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Plantwise Technical Factsheet

pearly underwing moth (Peridroma saucia)

Host plants / species affected
Abies balsamea (balsam fir)
Abies grandis (grand fir)
Acer (maples)
Acer negundo (box elder)
Acer saccharum (sugar maple)
Alcea rosea (Hollyhock)
Allium cepa (onion)
Alnus rubra (red alder)
Ambrosia artemisiifolia (common ragweed)
Amelanchier canadensis (thicket serviceberry)
Anthemis cotula (dog fennel)
Apium graveolens (celery)
Arachis hypogaea (groundnut)
Asparagus officinalis (asparagus)
Asparagus setaceus (asparagus fern)
Aster
Avena sativa (oats)
Beta vulgaris (beetroot)
Beta vulgaris var. saccharifera (sugarbeet)
Brassica napus var. napus (rape)
Brassica nigra (black mustard)
Brassica oleracea (cabbages, cauliflowers)
Brassica oleracea var. capitata (cabbage)
Brassica rapa subsp. oleifera (turnip rape)
Capsella bursa-pastoris (shepherd's purse)
Capsicum annuum (bell pepper)
Chamaecyparis thyoides (Atlantic white cedar)
Chenopodium quinoa (quinoa)
Chrysanthemum (daisy)
Cicer arietinum (chickpea)
Cichorium (chicory)
Cirsium (thistle)
Citrullus lanatus (watermelon)
Citrus limon (lemon)
Citrus sinensis (navel orange)
Conyza canadensis (Canadian fleabane)
Corylus
Cucumis melo (melon)
Cucumis sativus (cucumber)
Cucurbita moschata (pumpkin)
Cynara cardunculus var. scolymus (globe artichoke)
Dahlia
Datura stramonium (jimsonweed)
Daucus carota (carrot)
Dianthus (carnation)
Epilobium angustifolium (rosebay willowherb)
Erigeron (Fleabane)
Eupatorium
Fragaria ananassa (strawberry)
Geranium (cranesbill)
Gladiolus hybrids (sword lily)
Gleditsia triacanthos (honey locust)
Gossypium (cotton)
Helianthus annuus (sunflower)
Hordeum vulgare (barley)
Humulus lupulus (hop)
Inula helenium (Elecampane)
Ipomoea batatas (sweet potato)
Lactuca sativa (lettuce)
Lathyrus odoratus (sweet pea)
Linum usitatissimum (flax)
Lolium (ryegrasses)
Maclura pomifera (osage orange)
Malus domestica (apple)
Medicago sativa (lucerne)
Melia azedarach (Chinaberry)
Melilotus albus (honey clover)
Mentha piperita (Peppermint)
Mentha spicata (Spear mint)
Morus alba (mora)
Nicotiana tabacum (tobacco)
Parthenium argentatum (Guayule)
Persea americana (avocado)
Petunia
Phaseolus lunatus (lima bean)
Phaseolus vulgaris (common bean)
Phleum pratense (timothy grass)
Picea glauca (white spruce)
Pimenta dioica (allspice)
Pisum sativum (pea)
Plantago (Plantain)
Polygonum (knotweed)
Populus (poplars)
Portulaca oleracea (purslane)
Prunus (stone fruit)
Prunus armeniaca (apricot)
Prunus cerasus (sour cherry)
Prunus domestica (plum)
Prunus persica (peach)
Prunus salicina (Japanese plum)
Pseudotsuga menziesii (Douglas-fir)
Pteridium aquilinum (bracken)
Pyrus communis (European pear)
Raphanus sativus (radish)
Rheum hybridum (rhubarb)
Rhus (Sumach)
Ribes uva-crispa (gooseberry)
Rosa (roses)
Rubus fruticosus (blackberry)
Rubus idaeus (raspberry)
Rubus occidentalis (black raspberry)
Rumex (Dock)
Salix (willows)
Salvia officinalis (common sage)
Secale cereale (rye)
Sinapis alba (white mustard)
Solanum lycopersicum (tomato)
Solanum tuberosum (potato)
Solidago (Goldenrod)
Sonchus (Sowthistle)
Spinacia oleracea (spinach)
Stellaria media (common chickweed)
Trifolium (clovers)
Triticum aestivum (wheat)
Tropaeolum majus (common nasturtium)
Tsuga canadensis (eastern hemlock)
turfgrasses
Vaccinium (blueberries)
Vicia (vetch)
Vicia faba (faba bean)
Viola (violet)
Vitis vinifera (grapevine)
Xanthium strumarium (common cocklebur)
Zea mays (maize)
Zea mays subsp. mays (sweetcorn)
Zea mays subsp. mexicana (teosinte)
Zinnia
List of symptoms/signs
Fruit  -  external feeding
Growing point  -  external feeding
Inflorescence  -  external feeding
Leaves  -  external feeding
Seeds  -  external feeding
Stems  -  external feeding
Whole plant  -  cut at stem base
Whole plant  -  external feeding
Description
Eggs

The eggs are white when first laid, but within a few days they develop reddish-brown shading in a spot at the top and as a band around the middle. Eggs are rounded when viewed from above and slightly flattened, 0.51-0.58 mm wide and 0.40-0.45 mm high. Like those of most cutworms, the egg has a reticulate pattern formed by a series of raised ridges that radiate from the whorl of rosette cells at the top of the egg down almost to the bottom of the egg. In P. saucia there are 10 rosette cells at the top of the egg, a second whorl of about 15-17 cells surrounding this, then 34-39 longitudinal ridges radiating out from these. The series of transverse ridges which complete the reticulate pattern is not as prominent as the longitudinal ridges. The eggs are laid in groups one layer deep. The egg is described and illustrated by Salkeld, 1984 (electron micrographs) and Crumb, 1929 (egg mass).

Larvae

Keys to cutworm larvae with descriptions of the larvae of P. saucia are given by Crumb (1956), Beck (1960) and Godfrey (1987). A detailed description of all the larval stages (instars) is provided by Crumb (1929). Brief diagnoses with illustrations of the variegated cutworm are given by Rings (1977) and Rings and Musick (1976), and by Carter and Hargreaves (1986).

The mature larva is 35-46 mm long and 6 mm wide at the middle. The ground colour of the larva is pale yellowish-grey to pale reddish-brown, heavily speckled with dark brown to create an overall mottled dark reddish-brown colour. Along the middle of the back is a series of four to eight elongate yellow spots that are diagnostic for the variegated cutworm; these spots are most prominent on anterior segments of the abdomen and become smaller on the thorax and on the posterior part of the abdomen. In some larvae there is a subdorsal orange line on each side with a segmental series of black dashes on the upper margin of this line. A narrow black line extends along each side of the body at the top of the spiracles. The ventral half of the larvae below the spiracles may be distinctly paler than the dorsal half, or may be similar in colour to it. The head is pale yellow-brown with a dark brown reticulate pattern and two dark brown crescent-shaped submedial arcs on the front. In most larvae there is a black W-shaped mark or triangular patch on the posterior margin of abdominal segment eight, and the dorsal portion of abdominal segment nine has few dark flecks creating a clear yellowish area. Other significant structural characters are: spinneret short, about as long as wide and dorsoventrally flattened with margin of opening with a lacerate ragged fringe on upper and lower margins; inner surface of mandible with three longitudinal raised ridges but no projecting triangular tooth from inner surface of mandible; larval skin smooth.

Pupae

Crumb (1929) described the pupa of P. saucia and provided a key to cutworm pupae that attack tobacco in the USA. The pupa is 15-23 mm long and 5-6 mm wide, yellowish, and the cremaster is smooth with a pair of setae at the end of the abdomen that are parallel to each other, divergent only at the tips. There are no other setae on the abdomen.

Adult

Colour illustrations of the adults are given by Forster and Wohlfahrt (1971), Rockburne and Lafontaine (1976), Inoue et al. (1982), Covell (1984), Koch (1984) and Fibiger (1993). In the adult the forewing is 15-25 mm long (wing expanse 33-55 mm); at rest the wings are folded flat over the back and broadly overlap each other. The forewing is pale yellow-brown to dark reddish-brown, usually dusted heavily with black scales giving it a burnt yellow or orange colour. The black transverse lines are usually represented only by three pairs of black spots along the leading edge of the wing and a single black spot between the second and third pair. The hindwing is pale with dark blackish-grey shading on the wing margin and veins; the pale areas are translucent and have a distinctive pearly sheen.

External structural characters of the adults are: frons smooth, covered with scales; thorax with raised tuft of scales forming crest along middle of thorax; tibia of foreleg with row of sclerotized setae along inner margin and with one or two setae at apex on outer margin.

Male genitalia: apex of uncus curved abruptly upwards and ending in a short triangular spine; apex of valve with a straight row of 15-25 stout setae forming a comb-like corona; clasper (near middle of inner surface of valve) consisting of a flat, broad plate lying on inner surface of valve and an almost straight finger-like dorsal process projecting beyond dorsal margin of valve; digitus an elongated triangular plate distal to clasper with apex extending to lower end of apical corona of setae. The male genitalia are illustrated by Forster and Wohlfahrt (1971); Angulo and Jana-Saenz (1984); and Fibiger (1997).

Female genitalia: papillae anales truncated apically, covered with mixture of short and long setae; ductus bursae relatively short, about 1.5 mm long, largely membraneous except for a sclerotized plate in the ventrolateral wall of the left side that extends almost the full length of the ductus; bursa copulatrix bilobed with the corpus bursae elongate (about 8 mm long) and enlarged and pear-shaped at anterior end with two triangular signa, one in the dorsal wall and the other in the ventral wall near the anterior end; appendix bursae similar to the corpus bursae in shape but slightly thinner with the ductus seminalis at the apex of the appendix bursae. The female genitalia are illustrated by Fibiger (1997).
Prevention and control

Cultural Control

The presence of weeds in crop areas can greatly increase crop damage, and intensive weed control can reduce the need for and amount of other control measures taken against P. saucia (Machuca et al., 1990). Damage to the fruit on the lower branches of fruit trees is also largely due to the presence of tall weeds that provide ready access to the fruit for climbing cutworms (Molinari et al., 1995).

Biological Control

A wide variety of parasitoids have been reared from P. saucia (see Natural Enemies), but only the hymenopterous parasitoid Trichogramma and bacterial and viral agents have been applied to crops for control.

Chemical Control

Due to the variable regulations around (de-)registration of pesticides, we are for the moment not including any specific chemical control recommendations. For further information, we recommend you visit the following resources:


Impact
P. saucia is considered to be a minor agricultural pest in most of Europe (Carter, 1984) and eastern Asia, but is a more significant pest in southern Europe (for example, Italy) and in greenhouses on such crops as peppers and globe artichoke. It is a major pest in most of the USA, especially on potato, tomato, tobacco and lucerne, but estimates of financial loss are rarely reported. An exception was a major outbreak of the variegated cutworm on potato in the early 1900s where losses were estimated at 2.5 million dollars (Crumb, 1929). Damage to lucerne crops is most severe in terms of time delay between harvesting a crop and growth of the next crop. Infestations of P. saucia in lucerne stubble after harvesting can delay the regrowth of the next crop by several weeks or more (Buntin and Pedigo, 1985a, b, c; 1986a).
Related treatment support
Plantwise Factsheets for Farmers
Shinwari, N.; CABI, 2012, English language
Shinwari, N.; CABI, 2012, Dari language
Kenya, Kengap Horticulture Ltd; CABI, 2012, English language
 
 
External factsheets
University of California IPM Pest Management Guidelines, University of California, 2008, English language
University of California IPM Pest Management Guidelines, University of California, 2009, English language
Ontario CropIPM factsheets, Ontario Ministry of Agriculture, Food and Rural Affairs, Canada, 2015, English language
Ontario CropIPM factsheets, Ontario Ministry of Agriculture, Food and Rural Affairs, Canada, 2015, French language
University of California IPM Pest Management Guidelines, University of California, 2008, English language
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