Hylobius transversovittatus (Goeze, 1777)

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POLYPHAGA Emery, 1886

CURCULIONOIDEA Latreille, 1802

CURCULIONIDAE Latreille, 1802

MOLYTINAE Schönherr, 1823

HYLOBIINI Kirby, 1837

Hylobius Germar, 1817

This western Palaearctic species is known mostly from southern, central and eastern parts of Europe; it occurs from the Pyrenees to Ukraine in the south, although it is also known from Portugal, and extends sporadically north to the UK, Denmark and some southern provinces of Sweden and Finland, it is generally very local and scarce but in most northern countries recorded from only a few widespread sites. In the UK it has been known since the middle of the 20th century; it was formerly also recorded from South Devon but is now restricted to North Somerset where it is very local and rare. Adults generally occur in lowland and upland regions although they have been recorded from a few mountain localities e.g. in Poland, they occur mostly in wet meadows, drainage ditches, wetland margins and peat bogs and are associated with Purple-loosestrife (Lythrum salicaria L.) Adults occur year-round, they overwinter among leaf-litter away from water and are active from May until November, mating occurs in the summer and larvae develop within woody roots of the host, producing long meandering galleries as they feed. Adults are mostly crepuscular and nocturnal and may be swept as they feed on host foliage. During 1992 this species was introduced widely across the northern United States and Canada as a biocontrol agent for purple loosestrife (which is an invasive pest of North American wetlands) and now seems to have become established, before this introduction it was trialled on many native plants and found, given the option, to avoid all but two closely-related species, during these trials the life-cycle has become rather well understood although it may differ in detail from that in Europe. Adults live for several years, they emerge from the soil or leaf-litter etc. in the spring and feed on leaf margins at night, the peak of activity is from June to August and mating occurs mostly in the spring after a period of feeding. Females produce up to 200 eggs each year and oviposition continues over two or three months; eggs are deposited singly or in small batches low down into stems or in the soil below host plants. Larvae enter the roots from the soil or bore down through the stems, they feed initially

Hylobius transversovittatus

Hylobius transversovittatus

© Lech Borowiec

on soft tissue and then bore into centre of the roots and excavate long galleries, development may be complete in a single year or they may overwinter within the root and complete their development during the spring, they pass through three instars, all of which have been recorded overwintering and so fresh adults may occur over a long season. Mature larvae bore up through the root and form a pupation chamber near the soil surface, they pupate from late spring and adults emerge from July until October. Larval emergence and development may be interrupted by periods of flooding or drought and under such conditions all stages from egg to adults have been recorded overwintering.  Adults feeding does little to affect the host plant but larvae may seriously retard growth or kill plants completely, especially after a colony has been established for several generations and larvae are abundant; it has been predicted that purple loosestrife will be reduced by 90% over 90% of its range in North America although plants growing in flooded or heavily shaded situations tend to be avoided and Hylobius has been shown to be highly susceptible to many commonly used pesticides.

7.5-11.5 mm. A very distinctive species; elongate with a long and broad rostrum and sub-parallel elytra which are much broader than the rounded pronotum, body entirely reddish-brown, legs a little paler but usually with the femoral apices and tarsi darker, antennae dark brown with the club appearing pale due to dense pubescence, body with sparse yellowish pubescence except for the scutellum and various patches of dense pubescence which form two loose transverse series across the elytra. Head transverse with short diverging temples and convex eyes which form the outline and meet the base of the rostrum, surface densely and moderately strongly punctured, between the eyes with a small depression bordered with longer yellow scales. Rostrum long, weakly curved and directed down in front of the head, subparallel except at the apex where the lateral scrobes are visible, dorsal surface roughly sculptured and depressed medially. Antennae inserted at the rostral apex; scape long, narrow and gradually expanded in the apical third, funiculus 7-segmented, club broad and pointed. Pronotum quadrate, broadest about the middle and narrowed to a weak subapical constriction and rounded anterior angles, posterior angles slightly obtuse and basal margin gently produced to the centre, surface very strongly and, for the most part, discretely punctured. Scutellum triangular and densely pubescent. Elytra almost parallel from rounded shoulders to a distinct subapical constriction, surface obliquely sculptured towards the base, forming a rippled effect, otherwise smooth and finely punctured between striae that are strongly punctured in the basal half but fade towards the apex. The pattern of tufts of larger yellow pubescence is fairly constant; there is usually one around each shoulder and between four and ten forming transverse series across the middle and before the apex although in rare cases these may merge to form partial transverse lines. Legs long and robust, femora toothed below, tibiae slightly expanded internally about the middle and with a strong inward-pointing ‘hook-like’ spur, tarsi pseudotetramerous. Males can be distinguished by their impressed abdominal sternites, especially obvious on the apical segments.

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