Peridroma saucia
Peridroma saucia, the pearly underwing or variegated cutworm, is a moth of the family Noctuidae. The species was first described by Jacob Hübner in 1808. It is found in North and South America, Europe, Asia and Africa. The variegated cutworm feeds on many plants, especially common fruits and vegetables. The moth undergoes two to four generations per year. The development of the moth slows in colder temperatures, indicative of its migratory nature. All stages of the life cycle have a developmental threshold for temperature. The moth is known to migrate to the northern regions during warmer months, returning to the southern regions when the climate becomes colder.
The variegated cutworm has a number of wasp and fly parasites, which account for most of the larval deaths each year. The female P. saucia produces a sex pheromone to attract male moths. Most notably, the variegated cutworm is known as one of the most damaging garden pests. The larvae cause considerable damage to common garden vegetables and fruits, destroying large amounts of crops every year. There are many methods of pest control that are being implemented in order to control P. saucia and its damage to crops.
Geographic range
The variegated cutworm can be found in North and South America, the Hawaiian Islands, Europe, Asia, and North Africa. The origin of the moth is uncertain, but the earliest records with the description of the moth are from Europe in 1790. However, the moth was first observed in North America in 1841, where today it primarily inhabits Southern Canada and Northern United States. P. saucia was discovered in Japan in the 1970s, where it is dubbed "nise-tamanayaga", which directly translates to "false black cutworm moth". As Japanese populations of the variegated cutworm continue to grow, studies are still being conducted to identify the distribution areas in the region.Food resources
Common plants
The variegated cutworm larva feeds on many plants, and is known as a common garden pest. Some of these plants include:Vegetables
Fruits
Other plants
Weeds
P. saucia also feeds on weeds. Feeding on weeds is less common than feeding on fruits and vegetables, but has still been observed. The variegated cutworm feeds on the following weeds:- Datura sp. – jimsonweed
- Rumex sp. – dock
- Eupatorium capillifolium – dogfennel
- Ambrosia sp. – ragweed
- Capsella bursa-pastoris – shepherd's purse
Feeding habits
Parental care
Oviposition
The variegated cutworm begins laying eggs one to two weeks after the adults emerge from pupation. One of the reasons why P. saucia is such a common pest is because of its very high reproductive potential and the difficulty in controlling the moth's mass egg-laying. Studies show that although the moth tends to live longer at slightly colder temperatures, the total number of eggs laid is greater at slightly higher temperatures, suggesting the greater reproductive success at higher temperatures. However, studies have shown that this is due to an extension of the oviposition period, rather than an increase in the number of eggs the female moth lays per day. A female may lay between 1200 and 1400 eggs throughout her life.Life cycle
In one year, the variegated cutworm will have two to four generations. Generally, in colder areas, such as the Canadian populations of P. saucia, the moth undergoes two generations, whereas in warmer regions, P. saucia has three to four generations per year. Additionally, while pupa and larvae may be able to live through the winter, moths still migrate into cooler areas each spring and return to the warmer areas each fall. The moths travel long distances when migrating each year, so researchers have found it difficult to determine the exact number of generations based on just the adult populations of moths.Egg
The hemispherical egg is flattened at its end, where it generally is attached to a leaf or plant stem. The surface of the egg has ridges extending from the center to the edges. They are 0.55–0.58 millimeters in diameter, and 0.40–0.45 mm in height. The egg begins white, but turns brown as it matures. The developmental threshold of the egg is 3.0–6.0 °C. The eggs are generally laid in large groups. In warm weather, the egg stage lasts between four and six days, whereas in cold weather, the egg stage is extended to up to ten days.Larva
The larval stage of P. saucia has 6 instars. The developmental threshold for these larvae is 2.6–6.7 °C. The first instar has an average duration of 6.5 days, a head capsule width of 0.30–0.35 millimeters, and a body length of 2.0–3.0 millimeters; the second instar has an average duration of 4.6 days, a head capsule width of 0.46–0.62 millimeters, and a body length of 3.6–6.5 millimeters; the third instar has an average duration of 4.8 days, a head capsule width of 0.80–1.00 millimeters, and a body length of 5.3–9.0 millimeters; the fourth instar has an average duration of 4.7 days, a head capsule width of 1.20–1.65 millimeters, and a body length of 12–16 millimeters; the fifth instar has an average duration of 6.7 days, a head capsule width of 1.9–2.6 millimeters, and a body length of 25–28 millimeters; the sixth instar has an average duration of 16.8 days, a head capsule width of 3.0–3.2 millimeters, and a body length of 35–46 millimeters. The larvae are generally colored brownish-gray to grayish-black, with a distinctive yellow or white spot on the dorsal side of their first four to six abdominal segments. Additionally, P. saucia larvae have a black W-shaped mark on the 8th abdominal segment of their sixth instar and a black line laterally above their spiracles. The head of the larvae is generally orange-brown with darker spots.Pupa
The pupal stage of P. saucia lasts for an average of 33 days at colder temperatures and 13 days at warmer temperatures. The developmental threshold for the pupa is 4.3–8.5 °C. The pupa is 15–23 millimeters long and 5–6 millimeters wide, and mahogany brown in color. Larvae dig a small hole in the soil and pupate near the soil surface.Adult
The adult moth is fairly large, with a wingspan of 43–50 millimeters. The front wings of P. saucia are grayish-brown with a red undertone, with darker brown shades centrally and along the edges. The wings have seven short, black marks, a distinctive feature of the moth. The moth's hindwings are either opalescent or white with brown veins and brown shading on the edges. The head and thorax of the moth are dark brown, with a lighter brown abdomen.The subspecies margaritosa includes the more strongly marked and varied specimens, wholly grey in color. Ab. majuscula is fuscous black, while ab. nigrocosta is greyish fuscous, sometimes tinged with reddish or ochreous, with a broad black shade along the costal area which sometimes encloses the stigmata. On the contrary, ab. ochreacosta has the inner marginal area darker while the whole costal area is pale. Ab. rufa and brunnea are mere color varieties.