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Individual study: Rosy marsh moth Coenophila subrosea does not decline in the absence of fire, on a lowland raised mire at the Dyfi National Nature Reserve, Ceredigion, Wales

Published source details

Fowles A.P., Bailey M.P. & Hale A.D. (2004) Trends in the recovery of a rosy marsh moth Coenophila subrosea (Lepidoptera, Noctuidae) population in response to fire and conservation management on a lowland raised mire. Journal of Insect Conservation, 8, 149-158


The rosy marsh moth caterpillar Coenophila subrosea feeds mainly on bog myrtle Myrica gale. In the UK, it is found at five raised bog sites in mid-Wales. Measures to prevent fire had been implemented at one of these sites, the Cors Fochno raised mire on the Dyfi National Nature Reserve, Ceredigion, since 1968. There was concern that lack of fire could adversely affect the rosy marsh moth, which was thought to rely on frequent fires to generate new growth of its host plant. This study examined the long term impact of lack of fire on the moth population at the site.

Following an accidental fire in February 1986, rosy marsh moth larvae were monitored in fourteen 15 x 1 m permanent quadrats along a single transect, with seven in the burnt part and seven in the unburnt part of the raised mire. The unburnt area had experienced no fire for at least 30 years. Feeding moth larvae were counted between 23:00 and 03:00 h once every year from 1988 until 2003, on or near 20 May.

No further fires occurred. Management work aimed at reducing drainage continued, with large drains and peat cuttings around the mire being blocked.

There was no general decline in rosy marsh moth numbers in the absence of fire, and no long term beneficial effect of fire. A total of 436 larvae were recorded on the transect over the 16 years (1998-2003), with 238 found on the unburnt section and 198 on the burnt section.

In the first three years of monitoring (1988-1991) rosy marsh moth larvae were absent or scarce on the burnt quadrats (7 larvae found over three years compared to 36 in unburnt quadrats). From 1993 onwards, similar numbers were found on burnt and unburnt sections. The highest numbers of moth larvae were recorded in 2002, 14 years after the fire, when over 80 larvae were found in total.

The water table height increased from 42 cm to 48 cm above the five year mean during the 16 years. Growth studies on bog myrtle showed that in the centre of raised mire it frequently dies back. There was no evidence for the moth selecting shorter, younger stems.

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