noctua orbona (hufnagel) lunar yellow underwing larval surveys in the sandlings during 2002 to 2005

71 LUNAR YELLOW UNDERWING LARVAL SURVEY

Trans. Suffolk Nat. Soc. 41 (2005)

NOCTUA ORBONA (HUFNAGEL) LUNAR YELLOW UNDERWING LARVAL SURVEYS IN THE SANDLINGS

DURING 2002 TO 2005

A. W. PRICHARD

Introduction The Lunar Yellow Underwing Noctua orbona is a National Biodiversity Action Plan species of moth. In the latter half of the 20th Century the species underwent a national decline in its distribution and is now mainly known from areas of the Breck in Norfolk and Suffolk with only scattered colonies being found elsewhere in Britain.

The moth is in its adult phase (Plate 10) from June through to October, with aestivation (summer hibernation) occurring during the hotter mid-summer months, particularly July. It is a species associated with open dry habitats; acid and calcareous soils where fine-leaved grasses grow. It is in its larval stage (Plates 11 & 12) from September through to late April or May with the larvae feeding at night primarily on fine-leaved grasses. During the larval stage it may be readily found, where present, by searching with lights at night. The advantages of surveying for larvae are that the precise location and habitat used by the species can be identified and a more accurate assessment of populations can be achieved.

Map of all adult and larval Lunar Yellow Underwing records – half filled circles for adults and full circles for larvae.


Suffolk Natural History, Vol. 41 72

In the winter of 2001/2 Gerry Hagget et al. were formally surveying Breckland sites for N. orbona larvae, as part of a Butterfly Conservation (BC) sponsored survey (Haggett, 2002). Records of adult N. orbona attracted to light in the late 1990s seemed to suggest that populations of the moth may exist in the Sandlings area. In early 2002 nocturnal larval searches in the Sandlings located N. orbona larvae at two sites; Ipswich Golf Course and Rendlesham Forest.

For the winter of 2002/3 the BC sponsored survey was extended to include surveying for larvae in the Sandlings. The methodology used was aligned with that of the Breckland surveys being carried out by Gerry Haggett et al. and was reported in Haggett & Prichard (2003). Since then annual winter larval surveys have been carried out by members of the moth group in the Sandlings area using the same methodology and the results reported in Prichard (2004 and 2005).

Aims of the survey The aims of the survey during the first year of formal surveying were to better understand the species distribution within the Sandlings and to provide information on larval habitat and foodplant preferences that could be used for comparison/contrast with the survey work being carried in the Norfolk and Suffolk Brecks. Subsequent surveys, in addition to the above aims, have included a monitoring aspect in their aims.

During the first year’s survey larvae were found in fine-leaved grass habitats where a short sward resulted from rabbit grazing, an unusual habitat preference not previously noted in the Breckland surveys. Later surveys have sought to investigate the daytime resting places of larvae in this type of habitat.

Method Known areas of heathland in the Sandlings were identified and visited during the day to assess the habitat for its suitability for supporting N. orbona larvae. Identified suitable sites were then visited at night, when larvae were searched for with lights. The larva has a habit of climbing dried grass stems or other vegetation while it is dark and can be easily spotted in the light beam of a torch. The larva, with some experience, is readily identifiable and particularly in its early instars has a distinctive chocolate-coloured underside.

Experience of the larval habitat preferences from the Breckland survey proved useful in identifying potential survey sites in the Sandlings

Searches were carried out for noted periods of time with the number of larvae found being recorded. When this information is combined with the number of surveyors it allows the production of adjusted larval counts that can be used for comparison of results from different sites. This technique relies much on individual surveyor ability to locate larvae but the impact of this on the results of the surveys should be limited as the majority of survey work has been carried out by the same two to three surveyors.

Survey Site Descriptions Over the survey period 45 sites have been visited and surveyed. The following table summarises the details of each site surveyed.



Site name Grid reference Description

Aldringham Walks TM466611 Heather and Festuca clumps

Blaxhall Heath TM380565 Heather heathland with scattered clumps of Festuca

Ipswich Golf Course TM208432 Heathland golf course with scattered areas containing

mixture of Festuca and Agrostis

Martlesham Common TM243463 Acid grassland with primarily Festuca

Martlesham Heath TM237447 Acid grassland with primarily Festuca and other coarser grasses

Minsmere RSPB TM464671 Acid grassland, primarily Agrostis

North Warren RSPB TM455589 Acid grassland, recently cleared, with Agrostis and Festuca

Purdis Heath TM213427 Area cleared of bracken with recently established Agrostis

Rendlesham Forest Site A TM344506 Acid grassland with mixture of Festuca and Agrostis, scattered

bramble clumps

Rendlesham Forest Site B TM345505 Acid grassland with primarily Agrostis

Rendlesham Forest Site C TM354486 Forest track verge with mixture of Festuca and Agrostis

Rendlesham Forest Site D TM350480 Forest track verge with mixture of Festuca and Agrostis

Rendlesham Forest Site E TM345475 Forest track verge with mixture of Festuca and Agrostis

Rendlesham Forest Site F TM354473 Heather with clumps of Festuca

interspersed

Rendlesham Forest Site G TM362477 Forest track verge with mainly Agrostis

Rendlesham Forest Site H TM304493 Forest track verges with mainly Agrostis

Rendlesham Forest Site I TM3350 Acid grassland, with primarily Agrostis and occasional bramble

clumps and conifers

Rendlesham Forest Site J TM346471 Forest track verge, with primarily Festuca

Table 1 Details of Survey Sites




Rendlesham Forest Site K TM359466 Roadside verge, with Agrostis

and Festuca and other grasses, overshadowed by trees

Rendlesham Forest Site L TM357465 Forest track verge, mixture of Agrostis and Festuca with

heather and bracken

Rendlesham Forest Site M TM358464 Forest track verge, heather, Agrostis and Festuca and

bracken Rendlesham Forest Site N TM329491 Acid grassland, primarily

Festuca, with heather clumps

and birch scrub

Rendlesham Forest Site O TM334502 Acid grassland, primarily Agrostis, with clumps of

willowherb and wood-sage Rendlesham Forest Site P TM337493 Acid grassland with scattered

gorse and bracken, grass

primarily Festuca

Rendlesham Forest Site Q TM357496 Forest ride with heather and rough grasses with a small

proportion of fine-leaved grasses Rushmere Heath Site A TM198445 Mixture of heather and Festuca

Rushmere Heath Site B TM202447 Recently cleared area of heathland, with colonisation by

fine-leaved grasses, primarily Deschampsia

Rushmere Heath Site C TM203448 Small area of Festuca next to golf course fairway

Rushmere Heath Site D TM202449 Area cleared of gorse with newly established fine-leaved grasses,

primarily Agrostis

Sutton Heath TM306476 Acid grassland with Festuca and Agrostis

Thorpeness Golf Course TM457607 Acid grassland with Festuca and Agrostis with heather and

bracken, managed by mowing Tunstall Common Site A TM377553 Heather with areas of acid

grassland, alongside track, with

birch scrub

Table 1 continued




Tunstall Common Site B TM375547 Acid-grassland, grasses primarily

Festuca and Agrostis

Tunstall Common Site C TM377548 Clumps of primarily Agrostis

amongst heather

Tunstall Common Site D TM375551 Acid-grassland, with some heather and gorse, grasses

primarily Festuca

Tunstall Common Site E TM374547 Acid-grassland, primarily Agrostis and Festuca

Tunstall Forest Site A TM390554 Heather and acid grassland along forest track, predominantly

Festuca

Tunstall Forest Site B TM384554 Rough grassy area with gorse and heather along forest track,

predominantly Festuca

Tunstall Forest Site C TM396550 Heather and acid grassland strip along forest track, predominantly

Festuca

Upper Hollesley Common Site A

TM333472 Unmanaged area of acid grassland, predominantly

Festuca

Upper Hollesley Common Site B

TM332473 Unmanaged area of acid grassland, predominantly

Festuca

Walberswick, East Hill TM482739 Acid grassland with mixture of Festuca and Deschampsia

Wenhaston Black Heath TM423748 Heather and acid grassland mosaic, predominantly Festuca

Westleton Common TM442686 Heather with some areas of Festuca

Westleton Heath TM457696 Predominantly heather with areas of Festuca interspersed

Summaries of larval counts Adjusted larval counts remove the variation in larval counts produced by differing lengths of search periods and the number of people searching.

The formula used for calculating adjusted larval counts is as follows :

Adjusted larval count = (60 × larval count)/( search period in minutes × no of surveyors)

Table 1 continued



Date time

mins

No.

recorders

temp

°C

Site no: location

actual adjusted

14.12.02 65 18 8 2 7·5 Rendlesham Forest Site A

21.12.02 110 4 1 2 7 Rendlesham Forest Site I

27.12.02 60 16 5 3 8 Rendlesham Forest Site G

27.12.02 60 14 5 3 8 Rendlesham Forest Site F

28.12.02 60 0 0 2 8·5 Tunstall Common Site A

28.12.02 45 50 33 2 8·5 Tunstall Common Site B

14.01.03 20 9 9 3 9 Tunstall Forest Site A

14.01.03 20 4 4 3 9 Tunstall Forest Site B

14.01.03 45 3 1 3 9 Tunstall Forest Site C

16.01.03 30 0 0 2 6 Rendlesham Forest Site J

16.01.03 40 28 21 2 6 Rendlesham Forest Site E

16.01.03 45 23 15 2 6 Rendlesham Forest Site C

24.01.03 145 29 12 1 7·5 Ipswich Golf Course

26.01.03 65 30 9 3 12 Thorpeness Golf Course

26.01.03 25 0 0 3 13 Aldringham Walks

07.02.03 45 18 8 3 7 Sutton Common

07.02.03 15 30 51 2* 7 Upper Hollesley Common

07.02.03 35 2 1 3 7 Rendlesham Forest Site H

08.02.03 25 30 36 2 7·5 Rendlesham Forest Site D




23.02.03 30 9 9 2 5·5 Tunstall Common Site C

25.02.03 50 51 15 4 5 Rendlesham Forest Site A

25.02.03 30 28 14 4 5 Rendlesham Forest Site B

03.03.03 60 12 4 3 7·5 North Warren

07.03.03 60 23 11 2 7·5 Martlesham Heath


20.03.03 25 1 1 2 4·5 Rendlesham Forest Site E

20.03.03 30 0 0 2 2·5 Rendlesham Forest Site C

25.03.03 60 0 0 3 1·5 Rendlesham Forest Site G


14.04.03 40 11 8 2 13 Rendlesham Forest Site D

17.04.03 50 8 5 2 7 Tunstall Common Site D

17.04.03 15 1 2 2 6 Tunstall Common Site B

N. orbona numbers

*2 for 15 mins, 1 for 5 mins

Table 2. Summary of larval counts for 2002–3

The following three tables summarise for each year the N. orbona counts made at each visit to a survey site



Date time

mins

No.

recorders

temp

°C

Site no: location

actual adjusted


05.01.04 30 21 21 2 9 Tunstall Common Site E


05.01.04 15 1 2 2 9 Tunstall Common Site A




19.01.04 20 15 15 3 10 Upper Hollesley Common Site A

19.01.04 30 0 0 3 10 Rendlesham Forest Site K

19.01.04 15 0 0 3 10 Rendlesham Forest Site M

19.01.04 15 3 4 3 10 Rendlesham Forest Site L

23.01.04 25 0 0 3 7·5 Blaxhall Heath

23.01.04 20 2 2 3 7·5 Tunstall Common Site C


31.01.04 15 2 4 2 11·5 Rendlesham Forest Site N

02.02.04 25 6 5 3 12 Rendlesham Forest Site N

02.02.04 30 9 6 3 12 Rendlesham Forest Site O



13.02.04 35 2 1 3 7·5 Rendlesham Forest Site G

13.02.04 30 47 31 3 7·5 Rendlesham Forest Site F



05.03.04 45 2 1 2 4·5 Tunstall Forest Site C

05.03.04 50 10 6 2 4·5 Tunstall Forest Site A


06.03.04 20 16 16 3 4·5 Tunstall Common Site E

06.03.04 15 2 3 3 4 Tunstall Common Site C

13.03.04 40 12 5 4 7 East Hill, Walberswick

13.03.04 35 0 0 4 6·5 Westleton Heath





21.03.04 25 1 1 3 8·5 Sutton Common

21.03.04 20 14 14 3 8·5 Upper Hollesley Common Site A

21.03.04 20 5 5 3 8·5 Upper Hollesley Common Site B


01.04.04 15 8 11 3 11·5 Purdis Heath

03.04.04 30 2 1 3 10·5 Minsmere RSPB Reserve





N. orbona

numbers





Date time

mins

N. orbona

numbers

No.

recorders

temp °

C

Site no: location

actual adjusted



12.12.04 35 8 14 1 6 Martlesham Common






23.12.04 25 119 71 4 12 Upper Hollesley Site A

23.12.04 20 72 72 3 12 Upper Hollesley Site B

23.12.04 15 48 48 4 11·5 Sutton Heath

29.12.04 15 8 16 2 10 Rushmere Heath Site A

29.12.04 15 59 118 2 10 Rushmere Heath Site B

29.12.04 8 19 71 2 10 Rushmere Heath Site C

29.12.04 10 58 174 2 10 Rushmere Heath Site D

29.12.04 17 52 92 2 10 Purdis Heath

30.12.04 20 17 26 2 8 North Warren

30.12.04 25 10 12 2 8 Westleton Common

31.12.04 35 105 60 3 8 Rendlesham Forest Site P

31.12.04 20 2 2 3 4·5 Rendlesham Forest Site Q

31.12.04 15 18 24 3 2·5 Rendlesham Forest Site A

02.01.05 45 14 19 1 6 Martlesham Heath





07.01.05 35 0 0 2 11 Rendlesham Forest Site F







03.02.05 25 44 53 2 7 Martlesham Common

04.02.05 45 24 16 2 7 Wenhaston Black Heath

04.02.05 20 14 21 2 7 Thorpeness Golf Course







Results and Discussion

Distribution and abundance Over the three years of surveying N. orbona larvae were found at forty survey sites within the Sandlings area of Suffolk, with the majority of sites occurring in the more southerly heathland areas. The species was found to be more widespread and abundant than previously accepted based on records of adults at light. This finding is conservation significance as this population of the moth now represents the largest known population of the moth in the country after the Breckland population.

Adjusted larval counts from several of the Sandling sites have been significantly higher than any from the Breckland sites, suggesting that some of the Sandling habitats support a higher density of the larvae and presumably adult moth. Why this should be has not yet been established but climactic conditions will certainly vary between the two areas with the Sandlings areas having milder winters closer to the coast. Larval mortality is rather high and may be due to a number of factors, including parasitism. Most larval predators maybe inactive during the winter months but parasitic wasps were often observed searching the grass for larvae (not necessarily just for N. orbona larva) and later parasite cocoons were found on grass stems at survey sites.

Habitats The larvae utilise variations of the broadly classified acid-grassland habitat found within the Sandlings. The following three types of acid-grassland produced high larval counts during the surveys

• A dense sward consisting of Festuca clumps with no other grass species of note, at Upper Hollesley Common Site A.

• A tufted sward containing of a mixture of Festuca and Agrostis clumps, with bare patches between clumps, at Tunstall Common Site B and E

• Forest ride-side grass verges consisting of very short swards (due to rabbit grazing) with only a few Agrostis stalks upon which N. orbona larvae were mainly found, at Rendlesham Forest Sites D and E.

Table 4 continued





27.03.05 25 5 12 1 9 Upper Hollesley Site A



Date time

mins

N. orbona

numbers

No.

recorders

temp °

C

Site no: location

actual adjusted



The latter type of sites (track-side short sward grass verges – termed ‘lawn’ sites) would appear to offer the greatest contrast in habitat preference with the Breckland populations where a short sward due to sheep grazing is not beneficial. The grass verges would appear to be predominantly Agrostis with occasional scattered dry stalks that the larvae climb up during the hours of darkness. Our experience from the sites surveyed was that these short swards maintained by rabbit grazing supported above average numbers of N. orbona larvae. This presumably indicates that there will be some difference between the short swards due to sheep grazing and those due to rabbit grazing that is important to N. orbona larvae.

Larval foodplants Larvae were rarely noted feeding during the earlier instars and even in later instars sightings of feeding were not commonplace given the numbers of larvae found. Historically it appears that the foodplants of this species were not well known with some books listing ‘various grasses and lowing-growing plants’ and others not even listing the foodplants. Based on the results of the surveys it would appear that the two main foodplants used within the Sandlings are Festuca and Agrostis and to a lesser extent Deschampsia flexuosa and Holcus. Deschampsia is not a particularly common grass in the Sandlings compared with Festuca and Agrostis but is used by the larvae when present. Larvae reared in captivity will accept coarser grasses and feed up well on them.

Daytime resting site The generally accepted daytime behaviour of N. orbona larvae is that they spend the day sheltered within the bases of clumps of their foodplant. Other larvae of species in this group of moths are known for burrowing into the soil during the daytime but N. orbona is not generally recognised to have this behaviour. The ‘lawn’ sites have a very short sward (approximately 1–1·5 cm) over much of their area and would appear to offer very little cover for the larger larvae to hide up in during the day. Surveys made in April 2003 at these sites when final instar larvae were present showed that these large larvae could still be found in areas with a very short sward. As the larvae are thought to be relatively sedentary it is possible that they might be burrowing into the soil, although this remains to be confirmed. Attempts to verify this in subsequent years has not been possible due to low numbers of late instar larvae in these habitats.

Conservation Almost all survey sites within the Sandlings have been managed by means other than sheep-grazing. In the Brecks it has been shown that sheep-grazing has a detrimental effect on larval counts and presumably following from that on the population of the moth. It is a concern that sheep-grazing may be introduced as a more widespread habitat management regime on the Sandlings heaths and have a comparable effect on the population of this species as it has in the Brecks.

Other significant threats to suitable habitat are encroachment of the habitat by other plants, most notably bracken and to a lesser extent Carex arenaria



sand sedge. Larvae were rarely found in any numbers in areas of grassland where there is more than a scattered covering of bracken. During the winter any bracken present will have died back and so appears to have little impact on the habitat but it must be remembered that when the adult moth is laying eggs in late summer the bracken will alter the structure of the habitat and may cause shading of the foodplant.

Some evidence has been found of the moth readily exploiting newly created habitats during the last two winters. At Purdis Heath an area cleared of bracken and colonised by Agrostis in scattered clumps produced significant numbers of larvae. At Rushmere Heath where gorse clearance has opened up areas that have been colonised by fine-leaved grasses, mainly Deschampsia and Agrostis, larval counts were again significantly high.

For monitoring of populations the period from December to January with its higher larval counts is the preferred time for surveying. Sites should also be visited on more than one occasion as counts may vary from night to night, even under apparently similar weather conditions. The surveying carried out so far has produced base line data against which the status of populations in future surveys may be assessed.

Acknowledgements I would like to thank those who helped with the larval surveying, most notably Neil Sherman and Graham Bull who have spent many hours with myself in the field carrying out the surveys, and also Matthew Deans, Steve Woolnough, Mark Nowers, Nick Mason and Jon Clifton.

I would like to thank Gerry Haggett who provided invaluable assistance and guidance in the initial stages of the survey on the types of habitat to search and tips on larval identification.

I would also like to thank the landowners who gave the group permission to carry out surveys on their land; Richard Davies (Forest Enterprise), Tunstall Parish Council, Dave Thurlow (RSPB), Adam Burrows (English Nature), Robin Harvey (RSPB) and Thorpeness Golf Club.

Finally I would like to thank Butterfly Conservation who provided general support during the survey and financial assistance to cover travel expenses during the first year of the survey.

References Haggett, G. M. (2002). Lunar Yellow Underwing Noctua orbona (Hufnagel),

larval survey in Norfolk and Suffok Breckland. Haggett, G. M. & Prichard, A. W. (2003). Lunar Yellow Underwing Noctua

orbona (Hufnagel) larval survey in Norfolk and Suffolk Breckland and Suffolk Sandlings. Butterfly Conservation.

Prichard, A. W. (2004). Lunar Yellow Underwing Noctua orbona (Hufnagel), larval survey in the Suffolk Sandlings during 2003–2004. Suffolk Moth Group.

Prichard, A. W. (2005). Lunar Yellow Underwing Noctua orbona (Hufnagel), larval survey in the Suffolk Sandlings during 2004–2005. Suffolk Moth Group.

A. W. Prichard, 3 Powling Road, Ipswich, Suffolk, IP3 9JR

Plate 10: Lunar Yellow Underwing (Noctua orbona) adult – Rendlesham Forest (2003), reared (p. 71).

A. W

. P

richard

Plate 11: Lunar Yellow Underwing, Tunstall Common (23 February 2003). Early instar larva showing darker underside and habit of resting on dried grass stems (p. 71).

A. W

. P

richard

Plate 12: Lunar Yellow Underwing larva – final instar (Rendlesham Forest, 14 April 2003) (p. 71).

A. W

. P

richard

noctua orbona (hufnagel) lunar yellow underwing larval surveys in the sandlings during 2002 to 2005

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