Otiorhynchus sulcatus (Fabricius, 1775)
Black Vine Weevil
Until the early nineteenth century this species was restricted to central and northern Europe but with increased trade it rapidly expanded; it was first recorded in the New World in 1831 and is now widespread through the United States and Canada, and the modern distribution includes most of Europe, Central Asia, and the Far East including Japan, South America and Australasia. It occurs commonly throughout England and Wales, including the islands, and sporadically through Scotland including the Western Isles and Shetland. This weevil has been recognized as a serious pest of cultivated plants for centuries; formerly of grapevines, hence the common name, and cultivated berries, it has now been associated with more than 150 plant species from a wide range of families including conifers and monocotyledons, and the larvae can also develop within, and destroy, stored corms and bulbs. The species occurs both in the wild and in nursery environments where they are considered to be one of the worst pests of nursery stock worldwide; they attack potted plants in any environment, short term bedding is rarely affected but slower growing plants where the roots are restricted are particularly prone to attack; herbs and alpines are common hosts, as are ornamental herbaceous species grown under cover, but hardy broadleaved species grown outside e.g. rhododendron, camellia and euonymus seem to be especially favoured by the weevil. The increased use of containerized plants over recent decades, along with a general warming of the climate, have contributed to the rapid spread and increased abundance of the weevil. In warmer climates and under artificial conditions the species will breed continuously and all stages may be present year-round, even in the soil around a single plant, and often the first sign of an infestation is the adult feeding damage to leaf margins after the weevil has developed in the plant container. Adults rest near the base of stems or in the soil during the day and feed at night and so the easiest way to find them is by torchlight; larvae are not necessarily obvious by simply tapping a plant out of
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Otiorhynchus sulcatus larva
it's container. All adults are female and reproduce parthenogenetically, fertilization of the eggs is needed to produce males and these have never been found. In the wild the adults live for up to three years and are very fecund, producing between 500 and 1600 eggs over a month or two in the spring. The spherical white eggs, obvious among nursery stock to the trained eye, are deposited in soil around roots, they turn brown after a few days and larvae hatch after two or three weeks. Larvae can find roots from a few centimetres by following carbonic acid gradients in the soil and so can move between plants in the wild. The larval stage causes most of the damage although large infestations of adults can defoliate plants and destroy fruits and berries. Depending on climate the adults may feed and oviposit through the summer but in temperate regions there is a single generation with eggs laid in the spring and early summer producing larvae from June to October. Some adults will eclose in the autumn and overwinter among roots etc. but most larvae will overwinter among roots and pupate in the soil the following spring, producing adults in April and May. The entire life cycle takes between 9 and 18 months in the wild but generally much less under artificial conditions. Fully grown larvae are up to 13mm long, apodous, slightly curved and creamy-white with a brown head. Larvae develop entirely in the soil, feeding upon roots and cambium at the base of the main stem, and they generally occur in numbers. Although nocturnal the adults may often be seen during hot summer days on walls and pathways, sometimes in numbers and sometimes active. Beating shrubs, rather than herbaceous plants, or searching pathways and foliage at night is the easiest way to find the species in the wild, and they occasionally occur inside on walls during the evening.
A broad and very convex species; the short-oval form and dark colouration with patches of pale scales will soon be recognized in the field. 7.0-9.5mm although smaller, diminutive specimens very occasionally occur. Entirely black but for the claws which are red, although freshly-eclosed adults may be dark brown with pale appendages. The upper surface, but for a densely microgranulate area on the vertex, is clothed with sparse recumbent pale pubescence. The vertex is finely punctured with a well-defined pit between the weakly convex eyes. Temples transversely striate. Rostrum quadrate or nearly so with scrobes and antennal insertions visible from above. Antennal scape parallel for the basal two thirds then gradually thickened to the apex, funiculus 7-segmented; the second much longer than the first or third, 4-7 quadrate or weakly elongate, and the club narrow and pointed. Lateral margins of the pronotum evenly curved from above, the dorsal surface covered with small and shiny tubercles. Elytra broad-oval with rounded shoulders and a steep apical declivity, covered with small shiny tubercles, those in the interstices larger than those in the striae, the cuticle between these microgranulate and dull. With small and scattered groups of golden scales which lie mostly in the striae. Legs long and stout, femora smooth; without tubercles, and with a single-pointed tooth. Pro-tibiae broadened towards the apex on the inside only. Each tarsus with two claws which are clearly separate to the base.