About Aplocera plagiata (Linnaeus, 1758)
The treble-bar, also known as the St. John's wort inchworm (Aplocera plagiata), is a moth species in the family Geometridae. It was first described by Carl Linnaeus in the 10th edition of Systema Naturae, published in 1758. This species is found across the entire Palearctic region and the Near East. Aplocera plagiata varies significantly in size, with a wingspan ranging from 37 to 43 mm, as well as in colouration. Most individuals are generally grey, with three distinct dark bands crossing each forewing, which gives the species its common name "treble-bar". The hindwings of this moth are pale grey or buff. Many forms of the species have been formally described; more detailed coverage can be found in Prout (1912–16). Aplocera plagiata is hard to tell apart with certainty from its close relative Aplocera efformata; further information on this distinction is available in Townsend et al. This species produces either one or two generations of offspring per year. In the British Isles, adult moths can be observed at any point between May and September. Adults fly at night and are attracted to artificial light. The eggs of Aplocera plagiata are whitish and lack gloss. The micropylar rosette of the egg has 11 to 12 leaves, and the sides of the egg have regular polygonal mesh patterning, with each cell further subdivided in an irregular pattern. The larvae of this species are also highly variable in colour, ranging from green to reddish brown, with alternating darker and lighter stripes along their bodies. Larvae feed on a variety of St. John's wort species (members of the genus Hypericum). This species overwinters in the form of a small larva.
