The irrepressible march of the heather beetle……
I have had a few enquiries abut the current and devastating outbreak of Heather Beetle and so felt this technical note I wrote might be of wider interest.
Beetle plus larvae
Across areas of heather moorland and heath, like the Peak District National Park, or up in the North Yorks Moors for example, instead of the usual glorious purple swathes of colour rioting across the landscape, there is a dull brown. This is a heather-specific little herbivorous insect called the ‘heather beetle’ which can cause devastation to heathland.
The heather beetle or Lochmaea suturalis is a leaf-beetle or Chrysomelid. The adult beetle spends winter amongst moss or litter in the undergrowth of heather plants. At this stage they are in a dormant ‘diapause’, and remain as such until warmer spring weather brings a rise in soil temperature. This warmth brings the adults out of dormancy and they emerge, feed, and reproduce. Able to fly up to several miles after spring emergence, they generally only do this after fire, when heather in the immediate area is of poor quality, or if the heather has been replaced by grassland. The beetle does have a degree of resilience to adverse conditions and can survive for some time in grassland such as wavy hair-grass (Deschampsia flexuosa) for example.
So the big question is why is this year so bad and the beetle so devastating? Probably there is a big influence of hot weather and maybe climate change is having an impact. Heat and drought, and heather condition are important. It seems most likely that spring and summer conditions are the key and winter weather, such as cold, is less significant. Atmospheric pollution such as nitrogen fallout from things like car exhausts probably makes damage worse. On a particular site, the heather canopy structure has an impact too. Young heather shoots are the least affected. This means that seedlings and young re-growth are the least affected. The beetle needs about 50% heather cover too and so a greater mix of plant species and breaking up of heather age will help limit damage.
The beetle is behaving as a typical herbivore with the ability to breed fast and produce lots of offspring. Our glorious wide landscapes of massed heather are all it could ever desire!
A short review on current heather beetle status and control options was undertaken. Essentially, Natural England and Defra do not seem to have any robust current advice on how to proceed. There is an updated review from 2016 – A desk review of the ecology of heather beetle (NEER008), 2nd edition – June 2016, Natural England. However, the official view of possible control measures such as out-of-season burning for example seems to be ambivalent.
Some key points about the invasion are:
A. The beetle lifecycle is well-known and that might help in control measures;
B. A key thing will be knowing where they are and also maybe setting up some early-warning system / networking [GPS and uploading?] – So prompt action can be taken with new outbreaks;
C. Probably hot weather / climate change has an impact – heat and drought;
D. It is most likely that spring and summer conditions are the key and winter weather – such as cold, are less significant;
E. Atmospheric pollution e.g. nitrogen fallout makes damage worse;
F. Heather canopy structure has an impact with young heather least affected and the beetle needing about 50% heather cover – so breaking up heather age – and monocultures will help.
Much of the key work was done back in the 1970s / 1980s and followed outbreaks triggered by long hot, dry summers such as 1975 and 1976.
The 2010 report to the Heather Trust by Professor Rob Marrs at Liverpool is helpful. This report stresses the complexities of the outbreaks and the issues associated with them, and that current information (especially for upland areas) is very limited. However, they do make useful recommendations:
The role of management as a prevention and cure
Information is needed for three situations:
(1) Prevention, i.e. to try and stop outbreaks occurring in the first place;
(2) Control, where the aim is to minimise loss when an outbreak has occurred, and
(3) Recovery, where the aim should be to achieve rapid Calluna recovery.
The only current management options available for all three of these scenarios are to manipulate the management regime (burning, cutting, and grazing). Development of sound knowledge of the best approach to adopt would be to set up controlled experiments in a range of situations and formally assess the most appropriate methods for given situations. The treatments should include some of the common ones suggested for treating heather beetle(see the Moorland Association website), for example: (1) Burning affected Calluna-dominated land in mid-late summer when all the eggs have hatched and the larvae are feeding on the Calluna and therefore exposed; (2) Mowing the affected heather to expose the larvae to light and heat and removing their preferred moist conditions; and (3) Burning the grey-coloured dead Calluna early in the following year to provide conditions for seed germination and growth of new plants.
We suggest that these proposed methods; along with other combinations of different prescribed burning/cutting regimes need to be tested experimentally for Control and Restoration as defined above. Almost certainly this will involve attempts to compare “hot” versus “cool” burns to assess the importance of removal of the litter layer, and also restoration treatments such as re-seeding and perhaps also the use of graminicides if grass invasion is prolific (Todd et al,. 2000; Milligan et al., 2004).
‘The Heather Beetle: a review. Report to the Heather Trust’ by Angus Rosenburgh & Rob Marrs (2010)
The key issues appear to be
1) the condition of the sward, and the problem of large expanses of pure Calluna which are inherently vulnerable and especially so if single-aged;
2) Early warning of infestations and coordinated early interventions;
3) Longer-term strategic management to limit vulnerability;
and 4) Effective management to promote recovery following outbreaks.