Pest Of The Month: Imported Cabbageworm

Pest Of The Month: Imported Cabbageworm

Advertisement

Identification

The imported cabbageworm occurs throughout the temperate regions of the world. Cabbageworms feed primarily on foliage. If uncontrolled, they will reduce mature plants to stems and large veins. Mature larvae also may burrow into the heads of broccoli and cabbage. The larvae are often immobile and may be overlooked when cleaning produce. They also produce large quantities of fecal matter, which can contaminate and stain produce.
Pieris rapae is easily confused with other common cabbage white butterflies. The imported cabbage white has largely displaced native cabbage white butterflies in many areas. The butterfly has black-tipped front wings with one or two black dots and one black dot on each hind wing.
The larva is velvety green in appearance and bears five pairs of prolegs. All larval stages, except the first instar, have a narrow yellow line running along the center of the back. A broken yellow line, or series of yellow spots, may occur on each side.

Survival And Spread

The complete life cycle of this insect requires three to six weeks, depending on weather. The number of generations varies from three in northern states, to six or more in the south. Imported cabbageworms are present year round in Florida.
The females fly during daylight hours looking for suitable plants on which to lay their yellowish, elongated eggs on the underside of leaves. The eggs are laid singly, usually on the lower surface of outer leaves of plants.
The caterpillars are voracious eaters and reach full growth in about 15 days. The larvae grow to just more than an inch in length passing through five instar stages.
Pupation normally occurs on the host plant, but may occur in nearby debris.

Management Methods

A number of parasites and pathogens play a significant role in the natural control of imported cabbageworms. These include general predators such as shield bugs, ambush bugs, and wasps. They also are preyed on heavily by many insectivorous birds. A parasitic wasp (Apanteles glomeratus L.) attacks the early instars and emerges from the mature larva as it prepares to pupate. These wasps are frequently observed in the field searching foliage for larvae.
Scouting is important, and plants should be examined carefully for the presence of eggs and larvae. Caterpillars rest along the main leaf vein and are often very difficult to see as their body color closely matches the background. The presence of butterflies, which are more visible, suggests future problems.
Imported cabbageworms are readily killed by foliar application of insecticides, including most formulations of bacterial insecticide Bt.

Top Articles
Have a Plan For Climate Change? Why Fruit Growers Need To Act Now

0