Knot grass moth
Acronicta rumicis, the knot grass moth, is a species of moth which is part of the genus Acronicta and family Noctuidae. It was first described by Carl Linnaeus in his 1758 10th edition of Systema Naturae. It is found in the Palearctic region. A. rumicis lives and feeds on plants located in wide-open areas. At its larval stage, as a caterpillar, it causes such a large impact as a crop pest that it has received much attention and research. A. rumicis feeds on maize, strawberries and other herbaceous plants.
The moth's evolution has been affected by the industrial melanism that occurred in Europe during the late 19th and early 20th centuries, causing a dramatic increase in two aberrations (salicin and lugubris), which have darker grey wings. Today, A. rumicis is important to conservation efforts in the United Kingdom, because, like many other species, it is in decline. However, as it is part of a UK Priority Biodiversity Action Plan and receiving greater awareness and conservation, the species may become more abundant.
A. rumicis has a wingspan of 34–44 mm. The forewings are blotched with a mixture of dark and light-grey shades, while the hindwings are dark brown. A white spot is seen midway down the trailing edge of the forewing providing a distinct marker for A. rumicis not seen in other Acronicta moths. Chinese and Japanese moths tend to be larger than their European counterparts. The Asian moths also have lower forewings that have darker shades of grey.
C. rumicis L. (3i). Forewing dark grey, varied in places with whitish; lines and shades black; outer line marked by a white spot on the submedian fold ; hindwings brownish fuscous Larva marbled dark and light grey: a dorsal row of red spots on black blotches, and a row of white spots on each side; a pale line below spiracles, containing orange-red tubercles; segments 5 and 12 of dorsum humped; tubercles with fascicles of fuscous and fulvous hairs— turanica Stgr., a form from Central Asia, is much paler, with the hindwings whitish. — Chinese and Japanese examples (3k) are larger than European and in all cases darker; in particular the lower half of forewing is blacker and the white spot of outer line then often obscured ; possibly the scotch form figured by Curtis as salicis, a melanic form, may represent this aberration, though the larva figured as belonging thereto is unquestionably that of menyanthidis. — ab. alnoides Geest (3k) has the costal half of forewing grey, the inner half blackish, somewhat interrupted with a strong black dagger-shaped mark at base and above anal angle ; superficially resembles a dark grey alni ; recorded from Freiburg in Baden. — ab. euphorbiae Steph. nec. Hbn. is grey brown, with the stigmata and space between them pale; and ab. euphrasiae Steph. nec Dup. is pale yellowish grey with numerous black lines and the orbicular stigma faint or obsolete, occurring in Cornwall.
A. rumicis is distributed throughout the Palearctic. It is common in northwestern China, the Korean Peninsula, and Japan, although it has also been found in other parts of Eurasia, including Russia. A. rumicis is found in almost all parts of Europe, though it is absent in some areas of north-western Scandinavia. There has been much research about the species in England and Scotland.
These moths tend to spend their lives in plants located in wide-open areas like meadows, woodland clearings, gardens, and hedgerows, generally in non-humid areas.
A. rumicis species generally have two broods: the first generation flies in May and June, while the second flies in August and September. However, the number of generations can differ based on location; in southern Europe, it tends to have three broods, while in the north, it has only one, most likely due to diapause. The number of broods may be determined by the duration of light and temperature ranges. The larvae tend to feed from the summer onwards until winter, during which A. rumicis spend its time in the pupae stage in cocoons.
Overall, the population of A. rumicis is in a sharp decline. Focusing on the moths in the United Kingdom, current research suggests that moths are in danger due to habitat loss, poor habitat management, global warming, and environmental deterioration from pesticides and pollution. Since 1969, the population of A. rumicis has declined by nearly 75%. Recently, A. rumicis was assigned as a Priority Biodiversity Action Plan (BAP) species, meaning the moth was identified as most threatened and will immediately be part of conservation efforts.
Researchers are realizing that the conservation of woodland areas is a high priority, in order to sustain as many populations of BAP species as possible; they also found a positive correlation between the species richness of herbaceous plants and the population density of moths.
