Euxoa auxiliaris

Grote, 1873

Army Cutworm Moth, Miller Moth

, the , is a seasonal migrant and agricultural pest in the Great Plains of North America. The larval stage damages field by cutting stems and feeding on foliage, while undertake remarkable long-distance to alpine talus slopes in the Rocky Mountains to escape summer heat. These serve as a critical, high-calorie food source for grizzly bears during their pre- hyperphagia. Adults are commonly called '' due to the fine, easily-shed that resemble flour .

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Pronunciation

How to pronounce Euxoa auxiliaris: //juːkˈsoʊ.ə ɔːɡ.zɪlˈiː.ə.rɪs//

These audio files are automatically generated. While they are not always 100% accurate, they are a good starting point.

Identification

are recognized by their drab coloration and the distinctive dusty appearance from easily-shed . are identified by their shiny, greasy , C-shaped defensive posture when disturbed, and stem-cutting feeding damage at or near the soil surface. Distinguished from other by their surface-feeding and tendency to aggregate in large numbers. The is the most common cutworm attacking small grains in Texas.

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Habitat

inhabit agricultural fields, grassy areas, and weedy fields in the Great Plains, with highest in thin, late-planted, or poorly tillering stands. aggregate during summer in alpine talus slopes and rockslide interstices at high elevations in the Rocky Mountains, where they seek from extreme heat.

Distribution

North America: from Northwest Territories and Alberta south through Washington, Oregon, and Montana to Mexico, east to Minnesota, Nebraska, and Oklahoma. Scattered records include northern Michigan, Indiana, Missouri, Texas, and Florida. Summer documented in the Greater Yellowstone and, more recently, in the southern Canadian Rocky Mountains of British Columbia and Alberta.

Seasonality

laid in late summer and early autumn; hatching triggered by rains. feed through fall and winter on warmer days, with peak damage in February and March as grains green up. occurs in early spring; in late spring and early summer. Adults migrate to alpine sites for summer, returning to lowland plains in fall to reproduce.

Diet

are feeders on multiple , with cereal grasses especially vulnerable. They cut stems of young plants at or near the soil surface and consume foliage. feed nocturnally on flower nectar in alpine areas, accumulating substantial lipid reserves (approximately 70% body composition at summer peak).

Host Associations

Copidosoma bakeri - Polyembryonic ; rates reached 61% in southern Alberta fields in 1990. Parasitized feed longer and grow larger than unparasitized ones.
Meteorus leviventris - of in Oklahoma alfalfa fields
Apanteles griffin - of in Oklahoma alfalfa fields
Ursus arctos horribilis - Grizzly bears forage on as critical summer food source

Life Cycle

cycle with one per year. Females lay 1,000–2,000 on bare soil, particularly in cultivated or overgrazed conditions. Eggs hatch in 2–14 days, triggered by rainfall. feed through fall and winter, becoming active on warmer days. They overwinter as small larvae in soil or grass clumps, resuming feeding in spring until in early summer. emerge after 3–4 weeks, then migrate westward to alpine sites. Sexual maturation occurs during alpine residency; females lack developed during (- ). After summer, adults remigrate to natal ranges for .

Behavior

are surface feeders, hiding under soil clods and debris near bases during daylight. When disturbed, they assume a tight C-shaped defensive posture. undertake remarkable seasonal : westward to alpine talus slopes following spring flower bloom, where they aggregate in prodigious numbers. They are diurnally inactive in rock interstices, emerging at night to feed on nectar. Adults can more than 50 miles at a time; one tethered individual flew 23 hours at 5.8 mph (equivalent to 133 miles). They detect approaching bats via thoracic tympanic organs and execute evasive . When disturbed at rest, adults spray a defensive liquid from the .

Ecological Role

As : agricultural pest causing to small grains, alfalfa, and other field . As : critical summer food resource for grizzly bears in the Rocky Mountains, providing high-calorie nutrition (70% lipid, 25% ) during pre- hyperphagia. The 's and supports bear in the Greater Yellowstone and southern Canadian Rockies.

Human Relevance

Significant agricultural pest of wheat, barley, oats, alfalfa, potato, and sugarbeet. Larval feeding can reduce stands and yield; suggest treatment at 4–5 per square foot in conditions. Cultural controls include weed destruction, clean seedbed preparation, and delayed planting. are available but timing is complicated by larval activity. '' can become household nuisances around lights. The has developed to some organophosphorous insecticides in certain regions.

Similar Taxa

Agrotis spp.Other that damage sorghum and small grains; distinguished by 's surface-feeding and shiny, greasy larval appearance
Pseudaletia unipuncta (True Armyworm)Also attacks small grains; distinguished by green to coloration with light stripes, lack of inverted 'Y' on , and preference for cool, damp conditions
Spodoptera frugiperda (Fall Armyworm)Also infests of grasses; distinguished by inverted 'Y' between and four distinct black spots on eighth abdominal
Euxoa mimallonis (Ruddy-winged Dart)Congeneric with similar appearance; distinguished by specific patterns and lack of mass migratory to alpine sites

More Details

Thermal Tolerance

Critical thermal maximum (CTLmax) of 44.13°C for lab-reared and 43.28°C for wild-caught ; critical thermal (CTLmin) of approximately -2°C. This allows continued activity and feeding in chilly alpine environments.

Parasitism Complications

High rates of by Copidosoma bakeri can paradoxically increase damage because parasitized feed longer and more abundantly than healthy larvae, potentially complicating control recommendations.