Cabbage whites flourish from spring to fall, flitting about vegetable gardens.
Late autumn is cabbage season. Whether you grow them to eat or plant them as ornamentals to add color to your landscape, cabbages and kale thrive in the chilly nights and cool days of fall. While walking through a row of kale the other day, I noticed ragged holes and missing margins on several leaves. Closer inspection revealed scads of beautiful bristly green caterpillars beneath the leaves.
These bristly green caterpillars love to eat their vegetables.
Nearby, adult butterflies of these cabbageworms dashed about rows of kale and broccoli searching for mates and depositing eggs beneath leaves. Adults of the imported cabbageworm are called cabbage whites. They arrived in our country from Europe in the 1860’s. Cabbage whites are among the first butterflies seen each spring when they emerge from chrysalises that provide refuge during the winter. In addition to their fondness for kale, broccoli, and cabbage, they deposit eggs on cauliflower, Brussels sprouts, turnips, radishes, and weeds in the mustard family.
Several generations of this butterfly develop annually throughout much of their range in the United States from Canada to Mexico and coast to coast. Although I find the antics of the caterpillars and butterflies entertaining, some find the presence of these worms on their greens unpleasant.
Ragged holes and missing leaf margins are typical feeding damage of the imported cabbageworm.
Managing populations
The chrysalis provides winter refuge for the cabbageworm, which emerges as a butterfly in spring.
If you grow just a few cabbages, broccoli, or cauliflower, regular inspection of the plants and removal of the caterpillars can help reduce damage. Mother Nature’s army of parasitic wasps and predatory bugs greatly reduce the legions of cabbageworms when gardens and landscapes are diverse and sustainable. Some gardeners enshroud rows of cabbage and broccoli with netting to prevent cabbage whites from reaching leaves to lay their eggs – no eggs, no caterpillars, and no damage. Some varieties of cabbage, including Early Globe, Red Acre, and Round Dutch, are reported to show some resistance to cabbageworms. Many insecticides are available to control caterpillars including cabbageworms. Among the most environmentally friendly are products containing the microbial biological control agent, Bacillus thuringiensis, also known as Bt. Bt products are simply mixed with water and sprayed on the plant. As the caterpillar eats, Bt is ingested. This microbe and proteins produced by it destroy vital cells inside the gut of the caterpillar. The result is gut paralysis and starvation – a slow and painful death.
The imported cabbageworm is not without its own tricks. The hairs lining its body are glandular and produce secretions repellent to potential predators like ants. This may be part of the reason for the remarkable success of this alien species here in America.
The cabbage white butterfly plays an important role as pollinator.
References
The wonderful book “Secret Weapons” by Tom Eisner, Maria Eisner, and Melody Siegler was used in preparation of this episode.
To learn more about imported cabbageworm and cabbage white butterflies, please visit the following web sites:
http://www.uri.edu/ce/factsheets/sheets/importcabbageworm.html
http://www.monarchprogram.org/insects/cabbagewhite.htm
http://www.butterfliesandmoths.org/species?l=1398