Classification

Noctuoidea: Noctuidae: Noctuinae: Spodoptera exigua (Hübner)

Common name

beet armyworm, small mottled willow

Synonyms

Caradrina venosa, Laphygma exigua

Larval diagnosis (Detailed)

The larvalarva:
the stages between the egg and pupa of those insects having complete metamorphosis
of the beet armyworm, Spodoptera exigua, was partially described by Crumb (1956: 224), Okumura (1961)Okumura (1961):
Okumura, G. T. 1961. Identification of lepidopterous larvae attacking cotton. California Department of Agriculture Bureau of Entomology Special Publication 282. 80 pp., Peterson (1962)Peterson (1962):
Peterson, A. 1962. Larvae of insects: an introduction to Nearctic species. Part I: Lepidoptera and plant infesting Hymenoptera. Columbus, Ohio. 315 pp., Pogue (2002)Pogue (2002):
Pogue, M. G. 2002. A world revision of the genus Spodoptera Guenee (Lepidoptera: Noctuidae). Memoirs of the American Entomological Society 43. 202 pages., and Beck (1999-2000). The mouthparts were illustrated by Ahola and Silvonen (2005: 510). Dong et al. (1980)Dong et al. (1980):
Dong, N., T. C. Carlysle, H. L. Cromroy and D. H. Habeck. 1980. Morphological studies on the beet armyworm, Spodoptera exigua (Hubner) (Lepidoptera: Noctuidae). University of Florida Agricultural Experimental Station Bulletin 816. 38 pp. photographed the head and thorax of the first instarinstar:
the stage between molts
.

Typical New World interceptions of S. exigua are immediately recognized by the characteristic coloration, laterallateral:
to the side, or at the side of
black spot near the SD1 setaseta:
a hairlike projection of the body wall that is articulated in a socket; compare to spine
on the mesothoraxmesothorax:
the second thoracic segment
and a minute sclerotizedsclerotized:
hardened and tanned, so that it is yellow to black in color
bar connecting the SD1 setal base to an adjacent ventral muscle attachment (tonofibrillary platelettonofibrillary platelet:
a small, external, flattened, sclerotized area of the integument associated with muscle attachment
) on the meso- and metathoraxmetathorax:
the third thoracic segment
(Weisman 1974Weisman 1974:
Weisman, D. M. 1974. Some lepidopterous larvae of plant quarantine significance. U. S. Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine unpublished training aid. 22 pp., 1986; Passoa 1991Passoa 1991:
Passoa, S. 1991. Color identification of economically important Spodoptera larvae in Honduras. Insecta Mundi 5(3-4): 185-196.). The cuticle texture is smooth (at 20X).

There are two main color forms. The first one has a darkly marked dorsum with either dashes or rectangular bars, but never with a series of triangular markings (Levy and Habeck 1976Levy and Habeck 1976:
Levy, R. and D. H. Habeck. 1976. Descriptions of the larvae of Spodoptera sunia and S. latifascia with a key to the mature Spodoptera larvae of the eastern United States. Annals of the Entomological Society of America 69: 585-588., Passoa 1991Passoa 1991:
Passoa, S. 1991. Color identification of economically important Spodoptera larvae in Honduras. Insecta Mundi 5(3-4): 185-196., Beck 1999-2000Beck 1999-2000:
Beck, H. 1999-2000. Die Larven der Europaischen Noctuidae. Revision der Systematik der Noctuidae (Lepidoptera, Noctuidae). Herbipoliana 5/1(1): 1-864; 5/1(2): 1-448; 5/3(3): 1-512; 5/3(4): 1-336.: B668, Wagner et al. 2011Wagner et al. 2011:
Wagner, D. L., D. F. Schweitzer, J. B. Sullivan and R. C. Reardon. 2011. Owlet caterpillars of eastern North America. Princeton University Press, New Jersey. 576 pp.). The second, more common form, varies from light to dark olive green and is marked with a mixture of spots and dashes on the dorsum (Passoa 1991Passoa 1991:
Passoa, S. 1991. Color identification of economically important Spodoptera larvae in Honduras. Insecta Mundi 5(3-4): 185-196., Wagner et al. 2011Wagner et al. 2011:
Wagner, D. L., D. F. Schweitzer, J. B. Sullivan and R. C. Reardon. 2011. Owlet caterpillars of eastern North America. Princeton University Press, New Jersey. 576 pp.). There is often a large contrast between the pale dorsum and darker subdorsal area (Weisman 1986Weisman 1986:
Weisman, D. M. 1986. Keys for the identification of some frequently intercepted lepidopterous larvae. U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine series 81-47. 64 pp., Beck 1999-2000Beck 1999-2000:
Beck, H. 1999-2000. Die Larven der Europaischen Noctuidae. Revision der Systematik der Noctuidae (Lepidoptera, Noctuidae). Herbipoliana 5/1(1): 1-864; 5/1(2): 1-448; 5/3(3): 1-512; 5/3(4): 1-336.: B668).

Several issues complicated identification of S. exigua in the New World. Larvaelarva:
the stages between the egg and pupa of those insects having complete metamorphosis
resembling S. exigua, but without the mesothoracic black spot, are sometimes intercepted. It is unclear if these are S. exigua or not. In other cases, specimens are seen with long pointed spinnerets; these cannot be S. exigua. Both of these situations are best identified as "sp. of Noctuidae".

Spodoptera praefica has a rectangular, somewhat obscure, black spot on the mesothoraxmesothorax:
the second thoracic segment
. This is a western United States species with coloration totally unlike S. exigua (see Pogue 2002Pogue 2002:
Pogue, M. G. 2002. A world revision of the genus Spodoptera Guenee (Lepidoptera: Noctuidae). Memoirs of the American Entomological Society 43. 202 pages.:185). Some green forms of S. frugiperda resemble S. exigua if the pinaculapinaculum:
a small, flat, or slightly elevated chitinized area bearing a seta or setae
are very pale (Passoa 1991Passoa 1991:
Passoa, S. 1991. Color identification of economically important Spodoptera larvae in Honduras. Insecta Mundi 5(3-4): 185-196.). Crumb (1956)Crumb (1956):
Crumb, S. E. 1956. The Larvae of the Phalaenidae. U. S. Department of Agriculture Technical Bulletin 1135. 356 pp. separated these two species, in part, by the position of a line connecting the P1 setaeseta:
a hairlike projection of the body wall that is articulated in a socket; compare to spine
. The line is above the apex if the frontfront:
the frons or frontal area, sometimes including the clypeus
in S. frugiperda but below the apex in S. exigua (see illustrations in Okumura 1961Okumura 1961:
Okumura, G. T. 1961. Identification of lepidopterous larvae attacking cotton. California Department of Agriculture Bureau of Entomology Special Publication 282. 80 pp.).

More serious is the fact that S. exigua is easily confused with early instars of Copitarsia decolora and possibly other species of Copitarsia as well. The fastest way to seperate these two taxa is by counting the number of thoracic SD sclerotizedsclerotized:
hardened and tanned, so that it is yellow to black in color
bars. Spodoptera exigua has only one bar near SD1 whereas Copitarsia has two bars, one on SD1 and one on SD2 (Weisman 1986Weisman 1986:
Weisman, D. M. 1986. Keys for the identification of some frequently intercepted lepidopterous larvae. U.S. Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine series 81-47. 64 pp.). In addition, the spinneretspinneret:
a structure from which silk is spun, usually located on the labium of larvae
and labial palpilabial palpus:
a pair of small, segmented sensory structures arising on the distolateral portions of the labium
are different (see data sheet on Copitarsia for details).

Weisman (1974)Weisman (1974):
Weisman, D. M. 1974. Some lepidopterous larvae of plant quarantine significance. U. S. Department of Agriculture, Animal and Plant Health Inspection Service, Plant Protection and Quarantine unpublished training aid. 22 pp. grouped S. exigua with two other Old World relatives, S. exempta and S. mauritia, because all three species have a mesothoracic spot near SD1, no spot on A1 and muscle attachments between the prolegsprolegs:
fleshy, unjointed abdominal legs with or without crochets; false legs
on A3-6 that form a "Y". The mesothoracic spot on S. exempta appears to be absent or obscure at least in some color forms (SPIC). Spodoptera mauritia does have a small light brown mesothoracic marking near SD1 (Beardsley 1982Beardsley 1982:
Beardsley, J. W. Jr. 1982. A key to the late instar larvae of some Hawaiian Noctuidae. Proceedings of the Hawaiian Entomological Society 24: 37-49.). Fortunately, these three species have completely different color patterns and should not be confused with each other. However, it shows that one cannot focus just on a mesothoracic spot to identify S. exigua from the Old World.

Identification Authority (Detailed)

Being highly polyphagous and cosmopolitan, host/origin data usually does not help identify S. exigua. Larvaelarva:
the stages between the egg and pupa of those insects having complete metamorphosis
are not expected to be associated with dead plant material or woody conifers. Most countries and green plants are potential pathways, although in South America it is only reported from Bolivia, Brazil, Peru, and Chile (Zheng et al. 2011).

Specimens preserved in alcohol sometimes lose their color and are very pale. If a laterallateral:
to the side, or at the side of
mesothoracic spot is discernible, a few backup characters will help confirm S. exigua. These include presence of a minute sclerotizedsclerotized:
hardened and tanned, so that it is yellow to black in color
bar connecting the SD1 setal base to a ventral muscle attachment on the meso- and metathoraxmetathorax:
the third thoracic segment
, a bisetosebisetose:
two setae
SV group on A1, a smooth cuticle (at 20X) and the muscle attachments between the prolegsprolegs:
fleshy, unjointed abdominal legs with or without crochets; false legs
on A3-6 forming a short stemmed Y (Passoa 1991Passoa 1991:
Passoa, S. 1991. Color identification of economically important Spodoptera larvae in Honduras. Insecta Mundi 5(3-4): 185-196.). The mandible has no inner teeth or retinaculumretinaculum:
a projection or toothlike structure on the oral surface of the mandible
. However, none of the morphological characters that define S. exigua are very distinctive, and all expected to occur in other noctuid larvaelarva:
the stages between the egg and pupa of those insects having complete metamorphosis
, so specimens with atypical coloration from hosts other than economically important plants need to be examined very carefully. For example, Crumb (1956: couplets 1, 6) listed a few "Amphipyrinae group 7" and "Hadeninae with an open apicalapical:
at the end or the tip
silk pore [of the spinneret]" as two taxa with a sclerotizedsclerotized:
hardened and tanned, so that it is yellow to black in color
bar on SD1 of the mesothoraxmesothorax:
the second thoracic segment
. Early instars of S. exigua often show the black mesothoracic spot. If other characters fit, these can be identified to species.

Origin records

Spodoptera exigua has been intercepted from the following locations:

Argentina, Brazil, Canada, Chile, China, Colombia, Costa Rica, Dominica, Dominican Republic, Ecuador, Egypt, El Salvador, France, Guadeloupe, Guatemala, Haiti, Hawaii, Honduras, India, Israel, Italy, Jamaica, Japan, Kenya, Lebanon, Malaysia, Mexico, Micronesia, Netherlands, Nigeria, Palestinian Territory, Peru, Saudi Arabia, Singapore, South Korea, Spain, St. Lucia, St. Vincent and the Grenadines, Tanzania, Thailand, Trinidad and Tobago, Turkey

Host records

Spodoptera exigua has been intercepted on the following hosts:

Achillea sp., Aconitum sp., Agapanthus sp., Alchemilla sp., Allium ascalonicum, Allium cepa, Allium fistulosum, Allium porrum, Allium sativum, Allium schoenoprasum, Allium sp., Allium tuberosum, Alocasia sp., Alstroemeria aurantiaca, Alstroemeria sp., Amaranthus caudatus, Amaranthus hybridus, Amaranthus sp., Amaranthus spinosus, Ammi majus, Ananas comosus, Anemone sp., Anethum graveolens, Anethum sp., Anigozanthus sp., Antirrhinum majus, Antirrhinum sp., Apiaceae, Apium graveolens, Apium graveolens var. dulce, Apium sp., Aranthera sp., Artemisia dracunculus, Artemisia sp., Artemisia tridentata, Asclepias sp., Asclepias tuberosa, Asparagus officinalis, Asparagus sp., Asparagus sprengeri, Aster ericoides, Aster sp., Asteraceae, Astilbe sp., Bacopa sp., Basella sp., Bergera koenigii, Beta vulgaris var. cicla, Beta vulgaris var. vulgaris, Brassica campestris, Brassica chinensis, Brassica juncea, Brassica napus, Brassica oleracea, Brassica oleracea var. acephala, Brassica oleracea var. alboglabra, Brassica oleracea var. botrytis, Brassica oleracea var. capitata, Brassica oleracea var. italica, Brassica pekinensis, Brassica rapa, Brassica rapa ssp. chinensis, Brassica rapa ssp. pekinensis, Brassica rapa var. parachinensis, Brassica sp., Bupleurum sp., Calendula officinalis, Calendula sp., Callistephus chinensis, Callistephus sp., Capsicum annuum, Capsicum sp., Carthamus sp., Carthamus tinctorius, Celosia argentea, Celosia sp., Chamaemelum sp., Chenopodium album, Chenopodium berlandieri ssp nuttalliae, Chenopodium berlandieri ssp. nuttalliae, Chenopodium sp., Chlorophytum sp., Chrysanthemum sp., Cicer arietinum, Cichorium endivia, Cinnamomum verum, Citrus sp., Clematis sp., Codiaeum variegatum, Colocasia esculenta, Coriandrum sativum, Cucurbita maxima, Cucurbita sp., Cyathea sp., Cynara scolymus, Dahlia sp., Daucus sp., Davallia sp., Delphinium sp., Dendrobium sp., Dianthus barbatus, Dianthus caryophyllus, Dianthus sp., Dysphania ambrosioides, Echeveria sp., Echinodorus sp., Eremurus sp., Ericaceae, Eruca sativa, Eruca sp., Eryngium sp., Eucalyptus sp., Euphorbia sp., Eustoma grandiflorum, Eustoma sp., Fragaria ananassa, Fragaria sp., Genista sp., Gerbera sp., Gladiolus sp., Grevillea sp., Gymnocoronis spilanthoides, Gypsophila elegans, Gypsophila sp., Helianthus annuus, Helianthus sp., Helichrysum sp., Heliconia psittacorum, Heliconia sp., Hydrangea sp., Ipomoea batatas, Iris sp., Lactuca sativa, Lactuca sativa var. capitata, Lactuca sativa var. longifolia, Lactuca sp., Lilium sp., Limonium perezii, Limonium sinuatum, Limonium sp., Lippia sp., Lisianthus sp., Luffa acutangula, Luffa sp., Lycopersicon esculentum, Malvaceae, Matthiola incana, Matthiola sp., Mentha arvensis, Mentha longifolia, Mentha officinalis, Mentha piperita, Mentha sp., Mokara sp., Moluccella laevis, Moluccella sp., Momordica balsamina, Momordica charantia, Momordica sp., Musa sp., Nephelium lappaceum, Nephelium sp., Ocimum basilicum, Ocimum sp., Oncidium basilicum, Oncidium sp., Opuntia sp., Orchidaceae, Origanum majorana, Origanum sp., Origanum vulgare, Peperomia sp., Perilla sp., Petroselinum crispum, Petroselinum sp., Phaseolus sp., Phaseolus vulgaris, Philodendron sp., Phlox sp., Physalis philadelphica, Physalis pubescens, Physalis sp., Pisum sativum, Pisum sativum var. macrocarpon, Pisum sp., Pithecellobium dulce, Polianthes sp., Polianthes tuberosa, Porophyllum tagetoides, Portulaca oleracea, Portulaca sp., Psidium sp., Ranunculus sp., Raphanus sativus, Rosa sp., Rosmarinus officinalis, Rubus sp., Rumex acetosa, Ruscus sp., Saccharum officinarum, Salvia officinalis, Salvia sp., Sechium edule, Solanum lycopersicum var lycopersicum, Solanum sp., Solidago sp., Solidaster sp., Spinacia oleracea, Spinacia sp., Suaeda sp., Symphoricarpos sp., Tagetes erecta, Tagetes sp., Thymus caespititius, Thymus citriodorus, Thymus sp., Thymus vulgaris, Trachelium sp., Tulipa sp., Vaccinium angustifolium, Vaccinium corymbosum, Vaccinium sp., Veronica sp., Viburnum sp., Vigna sesquipedalis, Vigna sp., Vigna unguiculata, Xanthosoma hastifolium, Zea mays, Zingiber officinale