The thistle tortoise beetle (''Cassida rubiginosa'') is a species of
beetle
Beetles are insects that form the Taxonomic rank, order Coleoptera (), in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 40 ...
in the
subfamily
In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...
Cassidinae
The Cassidinae (tortoise and leaf-mining beetles) are a subfamily of the leaf beetles, or Chrysomelidae. The antennae arise close to each other and some members have the pronotal and elytral edges extended to the side and covering the legs so a ...
(tortoise beetles) and the genus ''
Cassida
''Cassida'' is a large Old World genus of tortoise beetles in the subfamily Cassidinae. The natural history of Cassida sphaerula in South Africa is a typical life cycle. Several species of ''Cassida'' are important agricultural pests, in partic ...
.'' The thistle tortoise beetle can be recognized by its green, rounded back and it can be found on
thistle
Thistle is the common name of a group of flowering plants characterized by leaves with sharp spikes on the margins, mostly in the family Asteraceae. Prickles can also occur all over the planton the stem and on the flat parts of the leaves. T ...
plants in many regions of
North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
and
Europe
Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
. The thistle tortioise beetle was first discovered in 1902 in
Lévis
Lévis () is a city in eastern Quebec, Canada, located on the south shore of the St. Lawrence River, opposite Quebec City. A ferry links Old Quebec with Old Lévis, and two bridges, the Quebec Bridge and the Pierre-Laporte Bridge, connect we ...
,
Quebec
Quebec is Canada's List of Canadian provinces and territories by area, largest province by area. Located in Central Canada, the province shares borders with the provinces of Ontario to the west, Newfoundland and Labrador to the northeast, ...
. In 1931, Nellie F. Paterson was the first to document the mature
larva
A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...
. Later, the
instar
An instar (, from the Latin '' īnstar'' 'form, likeness') is a developmental stage of arthropods, such as insects, which occurs between each moult (''ecdysis'') until sexual maturity is reached. Arthropods must shed the exoskeleton in order to ...
larva of this species was first recorded in 2004 by Jolanta Świętojańska. The thistle tortoise beetle exhibits multiple defense behaviors, such as a flexible shield, providing a barrier against the mandibles of predators, and an
excretion
Excretion is elimination of metabolic waste, which is an essential process in all organisms. In vertebrates, this is primarily carried out by the lungs, Kidney (vertebrates), kidneys, and skin. This is in contrast with secretion, where the substa ...
that protects the
egg
An egg is an organic vessel grown by an animal to carry a possibly fertilized egg cell (a zygote) and to incubate from it an embryo within the egg until the embryo has become an animal fetus that can survive on its own, at which point the ...
s as well.
Its ability to massively consume and damage
thistle plants has also made this beetle a well known
biological control agent
Biological control or biocontrol is a method of controlling pests, whether pest animals such as insects and mites, weeds, or pathogens affecting animals or plants by using other organisms. It relies on predation, parasitism, herbivory, or ot ...
in many countries, including the
United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
,
Canada
Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...
, and
Switzerland
Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...
. However, in some cases, the impact of these beetles has been limited due to
parasitism
Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...
preventing their accumulation in regions of thistle targeted for biological control.
Description
The thistle tortioise beetles measure 6.0–8.0 mm in length. Like all ''Cassida'', its head is covered by the
pronotum
The prothorax is the foremost of the three segments in the thorax of an insect, and bears the first pair of legs. Its principal sclerites (exoskeletal plates) are the pronotum (dorsal), the prosternum (ventral), and the propleuron (lateral) on e ...
, and the
elytra
An elytron (; ; : elytra, ) is a modified, hardened forewing of beetles (Coleoptera), though a few of the true bugs (Hemiptera) such as the family Schizopteridae are extremely similar; in true bugs, the forewings are called hemelytra (sometime ...
has a wide flange surrounding it. This species is highly rounded, with green or yellowish-green elytra, sometimes with a small, dark triangular spot around the
scutellum. The common name may be misleading for the identification of this species as rubiginosus, which is
Latin
Latin ( or ) is a classical language belonging to the Italic languages, Italic branch of the Indo-European languages. Latin was originally spoken by the Latins (Italic tribe), Latins in Latium (now known as Lazio), the lower Tiber area aroun ...
for "rusty or rust-coloured".
However, in preserved conditions, the green color quickly becomes brown.
Taxonomy
The thistle tortoise beetle belongs to the
Cassidinae
The Cassidinae (tortoise and leaf-mining beetles) are a subfamily of the leaf beetles, or Chrysomelidae. The antennae arise close to each other and some members have the pronotal and elytral edges extended to the side and covering the legs so a ...
subfamily
In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end botanical subfamily names with "-oideae", and zo ...
, which is part of the
Chrysomelidae
The beetle family Chrysomelidae, commonly known as leaf beetles, includes over 37,000 (and probably at least 50,000) species in more than 2,500 genera, making it one of the largest and most commonly encountered of all beetle families. Numerous s ...
family in the order
Coleoptera
Beetles are insects that form the Taxonomic rank, order Coleoptera (), in the superorder Holometabola. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 40 ...
. Cassidinae makes up around 16% of the Chrysomelidae species and represents the second largest sub-clade within the Chrysomelidae family.
Cassidinae was first seen during the late Jurassic period, and they have evolved into approximately 6,000 species that can be arranged into 43 tribes. Cassidinae species commonly serve as biological control agents for overgrown plants.
Distribution and habitat
This beetle inhabits
North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
and can be commonly found from
South Dakota
South Dakota (; Sioux language, Sioux: , ) is a U.S. state, state in the West North Central states, North Central region of the United States. It is also part of the Great Plains. South Dakota is named after the Dakota people, Dakota Sioux ...
to
Virginia
Virginia, officially the Commonwealth of Virginia, is a U.S. state, state in the Southeastern United States, Southeastern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States between the East Coast of the United States ...
within the
United States
The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...
. In
Canada
Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...
, it is found across several provinces, spanning from
Alberta
Alberta is a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...
to
New Brunswick
New Brunswick is a Provinces and Territories of Canada, province of Canada, bordering Quebec to the north, Nova Scotia to the east, the Gulf of Saint Lawrence to the northeast, the Bay of Fundy to the southeast, and the U.S. state of Maine to ...
. In
Europe
Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...
, it can be encountered from
Fennoscandia
__NOTOC__
Fennoscandia (Finnish language, Finnish, Swedish language, Swedish and ; ), or the Fennoscandian Peninsula, is a peninsula in Europe which includes the Scandinavian Peninsula, Scandinavian and Kola Peninsula, Kola peninsulas, mainland ...
to
Greece
Greece, officially the Hellenic Republic, is a country in Southeast Europe. Located on the southern tip of the Balkan peninsula, it shares land borders with Albania to the northwest, North Macedonia and Bulgaria to the north, and Turkey to th ...
and
Spain
Spain, or the Kingdom of Spain, is a country in Southern Europe, Southern and Western Europe with territories in North Africa. Featuring the Punta de Tarifa, southernmost point of continental Europe, it is the largest country in Southern Eur ...
. It is also found in
Great Britain
Great Britain is an island in the North Atlantic Ocean off the north-west coast of continental Europe, consisting of the countries England, Scotland, and Wales. With an area of , it is the largest of the British Isles, the List of European ...
and across
Siberia
Siberia ( ; , ) is an extensive geographical region comprising all of North Asia, from the Ural Mountains in the west to the Pacific Ocean in the east. It has formed a part of the sovereign territory of Russia and its predecessor states ...
.
In these regions, they live in areas where there are plenty of thistle. For example, these can include fields,
pasture
Pasture (from the Latin ''pastus'', past participle of ''pascere'', "to feed") is land used for grazing.
Types of pasture
Pasture lands in the narrow sense are enclosed tracts of farmland, grazed by domesticated livestock, such as horses, c ...
s,
orchard
An orchard is an intentional plantation of trees or shrubs that is maintained for food production. Orchards comprise fruit tree, fruit- or nut (fruit), nut-producing trees that are generally grown for commercial production. Orchards are also so ...
s,
meadow
A meadow ( ) is an open habitat or field, vegetated by grasses, herbs, and other non- woody plants. Trees or shrubs may sparsely populate meadows, as long as they maintain an open character. Meadows can occur naturally under favourable con ...
s, and
farmland
Agricultural land is typically land ''devoted to'' agriculture, the systematic and controlled use of other forms of lifeparticularly the rearing of livestock and production of cropsto produce food for humans. It is generally synonymous with bot ...
. The types of thistles they reside on include the
Canada thistle
''Cirsium arvense'' is a perennial species of flowering plant in the family Asteraceae, native throughout Europe and western Asia, northern Africa and widely introduced elsewhere.Joint Nature Conservation Committee''Cirsium arvense'' The standa ...
, the
bull thistle
''Cirsium vulgare'', commonly known as spear thistle, bull thistle, or common thistle, is a species of the Asteraceae genus ''Cirsium'', native throughout most of Europe (north to 66°N, locally 68°N), Western Asia (east to the Yenisei Valley) ...
, the
musk thistle
''Carduus nutans'' is a biennial plant in the daisy and sunflower family Asteraceae with the common names musk thistle, nodding thistle, and nodding plumeless thistle. It is native to regions of Europe, Central Asia, and North Africa, where it is ...
, the
plumeless thistle, and the
field thistle
''Cirsium discolor'', the field thistle, is a North American species of plants in the tribe Cardueae within the family Asteraceae. It is native to thirty-three states in the United States as well four Canadian provinces. It occurs across much of ...
.
Ecology
Diet
''C. rubiginosa'' feeds on various
Asteraceae
Asteraceae () is a large family (biology), family of flowering plants that consists of over 32,000 known species in over 1,900 genera within the Order (biology), order Asterales. The number of species in Asteraceae is rivaled only by the Orchi ...
, including thistles and many others.

Thistle beetle
larva
A larva (; : larvae ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects, some arachnids, amphibians, or cnidarians typically have a larval phase ...
e mainly stay on the leaves they were hatched on throughout their development and feed on them.
The adults are usually found on the underside of the leaves and the larvae on the uppersides. The time it takes for them to begin feeding depends on a few factors relating to the leaf's structure. The larvae wait until the thistle plants grow by 30% and for the
nitrogen
Nitrogen is a chemical element; it has Symbol (chemistry), symbol N and atomic number 7. Nitrogen is a Nonmetal (chemistry), nonmetal and the lightest member of pnictogen, group 15 of the periodic table, often called the Pnictogen, pnictogens. ...
levels in the leaves to drop by 50% before feeding. The time that they start feeding also affects the growth of the thistle plant. The plant's upward-growing capability is inhibited when feeding starts late in the season. However, no effect on the plants is detected when feeding begins in the early season. '
Adult feeding can damage the leaves more significantly than larvae feeding since they do not begin eating from the edges of the leaf but instead begin at the center and eat down from the surface.
Adults may also feed on pollen of
buttercups
''Ranunculus'' is a large genus of about 1750 species of flowering plants in the family Ranunculaceae. Members of the genus are known as buttercups, spearworts and water crowfoots.
The genus is distributed worldwide, primarily in temperate an ...
and
ox-eye daisies.
The beetle's consumption of these plants is facilitated by a
symbiotic
Symbiosis (Ancient Greek : living with, companionship < : together; and ''bíōsis'': living) is any type of a close and long-term biolo ...
relationship with the bacteria ''
Stammera'', which is housed in specialized structures within the
foregut
The foregut in humans is the anterior part of the alimentary canal, from the distal esophagus to the first half of the duodenum, at the entrance of the bile duct. Beyond the stomach, the foregut is attached to the abdominal walls by mesentery. ...
and allows the beetle to digest
pectin
Pectin ( ': "congealed" and "curdled") is a heteropolysaccharide, a structural polymer contained in the primary lamella, in the middle lamella, and in the cell walls of terrestrial plants. The principal chemical component of pectin is galact ...
, which is indigestible to most animals.
Predators
Larvae predators include ants and
lycosid spiders. Oftentimes, the egg excreta after being laid that engulfs the eggs are able to protect them from predators that target them. Later in development, the larvae's shield can protect them from ant attacks, but not from larger predators like lycosid spiders.
Other predators include the
coccinellid beetles. Similar to ant attacks, coccinellid beetles with their short mandibles had trouble attacking thistle tortoise beetles. However, the thistle tortoise can't protect themselves against those with longer mandibles.
In the
Switzerland
Switzerland, officially the Swiss Confederation, is a landlocked country located in west-central Europe. It is bordered by Italy to the south, France to the west, Germany to the north, and Austria and Liechtenstein to the east. Switzerland ...
population of thistle tortoise beetles, the main predator of larvae is ''
Polistes dominulus''. These
paper wasp
Paper wasps are a type of Eusociality, social vespid wasps. The term is typically used to refer to members of the Vespidae, vespid subfamily Polistinae, though it often colloquially includes members of the subfamilies Vespinae (hornets and yel ...
s were the dominant cause of thistle beetle mortality and were found to be responsible for 99.4% of predation on these beetles in that country.
As the larvae develop, they develop a shield with its feces to protect itself from danger. This protection mechanism is possible because of lateral spines, which can form a shield. It was found that this shield has the capability to protect different areas of the body by moving to areas that sense danger. In 1967,
Thomas Eisner
Thomas Eisner (June 25, 1929 – March 25, 2011) was a German-American entomologist and ecologist, known as the "father of chemical ecology." He was a Jacob Gould Schurman Professor of Chemical Ecology at Cornell University, and director of the ...
showed that thistle beetles without their shield were vulnerable to ants, which were able to attack them and bring them to their nests. When they had their shield, the ants no longer attacked them and quickly moved on. The larvae also had different protection mechanisms because their shields could protect them from all predators. When predators had longer mandibles, it was found that these shields became less effective. For example, it did not matter when the shield was present or not when facing a
lycosid spider. Another defense mechanism they have for stronger predators is that, when sensing danger, they begin moving erratically, which scares predators away.
Parasites
Parasites
Parasitism is a close relationship between species, where one organism, the parasite, lives (at least some of the time) on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The en ...
have a large impact on the survival rates of thistle beetles. In different regions of the world, different parasites affect these beetles.
In the
South Virginia population of thistle beetles, it was predicted that parasitism was a top two reason for mortality.
One of the most common parasites that accounts for almost a quarter of total thistle beetle parasitism is ''
Tetrastichus rhosaces.'' In certain cases, a larva or pupa would have up to 10 of these parasites at one time near the anal region. These parasites were difficult to detect and would usually be only seen during the last larval stage. For those that have parasites, the larvae had an abnormal color.
Another prominent parasite that affects these beetles is ''
Eucelatoria dimmocki
''Eucelatoria'' is a genus of flies in the family Tachinidae.
Species
*'' Eucelatoria argentea'' (Thompson, 1968)
*'' Eucelatoria armigera'' ( Coquillett, 1889)
*'' Eucelatoria aurata'' ( Townsend, 1927)
*'' Eucelatoria aurea'' (Thompson, 1968)
...
.'' They are a type of fly found in Virginia and
Maryland
Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. It borders the states of Virginia to its south, West Virginia to its west, Pennsylvania to its north, and Delaware to its east ...
. In some regions such as Maryland, these parasites accounted for almost 20% of total parasitism.
They target larvae and pupae. In Europe, the most prominent parasite of thistle beetle larvae and pupae that accounts for 96% of total parasitism are ''
Hexamermis'' species
Behavior
Parental care
Adult thistle beetles are
univoltine
Voltinism is a term used in biology to indicate the number of broods or generations of an organism in a year. The term is most often applied to insects, and is particularly in use in sericulture, where silkworm varieties vary in their voltinism.
...
. In March and April, females began laying their eggs.
Oviposition
The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typica ...
depends on many conditions, ranging from rain and wind to temperature and the length of the day.
Another factor females consider is the amount of food available and its quality because the females and their eggs will feed on the same plant. It was found that females often lay their eggs near their feeding sites. This phenomenon could be explained by females sampling areas of leaves and choosing the most optimal place to lay their eggs to ensure that they will also have an abundance of high-quality food. Females usually lay their eggs on the bottom of the leaf, which occurs at higher frequencies than the topside of the leaf and the stem.
Soon after the eggs are laid, a layer of
excreta
Excretion is elimination of metabolic waste, which is an essential process in all organisms. In vertebrates, this is primarily carried out by the lungs, kidneys, and skin. This is in contrast with secretion, where the substance may have specifi ...
is secreted that encloses them. Furthermore, after egg enclosure, the entire
ootheca
An ootheca (: oothecae ) is a type of egg capsule made by any member of a variety of species including mollusks (such as '' Turbinella laevigata''), mantises, and cockroaches.
Etymology
The word is a Latinized combination of ''oo-'', meaning " ...
is also enclosed with excreta. This provides thistle beetle eggs with a double layer of protection.
This is thought to protect the eggs by serving as a physical barrier against the environment and enemies and also acting as concealment.
It was found that this enclosure increased egg survival rates as it protected them from predators and parasites. Due to the covering, these enemies had difficulty penetrating the barrier to get access to the egg.
Migration
During the fall, it has been observed that these beetles migrate to the
forest floor
The forest floor, also called detritus or wikt:duff#Noun 2, duff, is the part of a forest ecosystem that mediates between the living, aboveground portion of the forest and the mineral soil, principally composed of dead and decaying plant matter ...
from thistles. Once they reach the forest floor, they find spaces under
leaf litter
Plant litter (also leaf litter, tree litter, soil litter, litterfall, or duff) is dead plant material (such as leaves, bark, needles, twigs, and cladodes) that has fallen to the ground. This detritus or dead organic material and its constituen ...
to hibernate. Those who have trouble accessing these locations had reduced survival rates. They remain in these shelters until early spring.
Reproduction
The
intromittent organ
An intromittent organ is any external organ of a male organism that is specialized to deliver sperm during copulation. Intromittent organs are found most often in terrestrial species, as most non-mammalian aquatic species fertilize their eggs ...
of male thistle leaf beetles is a long, tube-like structure that is called the
flagellum
A flagellum (; : flagella) (Latin for 'whip' or 'scourge') is a hair-like appendage that protrudes from certain plant and animal sperm cells, from fungal spores ( zoospores), and from a wide range of microorganisms to provide motility. Many pr ...
. The end of the flagellum is very thin and curved. As in many small beetles, this organ can become longer than its body. When not in use, the flagellum is stored inside the
abdomen
The abdomen (colloquially called the gut, belly, tummy, midriff, tucky, or stomach) is the front part of the torso between the thorax (chest) and pelvis in humans and in other vertebrates. The area occupied by the abdomen is called the abdominal ...
of the male. The muscles parallel to the lumen of the ejaculatory duct contract and push it out. The beetle needs such an organ because of the shape of the female
reproductive organ
A sex organ, also known as a reproductive organ, is a part of an organism that is involved in sexual reproduction. Sex organs constitute the primary sex characteristics of an organism. Sex organs are responsible for producing and transporting ...
, which includes a coiled duct that the male must penetrate with the contraction of ejaculatory muscles. These physical properties of the thistle beetle have been studied because the ability of a thin, flexible structure to penetrate without buckling or rupturing is mechanically challenging and may have important implications for the development of microscopic
catheter
In medicine, a catheter ( ) is a thin tubing (material), tube made from medical grade materials serving a broad range of functions. Catheters are medical devices that can be inserted in the body to treat diseases or perform a surgical procedure. ...
s in modern medicine.
Life cycle

The
oviposition
The ovipositor is a tube-like organ used by some animals, especially insects, for the laying of eggs. In insects, an ovipositor consists of a maximum of three pairs of appendages. The details and morphology of the ovipositor vary, but typica ...
period lasts on average 12 weeks. Most times, they lay around 3 eggs per
ootheca
An ootheca (: oothecae ) is a type of egg capsule made by any member of a variety of species including mollusks (such as '' Turbinella laevigata''), mantises, and cockroaches.
Etymology
The word is a Latinized combination of ''oo-'', meaning " ...
. However, this can increase up to 4-6 in different regions. The time it takes for eggs to hatch depends on the temperature. At lower temperatures, such as 18°C, eggs can take up to two weeks to hatch. Higher temperatures, such as 32°C, can facilitate the hatching of eggs in as little as four days.
There are five stages of larval development called
instar
An instar (, from the Latin '' īnstar'' 'form, likeness') is a developmental stage of arthropods, such as insects, which occurs between each moult (''ecdysis'') until sexual maturity is reached. Arthropods must shed the exoskeleton in order to ...
s. As with hatching rate, larvae development is temperature-dependent and shows a positive relationship with increasing temperature. It was also found that larvae develop faster during shorter days compared to longer days. Additionally, male larvae usually develop faster than female larvae.
Larvae remain on thistle leaves that were laid only throughout their development. Once ready, they move to the central portion of the leaf, which is thicker, for
pupa
A pupa (; : pupae) is the life stage of some insects undergoing transformation between immature and mature stages. Insects that go through a pupal stage are holometabolous: they go through four distinct stages in their life cycle, the stages th ...
tion. Pupation length depends on the temperature, and it was shown that it ranges from around 3 days to 10 days depending on the temperature. Higher temperatures nearing 32°C led to a shorter pupation period.
Between July and August, adults begin to appear.
As biological control
Thistle plants are known for their very fast-growing ability, which can quickly overpower local agriculture. They have few predators and are hard to kill through human activity due to their fast seed production.
It is estimated that Canada thistle costs landowners around $32 million per year in
Otago
Otago (, ; ) is a regions of New Zealand, region of New Zealand located in the southern half of the South Island and administered by the Otago Regional Council. It has an area of approximately , making it the country's second largest local go ...
and
Southland alone.
Due to the beetle's ability to
skeletonize leaves, they can damage several thistle types such as the plumeless thistles and nodding thistle. Because of this ability, these beetles were used as biological control agents against thistle weeds in many parts of the world.
''Cassida rubiginosa'' was introduced to
New Zealand
New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
for use as a biological control agent against ''
Cirsium arvense
''Cirsium arvense'' is a perennial species of flowering plant in the family Asteraceae, native throughout Europe and western Asia, northern Africa and widely introduced elsewhere.Joint Nature Conservation Committee''Cirsium arvense'' The standa ...
'' (Canada thistle) in 2006.
The beetle has subsequently been traded around
New Zealand
New Zealand () is an island country in the southwestern Pacific Ocean. It consists of two main landmasses—the North Island () and the South Island ()—and List of islands of New Zealand, over 600 smaller islands. It is the List of isla ...
as a control agent. For example, in 2016, beetles collected from
Ngaruawahia were released in
Duder Regional Park
Duder Regional Park ( ) is a regional park situated on the coast to the east of Auckland, New Zealand, on the Whakakaiwhara Peninsula.
The area was one of the first places in the Auckland Region visited by the ''Tainui (canoe), Tainui'' canoe, ...
in exchange for a group of the adult beetle ''
Neolema ogloblin'', which is a biological control agent for ''
Tradescantia fluminensis
''Tradescantia fluminensis'' is a species of spiderwort native to South America. It is one of several plants known by the common name wandering Jew. It is also known as small-leaf spiderwort, river spiderwort, inch plant, speedy Henry, wanderin ...
''.

Some states in the United States where thistle beetles are used as biological control agents are Virginia and Maryland. Significant results were seen in Maryland where musk thistle seed production was reduced by 72%. Flowering was inhibited after introducing thistle beetles to populations of thistle plants.
In Virginia, it was found that thistle growth was affected the most when more than 50% of leaf foliage was consumed. In dry years in Virginia, five parasite-free beetles per plant have been shown to reduce above ground thistle
biomass
Biomass is a term used in several contexts: in the context of ecology it means living organisms, and in the context of bioenergy it means matter from recently living (but now dead) organisms. In the latter context, there are variations in how ...
by 88%, with only 25% of these plants surviving to the end of the following year. In wet years the impact was less but still substantial.
Thistle beetles as a biological control were also widely used in Canada. In the province of
Saskatchewan
Saskatchewan is a Provinces and territories of Canada, province in Western Canada. It is bordered on the west by Alberta, on the north by the Northwest Territories, on the east by Manitoba, to the northeast by Nunavut, and to the south by the ...
, thistle beetles were able to defoliate thistles in the region.
In other regions of Canada, such as in the province of
Quebec
Quebec is Canada's List of Canadian provinces and territories by area, largest province by area. Located in Central Canada, the province shares borders with the provinces of Ontario to the west, Newfoundland and Labrador to the northeast, ...
, it was found that these beetles were not sufficient in helping reduce thistle populations.
One possible explanation for this was that parasitism was a challenge due to parasites preventing large populations of thistle beetles from thriving.
It was found that parasites that inhibited the accumulation of thistle beetles when used as biological control agents were ''
Tetrastichus rhosaces'', ''
Eucelatoriopsis dimmocki'', ''
Spilochalcis albifrons'', ''
Eupelmella vescicularis'', and ''
Itoplectis conquisitor''.
References
External links
Global biodiversity information*
{{Taxonbar, from=Q136153
Cassidinae
Beetles of Europe
Insects used for control of invasive plants
Biological pest control beetles
Beetles described in 1776