The small white butterfly (Pieris rapae) is a common insect whose dietary needs change completely across its lifecycle. While the adult butterfly is a harmless garden visitor, its larval stage is known as the destructive imported cabbageworm. The caterpillar focuses solely on growth, while the adult focuses on reproduction and dispersal. The food sources consumed at each stage are entirely separate, dictating the species’ impact on agriculture and wild plant populations.
The Larval Menu: Primary Host Plants
The feeding habits of the larva (imported cabbageworm) are highly specialized, focusing on the Brassicaceae family, often called the mustard family. The larvae are attracted to these plants because they contain glucosinolates, chemical compounds that act as feeding stimulants and cues for the female moth to lay eggs. This caterpillar is a chewing pest that targets the most economically significant members of this group.
The primary diet consists of the Brassica oleracea species group, which includes many common cultivated vegetables. These high-value crops suffer the most damage as the larvae consume leaf tissue to fuel their rapid growth. Specific targets include cabbage, broccoli, cauliflower, Brussels sprouts, and kale. Early-stage larvae chew small holes, but mature larvae become voracious feeders, creating large, irregular holes in the leaves.
Feeding Damage and Contamination
As the caterpillars grow, they often migrate toward the center of the plant, burrowing into the developing heads of cabbage or florets of broccoli. This behavior leads to significant crop loss through direct feeding damage and contamination. The larvae produce dark-green fecal material, known as frass, which stains and spoils the harvested produce. The damage can be severe enough to reduce a mature plant to a skeleton of stems and large veins if the population is left unchecked.
Secondary Food Sources and Weed Hosts
While the Brassica oleracea group is preferred, the cabbageworm’s diet extends to other commercially grown Brassicaceae. This broader menu includes root vegetables and greens such as radishes, turnips, kohlrabi, and various mustard greens. These secondary hosts sustain the larval population when primary food sources become scarce or damaged.
The larvae also feed on various wild weeds belonging to the same plant family, allowing the moth population to persist when commercial crops are unavailable. Common examples include shepherd’s purse, wild mustard, and hedge mustard. Managing these weeds is recommended because they serve as pest reservoirs, allowing new generations to migrate to nearby vegetable plots.
Occasionally, larvae may be found on plants from related families, such as nasturtium or sweet alyssum, which also contain the characteristic mustard oils. However, these instances are less common, and the larvae generally demonstrate a stronger preference for their primary Brassicaceae hosts. The ability to utilize these secondary and weed hosts contributes to the widespread success and persistent nature of the species as an agricultural pest.
Adult Moth Feeding Habits
In stark contrast to the destructive larval stage, the adult Pieris rapae moth does not consume any plant tissue and is entirely harmless to crops. The adult is a specialized nectar feeder, requiring liquid energy for flight, mating, and egg-laying. It uses a long, coiled proboscis to sip nectar from a variety of flowering plants.
The adult moths forage in open areas and prefer certain flower colors, including purple, blue, and yellow, to locate suitable nectar sources. They are generalist feeders and visit many different species, such as clovers, dandelions, and asters. This feeding behavior makes the adult a minor pollinator, contributing to the reproduction of the visited plants. The adult stage is relatively short, lasting only a few weeks, during which the focus shifts completely to reproduction.