Hypera postica (Gyllenhal, 1813)
Originally native to the Palaearctic and southwest Asian regions this weevil is now much more widespread, due mostly to the extensive global cultivation of various legume crops, it now occurs throughout Eurasia and Australasia and is a widespread adventive; first recorded in 1904 it is now widespread in the Nearctic region. In the U.K. it is generally common through England and Wales in a wide range of habitats, generally among unmanaged grassland vegetation on heaths and commons, agricultural borders, roadsides and open woodland, in fact anywhere the host plants thrive. These include a wide range of legumes; in the U.K. various species of Medicago and Trifolium but farther afield on Vicia, Astragalus, Cicer and Lupinus etc. as well as members of other families e.g. Atriplex (Chenopodiaceae) or Fragaria (Rosaceae). In many areas it is a serious pest e.g. on the southern steppe grasslands populations of 1500 larvae m-2 have been recorded, and in the United States various ichneumon flies e.g. Bathylplectus spp. have been imported as a biocontrol agent. The worst affected crop is lucerne and, while various clovers may be affected on a large scale, the economic significance of these is generally small. In temperate regions the adults become active early in the year, generally during mild spells in January or February, and become abundant to coincide with the developing hosts, they feed on leaf margins and buds and often cut through the main stem and side shoots. After a period of voracious feeding they mate in early spring and oviposition occurs from March onwards, females chew cavities into well-developed stems and insert batches of up to 25 eggs, sometimes several to a stem but often moving between plants to oviposit, each female is very fecund and may continue to lay eggs over a long period. Larvae emerge between 10 and 18 days later and move rapidly around the plant searching for leaf buds which they enter and quickly consume, this early season feeding causes most of the damage to growing crops, young larvae move between leaf buds but as they grow will feed on larger leaves, generally skeletonising them. Larvae are easy to see as they curl around leaves and stems while feeding, and in bad infestations fields of lucerne may appear grey compared to healthy crops. The
Hypera postica 1
Hypera postica 2
Hypera postica 3
larvae pass through four instars and development is completed in about four weeks; fully grown they are 8mm long and light green with a pale dorsal stripe. When full grown they stop feeding and move around the plant for a while before spinning an open lacy cocoon around themselves in which to pupate. Adults eclose after a week or two and feed for a while before aestivating through the warmest part of the summer, they resume feeding in late summer and autumn before entering the soil to overwinter. There is a single generation each year although in warmer climates they may breed from late August, producing eggs and larvae that will overwinter in the soil below the host and produce adults in the spring that will breed alongside overwintered adults.
A medium sized weevil; up to 5mm and easily identified by the pattern of pale scales to the pronotum and elytra but these become worn and late in the season may be almost completely abraded. The scales on the pronotum, elytra and abdominal sternites are broad and deeply bifid; the lobes about 2/3 the length of the scales. Head transverse with elliptical eyes that follow the outline and temples broadly expanded towards the base, entirely clothed with golden or grey scales, the interocular distance less than the width of an eye. The rostrum is long and parallel with scales becoming sparse towards the apex, and scrobes not visible from above. Antennae pale with a darker club; scape long and narrow and abruptly thickened near the apex; funiculus 7-segmented, segments 6 and 7 slightly transverse and the club narrow and pointed. Pronotum slightly transverse, about 8:7, or almost quadrate; widest a little in front of the middle and more strongly contracted towards the base than the apex, scales brown or coppery with the lateral margins and a central stripe paler. Elytra with strongly punctured striae and finely punctured and flat interstices but these are generally obscured by scales; the pattern is distinct, creamy yellow to grey but for a dark area across interstices 1-3 from the base to before the middle, then continuing apically across interstices 1 and 2, and ending above the declivity. Among the pale scaling odd-numbered interstices have patches of dark scales, and all interstices have a row of longer pale recumbent setae, most obvious towards the apex. Legs long and robust, completely covered with scales; femora not toothed on the inside, tibiae smooth along the inner margin; in the male the pro- and meso-tibiae are more strongly curved inwards towards the apex when compared with the female. The third segment is broadly bilobed on all the tarsi. Claws free. The female is generally much broader when compared with the male.