Otiorhynchus singularis (Linnaeus, 1767)
This generally common species is native to Europe but has a rather fragmented distribution; it is widespread in southern and western areas but absent from much of central and eastern Europe, in the north it extends to the UK and central Fennoscandia but is either absent or very sporadic and rare in the Baltic countries east of Poland, beyond its native range it is widespread in North America following introductions in the nineteenth century. Here it is generally common and often abundant throughout England and Wales, including the islands, and rather less so further north to Shetland; through much of its European range, including the UK, it is parthenogenetic with only females present, and males are known only from southern France. Adults occur year-round, they overwinter in the soil or among leaf-litter etc. and are active over a long season, from February until November, they are nocturnal and occur in a very wide range of habitats including woodland, parkland, coastal dunes, domestic gardens, roadsides, grassland and hedgerows. They are among the most widely polyphagous of weevils, developing on deciduous and coniferous trees and shrubs, herbaceous plants and a range of soft fruits; over much of the range they occasionally appear in large numbers and become serious pests of commercially grown trees and fruits. Species most affected are apple, pear, black currant, gooseberry, raspberry, grapevines and hops, most damage occurs through adult feeding; they are voracious and tend to attack developing buds and growing tips, especially in the spring as the plants are beginning to grow, on trees they may also consume tender bark, sometimes ringing leading shoots and causing extensive damage, and foliage as well as buds and flowers, in extreme cases whole plants are defoliated, this stunts the growth and deforms young tree stocks and may be commercially very serious. They are also known to feed on pine pollen. Adults are very difficult to control as they begin feeding very early in the year, they hide in the soil etc. during the day and may live for up to three years. Eggs are laid in the soil over a long season, from mid-May until late June, and again during September and October, they are not as fecund as other members of the genus and each female will lay about 100 eggs per season. Larvae develop in the soil, usually down to a depth of 50cm, feeding upon fine and tender roots, they grow through the summer and may pupate in earthen cells in the autumn, or late emerging larvae develop through the winter and pupate in early spring, giving rise to fresh adults from March. Overwintered adults appear earlier, they become active during the first mild days but have been observed feeding at 4°C and so temperature may not be severely limiting to their activity, and as new generation adults appear they soon become abundant. Adults are easily sampled by beating or sweeping after dark, their presence may be detected by extensively damaged foliage which tends to be very obvious, especially on low evergreen shrubs such as rhododendron where leaves close to the ground may have numerous lateral notches, here the adults are usually obvious by torchlight on the stems and foliage, this kind of damage is often seen in island shrubberies and sheltered beds in supermarket or shopping centre car parks.
Otiorhynchus singularis 1
Otiorhynchus singularis 2
Otiorhynchus singularis 3
Feeding damage on rhododendron
©James Hutton Institute https://www.hutton.ac.uk/
Adults are easily recognized by the size, 5.5-7.5mm, and mottled brown appearance. Body dark grey to black with extensive brown scales, appendages pale brown to reddish-brown. Head with dense elongate pale scales from the back margin of the eyes to the middle of the rostrum, the temples long and diverging and eyes widely separated and weakly convex. Rostrum short and transverse with the scrobes exposed from above, antennae long and robust, the scape curved and gradually broadened from about the middle to the apex, funiculus 7-segmented, club small and narrow. Pronotum quadrate, smoothly convex and evenly rounded laterally, the surface with sparse fine pubescence, dense round scales and small, dark and glabrous tubercles. Pronotum and elytra separately rounded, producing an acute angle and giving the species a characteristic appearance. Elytra with sloping shoulders, smoothly curved lateral margins which are often almost straight about the middle, and a continuously rounded apical margin. Surface with dense round scales which vary from pale to darker brown and give an overall random variegated pattern, interstices with rather random rows of small tubercles and outstanding pale setae. Legs long and robust, all femora with a single (sometimes very small) ventral tooth, front tibiae expanded internally into a sharp apical tooth, tarsi pseudotetramerous, the third segment widely bilobed. Tarsal claws small and not fused at the base. Only females are known from the UK.