Nephelodes minians Guenee Lepidoptera Noctuidae

Life History

Distribution. Bronzed cutworm is widespread in distribution, occurring throughout the United States except for the southernmost tier of states. It also is found in southern Canada, from the Maritime Provinces to British Columbia. Despite the broad distribution of this species, its economic impact is limited to the eastern portion of its range, as far west as the Rocky Mountains. Also, it rarely is known to be damaging south of Kansas, Missouri, and Virginia. It is a native species.

Host Plants. Bronzed cutworm larvae feed on grasses and such grain crops as barley and wheat. It is most frequently considered a pest of pasture and lawn grasses, especially Poa spp., and occasionally it damages field crops such as clover and sugarbeet. It commonly damages corn in the midwestern states, and when preferred plants are exhausted it may feed on other vegetables. On occasion, larvae also are observed to climb fruit trees and feed on the buds and leaves.

Natural Enemies. Parasitoids and predators, though observed, seem less significance as mortality factors than viral diseases. Wasps known to attack bronzed cutworm include Rogas terminalis (Cresson), Apanteles rufocoxalis Riley (both Hymenoptera: Braco-nidae), and Campoletis oxylus (Cresson) (Hymenoptera: Ichneumonidae). Among parasitic flies reared from bronzed cutworm are Aplomya trisetosa (Coquillett), Euexorista futilis (Osten Sacken), Phryxe pecosensis (Townsend), and Tachinomyia variata Curran (all Diptera: Tachinidae). Western yellowjacket, Vespula pen-sylvanica (Saussure), is reported to prey on bronzed cutworm moths (Warren, 1990). A polyhedrosis virus has long been considered to be an important mortality factor (Walkden, 1937), but a granulosis virus also has been reported (Steinhaus, 1957).

Life Cycle and Description. There is a single generation per year over the entire range of this insect.

Adults are present in the autumn. In New York, moth flights consistently occur in September (Chapman and Lienck, 1981), in Minnesota they occur in late August and early September (Knutson, 1944), and in the central Great Plains their flights occur in September and October (Walkden, 1950). The eggs overwinter; however, egg hatch occurs early in the year, often in January and February. Larvae complete their development in April or May, and become quiescent until July or August, when pupation occurs.

  1. Moths are reported to scatter eggs singly at the surface of the soil. In shape, the egg has a slightly compressed sphere. It measures about 0.93 mm wide and 0.77mm high. The egg is marked with about 250 minute ribs that radiate outward from the center. In color, the egg is initially grayish, but soon acquires a pinkish tint and then a hint of purple. Duration of the egg stage, which is the overwintering form, is quite variable, but Walkden (1937) reported a mean of 127 days (range 98-145 days).
  2. There are 6-7 instars. Head capsule widths are about 0.5, 0.8, 1.2, 2.1, 3.0, and 4.3 mm for instars 1-6, respectively. Mean development time for larvae with six instars is 30.0, 10.5, 9.0, 8.2, 13.5, and 158.3 days, respectively. For larvae exhibiting seven instars, the duration of the first five instars is the same as with six-instar larvae, but duration of instar six is 15.6 days, and instar seven is 147.3 days. Total larval development time is estimated to be 230 days. Body length increases from 3-5 mm in the first instar to about 3545 mm at maturity. The mature instar is very distinctive in appearance, with a shiny bronze body and five sharply defined, broad stripes running to the length of the body. The stripes are whitish to yellowish. The

Bronzed cutworm larva.

Bronzed cutworm larva.

head is orangish-brown. The first four instars differ in background color, in that they are green instead of bronze, but also are marked with longitudinal stripes as found in the latter instars. (See color figure 44.)

  1. Mature larvae form a small cell in the soil for pupation. The pupa is brown and measures 2333 mm long and 8-11 mm wide. Duration of the pupal stage is reported to average 27.3 days (range 24-34 days).
  2. The moth is reddish brown, the front wings marked with an irregular dark-brown band crossing the wing centrally. Both the front and hind wings may display a reddish or violet tint. The moth measures about 35-50 mm in wingspan. Adults live for about 14 days, and commence oviposition when about two-day old. Based on dissection of eggs from adults, oviposition potential of about 1000 eggs is estimated. (See color figure 229.)

Detailed description and biology of bronzed cutworm was given by Crumb (1926) and Walkden (1937). A bibliography was published by Rings et al. (1974a). A comprehensive key to larvae of the Noctui-dae, including this species, was presented by Crumb (1956). It is also included in less inclusive keys for caterpillar pests in Nebraska (Whelan 1935) and Colorado (Capinera, 1986), and in a key to armyworms and cutworms in Appendix A. Moths are included in pictorial keys by Rings (1977a) and Capinera and Schaefer (1983).

Damage

Larvae are defoliators, and consume the leaves and stems of young plants. As they are present early in the year they normally damage only early-season plants.

Management

Larvae have been controlled successfully with applications of residual insecticides to the soil and foliage. Bacillus thuringiensis is not often recommended for cutworms. Although there seems to be no report of experimentation with baits, treated bran would likely prove effective.

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