Tryphaena
(from a Greek proper name). Also written Triphoena. A genus of Night-moths, nearly related to Noctua (which see) and Agrotis; but the species are readily distinguished from those of both genera by the hind wings, which are yellow or orange, with a black band near the hind margin, from which it is separated only by a fringe similar in colour to the area of the wings. There is usually a dark, crescentic mark near the middle of each hind wing. These moths are well known to amateur entomologists as the "Yellow-Underwings." The fore wings are rather narrow, and vary in ground-colour from grey to olive-green or rich umber-brown. Their front margin is sometimes pale; and there are several narrow cross-bars (some paler and others darker than the ground-colour), and two spots near the middle of each wing outlined with grey. There are six British species, varying from 1 1/4in. to 2 1/4in. in spread of front wings. They differ, also, in the breadth of the black band, and in the depth of colour in the yellow or orange area of the hind wings. The larvae mostly belong to the group of Surface Caterpillars (which see) in general appearance and in habits. The body is smooth and cylindrical, and the head small. The colour varies from dingy ochreous, or dull yellowish-green, to dark brown, with (usually) a paler line down the back, and pale and dark mottlings; but space will not permit of giving minute details.
A very common species is T. pronuba (Common Yellow Underwing). The front wings expand to from 2in. to 2 1/4in.; the hind wings are yellow, with the black marginal band rather narrow, and there is no dark spot in their middle. The larvae of this species feed near the top of the roots of Lettuces, Cabbages, and almost all other kinds of garden vegetables, as well as on many flowering plants. They burrow into the plants, or hide just below the surface of the soil; and when full-fed, in spring, they make earthen cocoons, and become pupae in the soil. T. Ianthina (Lesser Broad-bordered Yellow Underwing) has an expanse of wing of about 1 1/2in. The front wings are rich brown, with purple tints, and three wedges of grey extending inwards from the front margin. The hind wings have the base black, and the broad, marginal band intense velvety-black; the crest of each wing is orange. The larvae feed in Primroses, and in other garden flowers, during winter, and become pupae, in spring, in cocoons in the soil. T. interjecta (Least Yellow Underwing) reaches only about 1 1/4in. in span. The front wings are rusty-brown or dull red, with darker lines, and a smoky band near the hind margin. The hind wings are dark at the base, with a smoky-black marginal band, a similar shade along the inner margin, and a dark spot in the yellow median area. The larvae feed on low plants, such as Dock and other weeds, in winter and spring, like those already mentioned. T. fimbria (Broad-bordered Yellow Underwing) has a spread of wings of 2in. to 2 1/4in. It is easily known by its size, and by the very broad, intensely black marginal band, and the deep orange, unspotted area (extending to the base) of the hind wings. The larvae feed in autumn on leaves of Birch, Sallow, and other trees, hybernate, and in spring eat the young leaves of the same trees, crawling down the trunk before daylight appears, and hiding in the ground all day, to crawl up again in the evening. T. orbona (Lesser Yellow Underwing) varies in spread of wings from 1 1/2in. to 1 3/4in. The front wings vary in depth of colour. The hind wings are yellowish, clouded with grey at the base, and have a dark grey, crescentic spot in the middle, and a rather narrow, blackish marginal band. The larvae feed in autumn on Chickweed and other low plants; but, after hybernation, in spring they ascend the stems of Hawthorn and Sallow, and eat the young leaves. T. subsequa is too uncommon to call for special mention here.
Remedies. These should be employed as recommended against Noctua.