Exapion ulicis (Forster, 1771)
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POLYPHAGA Emery, 1886
CURCULIONOIDEA Latreille, 1802
EXAPIINI Alonso-Zarazaga, 1990
Exapion Bedel, 1887
This species is native to central and northern Europe and North Africa and while it does not extend north to the Nordic countries it is locally common throughout England and Wales and sporadic and generally scarce across Scotland. It is oligophagous on various species of Ulex. Gorse, but in the UK apparently only on U. europaeus L. Adults occur year-round and are active from early spring to late in the autumn, they overwinter among litter etc. or in the soil around host plants and become active on the first warm days of spring, feeding upon soft tissue of stems and spines for a while before mating commences and continues over the next few months, at this time characteristic round feeding holes may be abundant and obvious on fresh growth. Females chew into young green seed pods and deposit several eggs, moving between pods over an extended period so that on some plants the majority may host the eggs, and larvae emerge in late spring and early summer. Larval development is rapid; they pass through four instars and are fully grown within six to eight weeks, they feed only on developing seeds and when several larvae are present in a single pod all the seeds may be consumed or destroyed. When fully grown the pale grey larvae measure about 3mm, they pupate in the seed pods and adults eclose after about two months, appearing from mid-summer and feeding into the autumn prior to overwintering. In the UK the species is univoltine. Adult feeding may weaken or destroy fresh growth but it does not significantly damage the plants, larval feeding on the other hand, especially when large populations build up, may severely reduce seed production and so reduce the rate of spread of the gorse and for this reason the species has been introduced as a biocontrol agent into North America, Australia and New Zealand where gorse is one of the most invasive of introduced plant and in each case the weevil has become established and expanded in range. Adults are readily sampled by sweeping or beating host material; they are generally common but, as we have seen locally in South Herts., numbers may fluctuate widely from year to year. Larvae are easy to find by opening under developed seed pods but sometimes these will also contain a variety of hymenopteran parasites.
Adults are easily recognized by the very convex form, uniformly coloured pale scales and long narrow rostrum with a distinct basal tooth.
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1.9-2.5mm. Elongate with long slender legs, entire body and legs with elongate and pale scales; they may vary from dull green to yellowish but they are all the same colour, those on the elytra may be patchy or form longitudinal stripes where they are denser but they form no particular pattern. Head usually partly inserted into the thorax so the temples are hidden, vertex narrow and obscurely punctured, eyes large and convex and rostrum cylindrical, finely punctured and with a distinct basal tooth on which the antennae are mounted. Pronotum quadrate or nearly so, widest behind the middle and narrowed to the apical and basal margins, surface coarsely and densely punctured and with a short basal furrow which is usually obscured by scales. Elytra widest a little behind the middle, with broad and deep striae which in places are about half the width of the interstices, base of interstices 6-8 raised into a strong humeral prominence. Appendages mostly dark; antennal base, femora and tibiae variously pale. In males the basal meso- and meta-tarsomere is produced into a sharp ventral tooth, in the female unarmed. Females are distinctly broader, have more rounded elytra and a rostrum longer than the head and pronotum combined.