Tanymecus palliatus (Fabricius, 1787)
This widespread Palaearctic species occurs throughout Europe and Asia Minor, extending north to the UK and central provinces of Fennoscandia and east through Russia and Ukraine to Central Siberia where it extends above the Arctic Circle, here it is widespread though very local and generally rare through Wales and southern and central England and there are a few scattered records further north to the Scottish border. The species is widely polyphagous and might be found in almost any situation; grassland and meadows, arable land, roadsides, disturbed land, dunes, heaths, allotments, parks and gardens etc. where they feed upon plants of a range of families including Fabaceae, Brassicaceae and Urticaceae but they are most frequently found on various Asteraceae, especially thistles of the genera Carduus L. and Cirsium Mill. and bindweed, Convolvulus arvensis L. Females are very fecund; under good conditions each will lay between 300 and 400 eggs and so large populations may quickly appear and in some continental regions, more especially in Asia, they may become pests of crops such as beet, lettuce, soybean, legumes, sunflower and grasses, this generally occurs when the natural hosts growing close to crops generates large populations of beetles which disperse and invade the crops. Adults are present year-round, they overwinter between 15 and 50cm below the soil surface where hosts are abundant and become active during March and April when the soil temperature reaches 4 C at a depth of about 20cm., at this time many seedlings are present and the weevils gnaw the shoots and cotyledons and so damage or kill them, but beyond the cotyledon stage they are generally safe from attack. Mating occurs after a period of feeding, towards the end of April and through May, and oviposition proceeds through May and June; females lay batches of about 20 eggs on the soil surface close to host plants and larvae emerge after 3 weeks. Larvae feed on roots and within the lower parts of stems and develop slowly; they feed until the autumn when they burrow down in the soil to overwinter, the following spring they ascend to continue feeding into June or July when they pupate in a cell below the soil surface, the
Tanymecus palliatus 1
Tanymecus palliatus 2
pupal stage lasts about 3 weeks and adults eclose during July and August, they may emerge to feed before overwintering or, in cooler latitudes, may remain in the pupal cells until the following spring. Over most of the range the life-cycle takes 2 years but under unfavourable conditions it may extend into a third year. In the UK adults are active from April until September, they are flightless and populations generally remain very local, adults usually being sampled by general sweeping in the morning and evening, during the day they usually hide among litter around the base of host plants or under low foliage.
The elongate habitus and parallel-sided, broad-shouldered elytra are strongly suggestive of Sitona but Tanymecus is larger and has a fringe of long setae along the antero-lateral pronotal margins, among other species of Enteminae it is distinguished by the free tarsal claws, the laterally-placed antennal scrobes, unarmed femora and overall habitus. 7.5-10.0mm. Entirely black, covered with fine elongate grey and yellow scales, giving an overall grey or pale-creamy colouration. Head transverse; across the base about as wide as the combined head and rostral length, eyes large and weakly convex, rostrum transverse with the scrobes lateral so that from above only the apex is visible. Antennal scrobe long and slender; gradually thickened from close to the apex, basal funicular segments elongate, distal segments quadrate, club slender and pointed. Pronotum quadrate or, in the male, slightly elongate, widest about the middle and weakly constricted to the base, anterior margin rounded, from above with indistinct angles, basal margin straight. Elytra parallel-sided and narrowed in the apical third to a continuously-rounded apical margin; with regularly punctured striae distinct among the scales and continuous to the apex. Legs long and robust; femora unarmed, tibiae dimorphic; in the male with a small tooth on the internal apical angle, in the female only the fore-tibiae are toothed. Females are generally longer and always broader, the head, pronotum and, especially, the elytra are always distinctively broader when viewed in a series.