Mythimna sequax

(Franclemont, 1951)

wheat armyworm

Mythimna sequax, commonly known as the wheat , is a noctuid whose larvae are significant agricultural pests of wheat and other cereals. Native to the Americas, it has become established in southern Brazil where it causes substantial damage to winter wheat crops. The species exhibits larval , sheltering under soil debris during daylight hours. Climate change research indicates its voltinism (number of per year) is sensitive to temperature increases, with nonlinear phenological models providing more accurate predictions than traditional approaches.

Pronunciation

How to pronounce Mythimna sequax: //mɪˈθɪmnə ˈsiːkwæks//

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Identification

: MONA/Hodges number 10438.1. Larvae: typically 4th-6th instar individuals exceed 1.5 cm in length; mature larvae larger. Specific diagnostic features for distinguishing M. sequax from congeneric such as M. unipuncta (true ) and M. separata (Oriental armyworm) are not documented in available sources.

Habitat

Agricultural agroecosystems, specifically wheat crop fields. Larvae require soil surface with mulch or soil clods for daytime shelter. In Brazil, occurs in winter cereal production regions of southern Paraná State.

Distribution

Native to North America; established in South America, specifically the southern region of Paraná State, Brazil (documented at 23°17′14″S, 51°05′26″W in Ibiporã, with occurrence in northeastern Paraná wheat-growing regions).

Seasonality

In southern Brazil, present in wheat crops from first visible leaf stage (late May) through grain maturation (early September). Parasitized larvae detected only during wheat reproductive stage (milky to soft grain phase). Voltinism varies with temperature and location; multivoltine under favorable conditions.

Diet

Larvae feed on wheat (Triticum aestivum) and other winter cereals. Laboratory rearing successful on kicuyo grass (Pennisetum clandestinum).

Host Associations

Triticum aestivum - plantprimary agricultural ; winter wheat in southern Brazil
Pennisetum clandestinum - laboratory kicuyo grass used for laboratory rearing
Microplitis mediator - larval endoparasitoidBraconidae; successfully parasitizes first through fourth instars, preferring second and third instars
Glyptapanteles muesebecki - larval Braconidae; predominant in field surveys (18.7% of parasitoids collected in southern Paraná)
Euplectrus ronnai - larval Eulophidae
Winthemia trinitatis - larval Tachinidae; first reported from M. sequax in Brazil, 2008
Winthemia tricolor - larval Tachinidae; first reported from M. sequax in Brazil, 2008
Lespesia aletiae - larval Tachinidae; first reported from M. sequax in Brazil, 2008
Lespesia archippivora - larval Tachinidae; first reported from M. sequax in Brazil, 2008
Peleteria sp. - larval Tachinidae; identified from parasitized larvae in Brazil
Ophion sp. - larval Ichneumonidae; identified from parasitized larvae in Brazil

Life Cycle

Complete with six larval instars. successful from first through fourth instars only; fifth and sixth instars do not produce parasitoid emergence. Larvae , sheltering under mulch or soil clods during day. Development to pre-pupa stage observed in laboratory at 25±2°C, 60±20% humidity, 12-hour photophase. caterpillars parasitized by Microplitis mediator continue to after ; single parasitoid larva emerges before host completes larval stage.

Behavior

Larvae exhibit strictly feeding , remaining beneath mulch or soil clods during daylight hours to avoid sunlight and desiccation. nocturnal, attracted to light. Field-collected parasitized larvae show lower progeny production than laboratory-reared individuals, suggesting or quality effects in natural conditions.

Ecological Role

Herbivorous agricultural pest causing defoliation of wheat and cereal crops. Serves as for diverse including at least seven hymenopteran and three dipteran parasitoid , supporting natural in agroecosystems. Potential candidate for programs in Brazil.

Human Relevance

Significant economic pest of winter wheat in southern Brazil, with damage potential requiring monitoring and management. Natural rates of 10.12% documented in field studies. Climate change vulnerability: voltinism predictions vary substantially based on phenological model choice, with nonlinear models recommended for accurate forecasting of numbers under warming scenarios.

Similar Taxa

Mythimna unipunctaTrue ; congeneric with similar and agricultural pest status. Distinguished by geographic distribution and specific larval , though detailed comparative diagnostic features not provided in sources.
Mythimna separataOriental ; congeneric and major corn pest in Asia. Separated by geographic range (Asia vs. Americas/Brazil) and associations.
Peridroma sauciaVariegated cutworm; shares Noctuidae , similar , and agricultural pest status. Both documented as nocturnal of apple in Arkansas study, though P. saucia not congeneric.

More Details

Taxonomic history

Originally described as Pseudaletia sequax Franclemont, 1951; subsequently transferred to Mythimna. Listed as accepted in GBIF and NCBI, though Catalogue of Life marks status as synonym (possibly reflecting subgeneric treatment as Mythimna (Pseudaletia) sequax).

Climate change research significance

Used as model organism in phenological modeling studies demonstrating that choice of model (linear vs. nonlinear) dramatically affects voltinism predictions under climate change scenarios. Location, model choice, and their interaction explained 94% of variance in estimated numbers.

Parasitoid biology notes

Glyptapanteles muesebecki females do not discriminate previously parasitized caterpillars, resulting in under laboratory conditions. Microplitis mediator exhibits instar-specific success, with second and third instars optimal for development.