Nanophyes marmoratus (Goeze, 1777)
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POLYPHAGA Emery, 1886
CURCULIONOIDEA Latreille, 1802
Nanophyes Schönherr, 1838
This is a common and generally abundant European species extending east to Western Siberia, it also locally common in the United States and Canada following introductions in the early 1990’s in the hope that it would help control the its invasive host, purple loosestrife (Lythrum salicaria L.); flower buds damaged by the larvae usually fail to produce seeds and the plants are damaged by the adults feeding, especially early in the season. In the U.K. it occurs throughout England and Wales except for the north east and there is a single Scottish record from Islay (NBN). The species may be present wherever the host occurs and, as this is perennial, invasive and persistent over long periods, the weevil is often present in large numbers; typical habitats are wood margins, wasteland, parks and gardens. Adults overwinter among leaf-litter and tussocks etc. near the host and become active in late April or May when they feed upon the tips of young leaves, later moving to the petals as the flowers begin to open. The females have a long egg-laying season, beginning in June and extending into September; single eggs are laid inside the tips of unopened buds and the larvae feed upon the ovaries and petals etc. causing the bud to remain closed and, after a day or two, drop to the ground. Buds already containing an egg are ignored by other females so that only a single larva will develop in each, pupation occurs within the bud and development from egg to adult takes about a month. New generation adults eclose from early August and occur alongside the previous one and so by late summer all stages are present and the adults are particularly abundant. Sampling is simple as sweeping or shaking the plants over a tray will usually dislodge large numbers, and late in the season it is often simple to find infected buds around the base of the plants; these will often have a round emergence hole near the base.
With experience this tiny weevil will be obvious in the field. 1.5-2.5mm. Body entirely black but for variable yellow or cream marking to the elytra; these vary in intensity and size and specimens may be entirely pale over the apical two-thirds or, conversely, entirely black. The head is very narrow between the eyes and finely punctured and pubescent across the base, the rostrum is longitudinally furrowed and rather strongly punctured; it is longer in the female, being as long as the head and pronotum combined. Antennae inserted in the apical half, the club elongate and pointed, rather loose with the segments obvious. The pronotum is broadest at the base and evenly narrowed towards the apex; the anterior margin about half the width of the posterior margin, the surface finely punctured and sparsely scaled, and without lateral borders. The scutellum is very small and hardly visible. Elytra broadly oval and convex, with striae well impressed to the apex and the interstices convex. Legs yellow with the coxae, and the femora and tarsi generally darkened to some extent; the male hind tibiae are strongly curved inwards while those of the female are straight. All tibiae lack subapical teeth, a feature that will distinguish the present genus from the superficially similar Dieckmanniellus.