Spodoptera exigua

(Hübner, 1808)

Beet Armyworm, Small Mottled Willow Moth, Asparagus Fern Caterpillar

, commonly known as the , is a highly agricultural pest native to Asia that has been introduced worldwide. The is a member of the Noctuidae and is particularly destructive in vegetable crops, though it occasionally damages soybean in the southern United States. Larvae are characterized by variable green coloration with pinkish or yellowish undersides and a white lateral stripe. The species has gained attention in molecular research due to its gut microbiome interactions and susceptibility, which have implications for strategies.

Spodoptera exigua (29683245587) by Donald Hobern from Copenhagen, Denmark. Used under a CC BY 2.0 license.

Spodoptera exigua (32504469731) by Donald Hobern from Copenhagen, Denmark. Used under a CC BY 2.0 license.

Spodoptera exigua? by Frank Falconer. Used under a CC BY-SA 2.0 license.

Pronunciation

How to pronounce Spodoptera exigua: /ˌspɒd.oʊˈtɪə.rə ɛɡˈzɪɡ.ju.ə/

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

Identification

Larvae can be confused with Spodoptera eridania (southern ) due to a dark lateral spot. The critical distinguishing character is spot location: in S. exigua, when present, the spot occurs on the , whereas in S. eridania the spot is located on the first abdominal segment. This character allows reliable separation of large larvae. Conclusive identification of young larvae is often not possible due to similarity in appearance among Spodoptera .

Images

Habitat

Agricultural environments, particularly fields of vegetable crops and occasionally soybean. In the southern U.S., larvae prefer foliage of seedling soybean plants but will feed on blossoms and small pods if present during reproductive stages. Laboratory colonies are maintained at 25±3°C with 60±5% relative humidity and 16-hour light:8-hour dark .

Distribution

Native to Asia; introduced worldwide and now found almost anywhere crops are grown. Established in North America, South America, Oceania, the Azores (São Miguel and Terceira), and the Middle East (United Arab Emirates). In the United States, regularly occurs in the southern states including Mississippi and Illinois. In the British Isles, present as an introduced but not known to breed.

Diet

Highly . Larvae feed on foliage of seedling plants; during reproductive stages of soybean, also feed on blossoms and small pods. Better known as a pest of vegetables than of soybean. In laboratory studies, reared on artificial diet or pepper (Capsicum) leaves. feed on sugar solution.

Host Associations

Capsicum - plantUsed in laboratory assays; larvae show reduced weight gain and delayed growth compared to artificial diet
Glycine max - plantSoybean; occasional pest in southern U.S., preferring seedling foliage but feeding on blossoms and pods when available

Life Cycle

Holometabolous insect with complete . Larval stage consists of multiple instars. Gut undergoes dramatic changes after metamorphosis. In laboratory colonies, kmo gene mutation affects larval-to- development with visible phenotypic changes including yellow , golden yellow wing pigmentation, and transparent white ocelli and brain coloration. Specific details on , pupal stages, or time in field conditions are not provided in sources.

Behavior

Oral secretion (regurgitation) contains 8-hydroxyquinoline-2-carboxylic acid (8-HQA) and bacterial content derived from gut. These oral secretions influence -plant interactions. Larvae exhibit group feeding early in development, with groups hatching from single masses and skeletonizing nearby foliage before dispersing as they grow larger.

Ecological Role

Agricultural pest that causes direct damage through foliar feeding and pod damage in legume crops. Gut influences nutrition, , and interactions with plants and . Enterococcus form part of core microbiota. Microbiota can shape trophic interactions with plants by producing toxin-degrading or modulating plant defense responses. Targeted for using ; understanding of caspase-mediated apoptosis provides insights for engineering improved viral .

Human Relevance

Significant agricultural pest causing economic damage to vegetable crops and occasional damage to soybean. Subject of extensive research on , including -based and gut microbiome manipulation. Laboratory studies have investigated resistance mechanisms to Bacillus thuringiensis and strategies to enhance baculovirus through of viral .

Similar Taxa

Spodoptera eridaniaLarvae can be confused due to similar coloration and presence of a dark lateral spot. Distinguished by spot location: in S. exigua versus first abdominal segment in S. eridania.
Spodoptera frugiperdaBoth are pests of soybean with overlapping distribution in the Americas. S. frugiperda is distinguished by pinaculae with single stout setae on abdominal segments and an inverted white Y-shaped mark on the .
Spodoptera ornithogalliLarvae have more uniform appearance with paired black triangular spots and prominent yellow stripes, lacking the variable green-pink coloration of S. exigua.

More Details

Gut Microbiome and Kynurenine Pathway

The kynurenine KMO (kynurenine 3-monooxygenase) produces 8-HQA, an iron-chelating compound that regulates gut microbial . CRISPR/Cas9-mediated kmo deletion abolishes 8-HQA production, reduces bacterial diversity, collapses compartment-specific bacterial , and promotes Enterococcus dominance. Mutants show reduced and increased susceptibility to Bacillus thuringiensis.

Baculovirus Interactions

Caspase-4 (SeCaspase-4) functions as an effector caspase in -induced apoptosis. Recombinant Autographa californica multiple (AcMNPV) expressing SeCaspase-4 shows increased against larvae by promoting apoptosis, despite reducing viral production. This provides a strategy for enhancing efficacy.