Lema cyanella (Linnaeus, 1758)

This is the only European member of the otherwise extensive genus Lema Fabricius, 1798; it is a generally common species extending from Spain to Turkey in the south and from Scandinavia through Siberia to China, Japan and Korea. There have been several attempts to introduce the species as a biocontrol agent against invasive thistle species e.g. in Canada and New Zealand but these have generally been unsuccessful despite the species being very fecund with each female laying up to 1500 eggs. In the UK it is widespread and locally common throughout England and Wales but so far absent further north. Host plants include various thistles e.g. cabbage thistle, Cirsium oleraceum (L.), marsh thistle, C. palustre (L.), spear thistle, C. vulgare (Savi), plumeless thistle, Carduus crispus L., musk thistle C. nutans L. and silver milk thistle Silybum marianum (L.). Adults are present year round, they are active from March to October, peaking in June and August/September, and are likely to be found in a wide variety of habitats where the host plants thrive e.g. wetland margins including river estuaries and salt marshes, woodland, parkland and wasteland, agricultural borders, roadsides and railway embankments etc. Adults appear from their overwintering sites early in the year and feed upon host foliage for a while before mating and commencing oviposition from May onwards. Single eggs, or sometimes pairs, are laid among foliage and larvae hatch after about 10 days, they usually cover themselves with a layer of excrement and debris as protection from predators and parasites and they feed openly above and below the leaves, consuming only the upper epidermis and leaving irregular translucent patches which may become extensive and cover entire leaves, and they are fully developed after about 3 weeks. Fully grown larvae ascend the stems or drop to the ground where they pupate in a cocoon within the soil among the host roots, this stage lasts about 2 weeks and new generation adults appear from late July or August. It is thought that a second generation may sometimes appear in the UK, producing late summer adults which will feed alongside the earlier summer generation to build up reserves before overwintering among litter or tussocks etc, often in marginal environments such as under hedgerows or on agricultural headlands. Adults may be swept from the hosts throughout the milder parts of the year, in the summer often appearing in numbers and sometimes remote from the host as they disperse by flight, through the winter they will occasionally appear among appropriate sieved or extracted samples.