Larinus Dejean, 1821
Larinus carlinae (Olivier, 1807)
Larinus Dejean, 1821 is a very widespread Old World genus of about 180 species; about 100 occur in the Palaearctic region and more than 60 in Europe; most occur in warmer southern regions but among these many are very widespread, much more so than the present species, extending into central and northern Europe, but only L. carlinae is established in the UK. L. carlinae is otherwise locally common throughout Europe north to the UK and southern provinces of Norway and Sweden and extending south into parts of Mediterranean North Africa and the Near East, and east into western Russia and Ukraine, it has also become widespread in North America since being introduced in the 1960s to help control accidentally introduced invasive weeds. Here it is locally common across Wales and England north to The Wash though more coastal in the West Country and absent from much of the midlands, typical habitats include open grassland, heathland and scrub, often on disturbed ground and sometimes in built-up areas. Adults overwinter and are active over a long season from April until early autumn; they are rarely found away from their host plants and generally occur in small numbers. Hosts include various Asteraceae; in the UK usually on species of Cirsium Mill. and Carduus L. but a wider range of hosts have been recorded on the continent including various species of Serratula L. (plumeless saw-worts). Reproduction occurs in the spring; adults emerge from tussocks, litter or the soil during the first mild days of April and ascend the stems of freshly growing host plants where they feed on tender young foliage and shoots for a few days before mating, this usually occurs after the first flower buds appear and continues into May or June. Soon after mating the female will chew a small hole into an unopened flower bud and insert a single egg, sometimes she will insert two eggs but then only one of the resulting larvae will survive, where several females are present on the same stem they may be observed searching flower
buds for a suitable place to oviposit as they can sense where buds already contains an egg and will ignore them, after inserting an egg she will seal the hole with a dark secretion which usually remains visible on the lower parts of the bud. Larvae develop rapidly inside the flower bud which usually becomes swollen due to callus tissue induced by the feeding larva, this is the damaging stage where flowers stop developing and fail to open and heavily infested plants will fail to reproduce, pupation takes place within the unopened bud and adults eclose within a few days. In temperate regions the cycle from egg to adult takes about 40 days and new generation adults appear from late May, these will feed through the summer but will not reproduce until the following spring after they have overwintered. The attempt to use this species as a biocontrol agent in North America has been a failure and suspended as the beetles found native thistles more attractive and ignored the invasive species.
This species is very distinctive among our fauna due to the parallel-sided and convex form, entirely dark colouration and long rostrum, the forebody is finely pubescent and the elytra have small patches of grey pubescence arranged in random transverse bands, in fresh specimens the dorsal surface has a yellow or creamy ‘bloom’ which soon wears off but may persist around the lateral margins. 5.0-9.5mm. Head small and transverse with weakly convex and widely transverse eyes and long diverging temples, entire surface, including the rostrum, finely rugose, rostrum convex, parallel-sided and slightly but distinctly curved towards the apex. Antennae short; scape about as long as the pre-rostrum and expanded before the apex, funiculus 7-segmented and club elongate-oval. Pronotum transverse, broadest at perpendicular posterior angles and narrowed to obtuse anterior angles, evenly convex and densely and rather strongly rugose, basal margin strongly bisinuate. Elytra broadest behind sloping shoulders and only weakly narrowed to a continuously rounded apical margin, striae weakly impressed but quite strongly punctured, interstices variably cross-rugose. Legs entirely dark brown or with lighter tarsi. Males may be distinguished by the slightly broader, more strongly rugose and duller rostrum.
Larinus turbinatus Gyllenhal, 1835
This is a mostly southern species in Europe; it is generally common throughout the northern Mediterranean region and is also present in Morocco, to the north it is generally rare and extends to the southern Baltic countries but is absent from Fennoscandia although it is probably spreading north via the trade in horticultural products e.g. it was first recorded from the Netherlands in 2007 and from Latvia in 2012, to the east it is widespread across Asia to Japan and Thailand, it has also recently (2011) been recorded from North America (Pennsylvania) following accidental introductions and is now established at several nearby sites. It is included in the UK list from a single specimen found in Kent during 2008, no doubt introduced with imported plants, but so far there is no evidence that it has become established. In northern Europe it inhabits open grassland and pastures, roadsides and woodland margins etc. and is often associated with disturbed sites. Host plants include various thistles: Carduus nutans L., Cirsium eriophorum (L.), C. arvense (L.) Scop., C. lanceolatum (L.) Scop., C. acaule (L.) and C. oleraceum (L.). Adults are active a little later than the previous species, from May until September, and reproduction occurs in the summer. Adults feed on tender foliage and flower parts and eggs are laid in unopened flower buds in July and August, larvae develop within and pupate within and both pupae and freshly eclosed adults occur from September. New generation adults will not reproduce until the following year; they feed for a few weeks before entering the soil to overwinter and resume feeding in the following spring.
Similar in size and morphology similar to the previous species but the form is overall broader and the elytra have more distinct shoulders and are less parallel-sided, tapering distinctly from behind the shoulders to the apex. They are most readily distinguished by the form of the rostrum, in the present species it is almost straight in lateral view and narrowed towards the apex, and from above it is narrowed from the base to the apex so that the width across the base is distinctly shorter than that across the apex; in L. carlinae it is curved and slightly wider towards the apex in lateral view, and more-or-less parallel-sided from above.