The Cabbage Looper (Trichoplusia ni) is a widely distributed moth whose larval stage is a significant pest to various garden and commercial crops. The caterpillar is a voracious feeder responsible for the plant damage that gives this insect its common name. The larva is a smooth, pale-green caterpillar that feeds continuously for several weeks before pupating. Understanding the specific plants this pest prefers is the first step toward effective garden management.
The Preferred Diet: Brassica Family Hosts
The Cabbage Looper earns its name from its strong preference for plants belonging to the Brassica family, commonly called cruciferous vegetables. This group includes popular garden staples like cabbage, broccoli, cauliflower, Brussels sprouts, kale, and collard greens. Larvae exhibit superior growth rates and survival when feeding on these plants, suggesting high nutritional value. The caterpillars are highly attracted to chemical compounds unique to the Brassica family, such as glucosinolates, which serve as feeding stimulants. Newly hatched larvae typically begin feeding on the outer, older leaves where the female moth laid the egg.
As the caterpillars mature, their feeding needs increase, and they often move toward the center of the plant. On head-forming crops like cabbage and cauliflower, the larvae will progress toward the developing head, which is the most destructive phase of their feeding. Their presence, even in small numbers, can quickly ruin the marketability of the harvest by contaminating the edible portions.
Wider Menu: Secondary Food Sources
While Brassica crops are the looper’s favorite, this insect is a polyphagous species. When preferred food sources are scarce or the population is high, the Cabbage Looper will readily consume over 160 different plant species from various families. This wide diet makes them a threat in nearly any vegetable garden setting.
Common non-Brassica crops they will target include leafy greens such as lettuce, spinach, and celery. They also feed on plants like tomatoes, potatoes, beets, and various types of beans. This adaptability means rotating crops away from Brassica does not guarantee immunity from a looper infestation.
Furthermore, many common weeds serve as important secondary hosts, allowing the pest population to persist in the environment. Weeds such as lambsquarters, wild lettuce, and curly dock can harbor Cabbage Looper larvae, acting as a reservoir for future generations. Clearing these weed hosts from the garden vicinity is a helpful measure in reducing the overall pest pressure.
Identifying the Damage: Looper Feeding Patterns
The characteristic damage caused by Cabbage Looper larvae is easily identifiable and differs from that of other chewing insects. The caterpillars consume leaf tissue, leaving behind irregular, ragged holes throughout the foliage. They tend to feed selectively, often leaving the tougher main veins and midribs of the leaf intact, which creates a distinct, skeletonized appearance.
Younger larvae feed on the underside of leaves, sometimes scraping away the tissue to create a thin, translucent layer that resembles a “windowpane” effect. As the larvae grow, they become more destructive, chewing completely through the leaves to create larger, more extensive holes. This heavier feeding can result in severe defoliation, especially in high-density plantings.
A key visual identifier is the presence of frass, which is the larval excrement. Cabbage Loopers produce dark, moist, greenish-brown pellets of frass that are often found stuck to the leaves or clustered near the feeding site. Because the larvae move by arching their bodies into a loop, they tend to feed and hide on the undersides of leaves or within the folds of the plant structure.