Distribution. There are several native pasture-dwelling webworms that occasionally damage crops.
Commonly they are called sod webworms, because they usually are associated with pasture and lawn grasses. They occur throughout the United States and southern Canada. Among the species known to cause damage are corn root webworm, Crambus caligi-nosellus Clemens; silverstriped sod webworm, Cram-bus praefectellus (Zincken); larger sod webworm, Pediasia trisectus (Walker); and striped sod webworm, Fissicrambus mutabilis (Clemens).
Food Plants. Sod and root webworms feed principally on pasture and sod grasses in the family Gramineae. However, if pasture or sod is tilled and the ground is planted to non-grass crops, they too may be injured by the residual webworm population. In addition to grasses such as bluegrass, corn, orchardgrass, rye, timothy, and wheat, some webworms have been known to attack alfalfa, cabbage, clover, mint and tobacco. Consumption of the latter hosts is unusual. Weed grasses such as crabgass, Digi-taria sanguinalis, and even some broad-leaf weeds such as sheep sorrel, Rumex acetosella, and aster, Aster eri-coides, are consumed by larvae. Corn root webworm displays a particular preference for plantain, Plantago lanceolata, and oxeye daisy, Chrysanthemum leucan-themum.
Natural Enemies. The natural enemies are not well known, but their impact is thought to be significant. Cockfield and Potter (1984) estimated 75% reduction in eggs within 48 h due to predation. Among those thought to be important are the mite egg predators Hypoaspis sp., Cosmolaelaps sp. (both Acari: Laela-pidae), and Parasitus sp. (Acari: Parasitidae); the ground beetles Anisodactylus rusticus Say, Amara cupreolata Putzeys, A. familiaris Duftschmidt, Calathus opaculus LeConte, and Stenolophus rotundata LeConte (all Coleoptera Carabidae); the rove beetles Meroneura venustula (Erichson), Neohypnus sp., Philonus sp., and Tachyporus jocosus Say (all Coleoptera: Staphylinidae) and ants, especially Phedole tysoni Forel. Birds also are common predators, and where webworms are abundant the sod or soil often is heavily disturbed by birds probing for larvae. Flies are not uncommon parasitioids, including Aplomya caesar (Aldrich), A. confusionis (Sellars), and Stomatomyia floridensis (Town-send) (all Diptera: Tachinidae). Wasp parasitoids known from larger sod webworm include Macro-centrus crambi (Ashmead), M. crambivorus Viereck, Apanteles crambi Weed, Orgilus detectiformis Viereck (all Hymenoptera: Braconidae), and Diadegma obscurum (Cresson) (Hymenoptera: Ichneumonidae). Macrocen-trus crambi and M. crambivorus have also been reared from corn root webworm. Species reared from striped sod webworm include Apanteles terminalis Gahan, A. ensiger (Say), and M. crambi (all Hymenoptera: Braco-
nidae) and Campoletis argentifrons (Cresson) (Hyme-noptera: Ichneumonidae).
Life Cycle and Description. Following is a description of larger sod webworm, but the other sod webworm species are similar except for the larger size of P. trisectus. Overwintering occurs in the larval stage. In Iowa and Tennessee, these larvae give rise to flights of moths in June, followed by an additional generation-producing flights of moths in August. Light trap catches from Ontario indicate two flights of moths for numerous sod webworm species (Arnott, 1934). Three generations are thought to occur for some sod webworms in the midwestern states, however.
Larger sod webworm larva.
The biology of corn root webworm was described by Runner (1914), striped sod webworm by Ainslie (1923a), silverstriped webworm by Ainslie (1923b),
and larger sod webworm by Ainslie (1927). Forbes (1904) and Ainslie (1922) provided a brief description of several sod webworms. Artificial diets have been developed by Ward and Pass (1969) and Dupnik and Kamm (1970).
Damage often occurs when larvae feed on the leaves of grasses, but feeding can also occur at the soil line or even on the roots. Under high density conditions or if there is a shortage of leaf material, the plant stems and growing point of grasses may be eaten and the plants killed. Larvae commonly chew pits into the side of underground stems or leave the foliage ragged. Plant mortality is most common during periods of drought, and consumption of leaf material by webworms in the pasture environment often goes unnoticed during periods of adequate rainfall.
Cultural Practices. Rotation from sod or pasture to crops, especially corn, is risky if webworms have been abundant. Disking and tilling can destroy overwintering larvae, but intense soil disturbance is necessary. Both autumn and spring tillage are suggested for effective suppression.
Was this article helpful?