''Hypera postica'', commonly known as the alfalfa weevil, is a species of

weevil Weevils are beetles belonging to the superfamily Curculionoidea, known for their elongated snouts. They are usually small – less than in length – and herbivorous. Approximately 97,000 species of weevils are known. They belong to several fa ...

; it can be found in

alfalfa Alfalfa () (''Medicago sativa''), also called lucerne, is a perennial plant, perennial flowering plant in the legume family Fabaceae. It is cultivated as an important forage crop in many countries around the world. It is used for grazing, hay, ...

fields throughout Europe. Considered a destructive threat to alfalfa production in North America, several accidental introductions have been successfully countered though the use of a variety of biological control species.

Description

The alfalfa weevil grows to a length of about . The rostrum or beak is short and broad. The frons is half as wide as the rostrum while the pronotum is broadest in the centre. The general colour of the insect is brown, with a dark mid-dorsal stripe. The larva has a distinctive black head and no legs; it is yellowish-green, with a white dorsal stripe and faint white lateral stripes. It is about long just before pupation. It

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 ...

tes in a white, pea-sized cocoon made of loosely-woven silk. It resembles the clover leaf weevil ('' Hypera punctata''), but that species is nearly twice as large, the larvae have tan heads and they seldom cause much damage to alfalfa crops.

Life cycle

Illinois Illinois ( ) is a U.S. state, state in the Midwestern United States, Midwestern United States. It borders on Lake Michigan to its northeast, the Mississippi River to its west, and the Wabash River, Wabash and Ohio River, Ohio rivers to its ...

, some eggs are laid in the late fall or the winter, when weather conditions permit. Adults also overwinter and become increasingly active in March and April. Eggs are laid in batches of up to 25 inside alfalfa stems. The larvae feed for three or four weeks, moulting three times, before pupating in the cocoons they make. They emerge as adults in about one or two weeks. After feeding for a week or two, they may experience

aestivation Aestivation ( (summer); also spelled estivation in American English) is a state of animal dormancy, similar to hibernation, although taking place in the summer rather than the winter. Aestivation is characterized by inactivity and a lowered m ...

during the remainder of the summer, in which they demonstrate a dampening of their metabolic, respiratory and nervous system activities. In fall, the adults hide in the crowns of alfalfa plants or move onto coarse vegetation in ditches or by fences or in nearby woodland.

Damage

Both the larvae and the adults are diurnal and feed on the foliage of alfalfa, the larvae doing the most damage. The adults eat the edges of the leaves, giving them a feathery appearance. At first, the larvae feed on terminal leaves leaving puncture marks, but they later move down the plant to feed on lower leaves. The leaves attacked are skeletonised as the larvae feed between the veins, and plant yields can be reduced by up to 15%. Sometimes the larvae are killed by the pathogenic fungus '' Zoophthora phytonomi'', especially in warm and humid weather. They may also be parasitized by

ichneumon Ichneumon may refer to: * ''Ichneumon'' (genus), a genus of wasps * ''Ichneumon'', species of wasps in the family Ichneumonidae * Ichneumon, an alternative name for the Egyptian mongoose * Ichneumon (medieval zoology) In medieval literature, th ...

wasps, '' Bathylplectes anurus'' and '' B. curculionis''. The female of these wasps is only about long, and lays an egg inside an early stage of the larva of the weevil. The developing wasp larva is a

parasitoid In evolutionary ecology, a parasitoid is an organism that lives in close association with its host (biology), host at the host's expense, eventually resulting in the death of the host. Parasitoidism is one of six major evolutionarily stable str ...

, living inside the weevil larva and devouring it, eventually pupating soon after its

host A host is a person responsible for guests at an event or for providing hospitality during it. Host may also refer to: Places * Host, Pennsylvania, a village in Berks County * Host Island, in the Wilhelm Archipelago, Antarctica People * ...

. The wasp's brownish cocoon has a broad white band in the case of ''B. curculionis'', and a narrower, raised one in the case of ''B. anurus''. When it is disturbed, the cocoon of the latter species can "jump" several centimetres to avoid

predation Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common List of feeding behaviours, feeding behaviours that includes parasitism and micropredation ...

. Both these species of wasp have been investigated for their potential for biological control of the weevil, and ''B. anurus'' is generally considered superior to ''B. curculionis'' because of its higher reproductive rate.

References

{{Taxonbar, from=Q7712239 Hyperinae Beetles described in 1813