural Forest Reserves of Caveiro (Pico); Pico Pinheiro (S. Jorge); Pico Galhardo, Serra de Sta Barbara and Terra Brava (Terceira); and Pico da Vara (S. Miguel). The extent of occurrence (EOO) is ca 11,600 km² and the maximum estimated area of occupancy (AOO) is 92 km².

Regions:
Portugal - Azores
Extent of Occurrence (EOO):
11600 (km2)
Area of Occupancy (AOO):
92 (km2)
Elevation Lower Limit:
300 (m)
Elevation Upper Limit:
1100 (m)
Biogeographic Realms:
Palearctic
Presence:
Extant
Origin:
Endemic Azores
Seasonality:
Resident

Population:

D. borgesi is a widespread and still an abundant species in some pristine sites. The species currently has a decreasing population density due to the spread of the invasive plant Hedychium gardnerianum that is changing the structure of the forest and the cover of bryophytes and ferns in the soil with impacts on the species.

Habitat and Ecology

This species has three subspecies: D. b. borgesi present in Terceira island, inhabits native forests (dominated by Juniperus brevifolia, Ilex perado subsp. azorica, Laurus azorica and Erica azorica) and Cryptomeria japonica plantations; D. b. centralis present in Faial, Pico, S. Jorge and Graciosa islands, inhabits in native and exotic forests, native plants on lavic formations (Erica azorica) and grasslands; and D. b. sanctmichaelis restricted to S. Miguel island, inhabits native forests. This species has an altitudinal range between 300 and 1100 m. Adults and larvae are herbivores and feed on plant tissues, mostly leafs and during the night. Based on seasonal data from SLAM traps obtained in several islands between 2012 and 2016, the adults are active all year, being most abundant in spring and summer.

Major Threat(s):

In the past, the species has probably strongly declined due to changes in habitat size and quality (Triantis et al., 2010; Terzopoulou et al., 2015). The most important ongoing threat to this species is the spread of invasive plants (e.g. Hedychium gardnerianum) that are changing the habitat structure, namely decreasing the cover of bryophytes and ferns in the soil and promoting the spread of other plants. 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 Pico S. Jorge, Terceira and S. Miguel). The Terceira Natural Park administration is currently starting control measures of the invasive plants. Degraded habitats should be restored and a strategy needs to be developed to address the future threat by climate change. A habitat management plan is needed and anticipated to be developed during the coming years. Since this species occurs in relict native Azorean forests, some awareness measures were put recently in practice using for instance images from extreme macro. Further research is needed into its ecology and life history in order to find extant specimens in more sites and obtain information on population size, distribution and trends. Monitoring every ten years using the BALA protocol will inform about habitat quality (see e.g. Gaspar et al. 2011).