Altica lythri Aubé, 1843
A generally common species throughout Europe extending east into Siberia and south across Mediterranean Africa, in the U.K. it is common and often abundant across England and Wales becoming local and sporadic in the north and southwest Scotland. The typical habitat includes a wide range of wetland habitats as well as parkland, gardens and wasteland, coastal salt marshes and dunes, wherever the host plants occur. The species is widely polyphagous developing in various Willowherbs (Epilobium sp.), Rose-bay (Chamerion angustifolium), Loosestrife (Lythrum salicaria) and Enchanter’s nightshade (Circaea lutetiana) etc. and it is also an occasional pest of cultivated plants such as Fuschias, Evening primrose (Oenothera) and Potentilla fruticosa. Adults occur throughout the year, they overwinter in leaf-litter, moss and tussocks etc. and become active during March or April when they assemble on the hosts and begin feeding upon the foliage and flowers. Mating begins after a period of feeding although mating pairs are sometimes seen in late summer as well, and dispersal and egg-laying begins in April. Small pale orange or yellow eggs are laid among the foliage and larvae emerge about a week later, they graze the leaves, often alongside the adults, and develop rapidly; they pass through three instars with each lasting about a week, when fully grown they measure about 12mm and are a dull grey-yellow with a black head and sclerites. Fully grown larvae descend the stems and create a pupal cell a few cm below the surface of the soil around the host stems, the pupal stage is brief and new generation adults appear from July to September. Adults become abundant from May to July and may be observed in large numbers on the host, by mid June many host plants begin to look skeletonised after both adults and larvae have been feeding. Adults fly well and so may occur in most situations during the summer.
Altica species are easily recognized by the 11-segmented antennae, the sub-basal transverse pronotal furrow which is not delimited by longitudinal depressions, the randomly punctured elytra and the outer margin of the hind tibiae which has a fine ridge but lacks any large teeth. Species generally need to be identified from the form of the genitalia but lythri becomes very distinctive once familiar; it is large 3.5-5.5mm with the basal protarsomere at most as wide as the third, the colour is a rather dull metallic deep blue or, rarely, with a purple overtone or almost black, this colour becomes obvious in the field, and the form is broad with the elytra widening behind the middle. The head is dull and the pronotum and elytra are densely punctured. All appendages are dark metallic. The median lobe of the aedeagus is distinctive with a small tubercle at the apex and an elongate groove either side in the apical third; these terminate at a transverse impression before the rounded apex. The form of the spermatheca is also characteristic but needs to be viewed against those of our other species in order to appreciate this. Good line-drawings are given of both the male and female structures in Beetles of Britain and Ireland volume 4.