The Very Hungry Sunflower Moth Caterpillar
You probably had a summer of coneflowers, sunflowers and zinnias in full bloom. Unfortunately, those plants looked good not only to you and your buyers, but they were a dream come true for hungry caterpillars.
In the fall of 2005 an herbaceous perennial grower asked our lab to identify a caterpillar that was tearing up Echinacea plants in his nursery. This caterpillar was the larva of the sunflower moth, Homoeosoma electellum. Since then we have found this caterpillar active in cut flower operations, nurseries and landscapes every year, and in growing frequency.
It might be that because coneflowers have become very popular as a cut flower, there is larger planting area for this moth to lay its eggs in. The pest could be flourishing with the increase in popularity of coneflower in landscape plantings. But Echinacea is not the only host. Homoeosoma also feeds on sunflower and zinnias, and a few other composite flowers. The young caterpillar stage of the sunflower moth is an active feeder and damages the bloom by chewing, webbing the cone part of the flower, and leaving fecal dropping on the center of the flower. As it matures it will bore into the center of the flower and feed on the developing seeds. Moths actively mate and lay eggs at night in newly opening flower heads.
The caterpillar itself is a rather handsome reddish brown, with racing stripes running down the length of the body. The larva overwinters but is rather sensitive to extreme cold and does not survive in more northern climates. With the warm winters of the last 8 years this caterpillar has survived very nicely here in Maryland. In the Midwest it is fairly common. Larvae do not overwinter well in the Northeast but the moth will migrate from the South during the summer and can be found late in the summer and early fall in New England. We find the adults out in late June through the fall, laying eggs on the flower heads of susceptible plants here in Maryland.
Adult moths fly at night and are gray to tan in color, 5/8 to 3/4 inch long (19 mm) and rest with the wings clasped tightly to the body, giving the moth a cigar shape. The forewings of the adult moth have a small, dark dot located at the center of the wing.
Flowers in the early stages of bloom are favored for oviposition. Females lay their eggs at the base of the florets. Females can lay 30 eggs per day. Eggs hatch within 43 to 72 hours and the newly emerged larvae feed on pollen and florets. As the caterpillar feeds on florets they cover the head with fine silk mixed with caterpillar frass (poop) which gives a very unpleasant appearance to the flower.
The larvae begin tunneling into seeds upon reaching the third instar (larval growth stage). This tunneling continues throughout the remainder of larval development. Larval development from hatching to full maturity takes about 15 to 19 days.
Newly hatched larvae are pale yellow, but darken to shades of brown or purple with longitudinal white stripes. Early instars feed on pollen and florets. Later instars bore into the head and consume receptacle tissue and seeds.
Tangled mats of webbing on the face of flowers are signs of larval feeding. The injury caused by larval feeding provides infection sites for Rhizopus head rot that can lead to complete yield loss. Although a portion of larvae pupate in the heads, the majority of maturing larvae descend to the ground on silken threads to pupate in crevices or under leaf litter. Diapausing larvae descend to find an overwintering site 2 to 3 inches underground. Under warm conditions, a generation can be completed in 30 days. Many overlapping generations occur throughout the summer, with the last generation occurring in September in Maryland.
Young caterpillars can be controlled using the bacterium Bacillus thuringiensis. Bt is sold under several names, including Dipel DF, Agree WG, Biobit HP, Deliver, and Javelin.
Another option for control is to apply spinosad, sold under the name Conserve. Both Bt and Conserve will be soft on beneficial insects and mites and pollinators. It is best to catch the caterpillars when they are small and feeding on the outside of the florets. Once they bore into the flower head it will be difficult to make contact with these insecticides.
Stanton Gill is an extension specialist (professor-ranked principal agent) in IPM and entomology with the University of Maryland Extension, based at the Central Maryland Research and Education Center in Ellicott City. He is also a professor in the Landscape Technology Program at the Germantown Campus of Montgomery College. Contact him at [email protected]