Distribution. Yellow woollybear is a native insect, and is found throughout the United States and southern Canada. Yellow woollybear's range as a pest is generally restricted to the Great Plains region to the west coast. Even within this area, however, it infrequently is numerous enough to be damaging.
Host Plants. Yellow woollybear is a very general feeder, and reported from over 100 different plants. Yellow woollybear has been observed to damage such vegetable crops as asparagus, bean, beet, cabbage, cantaloupe, carrot, cauliflower, celery, corn, eggplant, lima bean, parsnip, pea, potato, pumpkin, radish, rhubarb, squash, sweet potato, Swiss chard, turnip, and watermelon. Other economic plants damaged include field crops such as alfalfa, peanut, and sugarbeet; fruits such as blackberry, cherry, currant, gooseberry, grape, and raspberry; and flowers such as canna, dahlia, geranium, hollyhock, hyacinth, and verbena. Among weeds fed upon are dandelion, Taraxacum officinale; dock, Rumex sp.; pigweed, Amaranthus spp.; lambsquarters, Chenopodium album; plantain, Plantago major; Russian thistle, Salsola kali; Spanish needle, Bidens bipinnata; and sunflower, Helianthus spp.
Natural Enemies. The number of parasitoids found in association with this insects is quite large, though the importance of these natural enemies has not been well-studied. Arnaud (1978) listed several tachinids reared from yellow woollybear, including Aplomya caesar (Aldrich), Blondelia hyphantriae (Tothill), Bombyliopsis abrupta (Wiedemann), Carcelia diacrisiae Sellers, C. reclinata (Aldrich and Webber), Compsilura concinnata (Meigen), Exorista mella (Walker), Gymno-carcelia ricinorum Townsend, Hubneria estigmenensis
(Sellers), Lespesia aletiae (Riley), L. frenchii (Williston), Mericia ampelus (Walker), Thelaira americana Brooks, and Winthemia datanae (Townsend) (all Diptera: Tachi-nidae). Wasps reared from yellow woollybear include Apanteles diacrisiae Gahan, A. scitulus Riley, (both Hymenoptera: Braconidae); Coccygomius sanguinipes (Vierick), Cratichneumon unifasciatorius (Say), Vulgich-neumon subcyaneus (Cresson), Therion morio (Fabricius), Hyposoter rivalis (Cresson), Enicospilus glabratus (Say) (all Hymenoptera: Ichneumonidae); Psychophagus omnivorous (Walker), Tritneptis hemerocampae Vierick (both Hymenoptera: Pteromalidae); Elachertus marylandicus Girault, E. spilosomatis Howard (both Hymenoptera: Eulophidae); Telenomus nigriscapus Ashmead, and T. spilosomatis Ashmead (both Hymenoptera: Scelioni-dae). The fungus Beauveria bassiana has been reported to cause low levels of mortality, and a granulosis virus has been observed (Boucias and Nordin, 1977).
Life Cycle and Description. There likely are three generations of yellow woollybear annually, despite the numerous reports of only two generations. The discrepancy is due to the overlapping flights of the moths from overwintering pupae with those of the spring generation. In the most complete study of yellow woollybear population dynamics, conducted in Iowa, the apparent spring flight of moths was shown to consist of two reproductive populations, each represented by separate peaks in abundance within the overall spring flight period. There also was a late summer flight which produced overwintering pupae (Peterson et al., 1993). Elsewhere, moths also are abundant in spring (April-June) and autumn (July-October), but there is considerable geographic variation in the timing of flights. For example, the early-season flight activity occurs in mid-April in Arkansas and North Carolina, but not until late May in Maine. Late-season flight occurs in August in Maine, September in North Carolina, and October in Arkansas. The pupal stage reportedly overwinters throughout this insect's range.
The biology of yellow woollybear is not well documented. Brief treatment of yellow woollybear was provided by Riley (1871), Marsh (1912b), and Maxson (1948).
Larvae are defoliators. Young larvae are gregarious, and tend to feed together on the underside of foliage
and skeletonize the plant tissue. Larger larvae disperse and feed sporadically, creating irregular holes in foliage. When larvae are particularly numerous, and succulent vegetation scarce, many of the large larvae remain on crops and inflict injury. This most often occurs in irrigated cropland when adjacent weedy vegetation senesces, or dries up due to drought. Typically it is only the late summer generation that attains densities adequate to inflict injury. Capinera et al. (1987) measured bean foliage consumption by each instar, and recorded over 300 sq cm of foliage consumed during the life of a caterpillar. Further, they estimated that 1.2-2.2 mature caterpillars per plant could inflict 20% defoliation, a level adequate to cause yield loss.
Yellow woollybear is common among weeds growing along roadsides, fence rows, and irrigation ditches. Larvae disperse into crops only when native or weedy vegetation is depleted or otherwise unsuitable. Such sources of infestation should be monitored. Larvae are easily killed with foliar insecticides, though this is rarely warranted. Treatment of the source of infestation or the borders of crops is generally adequate to prevent damage. Burning of crop residues in the autumn is sometimes recommended to destroy overwintering larvae and pupae because they are located above-ground and very susceptible to fire. However, it is normally better to leave such organic matter on the soil surface, or tilled into the soil; the exception might be ditch banks or other small areas that are not tilled.
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