Lilioceris lilii (Scopoli, 1763)

Lily Beetle

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POLYPHAGA Emery, 1886

CHRYSOMELOIDEA Latreille, 1802

CHRYSOMELIDAE Latreille, 1802

CRIOCERINAE Latreille, 1804

Lilioceris Reitter, 1912

Originally native to parts of Asia the lily beetle has spread gradually since the nineteenth century over most of Europe, North Africa and Asia, this spread being accelerated in recent decades by the international movement of horticultural products. It was first discovered in Canada from Quebec in 1943 and in the United States from Massachusetts in 1992 and is now widespread although of local occurrence in the northern Nearctic zone. It now occurs as a horticultural pest in many temperate regions. It was first discovered in the U.K. by Stephens in 1839 but the first colony was not established until 1939 and it did not begin to spread until the 1970s, since when it has become widespread throughout the south of England north to South Yorkshire, it occurs sporadically further north and there are a few, mostly coastal, records from Wales, and a very few from Scotland and Ireland. The beetle is a pest of commercially grown lilies, fritillaries and other liliaceae but it is not known to attack day lilies, Hemerocallis, the adults have been seen to feed upon a range of plants e.g. Arum, Solanum, Smilax, Polygonatum and Nicotiana but these are not hosts. The typical habitats are nurseries, garden centres, parks and gardens where the hosts are grown and because the adults disperse by flight and the hosts are widely transported the beetles may suddenly appear in any suitable situation; often the first indication of their presence are the small masses of frass and leaf detritus which the larvae carry for concealment and protection. Adults occur throughout the year; they overwinter in soil near the host, sometimes in the pupal cells, and become active in the spring, at this time they are conspicuous on the pale emergent host stems and foliage or may be seen in flight searching for new hosts, they prefer cool and moist environments and may be attracted to particular plants or groups of plants in large numbers. Following a period of feeding they mate in early spring and the females begin laying elongate orange eggs in April; they are fecund and each will lay about 450 eggs in a season, they are laid in small batches of a dozen or so arranged in longitudinal rows alongside the base of the mid-ribs where they tend to be concealed. Larvae emerge after a week or two and begin

feeding on the edges of the lower leaves, gradually working their way up the leaves and stems until they reach the flowers or the unopened buds, which may also be consumed in bad infestations. Oviposition continues over a long period, often into August, and so all stages may be present together on a single plant or group of plants and in large infestations plants may be stripped of foliage and flowers within a few days. Larvae usually consume leaves from the underneath near the edges, starting near the nodes, while adults feed from above producing round holes in the leaves. Small larvae tend to be covered in a protective mass of frass and leaf debris but larger ones are easily spotted, usually large and bloated, and orange or red with the head and appendages dark, and carrying or dragging a mass of frass and leaf fragments. They are fully grown within three or four weeks and at this stage they stop feeding and descend the stems to burrow into the soil among the roots to pupate in a silk-lined shell. Adults eclose after about twenty days and emerge to feed until the onset of cold weather. In the U.K. there is a single generation each year but in warmer continental areas up to three are common. When disturbed the adults usually fall to the ground and remain upside-down and still (thanatosis) for some time, and when handled they often stridulate. Plants grown on a commercial scale occasionally host large populations of the beetles and these are ‘dealt with’ using insecticides but nonetheless the species continues to increase in range and abundance.

At 6-8mm this is by far the largest U.K. member of the Criocerinae and coupled with the striking colouration it should not be confused with any other species. Completely black but for the vivid red pronotum and elytra. Head transverse, with strongly protruding eyes which are deeply emarginate anteriorly, and temples which are strongly constricted to a bulbous neck. Antennae filiform and inserted on the front of the head before the eyes. Clypeus and vertex longitudinally impressed; the inner margin of the eyes with two rows of punctures and the temples deeply striate behind the eyes. Pronotum strongly constricted behind the middle, without lateral borders and with strong punctures along the centre of the disc. Scutellum black. Elytra broadly elongate with prominent shoulders; each with ten strongly punctured striae which tend to be confused towards the base where a partial scutellary row may be seen.  Sutural stria distinct from the middle and deepened towards the apex. Ventral surface black and clothed with fine yellow pubescence. Legs long and slender, each tibia with two small apical spurs. The first and second tarsomeres are elongate-triangular, the third deeply bilobed, the fourth tiny and often hidden within the lobes of the third, the last elongate and curved. Claws simple.

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