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Woolly Caterpillars In Soybeans And Sunflowers

Anitha Chirumamilla

Figure 1. Adult yellow woolly bear caterpillar (Virginia tiger moth). Photo by: Beatriz Moisset, bugguide.net

Numerous woolly caterpillars in varying colors have been observed feeding on soybeans and sunflowers in South Dakota. These caterpillars belong to a group of moths called woolly bear caterpillars and are members of the family Arctiidae.



Figure 2. Mature yellow wooly bear caterpillars feeding on soybean and sunflower leaves. Photo by: Anitha Chirumamilla, SDSU

It appears that the predominant species found in soybean and sunflower fields is the yellow woolly bear caterpillar also called the Virginia tiger moth, Spilosoma virginica. The adult is a beautiful white colored moth with black spots on the wings (Figure 1). The caterpillars have dense short and long hairs covering the body, which appear reddish brown or white to yellow in color (Figure 2). These caterpillars are usually not seen early in the summer, but appear during late July to early August. Female moths deposit batches of eggs on broad leaf weeds and the hatched larvae feed in clusters under the leaf surface (Figure 3). Early instar larvae feed on weeds and the later instars move to crops in search of food. In early stages of feeding, larvae skeletonize the leaves and in later stages the damage looks like chunks of leaf tissue removed (Figure 4). Mature caterpillars drop to the ground and spend the winter in a silken cocoon. Yield loss occurs when the caterpillar numbers are very high and their feeding results in extensive defoliation that significantly reduces the primary productivity of plants.



Figure 3. Egg mass and larvae of yellow woolly bear caterpillar. Photo by: Anitha Chirumamilla, SDSU

Although the yellow woolly bear caterpillar is not considered a serious pest in South Dakota, insecticide application is recommended when the defoliation exceeds 30% pre-bloom and 20% between bloom and pod set in soybeans. No economic thresholds are available for sunflowers. Early planted soybeans and sunflowers are past the sensitive stages for damage, but late planted fields may be at risk.



Figure 4. Defoliation in sunflower field by yellow woolly bear caterpillars. Photo by: Anitha Chirumamilla, SDSU

Source : SDSU


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