Cabbage whites

Pieris brassicae

Overview:

Pieris brassicae, the Large White Butterfly or Cabbage White Butterfly, is a common pest that poses a threat to cruciferous crops, including cabbage, broccoli, and cauliflower. Belonging to the Pieridae family, this butterfly is recognized for its large size and widespread distribution.

Detailed Appearance:

The adult Large White Butterfly has a wingspan ranging from 6 to 9 centimeters (2.4 to 3.5 inches). The wings are predominantly white, with black markings near the tips. Females typically have two spots on each forewing, while males have one. The larvae, commonly known as cabbage caterpillars, are velvety green with a yellow stripe along each side and reach lengths of approximately 4 centimeters (1.6 inches).

Life Cycle:

The life cycle of Pieris brassicae follows four stages: egg, larva, pupa, and adult. Adult butterflies lay eggs on the undersides of host plant leaves. Upon hatching, the larvae feed voraciously on the foliage, causing damage. Larvae then pupate on plant surfaces or nearby structures, and adult butterflies emerge to continue the cycle.

Identifying Infected Crops:

  1. Leaf Damage: Look for irregularly shaped holes in leaves caused by the feeding activity of cabbage caterpillar larvae. Severe infestations can lead to extensive damage to the plant's foliage.

  2. Frass Presence: The presence of small greenish-black droppings, known as frass, on leaves is an indicator of cabbage caterpillar activity.

  3. Caterpillar Identification: Identify the velvety green caterpillars with a yellow stripe along each side actively feeding on plant foliage.

  4. Adult Butterfly Observation: Monitor for the presence of adult butterflies, especially during the growing season, using visual inspections or yellow sticky traps.

Additional Identification Features:

  1. Chewing Mouthparts: Cabbage caterpillar larvae have chewing mouthparts, contributing to the characteristic feeding damage on leaves.

  2. Silken Cocoons: Larvae may create silken cocoons on plant surfaces or nearby structures for pupation, which can be observed during the later stages of their development.

Management: 

  1. Handpicking: Actively inspect plants and manually remove cabbage caterpillar larvae when their numbers are manageable. This is particularly effective in smaller gardens.
  2. Biological Control: Introduce natural predators such as parasitic wasps and predatory insects like ladybugs and lacewings to help control cabbage caterpillar populations.
  3. Bt (Bacillus thuringiensis) Sprays: Apply Bt-based insecticides, which are specific to caterpillars and are environmentally friendly. Dilute 15 to 30 milliliters (1 to 2 tablespoons) of Bt per liter (1 quart) of water.
  4. Floating Row Covers: Use floating row covers to physically exclude adult butterflies from laying eggs on the plants.