The tansy beetle (Chrysolina graminis) is a species of leaf beetle. The common name derives from its main foodplant, tansy (Tanacetum vulgare), but it can also use other wetland plants such as gypsywort (Lycopus europaeus) and water mint (Mentha aquatica). It measures 7.7–10.5 mm in length and has a characteristic bright metallic green colouration, with pitted elytra and a coppery tinge. In addition to the nominotypical subspecies, which repeats the specific name, C. graminis graminis, there are five further distinct subspecies of tansy beetle, which, collectively, have a Palearctic distribution, although in the majority of countries where it is found the species is declining. In the United Kingdom it is designated as 'Nationally Rare'. Other, small, fenland populations exist at Woodwalton Fen and at Welney Wildfowl and Wetlands Trust (WWT) reserve.

Taxonomy

The tansy beetle was first described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae as Chrysomela graminis and was later transferred to the genus Chrysolina. The genus Chrysolina currently contains 39 subgenera. C. graminis (with its several subspecies) is located in the subgenus Euchrysolina which contains only one other species – C. virgata; this subgenus was first established in 1950.

Its specific name graminis is a form of the Latin noun gramen, meaning "of grass" or "grass-like". Chrysolina graminis sensu lato has at least three later binomial names which are considered to be synonyms: Chrysomela fulgida Fabricius, 1801, Chrysolina nigrocuprea Mallet, 1924, and Chrysolina taupini Mallet, 1924.

There are six subspecies of tansy beetle. The nominotypical subspecies C. graminis graminis was established via the original description of the species in 1758. C. graminis santonici (named after the Italian name, Santonico, for its host plant Artemisia caerulescens) was described by N. B. Contarini in 1847. In 1860 Victor Motschulsky described two subspecies – C. graminis artemisiae and C. graminis auraria. These were added to in the 20th century with C. graminis christianae (Mallet, 1933) and C. graminis mediterranea Bechyné, 1950.

The subspecies of C. graminis have localised distributions: C. graminis artemisiae is located in south-east Europe, central Asia, and southern Siberia; C. graminis auraria is located in Dauria, eastern Mongolia, and China; C. graminis christianae is located in France; C. graminis mediterranea is located in Corsica and Spain; C. graminis santonici is located in the central Alps. The body is dorsally bright green, the elytra mostly with golden-red or golden lateral margins and stripe near the suture. The iridescence on the elytra visibly contrasts with the head and pronotum. The punctuation on the elytra is easily visible by eye, but any punctuation is very difficult to see on the pronotum (with the exception of the side margins). There is a smooth lip running the entire length of the ventral edge of the elytra. Larvae are brown, and dorsally convex with spiracles evident on eight segments. The head of each larva is a darker brown than the body and has six ocelli on each side. The mandibles have five apical teeth. This has previously led to the misidentification of C. herbacea as C. graminis. C. herbacea measures 7–11 mm in length. It is coloured iridescent green on dorsal surface throughout. The punctuation on the pronotum and elytra is distinctly similar, unlike in C. graminis. There is a smooth lip running only half the length of the ventral edge of the elytra, whereas this lip runs the full length on C. graminis. The beetles may be found on tansy (Tanacetum vulgare) and water mint (Mentha aquatica) in fen land and the banks of rivers with broad floodplains in Britain. Larvae are also recorded from other host plants: Achillea ptarmica (sneezewort) in France and various plants of the genus Artemisia in Russia.

Distribution

In continental Europe, C. graminis is widespread from Scandinavia to the Mediterranean Sea. It may also be found in central Asia and China.

United Kingdom

In the United Kingdom, its range is currently restricted to about 45 km of the banks of the River Ouse centred on York, North Yorkshire. following this a translocation programme of Yorkshire beetles was attempted to boost the population. However, this was unsuccessful, likely due to potentially differing biologies between the two populations.

As of 2006 there were 19 British hectads (10 km squares) with records of the tansy beetle, but it has only been seen in 11 of these since 1970, six of which are centred around York. In 2015, the total number of individuals estimated from a survey of this area on the banks of the River Ouse was 24,000. In 2016 this number increased significantly to 40,000. Since 2018, the beetle has also been discovered at the Wildfowl and Wetlands Trust (WWT) reserve at Welney, west Norfolk.

Threats to habitat

The decline in C. graminis is likely to be due to habitat loss resulting from land improvement and arable conversion, over-grazing, development, drainage and lowering of water-tables due to over-abstraction. despite having fully working wings and being capable of doing so. The loss of habitat impacts upon the ability of the tansy beetle to find an alternative source of the host plant. Additionally, tansy is a ruderal species and thus has a naturally high rate of turnover of plants, forcing beetles to regularly seek out new tansy patches to colonise.

A 2009 study of tansy beetle occupancy amongst 1305 patches (stems separated by no more than 50 cm) of the tansy plant on the banks of the River Ouse (York, UK) intended to establish data on the distribution of tansy plants and relate this to existing tansy beetle populations in order to contribute to the conservation effort of the species. The results were analysed using generalised additive models to conclude that the tansy patches should be managed towards volumes of 3 m and that these patches should be targeted within 200 m of existing beetle subpopulations on the same river bank in order to help the beetle population disperse and survive.

Life cycle

thumb|right|Tansy ([[Tanacetum vulgare), a medicinal herb]]

Both adults and larvae use the same host plant during their life cycle. As tansy often grows in discrete clumps, the total population of C. graminis in an area may be divided and individuals may spend their entire life cycle within an area of a few square metres. Mated females lay batches of 3–15 elongated, yellow eggs (each 2 mm long) on the underside of the tansy leaves. The subspecies C. graminis santonico is associated with Artemisa caerulescens. The tansy beetle is resistant to these chemicals. However, tansy is a repellent to other Chrysomelid beetles. For example, the steam distillate of fresh leaves and flowers of tansy contains high levels of camphor and umbellulone and is strongly repellent to the Colorado potato beetle (Leptinotarsa decemlineata).

Predation

thumb|The [[scorpionfly Panorpa germanica has been observed preying on tansy beetle larvae.]]

thumb|Tansy beetle with damaged elytra on tansy flower heads

Beetle remains bearing what appeared to be the marks of bird attacks have been found by the River Ouse and hardened adults often bear symmetrically indented elytra, interpreted as 'pinch marks' inflicted by a beak whilst newly emerged adults are still hardening. Dead beetles have also been found in the webs of spiders in a captive population. The adult fly deposits fully incubated eggs or newly hatched larvae into the vicinity of the host larvae. all of which are common on the tansy around the York population.

Parasites

A mite, Chrysomelobia mahunkai (family Podapolipidae) has been recorded from a single adult specimen of C. graminis, and Eulophus chrysomela (a species of hymenopteran of the family Eulophidae) is recorded as an endoparasite of the pupal stage. A recovery programme started, involving annual surveys of both tansy and beetles, control of tree shading and invasive plants that compete with tansy, such as Himalayan balsam, and limited re-introductions within the current species range. New clumps of tansy have been planted, particularly between isolated existing patches which may be beyond the 200 m walking range of the beetle. That same year, a team of 30 volunteers surveyed a 90 km stretch of the banks of the River Ouse.

thumb|A stone plaque at Fulford Ings to the conservation efforts of the tansy beetle dedicated by the [[List of lord mayors of York|Lord Mayor of York]]

Public reception in York

thumb|Tansy beetle sculpture commemorating the archaeologist [[Mary Kitson Clark in the Museum Gardens, York]]

The Tansy beetle's relationship to York has led to it having a prominent public presence. In January 2022 a large mural depicting a tansy beetle was painted on a building on Queen's Street, York by street artist ATM. In August 2024 a series of 17 metal tansy beetle sculptures were displayed in York and decorated by local artists to highlight historical 'trailblazers' in the city. One of them, featuring the tansy beetle life cycle, can still be seen at St Nick's Nature Reserve & Environment Centre, York.

References

  • cycle/ Tansy beetle life cycle in images
  • Photographic comparison of tansy beetle and mint beetle
  • Distribution map showing range of tansy beetle on the River Ouse, North Yorkshire in 2009
  • Video of mating tansy beetles
  • List of published resources on Chrysolina graminis at Biodiversity Heritage Library