Lixus concavus
Encyclopedia
Lixus concavus is a member of the weevil
s group, also called the snout beetles. Rhubarb
(Rheum species) is a host, together with dock, sunflower and thistle.
with small clubs. The beetle is about half an inch in length, black, covered with yellow dust, and hibernates as an adult. Eggs are a yellow-white colour and oblong in shape; the legless larva is a grub, about 3/4 inch in length, with a brown head that usually bears an inverted Y-shaped mark.
, often with extraneous material trapped within. The eggs that are laid in rhubarb do not hatch, but are killed by the sap or crushed by the developing tissues.
Lixus concavus is able to complete its life cycle in the stalks of curly dock, sunflower
s and thistle
s; eggs are laid singly in 1/8 in cavities, created by feeding activity, and hatch within a week to ten days. One grub usually develops per plant, the larva having borrowed through the stalk down to ground level, where pupation occurs after around nine weeks; the larva chews an exit hole for the adults before pupating. The pupa is whitish and measures 14–15 mm long. The head bears the long snout of the adult form. The abdominal segments are marked with short spines. The larva takes a few weeks to develop into an adult that feeds for a few weeks before seeking out a site to overwinter. The weevil has one generation per year. The adult weevil feeds upon the margins of the leaves besides puncturing the stalks; damage appears as distinct notches in the plant tissues.
Rhaconotus fasciatus is the only recorded parasitoid
of the rhubarb curculio. As stated, only a single larva develops to maturity in hosts other than rhubarb; it is not uncommon however to find several young larvae in the stalk of a host plant, indicating that the larvae may be cannibalistic
.
west to Idaho
, Utah
, and Texas
. In Canada
it is known from Ontario
. It is found in the United Kingdom
.
Weevil
A weevil is any beetle from the Curculionoidea superfamily. They are usually small, less than , and herbivorous. There are over 60,000 species in several families, mostly in the family Curculionidae...
s group, also called the snout beetles. Rhubarb
Rhubarb
Rhubarb is a group of plants that belong to the genus Rheum in the family Polygonaceae. They are herbaceous perennial plants growing from short, thick rhizomes. They have large leaves that are somewhat triangular-shaped with long fleshy petioles...
(Rheum species) is a host, together with dock, sunflower and thistle.
Characteristics
L. concavus has a distinctive long snout and geniculate antennaeAntenna (biology)
Antennae in biology have historically been paired appendages used for sensing in arthropods. More recently, the term has also been applied to cilium structures present in most cell types of eukaryotes....
with small clubs. The beetle is about half an inch in length, black, covered with yellow dust, and hibernates as an adult. Eggs are a yellow-white colour and oblong in shape; the legless larva is a grub, about 3/4 inch in length, with a brown head that usually bears an inverted Y-shaped mark.
Life cycle
The adult Rhubarb curculio overwinters in leaf litter or other similar sites and appears in mid-May. The adult makes feeding and egg punctures in the crowns, roots and stalks; a jelly-like sap exudes from the wounds as glistening drops of gumGummosis
Gummosis is the formation of patches of a gummy substance on the surface of certain plants, particularly fruit trees. This occurs when sap oozes from wounds or cankers as a reaction to outside stimuli such as adverse weather conditions, infections, insect problems, or mechanical damage. It is...
, often with extraneous material trapped within. The eggs that are laid in rhubarb do not hatch, but are killed by the sap or crushed by the developing tissues.
Lixus concavus is able to complete its life cycle in the stalks of curly dock, sunflower
Sunflower
Sunflower is an annual plant native to the Americas. It possesses a large inflorescence . The sunflower got its name from its huge, fiery blooms, whose shape and image is often used to depict the sun. The sunflower has a rough, hairy stem, broad, coarsely toothed, rough leaves and circular heads...
s and thistle
Thistle
Thistle is the common name of a group of flowering plants characterised by leaves with sharp prickles on the margins, mostly in the family Asteraceae. Prickles often occur all over the plant – on surfaces such as those of the stem and flat parts of leaves. These are an adaptation that protects the...
s; eggs are laid singly in 1/8 in cavities, created by feeding activity, and hatch within a week to ten days. One grub usually develops per plant, the larva having borrowed through the stalk down to ground level, where pupation occurs after around nine weeks; the larva chews an exit hole for the adults before pupating. The pupa is whitish and measures 14–15 mm long. The head bears the long snout of the adult form. The abdominal segments are marked with short spines. The larva takes a few weeks to develop into an adult that feeds for a few weeks before seeking out a site to overwinter. The weevil has one generation per year. The adult weevil feeds upon the margins of the leaves besides puncturing the stalks; damage appears as distinct notches in the plant tissues.
Control
L. concavus are usually present in fairly small numbers and can be handpicked and then destroyed. Removal of the other host plants, such as curly dock, wild dock, sunflower and thistle, during mid-summer, when the L. concavus larvae are still in them, may also help to reduce pest populations. Infested plants should be dug up and burned.Parasites and cannibalism
The braconid waspBraconidae
Braconidae is a family of parasitoid wasps and one of the richest families of insects. Between 50,000 and 150,000 species exist worldwide. The species are grouped into about 45 subfamilies and 1,000 genera, some important ones being: Ademon, Aphanta, Asobara, Bracon hebetor, Cenocoelius, Chaenusa,...
Rhaconotus fasciatus is the only recorded parasitoid
Parasitoid
A parasitoid is an organism that spends a significant portion of its life history attached to or within a single host organism in a relationship that is in essence parasitic; unlike a true parasite, however, it ultimately sterilises or kills, and sometimes consumes, the host...
of the rhubarb curculio. As stated, only a single larva develops to maturity in hosts other than rhubarb; it is not uncommon however to find several young larvae in the stalk of a host plant, indicating that the larvae may be cannibalistic
Cannibalism (zoology)
In zoology, cannibalism is the act of one individual of a species consuming all or part of another individual of the same species as food. Cannibalism is a common ecological interaction in the animal kingdom and has been recorded for more than 1500 species...
.
Distribution
L. concavus is found throughout the eastern United StatesEastern United States
The Eastern United States, the American East, or simply the East is traditionally defined as the states east of the Mississippi River. The first two tiers of states west of the Mississippi have traditionally been considered part of the West, but can be included in the East today; usually in...
west to Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....
, Utah
Utah
Utah is a state in the Western United States. It was the 45th state to join the Union, on January 4, 1896. Approximately 80% of Utah's 2,763,885 people live along the Wasatch Front, centering on Salt Lake City. This leaves vast expanses of the state nearly uninhabited, making the population the...
, and Texas
Texas
Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...
. In Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
it is known from Ontario
Ontario
Ontario is a province of Canada, located in east-central Canada. It is Canada's most populous province and second largest in total area. It is home to the nation's most populous city, Toronto, and the nation's capital, Ottawa....
. It is found in the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
.