Taxonomic name: Hyphantria cunea (Drury)
Synonyms: Hyphantria textor (Harris)
Common names: American white moth (English), Amerikanischer Webebär (German-Germany), Amerikanischer weisser Bärenspinner (German-Germany), Amerika-siro-hitori (Japanese-Japan), black-headed webworm (English), chenille à tente estivale (French-France), chenille blanche (French-France), ecaille fileuse (French-France), écaille fileuse (French-France), falena tessitrice (Italian-Italy), fall budworm (English), fall webworm (English), fall webworm moth (English), gusano de la bolsa (Spanish-Spain), hvid bjoernespinder (Danish-Denmark), hvid bjørnespinder (Danish-Denmark), hvit bjoernespinner (Norwegian-Norway), hvit bjørnespinner (Norwegian-Norway), ifantria americana (Italian-Italy), mulberry moth (English), noctuelle d'automne (French-France), redheaded webworm (English), Spinner, Weisser Baeren (German-Germany), vid bjöernspinnare (Swedish-Sweden), Webebär, Amerikanischer (German-Germany), weiser Bärenspinner (German-Germany), weisser amerikanischer Bärenspinner (German-Germany), weisser Bär (German-Germany)
Organism type: insect
Biological invasions of insects, plants and fungal pest species often cause substantial disturbance to forest ecosystems as well as severe socio-economic impacts. Posing an agricultural and economic threat, Hyphantria cunea is significant due to its high polyphagy, which puts a wide variety of plant species at potential risk. Hyphantria cunea is commonly known as the fall webworm and can be a pest in both natural and planted forests.
The adult fall web worm (Hyphantria cunea) has a wingspan of 25-31mm and is snowy white, usually with dark spots on the wings (Virginia State University 1996). Larvae are brownish-grey, 25 - 30/40mm long, and have 12 small warts surmounted by characteristic tufts of hair (Virginia State University 1996; Wittenberg, R. (ed.) 2005). Their silk nests enclosing a number of leaves are characteristic (Wittenberg, R. (ed.) 2005). Eggs are small, yellow or light green, and usually located in hair-covered masses on the underside of leaves. Mature larvae are 25-31mm long and covered with silky hairs. Colour varies from pale yellow to green, with a black stripe on the back and a yellow stripe on each side. Head colour varies from red to black. Pupation occurs in thin cocoons usually spun in the duff or just beneath the surface of the soil (Virginia State University 1996).
agricultural areas, natural forests, planted forests, ruderal/disturbed, scrub/shrublands
Because of its polyphagy the adult fall web worm (Hyphantria cunea) can invade most types of habitats (with respect to European habitats) (Wittenberg, R. (ed.) 2005). However it seems to be unable to establish itself in the northern half of Europe, probably because of climatic constraints (Wittenberg, R. (ed.) 2005).
The fall web worm (Hyphantria cunea) can impact a wide variety of crop and cultivated broadleaf plant species. In Europe it is a serious pest in Bulgaria, Romania, Hungary, former Yugoslavia, Russia and northern Italy.
According to Biosecurity New Zealand heavy feeding by the caterpillars over time, can lead to defoliation (leaf loss) and limb and branch dieback. Trees/plants are often totally defoliated by the late-instar larvae, particularly in the second generation (Wittenberg, R. (ed.) 2005). Environmental impacts are likely given the high polyphagy and impact on individual plants. H. cunea is a threat to orchards, ornamentals and forest trees in some regions in Central and eastern Europe, as well as in eastern Asia. It is particularly damaging to ornamentals (Wittenberg, R. (ed.) 2005).
Newly emerged larvae immediately begin to spin a silken web over foliage on the terminal portions of the branches. The larvae feed on the leaves within the webs. As the larvae grow, webs enlarge and enclose more foliage. Large portions of tree branches are commonly enclosed by such webs, and are most apparent from mid- to late-summer. Early stage larvae feed on the upper surfaces of the leaves, and late instar larvae eat entire leaves except for larger veins and midribs. The insect is considered an ornamental pest due to the unsightliness of the webs; however, it is ordinarily of no great importance as a forest pest (Virginia State University 1996). Experiments showed that sixth-instar larvae of H. cunea can consume a daily average of 435mm² of fresh ash foliage while seventh-instar larvae brought it to an average of 814mm² (Jarfas and Miklos 1986, in Smith et al. 1992).
Native range: The adult fall web worm (Hyphantria cunea) is native to North America and Mexico.
Known introduced range: The fall webworm has established in Europe and parts of Asia (Biosecurity New Zealand). It arrived in Europe in the 1940s in Hungary and spread throughout Europe. It has also been introduced into eastern Asia (Wittenberg, R. (ed.) 2005). It was reported in China in 1979 and is now established in the country (FAO 2007).
Introduction pathways to new locations
Forestry: Transportation of the pest also occurs relatively often in wood logs where it inhabits cracks or holes in the bark (Shu and Yu 1984, in Smith et al. 1992).
Nursery trade: International trade can facilitate movement to new areas (Smith et al. 1992).
Other: Hyphantria cunea can spread with vehicles, packing material, host plant material, etc. (CABI Bioscience 2005).
Other: Adults are good flyers. Furthermore Hyphantria cunea can spread with vehicles, packing material, host plant material, etc. (CABI Bioscience 2005).
Road vehicles (long distance): The facility of the larvae to withstand starvation for up to 2 weeks means that they can easily be transported on vehicles to different areas and survive to initiate new infestations (Smith et al. 1992).
Transportation of habitat material: Hyphantria cunea is liable to be carried on vegetative host-plant material as well as on packing materials and in vehicles (Smith et al. 1992).
Local dispersal methods
Road vehicles: Mass migrations due to exhausted food plants or the search for new sites often end up in urban areas where the pest invades wood piles, houses, roads and vehicles (which can transport it to new and uninfested areas) (Giovanni et al. 1986, in Smith et al. 1992).
The fall web worm (Hyphantria cunea) is a highly polyphagous Lepidoptera and eats a wide range of forest and fruit trees, shrubs and herbaceous plants. Some of 600 host plant species have been recorded as food. In Romania, it was demonstrated that, although H. cunea is polyphagous, normal development will occur only on the few preferred food plants: mulberries, maples, apples, cherries, pears and plums (rather than grapes, strawberries, roses, hops or Ailanthus altissima) (Iamandei et al. 2004; Smith et al. 1992). The most favourable for development are Morus spp., maple (Acer spp.), cottonwood (Populus spp.), Platanus spp., Malus spp. and Prunus spp. (Wittenberg, R. (ed.) 2005). Host plants also include willow (Salix spp.), Fraxinus spp., Betula spp., alder (Alnus spp.), pecan and hickory (Carya spp.), walnut (Juglans spp.), elm (Ulmus spp.), persimmon (Diospyros spp.) and sweetgum (Liquidambar) spp. (FAO 2007). Other cultivated plants such as grapevine, maize or soyabean can be attacked (Wittenberg, R. (ed.) 2005).
According to Biosecurity New Zealand and the FAO (2007) a female fall webworm (Hyphantria cunea) may lay up to 500/600 eggs at a time and there can be up to four generations of the moth in a single year.
In Central Europe there are usually 2 generations per year. Pupae overwinter in the bark cracks or in the soil. Adults fly in April-May and lay eggs in groups, usually on the underside of leaves. Larvae usually have 7 instars, but up to 11 can be observed. Early instars are gregarious and build colonial silk nests enclosing leaves, in which they live to the fifth to sixth instars when they become solitary and disperse. Then, they pupate in refuges and emerge for a second generation, which flies in July-August (Wittenberg, R. (ed.) 2005). In North America from May to July, adult moths lay their eggs. Eggs hatch within two weeks and the larvae immediately begin feeding and constructing webs. Larvae feed and webs continue to enlarge for four to eight weeks. There are at least two generations per year in the South (Virginia State University 1996).
Reviewed by: Expert review underway
Compiled by: IUCN/SSC Invasive Species Specialist Group (ISSG) with support from the Forestry Division (Council Of Agriculture) Taiwan
Last Modified: Monday, 1 October 2007