NPIPM:Arctiidae (soybean)

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Authors: Buyung Hadi, Ken Ostlie, Robert J. Whitworth, J. P. Michaud and Phillip E. Sloderbeck

Saltmarsh caterpillar and other wooly bear caterpillars are larvae of various moths from the family Arctiidae. These caterpillars are generalists, feeding on broadleaf weeds and various vegetables including beans, beets, cabbage, carrots, celery, lettuce, tomato and many others.

Contents

Identification

The caterpillars are generally characterized by numerous elongated hairs (setae) protruding from the body. The hairs are typically bunched on fleshy warts on the caterpillars body surface.

Saltmarsh caterpillar, Estigmene acrea, is grayish to yellowish brown with dark gray or brown stripes and long hairs all over the body. As the caterpillar matures,the body color gets darker. The front wings of the adult moth of saltmarsh caterpillar are white with black speckles. The hind wings are white on the female and yellowish-brown on the male.

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Photo by Frank Peairs, Colorado State University, Bugwood.org
A saltmarsh caterpillar
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A saltmarsh caterpillar
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Photo by Frank Peairs, Colorado State University, Bugwood.org
A saltmarsh caterpillar, notice the variation in color between the two pictures
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A saltmarsh caterpillar, notice the variation in color between the two pictures

There are multiple species of other woolly bear caterpillars that may feed on soybean. An example is the yellow woolly bear caterpillar, Spilosoma virginica. The yellow woolly bear ranges from white to yellow and reddish in color, about 0.19 inch (0.5 cm) long. The yellow woolly bear caterpillar is densely covered with long and short hairs of uniform color. The adult moth is nearly pure white except for the abdomen. The wings are white with a few black spots.

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Photo by David Cappaert, Michigan State University, Bugwood.org
A yellow woolly bear caterpillar, notice the dense hair covering the body
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A yellow woolly bear caterpillar, notice the dense hair covering the body
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Photo by Whitney Cranshaw, Colorado State University, Bugwood.org
A yellow woolly bear caterpillar, notice the variation in color between the two pictures
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A yellow woolly bear caterpillar, notice the variation in color between the two pictures
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Photo by Whitney Cranshaw, Colorado State University, Bugwood.org
Saltmarsh caterpillar's egg clusters and adult moth
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Saltmarsh caterpillar's egg clusters and adult moth

Life Cycle and Seasonal History

Both saltmarsh caterpillar and yellow woolly bear caterpillar overwinter as pupae inside thin silken cocoons heavily covered with hairs from the caterpillar body. The adult emerge from the cocoons in spring and lay their eggs in clusters on the underside of host leaves. It takes a month or two for the eggs to hatch and the resulting caterpillars to attain the full size and begin pupation. During their development, the caterpillars feed on host leaves. Typically there are two generations produced by these species in the northern states.

Plant Injury and Damage

Young caterpillars feed gregariously on the underside of the leaves and, in high infestation, may produce leaf skeletonization. The mature caterpillars are solitary feeders on more exposed sites and may chew sizable holes on the leaves. The population of these caterpillars are easily overestimated due to the striking appearance of the caterpillars and the conspicuous damage the mature larvae produce on plants. Full sized caterpillars may move long distance on the ground in search of food.

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Photo by Whitney Cranshaw, Colorado State University, Bugwood.org
Holes on soybean leaf due to mature yellow woollybear caterpillar feeding
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Holes on soybean leaf due to mature yellow woollybear caterpillar feeding
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Photo by Whitney Cranshaw, Colorado State University, Bugwood.org
Heavy infestation of yellow woollybear caterpillar on soybean
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Heavy infestation of yellow woollybear caterpillar on soybean

Management Approaches

Scouting and Threshold

The injury due to saltmarsh and other woolly bear caterpillars alone may not be damaging enough to warrant management action on soybean. The feeding injuries of these caterpillars should be considered together with other defoliating pests of soybean. Threshold based on the defoliation rate of soybean plants is available. Management action is recommended if defoliation reaches 40% in pre-bloom, 20% during bloom and pod-fill and 35% from pod-fill to harvest.

Other Online Resources

University of Minnesota

Kansas State University

For information regarding labels of chemical control options, please visit Agrian.com

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