Hylobius transversovittatus
Encyclopedia
Hylobius transversovittatus is a species
of weevil
in the family Curculionidae
. It is native to the Old World
where both adults and larvae feed on purple loosestrife (Lythrum salicaria). This plant is regarded as an invasive species
in North America and the weevil has been introduced into both the United States and Canada in an effort to control the plant.
. The antennae
are elbowed and the legs reddish. The eggs
are white or pale yellow and oval in shape and hatch within about two weeks. The larva
e are a creamy colour with dark brown heads and adopt a crescent shape.
s before burrowing their way into the root where they feed on tissue within the woody rootstock. Stem-laid larvae tunnel into the stem and work their way down to the root. Larval development may be interrupted by periods of flooding and resume when the water level falls. The larvae undergo two moults over a period of one to two years before forming pupation chambers in the upper part of the root. They then moult again and become pupa
e. When metamorphosis is complete, the adult beetles chew their way out, usually emerging between July and October. The weevils can overwinter in any of their life stages, as eggs, larvae, pupae or adults.
to purple loosestrife (Lythrum salicaria). Before it was introduced into North America the weevil was tested on about fifty plants native to the continent to see whether they were susceptible to attack. Of these, only swamp loosestrife (Decodon verticillatus
) and winged loosestrife (Lythrum alatum
) were found to be potential hosts. It was found however that if purple loosestrife was available, it was preferred over these native species and the weevil was considered not to be a threat to non-target plants.
The weevils and their eggs were introduced to test sites in Virginia from 1992 onwards. They became successfully established and six years after the introduction, 28% of the roots of purple loosestrife plants were found to be infested. Larvae were also detected in roots four hundred metres downstream from the release point. Although the feeding of the adult weevils does little damage to the plant, the activities of the larvae, especially if there are several in one rootstock, weaken the plant, make it more susceptible to stressful conditions and reduce the quantity of seed produced.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of weevil
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...
in the family Curculionidae
Curculionidae
Curculionidae is the family of the "true" weevils . It was formerly recognized in 1998 as the largest of any animal family, with over 40,000 species described worldwide at that time...
. It is native to the Old World
Old World
The Old World consists of those parts of the world known to classical antiquity and the European Middle Ages. It is used in the context of, and contrast with, the "New World" ....
where both adults and larvae feed on purple loosestrife (Lythrum salicaria). This plant is regarded as an invasive species
Invasive species
"Invasive species", or invasive exotics, is a nomenclature term and categorization phrase used for flora and fauna, and for specific restoration-preservation processes in native habitats, with several definitions....
in North America and the weevil has been introduced into both the United States and Canada in an effort to control the plant.
Description
The adult Hylobius transversovittatus is a dark brown colour with two irregular transverse lines of tufts of white hair. It is about thirteen millimetres long and six millimetres wide and has a narrow head and thorax and a curved trunk-like proboscisProboscis
A proboscis is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In simpler terms, a proboscis is the straw-like mouth found in several varieties of species.-Etymology:...
. The antennae
Antenna (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....
are elbowed and the legs reddish. The eggs
Egg (biology)
An egg is an organic vessel in which an embryo first begins to develop. In most birds, reptiles, insects, molluscs, fish, and monotremes, an egg is the zygote, resulting from fertilization of the ovum, which is expelled from the body and permitted to develop outside the body until the developing...
are white or pale yellow and oval in shape and hatch within about two weeks. The larva
Larva
A larva is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle...
e are a creamy colour with dark brown heads and adopt a crescent shape.
Biology
Adult Hylobius transversovittatus beetles emerge in the spring from the soil or leaf litter where they have been overwintering. They feed on the leaves of purple loosestrife (Lythrum salicaria) and are mostly nocturnal. Their presence is evidenced by the ragged edges to leaves caused by their chewing. They are most active from June to August and may live for several years. The females lay about 200 eggs over a period of two to three months with each being deposited singly near the roots of purple loosestrife or occasionally on the stem. On hatching, the soil-laid larvae feed on root hairRoot hair
A root hair, the rhizoid of a vascular plant, is a tubular outgrowth of a trichoblast, a hair-forming cell on the epidermis of a plant root. That is, root hairs are lateral extensions of a single cell and only rarely branched, thus invisible to the naked eye. They are found only in the region of...
s before burrowing their way into the root where they feed on tissue within the woody rootstock. Stem-laid larvae tunnel into the stem and work their way down to the root. Larval development may be interrupted by periods of flooding and resume when the water level falls. The larvae undergo two moults over a period of one to two years before forming pupation chambers in the upper part of the root. They then moult again and become pupa
Pupa
A pupa is the life stage of some insects undergoing transformation. The pupal stage is found only in holometabolous insects, those that undergo a complete metamorphosis, going through four life stages; embryo, larva, pupa and imago...
e. When metamorphosis is complete, the adult beetles chew their way out, usually emerging between July and October. The weevils can overwinter in any of their life stages, as eggs, larvae, pupae or adults.
Host species
Hylobius transversovittatus seems to be host-specificHost (biology)
In biology, a host is an organism that harbors a parasite, or a mutual or commensal symbiont, typically providing nourishment and shelter. In botany, a host plant is one that supplies food resources and substrate for certain insects or other fauna...
to purple loosestrife (Lythrum salicaria). Before it was introduced into North America the weevil was tested on about fifty plants native to the continent to see whether they were susceptible to attack. Of these, only swamp loosestrife (Decodon verticillatus
Decodon verticillatus
Decodon verticillatus, the sole species in the genus Decodon, is a flowering plant in the Lythraceae family. It is commonly known as waterwillow or swamp loosestrife. It is endemic to wetlands in the eastern half of the United States.-Description:Waterwillow is a clump-forming shrubby perennial...
) and winged loosestrife (Lythrum alatum
Lythrum alatum
Lythrum alatum, commonly known as winged loosestrife or winged lythrum, is a species of flowering plant belonging to the family Lythraceae. It is endemic to wetland areas in central and eastern United States and Ontario.-Description:...
) were found to be potential hosts. It was found however that if purple loosestrife was available, it was preferred over these native species and the weevil was considered not to be a threat to non-target plants.
Use in biological control
Purple loosestrife is a native of Europe, Asia, northwest Africa and parts of Australia. In these countries a number of insects are associated with it. These include Hylobius transversovittatus, the adults of which eat the foliage and the larvae of which tunnel through and eat the root. When purple loosestrife was introduced into North America these insects were not available to keep it under control and it became rampant. It is now found in large stands throughout the northeastern United States, southeastern Canada and the American Midwest where it crowds out other species and is a threat to biodiversity.The weevils and their eggs were introduced to test sites in Virginia from 1992 onwards. They became successfully established and six years after the introduction, 28% of the roots of purple loosestrife plants were found to be infested. Larvae were also detected in roots four hundred metres downstream from the release point. Although the feeding of the adult weevils does little damage to the plant, the activities of the larvae, especially if there are several in one rootstock, weaken the plant, make it more susceptible to stressful conditions and reduce the quantity of seed produced.