Donacia aquatica – the zircon reed beetle
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Donacia aquatica (Linnaeus, 1758)
Family: Chrysomelidae
Donacia aquatica is a rainbow-coloured beetle found on sedges in early summer. It has one of the most restricted distributions of Irish leaf beetles.
In brief
- D. aquatica is currently only known from Inishfendra Island, Fermanagh, with old records for Counties Armagh and Down
- It is found on sedges (Carex spp.) near to water
- Adult beetles can be found from May to July, and then in very small numbers in the autumn
- It is listed as a UK Priority Species
- The main threat to this species is loss of marginal sedge beds, for example, through eutrophication and succession
- Recent discoveries in the Republic of Ireland, and rediscoveries in England and Scotland, indicate that targeted surveys could be successful in locating further colonies.
Species description
The adults are 6.8 to 9.6mm long and are strikingly coloured. They are gold on the undersurface, legs and thorax, with the elytra each having a broad reddish-purple, longitudinal band which is iridescent – light blue in the middle, then green, red, gold and finally green or greenish-blue to the sides. It flies readily to avoid capture and consequently individuals can be found on a range of aquatic plants other than sedges. The larvae are cream-coloured and maggot-like but with three pairs of short thoracic legs.
Life cycle
Adults overwinter during or close to the winter months, often in tough fibrous pupal cocoons. They become active in May and die out by July. Eggs are laid at the base of hostplants in early summer and larvae develop with their rear ends attached to roots under the water. The pupae, which are also attached to the air spaces in aquatic root systems, develop in late summer and some adults may be briefly active in September and October. All reed beetles are plant-feeders, but the host range of D. aquatica requires further study. The adult is known from lesser pond sedge (Carex acutiformis), beaked or bottle sedge (C. rostrata), bladder sedge (C. vesicaria) and several other species, but not great pond sedge (C. riparia). The only host plant recorded for the larvae of this species is, surprisingly, greater spearwort (Ranunculus lingua), but this requires confirmation.
Similar species
D. aquatica is one of nineteen species of reed beetle (Coleoptera, Donaciinae) recorded from Ireland. There should be little doubt about recognising such a distinctive beetle but two other species, Donacia marginata Hoppe, associated with bur-reeds, and D. vulgaris Zschach, mainly found on reedmaces (Typha spp.), have a similar combination of bright colours. In the field, the mainly green and red upper surface of D. aquatica and its golden underside, should set it apart. The individual species of Donacia larvae cannot be identified.
How to see this species
D. aquatica occurs at Inishfendra Island, Fermanagh, where it is found on sedges near to water. Adult beetles can be found from May to July, and then in very small numbers in the autumn. To see these beetles can be very difficult; one needs a long-handled sweep net or, more frequently, a good camera. Adult beetles are alert to movement and will at first move to the other side of a leaf to avoid detection, and then may fly off. Relevant access permissions should always be sought prior to visiting any sites.
Current status
D. aquatica is currently only known from Inishfendra Island, Fermanagh, with old records for Armagh and Down. Decline rates, based on comparison of data before and from 1980 onwards, indicate a 67% loss in Northern Ireland (but based on only three sites) and 41% loss in the Republic of Ireland. In Scotland, Wales and England, distributional data indicate an 81% loss of sites up to 1980 based on 10km square counts in Scotland, Wales and England, and an 86% decline to 1970 based on vice-county counts.
Why is this species a priority in Northern Ireland?
- Listed as a UK Priority Species
- Rare with Northern Ireland being the stronghold in Ireland.
Threats/Causes of decline
- Eutrophication of loughs, resulting in loss of marginal sedge beds
- Successional phenomena, such as encroachment of water margins by reedbeds and carr
- Excessive lake management may result in loss of sedge beds
- Excessive numbers of waterfowl will destroy vegetation and increase the risk of algal blooms.
Conservation of this species
Current action
There is a UK Species Action Plan which was published in 1999.
- The site for this species, Inishfendra Island, lies within the Upper Lough Erne Ramsar site, SPA and SAC. It is also designated as an ASSI
- Implementation of the Northern Ireland Habitat Action Plans for Fens, Reedbeds and Eutrophic Standing Waters.
Proposed objectives/actions
- Maintain populations at the known site.
What you can do
Keep an eye open for colourful beetles beside water but beware, there are more common species that are also brightly marked. Report any sightings to CEDaR at National Museums Northern Ireland, 153 Bangor Road, Cultra, Co. Down, BT18 0EU. Tel: 028 9039 5256 or Email: cedar.info [at] nmni.com, with a digital photograph if possible.
Further information
Links
NBN Gateway
Northern Ireland Habitat Action Plans
Literature
Foster, G.N. (2006). Unpublished reports to Scottish Natural Heritage and the Environment Agency.
Menzies, I.S. & Cox, M.L. (1996). Notes on the natural history, distribution and identification of British reed beetles. British Journal of Entomology and Natural History 9: 137-162, 2 plates.
Nilsson, A.N. (Ed.) (1996). Aquatic Insects of North Europe. Volume 1: Ephemeroptera, Plecoptera, Heteroptera, Megaloptera, Neuroptera, Coleoptera, Trichoptera and Lepidoptera. Apollo Books, Stenstrup.
Text written by:
Dr Garth Foster