Mecinus janthinus Germar, 1821

This species is native to southern and central Europe and southwest Russia extending north to the south of Scandinavia and, recently (1948), the U.K. where it is now widespread albeit very local in southeast England. From 1991 several populations from the Rhine valley in France have been released in North America to help control Dalmatian Toadflax, Linaria dalmatica and Common Toadflax, L. vulgaris, two noxious weeds native to Europe and western Asia but now established across the northern United States and southern Canada. In the U.K. the host is the very widespread and generally abundant Common Toadflax, but other species of Linaria are known to be hosts on the continent. Typical habitats are wherever the host thrives e.g. roadsides, grassland, wooded borders and disturbed ground generally; on the continent the species prefers open and dry grassland or woodland exposed to the sun. Adults are active from the middle of May and immediately begin feeding upon tender growing tips of the host, this continues for a brief period before mating and oviposition occurs; eggs are laid over a long period extending into July, the female will chew a cavity into the stem and insert either a single or sometimes several eggs, these need to be upright and at least a millimetre wide, and they will ignore any prostrate stems. The area around the egg darkens and a conspicuous callus forms. The larvae emerge after a week or so and develop rapidly; they are fully grown within a month and they will then construct a pupal cell within the stem. Larval feeding may be detected by wilted shoots, discoloured stems and dead apical shoots or flowers, in heavy infestations more than 100 larvae have been found in a single stem, each mine from 1-3 cm long and closely packed among the others, such infestations may be recognized by an abundance of dead and wilting stems and plants devoid of flowers. Drought-stressed plants seem especially prone to attack. In such cases a single stem may host large numbers of larvae, pupae and adults. The pupal phase lasts for a couple of weeks and adults eclose from August but they remain in the stems to overwinter. When the temperature increases in the spring they will chew distinctive round circular holes and move on to freshly developing foliage.